NREL is a national laboratory of the U.S. Department of Energy, 

Office of Energy Efficiency & Renewable Energy, operated by the 

Alliance for Sustainable Energy, LLC.

Contract No. DE-AC36-08GO28308

Best Practices for Siting Solar 

Photovoltaics on Municipal Solid 

Waste Landfills

A Study Prepared in Partnership with the Environmental 

Protection Agency for the RE-Powering America’s Land Initiative: 

Siting Renewable Energy on Potentially Contaminated Land and 

Mine Sites

Kosol Kiatreungwattana and Gail Mosey

National Renewable Energy Laboratory

Shea Jones-Johnson and Craig Dufficy

U.S. Environmental Protection Agency

Joe Bourg, Angela Conroy, Meghan Keenan, 

and William Michaud

SRA

Katie Brown

AAAS Science & Technology Fellow

The National Renewable Energy Laboratory’s contribution was 

produced under direction of the U.S. Environmental Protection Agency 

(EPA) through Interagency Agreement IAG-09-1751 and Task No. 

WFD6.1001.

Technical Report

NREL/TP-7A30-52615

February 2013
NREL is a national laboratory of the U.S. Department of Energy, Office of Energy 

Efficiency & Renewable Energy, operated by the Alliance for Sustainable Energy, LLC.

Contract No. DE-AC36-08GO28308

National Renewable Energy Laboratory

15013 Denver West Parkway

Golden, CO 80401

303-275-3000 • www.nrel.gov

Best Practices for Siting Solar 

Photovoltaics on Municipal 

Solid Waste Landfills

A Study Prepared in Partnership with the Environmental 

Protection Agency for the RE-Powering America’s Land 

Initiative: Siting Renewable Energy on Potentially 

Contaminated Land and Mine Sites

Kosol Kiatreungwattana and Gail Mosey

National Renewable Energy Laboratory

Shea Jones-Johnson and Craig Dufficy

U.S. Environmental Protection Agency

Joe Bourg, Angela Conroy, Meghan Keenan, 

and William Michaud

SRA

Katie Brown

AAAS Science & Technology Fellow

The National Renewable Energy Laboratory’s contribution was 

produced under direction of the U.S. Environmental Protection 

Agency (EPA) through Interagency Agreement IAG-09-1751 and 

Task No. WFD6.1001.

Technical Report

NREL/TP-7A30-52615

February 2013
NREL PUBLICATION NOTICE

This manuscript has been authored, in part, by employees of the Alliance for Sustainable Energy, LLC (“Alliance”) 

under Contract No. DE-AC36-08GO28308 with the U.S. Department of Energy (“DOE”).

This report was prepared as an account of work sponsored by an agency of the United States government. 

Neither the United States government nor any agency thereof, nor any of their employees, makes any warranty, 

express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of 

any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately 

owned rights. Reference herein to any specific commercial product, process, or service by trade name, 

trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, 

or favoring by the United States government or any agency thereof. The views and opinions of authors expressed 

herein do not necessarily state or reflect those of the United States government or any agency thereof.

Cover Photos: (left to right) PIX 16416, PIX 17423, PIX 16560, PIX 17613, PIX 17436, PIX 17721

Printed on paper containing at least 50% wastepaper, including 10% post consumer waste. 
Best Practices for Siting Solar Photovoltaics 

on Municipal Solid Waste Landfills

NREL/TP-7A30-52615
Best Practices for Siting Solar Photovoltaics on MSW Landfills February 2013 

i 

This document is a joint publication of the U.S. Environmental Protection Agency (EPA) and the National 

Renewable Energy Laboratory (NREL). NREL is a national laboratory of the U.S. Department of Energy, Office of 

Energy Efficiency and Renewable Energy, operated by the Alliance for Sustainable Energy, LLC. 
Best Practices for Siting Solar Photovoltaics on MSW Landfills February 2013 

ii

Contents

1. Introduction ................................................................................................................................................................ 1

1.1 Purpose and Audience for this Document ........................................................................................................... 2

1.2 Document Organization ....................................................................................................................................... 4

2. Landfill Overview........................................................................................................................................................ 5

2.1 Background on Federal MSW Landfill Regulations ............................................................................................. 5

2.1.1 MSW Landfills .............................................................................................................................................. 5

2.2 Major System Components and Requirements ................................................................................................... 6

2.3 Closure and Post-Closure Care........................................................................................................................... 7

3. Solar PV Overview..................................................................................................................................................... 9

3.1 How PV Works..................................................................................................................................................... 9

3.2 Major System Components................................................................................................................................10

3.2.1 PV Module..................................................................................................................................................10

3.2.1.1 Crystalline Silicon ................................................................................................................................. 10

3.2.1.2 Thin Film...............................................................................................................................................11

3.2.2 Inverter.......................................................................................................................................................11

3.2.3 Balance-of-System Components................................................................................................................12

3.2.3.1 Mounting Systems ................................................................................................................................12

3.2.3.2 Wiring for Electrical Connections..........................................................................................................15

3.2.4 PV System Monitoring................................................................................................................................15

3.3 Cost Overview........................................................................................................................................................16

3.3.1 Cost Trends & General Rule of Thumb for PV Costing..............................................................................16

3.3.2 Cost per Watt Breakdown ..........................................................................................................................16

4. Feasibility Considerations Unique to Landfills..........................................................................................................17

4.1 General Physical Setting ...................................................................................................................................19

4.1.1 Meteorological Setting................................................................................................................................19

4.1.2 Solar Resource Availability.........................................................................................................................20

4.1.3 Land Use and Ecological Conditions..........................................................................................................21

4.1.4 Transportation and Electrical Transmission Infrastructure .........................................................................21

4.2 Siting..................................................................................................................................................................21

4.2.1 Acreage of the Site.....................................................................................................................................21

4.2.2 Landfill Characteristics ...............................................................................................................................22

4.2.2.1 Closure Status ......................................................................................................................................22

4.2.2.2 Cap Characteristics ..............................................................................................................................23
Best Practices for Siting Solar Photovoltaics on MSW Landfills February 2013 

iii

4.2.2.2.1 Type................................................................................................................................................23

4.2.2.2.2 Age and Thickness .........................................................................................................................25

4.2.2.3 Slope and Stability................................................................................................................................25

4.2.2.4 Settlement ............................................................................................................................................26

4.2.2.5 Erosion Control and Vegetative Cover ................................................................................................. 27

4.2.2.6 Control of Leachate and Landfill Gas ...................................................................................................27

4.2.2.7 Stormwater Management .....................................................................................................................28

4.2.3 Institutional controls ...................................................................................................................................28

4.2.4 Long term maintenance requirements........................................................................................................29

4.3 PV Technology Selection and Technical Design ...............................................................................................29

4.3.1 Matching Appropriate PV Technology to Landfill Characteristics...............................................................29

4.3.2 Conceptual Design of Major System Components.....................................................................................31

4.3.3 Energy Prediction.......................................................................................................................................32

4.3.4 Economic Considerations...........................................................................................................................32

4.4 Other Potential Feasibility Factors .....................................................................................................................32

4.4.1 Community Engagement & Support...........................................................................................................33

4.4.1.1 Benefits of Community Engagement ....................................................................................................33

4.4.1.2 Openness and Transparency ...............................................................................................................33

4.4.1.3 Facilitating Community Engagement ....................................................................................................33

4.4.2 Visual Impacts and Mitigation Strategies ...................................................................................................34

4.4.3 Interconnection...........................................................................................................................................34

4.4.4 Net Metering...............................................................................................................................................35

4.4.5 Virtual Net Metering ...................................................................................................................................35

5. Design Considerations Unique to Building PV Projects on Landfills .......................................................................36

5.1 Landfill Characteristics.......................................................................................................................................36

5.1.1 Cap Characteristics....................................................................................................................................36

5.1.2 Waste Composition ....................................................................................................................................37

5.1.2.1 Differential Settlement ..........................................................................................................................37

5.1.2.1.1 Differential Settlement Forecasts....................................................................................................37

5.1.2.1.2 Differential Settlement – System Design Considerations................................................................38

5.1.2.2 Landfill Gas and Leachate....................................................................................................................39

5.2 Anchoring Systems............................................................................................................................................39

5.2.1 Shallow Poured Concrete Footers and Pre-fabricated Concrete Footers ..................................................40

5.2.2 Concrete Slabs...........................................................................................................................................40

5.2.3 Augers or Helical Piles ...............................................................................................................................41
Best Practices for Siting Solar Photovoltaics on MSW Landfills February 2013 

iv

5.2.4 Ballasted Systems......................................................................................................................................41

5.2.5 PV Integrated Geomembranes...................................................................................................................41

5.3 Mounting Systems .............................................................................................................................................42

5.3.1 Fixed-tilt Mounting Systems .......................................................................................................................43

5.3.2 PV Integrated Geomembranes...................................................................................................................44

5.4 Modules .............................................................................................................................................................44

5.4.1 Mono-crystalline .........................................................................................................................................44

5.4.2 Poly-crystalline ...........................................................................................................................................44

5.4.3 Thin Film PV Products................................................................................................................................45

5.5 System Weight Considerations..........................................................................................................................45

5.6 Stormwater Management...................................................................................................................................46

5.7 Wind/Snow Loading and Frost Protection..........................................................................................................47

5.8 Lightning Protection and Grounding ..................................................................................................................47

5.9 Cover Management ...........................................................................................................................................47

5.10 Security............................................................................................................................................................48

5.11 Integration with Landfill Gas Monitoring and Production Systems ...................................................................48

5.12 PV System Engineering Design and Layout ....................................................................................................49

6. Construction Considerations Unique to Building PV Projects on Landfills ...............................................................50

6.1 Site Preparation and Grading Considerations ...................................................................................................50

6.2 Site Compaction ................................................................................................................................................50

6.3 Penetrations of the Landfill Cap.........................................................................................................................51

6.4 Avoidance of Landfill Gas Monitoring, Piping, and Production Equipment ........................................................51

6.5 Dust Control.......................................................................................................................................................51

6.6 Stormwater Management...................................................................................................................................52

6.7 Security..............................................................................................................................................................52

7. Operations and Maintenance Considerations for PV Projects on Landfills ..............................................................53

7.1 Adherence with Landfill Post-Closure Operation, Maintenance, and Monitoring Plans .....................................53

7.2 Panel Washing and Water Management Plan or Natural Cleansing ................................................................. 53

7.3 Stormwater Management...................................................................................................................................54

7.4 Vegetation and Cover Management ..................................................................................................................54

7.5 System Monitoring and Troubleshooting ...........................................................................................................54

7.6 System Security.................................................................................................................................................54

8. A Summary of Best Practices for Siting Solar PV Projects on Landfills ...................................................................55

Appendix A: Solar PV on Landfill Projects ................................................................................................................. A-1
Best Practices for Siting Solar Photovoltaics on MSW Landfills February 2013 

v 

Appendix B: Tools and Resources............................................................................................................................. B-1

EPA’s RE-Powering America’s Land Initiative, Renewable Energy Interactive Mapping Tool.............................. B-1

Siting Renewable Energy on Contaminated Properties: Addressing Liability Concerns Fact Sheet ..................... B-2

NREL System Advisor Model ................................................................................................................................ B-2

NREL PV Watts ..................................................................................................................................................... B-4

Solar Decision Tree ............................................................................................................................................... B-6

Appendix C: Financing and Procurement Options ..................................................................................................... C-1

Owner and Operator Financing ............................................................................................................................. C-1

Third Party Developers with Power Purchase Agreements (PPA)......................................................................... C-1

Third Party “Flip” Agreements................................................................................................................................ C-1

Hybrid Financial Structures.................................................................................................................................... C-2

Solar Services Agreement and Operating Lease................................................................................................... C-2

Sale/Lease Back.................................................................................................................................................... C-2

Community Solar Gardens .................................................................................................................................... C-2

Appendix D: References ............................................................................................................................................ D-1

List of Figures

Figure 1-1: Sample conceptual design of solar PV on a closed landfill.......................................................................... 2

Figure 2-1: Typical MSW landfill components ................................................................................................................ 7

Figure 3-1: Generation of electricity from a PV cell........................................................................................................ 9

Figure 3-2: Ground mount array diagram.....................................................................................................................10

Figure 3-3: Mono- and multi-crystalline solar modules................................................................................................. 11

Figure 3.4: Thin-film solar modules installed on (i) solar energy cover and (ii/iii) fixed tilt mounting systems..............11

Figure 3-5: String inverter ............................................................................................................................................12

Figure 3-6: 2-MWp PV system with fixed tilt on former landfill in Fort Carson, Colorado.............................................14

Figure 3-7: PV system with single-axis trackers installed on former landfill at Nellis Air Force Base, Nevada ............14

Figure 3-8: PV system with dual-axis trackers .............................................................................................................15

Figure 3-9: Average PV system cost from Q1 2010 to Q2 2011 ..................................................................................16

Figure 3-10: Cost contributions of PV system components .........................................................................................16

Figure 4-1: MSW landfill and PV technology as an integrated system.........................................................................18

Figure 4-2: Photovoltaic solar resource .......................................................................................................................20

Figure 4-3: Possible cover systems .............................................................................................................................23

Figure 4-4: Example of an alternative final cover design .............................................................................................24

Figure 4-5: Sample solar PV and landfill integrated system design .............................................................................30
Best Practices for Siting Solar Photovoltaics on MSW Landfills February 2013 

vi

Figure 5-1: Precast ballast foundation for fixed tilt PV on a landfill ..............................................................................40

Figure 5-2: Slab foundation for PV system at Boulder, Colorado.................................................................................40

Figure 5-3: Ballasted anchoring system at Landfill 1A project at New Jersey Meadowlands.......................................41

Figure 5-4: Hickory Ridge Road Landfill – Geomembrane solar cover ........................................................................42

Figure B-1: Google Earth Interactive Mapping Tool................................................................................................... B-1

Figure B-2: SAM block diagram................................................................................................................................. B-2

Figure B-3: PV system inputs..................................................................................................................................... B-3

Figure B-4: Sample of SAM simulation results........................................................................................................... B-4

Figure B-5: Example of input and output of PVWatts................................................................................................. B-5

Figure B-6: Solar Decision Tree................................................................................................................................. B-6

List of Tables

Table 4-1: Technical and Economic Factors Impacting Solar Project Feasibility on Landfills......................................18

Table 4-2: Energy Density by Module and System Type for Ground-mounted PV ......................................................32

Table 5-1: Inter-relationships Between Landfill Cap Characteristics and PV System Design ......................................36

Table 8-1: Summary of Technical Considerations, Challenges, and Best Practices....................................................55

Table A-1: Completed Solar Landfill Projects............................................................................................................. A-1

List of Highlights 

Highlight 2-1: Trends in MSW Landfill Ownership.......................................................................................................... 5

Highlight 4-1: Solar Geomembrane Covers for Landfill Applications ...........................................................................22

Highlight 4-2: Examples of Community Engagement...................................................................................................33

Highlight 5-1: Major Considerations Impacting Solar PV Project Design on Landfills ..................................................36

Highlight 6-1: Major Construction Considerations for Building PV Projects on Landfills .............................................50

Highlight 7-1: Major Considerations and Best Practices .............................................................................................53
Best Practices for Siting Solar Photovoltaics on MSW Landfills February 2013

1 

1. Introduction 

Through the RE-Powering America’s Lands Initiative1, the U.S. EPA promotes the reuse of potentially contaminated 

properties, landfills, and mining sites for renewable energy generation. EPA has identified several benefits for siting 

solar photovoltaics (PV) facilities on potentially contaminated lands and municipal solid waste (MSW) landfills, noting 

that these sites: 

• May provide an economically viable reuse for sites that may have significant cleanup costs or low real 

estate development demand; 

• May have environmental conditions that are not well suited for commercial or residential redevelopment; 

• Can be developed in place of limited open space, preserving the land as a carbon sink and/or for other 

ecosystem services; 

• Generally are located near existing roads and energy transmission or distribution infrastructure; 

• May be adequately zoned for renewable energy;

• Can provide job opportunities in urban and rural communities; 

• Can advance cleaner and more cost effective energy technologies; and 

• May reduce the environmental impacts of energy systems (e.g., reduce greenhouse gas emissions). 2

EPA has screened more than 11,000 potentially contaminated sites and MSW landfills3 — covering nearly 15 million 

acres across the United States — for suitability to site renewable energy generation facilities, including utility-scale 

solar. Maps depicting the locations of these EPA tracked sites and their potential for supporting renewable energy 

generation can be found at: www.epa.gov/oswercpa/mapping_tool.htm. These maps enable users to view screening 

results for various renewable energy technologies at each site. 

In 1988, before municipal solid waste regulations in 40 CFR 258 were promulgated, there were an estimated 7,924 

landfills in the U.S. In 2009, that number dropped to 1,908 landfills. The landfills that closed over the intervening 

years—plus portions of active landfills with closed cells—represent thousands of acres of real property that may be 

suitable for siting solar PV. At least one study estimates the area of closed landfills to be hundreds of thousands of 

acres. As part of the EPA mapping effort, over 1,600 of the country’s landfills have been pre-screened for renewable 

energy potential.

Many MSW landfills are particularly well-suited for solar development because they are often: 

• Located near critical infrastructure including electric transmission lines and roads;

• Located near areas with high energy demand (e.g., large population bases); 

• Constructed with large areas of minimal grade (0-2 percent) needed for optimal siting of solar photovoltaic 

(PV) structures; 

• Offered at lower land costs when compared to open space; and

• Able to accommodate net metered or utility scale projects.

 

1 EPA OSWER Center for Program Analysis. Siting Clean and Renewable Energy on Contaminated Lands and Mining Sites. Factsheet. Undated. 2 EPA. RE-Powering America’s Land: Siting Renewable Energy on Potentially Contaminated Land and Mine Sites. Anywhere the Sun Shines: Developing Solar 

Energy on Contaminated Land. October 2009. 3 The Landfill Methane Outreach Program (LMOP) maintains a list of MSW landfills which are candidates for landfill gas (LFG) projects, have potential for LFG, 

LFG systems under construction, operational LFG or shutdown LFG facilities. This program is a voluntary assistance and partnership program that promotes 

the use of landfill gas as a renewable, green energy resource. These landfills were mapped as part of the RE-Powering initiative to show landfills which could 

be developed for LFG and solar PV renewable energy. Visit EPA’s LMOP website at www.epa.gov/lmop/ for more information on landfill gas energy projects.
Best Practices for Siting Solar Photovoltaics on MSW Landfills February 2013

2 

Source: PV Navigator

Figure 1-1: Sample conceptual design of solar PV on a closed landfill4

1.1 Purpose and Audience for this Document

This document is a joint publication of EPA and the National Renewable Energy Laboratory (NREL). EPA and NREL 

created this document to provide assistance in addressing common technical challenges for siting PV on MSW 

landfills, and in this respect EPA and NREL expect that stakeholders, such as solar developers, landfill owners, and 

federal, state, and local governments, may find this information useful. The information in this document is primarily 

targeted toward a technical audience geared toward the functional integration of a PV system and the engineered 

systems typically at MSW landfills. This document focuses on MSW landfills, including but not limited to those that 

are regulated under EPA’s Resource Conservation and Recovery Act (RCRA) regulations at 40 CFR Part 258. 

However, it may be determined on a site-by-site basis if this information may be useful for siting PV solar on other 

types of landfills such as those that are exempt from 40 CFR Part 258 and hazardous waste landfills. Note that MSW 

landfills are subject to varying regulatory requirements, under RCRA and other authorities at the federal, state, and/or 

 

4 This figure has been modified from the original PV Navigator file for the use of this report
Best Practices for Siting Solar Photovoltaics on MSW Landfills February 2013

3 

local level. Therefore, this document does not attempt to apply the best practices discussed to a particular regulatory 

context, and the strategies discussed may or may not be available at a particular site.5

Currently, there are only a handful of completed PV projects on landfills throughout the country, with many more in 

the planning stages (see Appendix A for a list of identified projects). EPA and NREL, along with our state and local 

partners, have examined many of these projects and reviewed current designs and approaches in an ongoing effort 

to identify best practices for siting PV on MSW landfills. The data and case studies contained in this document reflect 

current engineering and scientific practices. Furthermore, this is not an exhaustive list of best practices. Project 

stakeholders should consider whether different or additional approaches are appropriate in light of site specific 

conditions.

 

5 This document does not address what activities associated with siting solar PV may be appropriate on landfills that may be subject to cleanup actions taken 

pursuant to CERCLA and/or RCRA Corrective Action. Further, this document is not intended to discuss CERCLA liability considerations. For more 

information on the EPA’s cleanup enforcement programs, see http://www.epa.gov/enforcement/waste/index.html#Cleanup. 

Disclaimer 

This document provides general information and guidance regarding siting solar PV facilities on MSW landfills. It 

does not address all information, factors, or considerations that may be relevant in a particular situation. This 

document is not legally binding. The word “should” and other similar terms used in this document are intended as 

general recommendations or suggestions that might be generally applicable or appropriate and should not be taken 

as providing legal, technical, financial, or other advice regarding a specific situation or set of circumstances.

This document describes and summarizes statutory provisions, regulatory requirements, and policies. The 

document is not a substitute for these provisions, regulations, or policies, nor is it a regulation itself. In the event of 

a conflict between the discussion in this document and any statute, regulation, or policy, this document would not 

be controlling and cannot be relied upon to contradict or argue against any EPA position taken administratively or 

in court. It does not impose legally binding requirements on EPA or the regulated community, and might not be 

applicable in a particular situation based upon the specific circumstances. This document does not modify or 

supersede any existing EPA guidance document or affect the Agency’s enforcement discretion in any way.

References to third-party publications, websites, commercial products, process, or services by trade name, 

trademark, manufacturer, or otherwise, are for informational purposes only. No endorsement or recommendation 

should be inferred and is not implied. EPA, NREL and the United States Government do not endorse any nonfederal product, service or enterprise.
Best Practices for Siting Solar Photovoltaics on MSW Landfills February 2013

4 

1.2 Document Organization 

The document is organized into eight major chapters: 

Chapter 1. Provides a brief overview of the document. 

Chapter 2. Landfill Overview: Discusses waste disposal practices in the U.S., benefits for siting solar technologies on 

MSW landfills, and typical landfill components. 

Chapter 3. PV Overview: Describes the types of PV technology currently sited on landfills and provides a brief 

overview for typical PV system components, and outlines estimated costs for PV technologies currently sited on 

landfills, including installation costs. 

Chapter 4. Feasibility Considerations Unique to Landfills: Provides a detailed discussion on the decision-grade

feasibility assessment process with a focus on the unique considerations (e.g., siting, technology selection) that 

should be taken into account when planning for PV system development on a landfill. 

Chapter 5. Design Considerations Unique to Building PV Projects on Landfills: Outlines landfill characteristics to be 

taken into account when designing a solar project on a landfill, PV system layout and component system designs, 

and considerations regarding the integrated PV-landfill system. 

Chapter 6. Construction Considerations Unique to Building PV Projects on Landfills: Discusses site preparation, 

grading, site compaction, working around landfill features, and other site-specific aspects that should be considered 

before starting construction of a PV system on a landfill. 

Chapter 7. Operations and Maintenance Considerations for PV Projects on Landfills: Outlines the types of longer 

term actions (e.g., adherence with post-closure plans, water management, module cleaning) that should be taken to 

ensure continued safe and effective operation of the PV system once it is established. 

Chapter 8. A Summary of Best Practices for Siting Solar PV Projects on Landfills: Summarizes the best practices for 

siting solar PV projects on landfills as discussed throughout the document. 

This document also contains the following appendices: 

Appendix A. List of Completed Solar PV on Landfill Projects

Appendix B. Tools and Resources 

Appendix C. Financing and Procurement Options

Appendix D. References
Best Practices for Siting Solar Photovoltaics on MSW Landfills February 2013

5 

Highlight 2-1: Trends in MSW Landfill 

Ownership

EPA promulgated federal regulations in 1991 

governing the technical criteria for municipal 

solid waste (MSW) landfills under Subtitle D of 

the Resource Conservation and Recovery Act. 

While compliance with these regulations 

provided greater protection to human health and 

the environment, they also made it more 

complex to operate MSW landfills. 

The result was a trend towards larger, regional 

and privately-owned MSW landfills. In 2004, an 

estimated 64% of landfills were publicly owned; 

however, these landfills account for only 17% of 

permitted MSW landfill capacity while the 595 

privately owned MSW landfills account for 83% 

of capacity nationwide. 

2. Landfill Overview

This chapter of the document provides an overview of landfills and the related RCRA regulation, and, in particular, 

the requirements for MSW landfills. This chapter also provides an overview of common system components, EPA’s

design standards for MSW landfills, and closure and post-closure requirements to provide a quick background on 

landfill components and activities that should be considered when siting solar technologies. 

2.1 Background on Federal MSW Landfill Regulations 

Landfills constructed before the 1960s were often not much more 

than open pits in the ground used to dispose of all types of waste. 

These facilities were generally constructed without any 

engineering design or siting criteria and with few regulatory 

controls. Thus, volatile organic compounds, pesticides, PCBs, 

polynuclear aromatic hydrocarbons (PAHs), cyanides, heavy 

metals, and other contaminants were at risk to migrate, potentially

endangering public health and the environment.6 

Pursuant to the Solid Waste Disposal Act, as amended (typically 

referred to by the name of one of those amendments, the 

Resource Conservation and Recovery Act of 1976, or RCRA), 

EPA has established standards for hazardous waste 

management, including disposal, as well as minimum standards 

(criteria) for non-hazardous waste disposal facilities and practices. 

EPA has regulations defining when a RCRA “solid waste” is also a 

“hazardous waste” for purposes of its hazardous waste 

regulations. Hazardous wastes are subject to comprehensive 

“cradle to grave” management under EPA’s RCRA Subtitle C Part 40 CFR 260-268, 270-273, 278-279. Due to 

additional complexities associated with the different requirements for hazardous waste landfills, this document does 

not discuss siting PV on these types of disposal units. However, PV may be viable on these landfills as well.

2.1.1 MSW Landfills 

This document focuses on MSW landfills, including those subject to EPA’s MSW landfill regulations at 40 CFR Part 

258. As a general matter, those regulations provide for location restrictions, operating criteria, design criteria, ground 

water monitoring and corrective action, closure and post-closure care criteria, and financial assurance criteria 

applicable to owners and operators of municipal solid waste landfill units. Note that the full set of regulations at 40 

CFR Part 258 does not apply to all MSW units. Depending on the circumstances (e.g. closure date), a particular 

MSW landfill unit may be subject to only particular requirements under 40 CFR Part 258, or not subject to those 

standards at all.

For example, if a landfill stopped receiving waste prior to:

• October, 9, 1991, then 40 CFR part 258 (Subtitle D) does not apply to the landfill. 

• October, 9, 1993, then the landfill is subject only to final cover requirements in 40 CFR 258 Subpart C. 

If a landfill received waste after October, 9, 1993, the landfill is subject to all provisions in 40 CFR Part 258.

EPA’s regulations under 40 CFR Part 258.2 define a MSW landfill unit in part as a discrete area of land or excavation 

that receives household waste. In addition, EPA’s regulations provide that MSW landfill units may also receive other 

types of RCRA non-hazardous wastes, such as commercial solid waste, non-hazardous sludge, conditionally exempt 

 

6 Department of Health and Human Services, Agency for Toxic Substances and Disease Registry. Landfill Gas Primer: An Overview for Environmental Health 

Professionals. November 2001.
Best Practices for Siting Solar Photovoltaics on MSW Landfills February 2013

6 

small quantity generator (CESQG) waste, and industrial solid waste. Note that the management of non-hazardous 

waste is not necessarily without risk even if classified as non-hazardous waste under the RCRA regulations. Under 

RCRA, states are to adopt and implement permit programs or other systems of prior approval to ensure that MSW 

landfills comply with the relevant federal criteria. RCRA requires that EPA determine whether state permit programs 

are adequate to ensure such compliance. EPA continues to monitor state permitting programs and maintains a list of 

approved states.7

EPA’s criteria for MSW landfill units apply regardless of whether the unit is in an approved state or not. However, 

owners and operators in approved states have more flexibility in how they comply with the federal standards. Note 

that some states may impose additional requirements that are more stringent or broader in scope than the federal 

requirements.

Finally, note that requirements under other federal, state or local authorities may apply to a particular MSW landfill. 

Developers must work closely with state and local regulators to ensure compliance with applicable regulatory 

requirements. 

2.2 Major System Components and Requirements 

Federal landfill regulations include requirements for specific features and specific practices. Depending on the date 

when the landfill started accepting waste, federal RCRA regulations for MSW landfills may include requirements for: 

• Location – Location restrictions include proximity to airports, floodplains, wetlands, unstable areas, fault 

areas, and seismic impact zones. 

• Design – These requirements may include: 

o A composite liner comprised of a flexible membrane (geomembrane) overlaying two feet of 

compacted soil lining the bottom and sides of the landfill. A landfill liner serves to protect ground

water and the underlying soil from leachate releases. 

o A leachate collection and removal system. These are generally located on top of the composite 

liner to remove leachate from the landfill for treatment and disposal. 

• Operating practices – These include covering waste frequently with soil or other materials to control odor, 

blowing litter, fires, disease vectors, such as insects and rodents; and scavenging. Also, owners/operators 

must implement a program for detecting and preventing the disposal of regulated hazardous waste. See 40 

CFR 258.20(a).

• Ground water monitoring and corrective action – These include installation and testing of ground water 

wells to detect and assess ground water contamination, and establishment of necessary corrective 

measures for identified releases. 

• Closure and post-closure care – These include installation of a final landfill cover and providing long-term 

care of closed landfills.8 

Under the Clean Air Act, a landfill gas collection system is required on landfills with a design capacity greater than 2.5 

million megagrams (Mg), and with an emission greater than 50 Mg/year of non-methane organic compounds as 

defined by the US EPA new source performance standards (NSPS) and emission guidelines (40 CFR 60.752). 9 

Figure 2-1 shows common MSW landfill components. 

 

7 Approved state means a state whose Subtitle D permit program or other system of prior approval and conditions required under section 4005(c)(1)(B) of 

RCRA has been determined to be adequate by EPA, as defined in 40 CFR 239. 8 Waste – Non-Hazardous Waste – Municipal Solid Waste.” EPA. Accessed April 22, 2012: http://www.epa.gov/osw/nonhaz/municipal/landfill.htm. 9 EPA’s New Source Performance Standards for MSW Landfills (NSPS) prescribe a landfill surface emissions monitoring methodology that relies on 

identification of discrete exceedances of a 500 ppm methane standard. After the installation of extraction wells, the landfill surface must be monitored for 

methane concentrations less than 500 ppm above background levels. If an exceedance is detected, corrective action must be taken by performing cover 

maintenance or adjusting the collection system operating parameters (40 CFR 60 Subpart).
Best Practices for Siting Solar Photovoltaics on MSW Landfills February 2013

7 

Source: EPA

Figure 2-1: Typical MSW landfill components10

EPA encourages all parties to fully examine federal, state, and local standards before undertaking solar planning and 

construction activities on a landfill. Overall, PV systems sited at landfills should be integrated with, and designed with 

careful attention to, these regulatory requirements. 

2.3 Closure and Post-Closure Care

Once a landfill has been filled, it must be closed according to applicable regulations. Under EPA’s MSW landfill 

regulations, the applicability of closure and post-closure requirements varies depending upon a number of 

considerations, including date of final receipt of waste, volume of waste disposed of, and other considerations. State, 

local, and/or tribal law requirements may also apply to the closure and post-closure processes. 

Under EPA’s MSW landfill regulations, owners or operators, where applicable, are required to install a final cover on 

the unit as part of the closure process. The regulations specify design parameters, although the director of an 

approved state may approve an alternative design. The regulations also specify timeframes for closure generally 

after receiving its final shipment of waste, a unit must begin closure operations within 30 days, although an owner or 

operator may delay closure for up to one year if additional capacity remains and there is a reasonable likelihood that 

the unit will receive additional wastes. Any further delays after one year require approval from the director of an 

approved state. All closure activities must be completed within 180 days of beginning closure (with the exception of 

an extension from the director of an approved state), and the owner/operators must certify that the closure has been 

completed in accordance with the closure plan, and must place the certification in the operating record. 

Technical issues that are typically addressed during closure include the following: 

• Degree and rate of post-closure settlement and stresses imposed on soil liner components;

• Long-term durability and survivability of cover system;

• Long-term waste decomposition and management of landfill leachate and gases; and

• Environmental performance of the combined bottom liner and final cover system.

 

10 Adapted from RCRA Orientation Manual 2008: Resource Conservation and Recovery Act. (2008). EPA. p II-11.

Explosive Gas

Monitoring Well

Gas

Vent

Leachate

Collection

Ground Water Liner

Monitoring Well

Waste
Best Practices for Siting Solar Photovoltaics on MSW Landfills February 2013

8 

EPA’s MSW landfill regulations also generally provide that for 30 years11 after closure, the owner/operator is 

responsible for conducting post-closure care. Activities required during post-closure care can include: 

• Maintaining the integrity and effectiveness of any final cover;

• Maintaining and operating the leachate collection system; 

• Monitoring ground water; and

• Maintaining and operating the gas monitoring system

The regulations specify that any use of the land during the post-closure period must not disturb the integrity of the 

waste containment systems or the functioning of the monitoring systems, except in specified circumstances as 

provided in 40 CFR 258 Subpart F. In addition, the owner or operator must prepare a written post-closure plan, and 

include within it a description of planned uses during the post-closure care period. At the end of the post-closure care 

period, the owner/operator must certify that the post-closure care has been completed in accordance with the postclosure care plan and must place the certification in the operating record. 

Any solar project development activities on closed landfills must be planned to take into account these closure and 

post-closure activities and requirements. To do so, all solar projects on MSW landfills must be coordinated closely 

with state and local authorities, as they are mainly responsible for ensuring that these requirements and other state 

law requirements are met. 

 

11 Approved states may vary this interval. In addition, states and local authorities may approve the use of alternative final covers and grant extensions for 

beginning and ending closure activities. 
Best Practices for Siting Solar Photovoltaics on MSW Landfills February 2013

9 

3. Solar PV Overview

3.1 How PV Works

Solar PV technology converts energy from solar radiation directly into electricity. Solar PV cells are the electricitygenerating component of a solar energy system. When sunlight (photons) strikes a PV cell, an electric current is 

produced by stimulating electrons (negative charges) in a layer in the cell designed to give up electrons easily. The 

existing electric field in the solar cell pulls these electrons to another layer. By connecting the cell to an external load, 

this current (movement of charges) can then be used to power the load, e.g., light bulb. 

(-)

(+)

-

- -

-

Electron

Current flow

-

Solar cell

- - -

Load

Source: EPA 

Figure 3-1: Generation of electricity from a PV cell

PV cells are assembled into a PV panel or module. PV modules are then connected to create an array. The modules 

are connected in series and then in parallel as needed to reach the specific voltage and current requirements for the 

array. The direct current (DC) electricity generated by the array is then converted by an inverter to useable 

alternating current (AC) that can be consumed by adjoining buildings and facilities or exported to the electricity grid. 

PV system size varies from small residential (2-10 kilowatts (kW)), commercial (100-500 kW), to large utility scale

(10+ megawatts (MW)). Central distribution plants are also currently being built on the 100 MW+ scale. Electricity 

from utility-scale systems, such as solar on landfills, is commonly sold back to the electricity grid.
Best Practices for Siting Solar Photovoltaics on MSW Landfills February 2013

10

3.2 Major System Components

Source: NREL

Figure 3-2: Ground mount array diagram

A typical PV system is made up of several key components including:

• PV modules

• Inverter

• Balance-of-system components

These, along with other PV system components, are discussed in turn below. 

3.2.1 PV Module

Module technologies are differentiated by the type of PV material used, resulting in a range of conversion efficiencies 

from light energy to electrical energy. The module efficiency is a measure of the percentage of solar energy 

converted into electricity. 

Two common PV technologies that have been widely used for commercial- and utility-scale projects are crystalline 

silicon and thin film. Additional PV technologies are also commercially available, but are not covered in this 

document.

3.2.1.1 Crystalline Silicon

Traditional solar cells are made from silicon. Silicon is quite abundant and nontoxic. It builds on a strong industry 

from both the supply (silicon industry) and product side. This technology has been demonstrated as a consistent and 

high efficiency technology over 30 years in the field. The performance degradation, a reduction in power generation 

due to long-term exposure, is under 1 percent per year. Silicon modules have typical power-production warranties in 

the 25-30-year range but can continue producing energy beyond this timeframe. 
Best Practices for Siting Solar Photovoltaics on MSW Landfills February 2013

11

Typical overall efficiency of silicon solar modules is between 12-18 percent. However, some manufacturers of monocrystalline modules have demonstrated an overall efficiency nearing 20 percent. This range of efficiencies represents 

significant variation among the crystalline silicon technologies available. The technology is generally divided into 

mono- and multi-crystalline technologies, which indicates the presence of grain-boundaries (i.e., multiple crystals) in 

the cell materials and is controlled by raw material selection and manufacturing technique. Crystalline silicon modules

are widely used based on deployments worldwide.

Figure 3-3 shows two examples of crystalline solar modules: mono- and poly-silicon installed on tracking mounting 

systems. 

Source: SunPower Corporation Source: NREL PIX 13823

Figure 3-3: Mono- and multi-crystalline solar modules

3.2.1.2 Thin Film

Thin-film PV cells are made from amorphous silicon (a-Si) or non-silicon materials such as cadmium telluride (CdTe)

or copper indium gallium (di)selenide (CIGS). These cells use layers of semiconductor materials only a few 

micrometers thick. Due to the unique nature of thin films, some thin-film cells are constructed into flexible modules, 

enabling unique mounting option such as solar energy covers for landfills. Other thin film modules are assembled into 

rigid constructions that can be used in fixed tilt or, in some cases, tracking system configurations.

The efficiency of thin-film solar cells is generally lower than for crystalline cells. Current overall efficiency of a thin-film 

module is between 6-8 percent for a-Si, 11-14 percent for CIGS, and 11-12 percent for CdTe. Figure 3-4 shows thinfilm solar modules. 

Source: Republic Services Inc. Source: NREL PIX 14726 Source: NREL PIX 17395

Figure 3.4: Thin-film solar modules installed on (i) solar energy cover and (ii/iii) fixed tilt mounting systems 

Industry standard warranties of both crystalline and thin film PV modules typically guarantee system performance of 

80 percent of the rated power output for 25 years. After 25 years, they will continue producing electricity at a lower 

performance level.

3.2.2 Inverter

Inverters convert DC electricity from the PV array into AC and can connect seamlessly to the electricity grid. Inverter 

efficiencies can be as high as 98.5 percent. 
Best Practices for Siting Solar Photovoltaics on MSW Landfills February 2013

12

Inverters also sense the utility power frequency and synchronize the PV-produced power to that frequency. When 

utility power is not present, the inverter will stop producing AC power to prevent “islanding” or putting power into the 

grid while utility workers are trying to fix what they assume is a de-energized distribution system. This safety feature 

is built into all grid-connected inverters in the market. Electricity produced from the PV system may be fed to a stepup transformer to increase the voltage to match the grid.

There are two primary types of inverters for grid-connected systems: string and micro inverters. Each type has 

strengths and weakness and may be recommended for different types of installations.

String inverters are most common and typically range in size from 1.5 kW to 1,000 kW. These inverters tend to be 

cheaper on a capacity basis, as well as have high efficiency and lower O&M costs. String inverters offer various sizes 

and capacities to handle a large range of voltage output. For larger systems, string inverters are combined in parallel 

to produce a single point of interconnection with the grid. Warranties typically run between 5 and 10 years, with 10 

years being the current industry standard. On larger units, extended warranties up to 20 years are possible. Given 

that the expected life of the PV modules is 25-30 years, an operator can expect to replace a string inverter at least 

one time during the life of the PV system. 

Microinverters are dedicated to the conversion of a single PV module’s power output. The AC output from each 

module is connected in parallel to create the array. This technology is relatively new to the market and in limited use 

in larger systems due to potential increase in O&M associated with significantly increasing the number of inverters in 

a given array. Current microinverters range in size between 175 W and 380 W. These inverters can be the most 

expensive option per watt of capacity. Warranties range from 10 to 20 years. Small projects with irregular modules 

and shading issues typically benefit from microinverters. 

With string inverters, small amounts of shading on a solar module will significantly affect the entire array production. 

Instead, it impacts only that shaded module if micro-inverters are used. Figure 3.5 shows a string inverter.

Source: NREL PIX 07985

Figure 3-5: String inverter 

3.2.3 Balance-of-System Components

In addition to the solar modules and inverter, a solar PV system consists of other parts called balance-of-system 

components, which include:

• Mounting racks and hardware for the modules

• Wiring for electrical connections

3.2.3.1 Mounting Systems

The structure holding the PV modules is referred to as the mounting system. The mounting system can be either 

directly anchored into the ground (via driven piers or concrete footers) or ballasted on the surface without ground 
Best Practices for Siting Solar Photovoltaics on MSW Landfills February 2013

13

penetration. Mounting systems should be selected and designed to withstand local wind loads, which range from 90–

120 mph range for most areas or 130 mph or more for areas with hurricane potential. Depending on the region, snow 

and ice loads should also be design considerations for the mounting system. For landfill applications, mounting 

system designs will be primarily driven by these considerations coupled with settlement concerns. More details on 

settlement and anchoring systems can be found can be found in Sections 4.2.2.4 and 5.2, respectively. 

Typical ground-mounted systems can be categorized as fixed tilt or tracking. Fixed-tilt mounting systems are 

characterized by modules installed at a set angle, typically based on site latitude and wind conditions, to increase 

exposure to solar radiation throughout the year. Fixed-tilt systems are used at many landfill sites. Fixed-tilt systems may 

have lower maintenance costs but generate less energy (kWh) per unit power (kW) of capacity than tracking systems

(Figure 3-6). 

Tracking systems rotate the PV modules so they are following the sun as it moves across the sky. This increases 

energy output but also may increase maintenance and equipment costs slightly. Single-axis tracking, in which PV is 

rotated on a single axis, can increase energy output up to 25 percent or more (Figure 3-7). With dual-axis tracking, 

PV is able to directly face the sun all day, potentially increasing output up to 35 percent or more. Due to alignment 

requirements of the mounting system, single- and dual-axis trackers are not generally deployed on landfill cells, as 

discussed below. Tracking systems may be more appropriate for landfill buffer zones when permitted, since 

settlement concerns are typically less significant. 

The selection of mounting type is dependent on many factors including installation size, electricity rates, government 

incentives, land constraints, latitude, and local weather. Landfill applications raise additional design considerations 

due to differential settlement, which can impact both structural integrity and energy generation of the PV system. 

Mitigation for settlement effects should be taken into account in the design of both fixed tilt and tracking systems. 

Impacts on energy performance may be more severe for tracking systems due to alignment requirements. Depending 

on the degree of predicted settlement, fixed tilt systems may be preferable, while trackers may be sited primarily in 

buffer areas around the closed landfill cell when permitted. In addition, all of the PV systems need to take into 

account the landfill monitoring operations and ongoing site conditions noted in Chapters 2.2 and 2.3. 

Selection of the mounting system is also heavily dependent on anchoring or foundation selection. The mounting 

system design will also need to meet applicable local building code requirements with respect to snow, wind, and 

earthquake factors. Selection of mounting types should also consider frost protection needs especially in cold 

regions, such as New England. This topic is covered in additional detail in Chapter 5.2 and 5.3, including site-specific 

considerations for landfill applications. 
Best Practices for Siting Solar Photovoltaics on MSW Landfills February 2013

14

Source: NREL PIX 17394

Figure 3-6: 2-MWp PV system with fixed tilt on former landfill in Fort Carson, Colorado 

Source: NREL PIX 15280

Figure 3-7: PV system with single-axis trackers installed on former landfill at Nellis Air Force Base, Nevada
Best Practices for Siting Solar Photovoltaics on MSW Landfills February 2013

15

Source: NREL PIX 04827

Figure 3-8: PV system with dual-axis trackers

3.2.3.2 Wiring for Electrical Connections

Electrical connections, including wiring, disconnect switches, fuses, and breakers are required to meet electrical code 

(e.g., NEC Article 690) for both safety and equipment protection.

In most traditional applications, wiring from (i) the arrays to inverters and (ii) inverters to point of interconnection is 

generally run as direct burial through trenches. In landfill applications, this wiring may be required to run through 

above-ground conduit due to restrictions with cap penetration or other concerns. Therefore, landfill owners or 

operators should disclose any such restrictions, if applicable. Similarly, it is recommended that developers reflect 

these costs in the quote when costing out the overall system. 

3.2.4 PV System Monitoring 

Monitoring PV systems can be essential for reliable functioning and maximum yield of a system. It can be as simple 

as reading values such as produced AC power, daily kilowatt-hours, and cumulative kilowatt-hours locally on an LCD 

display on the inverter. For more sophisticated monitoring and control purposes, environmental data such as module 

temperature, ambient temperature, solar radiation, and wind speed can be collected. Remote control and monitoring 

can be performed by various remote connections. Systems can send alerts and status messages to the control 

center or user. Data can be stored in the inverter’s memory or in external data loggers for further system analysis. 

Collection of this basic information is standard for solar systems and not unique to landfill applications.

Weather stations are typically installed at large scale systems. Weather data such as solar radiation and temperature 

can be used to predict energy production, enabling comparison of the target and actual system output and 

performance and identification of under-performing arrays. Operators may also use this data to identify required 

maintenance, shade on modules, accumulated soiling on modules, etc. Monitoring system data can also be used for 

outreach and education. This can be achieved with publicly available, online displays; wall-mounted systems; or even 

smart phone applications. 
Best Practices for Siting Solar Photovoltaics on MSW Landfills February 2013

16

3.3 Cost Overview

3.3.1 Cost Trends & General Rule of Thumb for PV Costing 

The cost of a PV system depends on the system size and other factors such as geographic location, mounting

system, type of PV module, among others. Based on significant cost reductions seen in 2011, the average cost for 

utility-scale ground mounted systems have declined from $4.80 per watt in Q1 2010 to $3.75 per watt in Q2 2011. 

With a growing market and an increasing supply, further cost reduction is expected as market conditions evolve.

Figure 3-9 shows the cost per watt of PV system from 2010 to 2011 for utility scale projects.

Source: U.S. Solar Market Insight 2nd Quarter 2011, Solar Energy Industries Association

Figure 3-9: Average PV system cost from Q1 2010 to Q2 201112

3.3.2 Cost per Watt Breakdown 

Historically, PV modules have represented approximately half of the system cost. Based on significant price 

reductions due to a variety of market forces, the module cost represented about 31 percent of overall system costs

as of a 2011 assessment. Costs for each component category are shown below as a proportion of overall system 

cost. 

Source: U.S. Solar Energy Trade Assessment 2011, Solar Energy Industries Association

Figure 3-10: Cost contributions of PV system components

 

12 US Solar Market Insight 2010 Year-end Review.” Solar Energy Industries Association. Accessed November 15, 2011: www.seia.org/cs/research/SolarInsight 
Best Practices for Siting Solar Photovoltaics on MSW Landfills February 2013

17

4. Feasibility Considerations Unique to Landfills

Many MSW landfills are well-suited for solar development; however, not every landfill is an ideal candidate. Since 

some landfills are better suited than others for solar PV development, candidate landfills should be carefully selected. 

Determining the feasibility of siting solar PV on a landfill is typically conducted through a two-step process: 1) a 

preliminary feasibility assessment, and 2) an investment-grade technology and economic feasibility study. 

A decision-grade feasibility assessment usually occurs through gathering readily available information regarding the 

general setting for the project, landfill characteristics, appropriate PV technologies, and regulatory requirements to

determine if a project merits a more serious investment of the time and resources required by an investment-grade 

feasibility study. EPA’s Google Earth mapping tool (described in greater detail in Appendix B) and the landfill-specific 

section of the solar PV decision tree (provided in Appendix B) are examples of tools that could be useful in 

conducting a decision-grade feasibility assessment. A decision-grade feasibility assessment typically involves 

development of a “conceptual design” of the PV system, which is a more generalized characterization of the PV 

system components in terms of module type, mounting system, anchoring system, and inverters, plus cost estimates 

for these components and their installation. This conceptual design is then used to develop estimates of the PV 

system’s costs, benefits, and performance characteristics, and to determine if a project warrants further consideration 

based on economic metrics, operational requirements, and regulatory considerations. Decision-grade feasibility 

assessments might be performed by landfill operators, PV developers, or independent consultants to arrive at a “go 

or no-go” decision on a landfill-based PV project.

Following the decision-grade feasibility assessment, qualified projects may undergo a more in-depth, investmentgrade feasibility study. Project sponsors generally conduct these studies in order to: (i) verify the information and 

assumptions contained in the decision-grade feasibility assessment; (ii) collect and analyze additional information as 

necessary; and (iii) to develop a preliminary engineering design of the system that is optimized for the desired 

performance characteristics of the system and the site conditions. The investment-grade feasibility study builds upon 

the decision-grade analysis, and typically provides a study that may be used for obtaining financing of the project, if 

desired. These studies typically include detailed performance modeling of the PV system’s projected energy output 

characteristics over the life of the system, as well as a financial pro forma detailing the costs, revenues/savings, and 

economic metrics (e.g., internal rate of return, levelized cost of energy, and payback period) of the project over the 

system life. Investment grade feasibility studies are typically conducted by professionals such as project developers 

or independent consultants with experience in PV system design and development, PV system performance 

modeling, and financial analysis of PV projects. 

Typically the main factors that are examined in both the decision-grade feasibility assessment and the investmentgrade feasibility study are essentially the same, although the level of detail in the information collected and the rigor 

of the analyses conducted are much higher for the investment-grade feasibility study. An overview of the main factors 

impacting net-metered13 and utility scale solar project feasibility on landfills is provided in Table 4-1, with the factors 

likely to be relevant for each type of project marked with a dot “•”. Each factor is examined in more detail in the 

remaining sections of this chapter.

It is important when analyzing the feasibility of siting a solar project on a landfill to think of the landfill in terms of 

functional requirements—i.e., to characterize the landfill in terms of not only its physical components and systems but 

also the functions that those systems are intended to serve. Functional requirements of a landfill cap, for example, 

can include ensuring no direct contact with waste, preventing water infiltration, and contributing to the effectiveness 

of landfill gas and stormwater management systems. This focus on function will help ensure that the feasibility 

analysis asks the right questions and explores appropriate PV technologies and alternatives for adapting these 

technologies in landfill applications.

 

13 Net metering is a utility policy incentive that encourages development of PV and other renewable energy systems by its customers to offset on-site energy 

requirements.
Best Practices for Siting Solar Photovoltaics on MSW Landfills February 2013

18

Figure 4-1: MSW landfill and PV technology as an 

integrated system. The analyst should base feasibility 

considerations on the predicted settlement of the MSW 

landfill with the PV system, not the baseline forecast.

In addition, it is important to think about PV 

projects on landfills in terms of an integrated 

system, not as separate landfill and PV 

systems. For example, at the outset of the 

analysis, existing forecasts may predict 

settlement based on historic data. These 

forecasts represent predicted settlement in the 

absence of a PV system. When a PV system is 

installed, it could affect the rate and/or pattern 

of settlement. The analysis should consider the 

interplay of the PV system and the landfill. 

Using this example, the analyst should not 

accept settlement forecasts as a given 

condition, but should consider future settlement 

in the context of the integrated landfill-PV 

system. Figure 4-1 illustrates this point. In this 

example, the integrated system results in 

greater settlement in the landfill over time, 

perhaps because of the greater weight of the 

PV installation.

The following sections of this chapter provide 

an overview of feasibility considerations that 

are likely to be relevant when conducting preliminary decision-grade feasibility assessments and investment-grade 

feasibility studies of solar projects on landfills. These sections examine in greater detail issues surrounding the site 

characteristics, the selection of PV technology applications and development of a conceptual system design based 

on site characteristics, and regulatory factors to consider in assessing the technical and economic potential of landfillbased PV systems. 

Note that this is not an exhaustive list of feasibility considerations. Project stakeholders should consider whether 

different or additional approaches are appropriate in light of site specific conditions. 

Table 4-1: Technical and Economic Factors Impacting Solar Project Feasibility on Landfills

Factor Net-Metered Project Utility-Scale Project for 

Export to Grid

Age of Landfill • •

Useable Acreage • •

Slope • •

Cap Characteristics • •

Landfill Maintenance Requirements • •

Liability • •

Site Control • •

Solar Resource • •

Solar Access/Shading • •

Distance to Transmission/ Distribution Lines • •

Available Capacity on Transmission/ Distribution • •
Best Practices for Siting Solar Photovoltaics on MSW Landfills February 2013

19

Table 4-1: Technical and Economic Factors Impacting Solar Project Feasibility on Landfills

Factor Net-Metered Project Utility-Scale Project for 

Export to Grid

Lines

Interconnection Costs • •

Existing Utility Interconnection •

Local Net Metering Policy •

Utility Rebates /Incentives •

Solar Renewable Energy Credit (SREC)/Power 

Purchase Agreements (PPA) Prices •

Retail Electricity Prices •

Existing On-Site Load •

Project Cost • •

Finally, landfill owners and PV system developers tend to approach the feasibility analysis from different 

perspectives, and thus may analyze the issues in different orders. Landfill owners or operators typically start with an 

evaluation of the site and landfill characteristics, and then seek out a PV technology to meet those characteristics. 

Rather than trying to find a technology solution for a challenging landfill site, a developer may look for a landfill site to 

match its preferred technology or mounting system. This document takes the first approach, starting with site 

characteristics and then exploring PV system considerations. EPA and NREL expect the information provided to be 

pertinent to landfill owners or operators, as well as PV system developers when evaluating a given site, as the basic 

considerations are similar. 

4.1 General Physical Setting

Typically one of the first steps in conducting a feasibility analysis is to characterize the general physical setting of the 

landfill and solar project, including meteorological conditions, land use and ecological conditions, and electric 

transmission infrastructure.

4.1.1 Meteorological Setting

The meteorological conditions (e.g. rainfall, solar radiation, wind speed and direction, and temperature) affect the PV 

system and landfill system performance and design, both individually and in combination. For example, landfill-based 

PV systems can alter landfill system’s performance by changing the path of stormwater flows and changing exposure 

to sun and wind, which in turn can impact cap integrity and stability, leachate generation and control systems, 

vegetative cover and erosion control systems, and stormwater management systems. Therefore, in order to 

understand the potential impacts of alternative solar project designs, it is important to understand the relevant 

meteorological conditions and their likely effects on the combined PV/landfill system performance. 

There is significant overlap with the meteorological data needed to assess landfill performance, and PV system 

performance. For example, both landfill system performance and PV system performance are affected by global 

radiation, relative humidity, atmospheric pressure, wind velocity, and temperature. For PV systems, these factors 

affect potential output. For landfills, they affect evapotranspiration, water balance, and leachate generation rates.

Rainfall data, both annual rainfall rates and the nature of peak storm events, are important to understand the 

potential effects of PV system alternatives on the performance of different landfill systems. These data can help 

identify potential impacts from changes in permeable surface area and ground cover; effects on stormwater runoff 

and the adequacy of existing stormwater management controls; potential for localized erosion; and potential for slope 

instability due to seepage and/or leachate head effects. These data are available from many different sources. For 
Best Practices for Siting Solar Photovoltaics on MSW Landfills February 2013

20

example, “precipitable water” is included in the typical meteorological year (TMY) data sets derived from the 1961-

1990 National Solar Radiation Data Base (NSRDB). 

4.1.2 Solar Resource Availability

Among the factors that are most important in evaluating whether a particular site is a good candidate for a PV system 

is whether the site receives abundant sun most of the day. To be economically viable, PV systems generally require 

a minimum solar radiation of 3.5 kWh/m2/day. However, state or utility incentives or insufficient access to electrical 

infrastructure may sufficiently improve the economics to enable PV systems in lower resource locations.

Figure 4-2 shows the national solar PV resource potential for the United States. This map is intended only to provide 

general guidance on available solar resource, and site-specific conditions may vary. For this reason, developers 

typically conduct an individual site assessment for purposes of evaluating and siting a solar system.

Source: NREL

Figure 4-2: Photovoltaic solar resource14

Site evaluations typically seek to identify portions of a given site that will receive sufficient sunlight throughout the 

year. This on-site assessment is generally carried out using industry tools, e.g. Sun Eye or Solar Pathfinder. These 

devices enable the user to estimate shading and solar access for a given location throughout the year. As a rule of 

thumb, a site should receive a minimum of six hours of sunlight (9 am to 3 pm) on the winter solstice. This baseline 

typically represents the lowest sunlight exposure for the year, given the seasonal progression of the sun, and is used 

by the industry as a gauge to assess year-round solar availability for a given site. 

 

14 “Solar Map.” National Renewable Energy Laboratory. Accessed August 24, 2011: www.nrel.gov/gis/solar.html.
Best Practices for Siting Solar Photovoltaics on MSW Landfills February 2013

21

In general, open areas, either flat or gently south-facing slopes, are best suited for solar PV projects for maximum 

exposure to the sun. Depending on landfill design, the areas of maximum exposure may be directly on the former 

landfill site or in buffer zones.

4.1.3 Land Use and Ecological Conditions

Land use and land cover in the area surrounding the potential solar project on a landfill can affect access to solar 

radiation, as buildings and wooded areas can create obstructions or shading. Land use in the surrounding area also 

needs to be considered when assessing visual impacts of project alternatives and associated community 

acceptability.

In addition to characterizing the built environment in the vicinity of a potential project, it is important to understand its

ecological context. This information will be useful when considering the impacts of PV system alternatives on the 

natural environment, either directly (e.g., by requiring forest management to maintain access to sunlight, or altering 

vegetative cover that could serve as habitat, etc.) or indirectly (e.g., changing hydrologic conditions and associated 

sedimentation).

4.1.4 Transportation and Electrical Transmission Infrastructure

Landfills can leverage existing infrastructure of graded roads and transmission lines for equipment transport during 

construction and tie-in to the grid, respectively. 

Existing roads may be sufficient to transport materials required for construction of the solar system as they are likely 

designed to accommodate the large trucks typically used to haul waste to the landfill. Additional access roads may be 

necessary to support operation and maintenance of the PV plant and to comply with local fire codes.

It is also important when assessing solar projects on landfills to identify the location and to characterize the total and 

available carrying capacity of electrical distribution or transmission lines near the landfill site. 

Identifying the overall carrying capacity and the remaining available capacity of the existing infrastructure will be 

necessary to identify whether the power from a proposed solar project can be added to existing distribution or 

transmission lines or whether existing lines will need to be upgraded to accept planned and potential future levels of 

power from the project.

Reducing the overall electrical-run lengths to the point of interconnection is important to controlling costs. A generally 

accepted rule of thumb is that the distance to transmission lines should be within 1/2 mile. However, depending on 

system size, a distance of 1-3 miles may still yield acceptable economics for the overall system. 

A grid-connected PV system should also consider whether the site has adequate transmission interconnection 

opportunities that meet any interconnection requirements of the local utility. Many states have legislation in place to 

require interconnection of many customer-owned power projects. Note that some states limit the size of a project that 

can be interconnected or place a grid-wide limit on the amount of capacity that a utility may interconnect. 

4.2 Siting

The following information reviews landfill characteristics that can be relevant to analyze the potential siting of a solar 

project on a landfill and when analyzing alternative solar project designs, siting alternatives, and visual impact 

mitigation alternatives.

4.2.1 Acreage of the Site

To reduce the length of DC electrical wiring runs, selecting an area with large sections of contiguous land is 

recommended. As a rule of thumb, NREL uses the following land-use assumptions for modeling purposes: 65 W/m2
Best Practices for Siting Solar Photovoltaics on MSW Landfills February 2013

22

Highlight 4-1: Solar Geomembrane Covers for Landfill Applications

Source: Republic Services

At the Tessman Road Landfill, a PV integrated geomembrane cap was 

used to both cover the landfill and provide electricity. In general, this type 

of technology is best planned for while the landfill is still active and 

incorporated into the closure plan. The PV integrated cap must also be 

carefully designed to meet federal, state, local and/or tribal landfill closure 

requirements. 

PV systems using structural mounting systems, as opposed to 

geomembranes, can be constructed on closed landfills and on closed cells 

in larger operating landfills. Siting solar technologies on a closed landfill 

requires some understanding of both the closure process and general 

closure requirements. 

or 263 kW/acre for ground-mounted fixed tilt and 48 W/m2 or 194 kW/acre for single-axis tracking.15 The area 

necessary for a given system size is highly dependent on the module efficiency and mounting system. In general, a 

minimum area of two acres is recommended for development.

4.2.2 Landfill Characteristics

The feasibility of siting solar PV systems 

on a landfill can depend on landfill 

characteristics, including the presence of 

pre-existing engineered systems, cap 

characteristics, landfill slope and 

stability, waste composition, settlement, 

erosion control and vegetative cover, 

leachate and gas collection and 

treatment systems, and stormwater

management.

The remainder of this chapter addresses 

these landfill characteristics in the 

context of a feasibility analysis.

4.2.2.1 Closure Status 

It is likely that considerations for siting 

PV on a landfill will vary depending on 

whether the landfill and/or targeted area 

of the landfill is already closed or has yet 

to be closed. Where the landfill has yet 

to be closed, opportunities may exist to 

design the solar project as an integrated 

component of the overall landfill closure 

project. Where the landfill has already 

been closed, feasible alternatives may be more constrained, and the feasibility analysis should take into account the 

characteristics of the existing cap and other landfill systems. 

A feasibility analysis should also consider whether there are pre-existing engineered systems at the landfill that the 

PV system will need to integrate with. Where they exist, modifying those systems to accommodate some PV designs 

may be cost prohibitive, or subject to other limitations. In this respect, a developer may have more flexibility at 

landfills or units that have not yet been closed, by designing the various systems in conjunction with one another. For 

example, when a PV system is being designed as part of the landfill cap, the impervious surface area and surface 

flow restrictions associated with the PV system can be taken into account in the design of the stormwater collection 

and treatment system. Thus, the feasibility analysis might include analyses of trade-offs among different PV system 

and stormwater system designs. In contrast, if a PV system is being considered on a closed landfill, options for 

reconfiguring the stormwater system might be limited by physical site constraints or permit requirements. Also, the 

cost of deconstructing and rebuilding stormwater management features could make some options cost prohibitive 

that would have been viable if a PV system had been anticipated in the original stormwater system design.

The feasibility analysis should also consider applicable closure and post-closure regulatory requirements, including 

permit conditions contained in any permit, to determine whether a PV project would be consistent with those 

requirements.

 

15 Denholm, P.; Margolis, R.M. (2008). “Land Use Requirements and the Per-Capita Solar Footprint for Photovoltaic Generation in the United States.” Energy 

Policy (36); pp. 3531–3543
Best Practices for Siting Solar Photovoltaics on MSW Landfills February 2013

23

The remainder of this chapter is devoted to considerations that are generally relevant for conducting feasibility 

analyses where the landfill has already been closed.

4.2.2.2 Cap Characteristics

Landfill sites present significant challenges for PV system selection and design. Cap penetration and settlement 

limitations will likely guide mounting system and foundation selection and design. 

4.2.2.2.1 Type

To assess the feasibility of a solar project and evaluate alternative designs, it is necessary to understand the nature 

of the cap and the functions that the cap and its components are intended to perform. Units closed under 40 CFR 

258 must meet minimum performance standards for the final cover system or may have an alternative cap designed 

to meet performance-based standards and approved by the director of an approved state.16,17 Figures 4-3 and 4-4 

show typical components of possible MSW landfill cover options designed to provide a hydraulic barrier and maintain 

the water balance in a landfill.

 

Source: Adapted from EPA (1993)

Figure 4-3: Possible cover systems

 

16 Solid Waste Disposal Facility Criteria: Technical Manual. (2003). EPA/530-R-93-017. Washington, DC: U.S. Environmental Protection Agency, Office of Solid 

Waste and Emergency Response. Accessed April 23, 2012: http://www.epa.gov/waste/nonhaz/municipal/landfill/techman/index.htm. 

17 Bonaparte, R.; Gross, B.; Daniel, D.; Koerner, R.; Dwyer, S. (2004). Technical Guidance for RCRA/CERCLA Final Covers. EPA/540-R-04-007. Washington, 

DC: U.S. Environmental Protection Agency, Office of Solid Waste and Emergency Response. Accessed April 23, 2012: 

http://nepis.epa.gov/Exe/ZyPURL.cgi?Dockey=P10074PP.txt. 
Best Practices for Siting Solar Photovoltaics on MSW Landfills February 2013

24

Source: Adapted from EPA (1993)

Figure 4-4: Example of an alternative final cover design

The functions of the different components of a hydraulic barrier cap system include:

• The surface layer, identified as the vegetation/soil top layer in Figure 4-4, is intended to resist erosion by 

water and wind, facilitate cap maintenance, and provide a growing medium for vegetation, if present. Other 

functions can include promoting evapotranspiration or satisfying aesthetic and ecological requirements.

• The protection layer provides a barrier to help protect underlying layers from degradation due to wet-dry and 

freeze-thaw cycles and to prevent human, burrowing animal, or plant root intrusion. The protection layer can 

sometimes also be designed to provide a temporary reservoir for infiltrated water prior to evapotranspiration 

via the surface layer. In Figure 4-4, the protection layer is comprised of the filter and biotic barrier layers.

• A drainage layer may be required under the protection layer and above the hydraulic barrier to provide a 

preferential drainage pathway and drain infiltrated water. This prevents build-up of a hydraulic head and 

helps minimize percolation through hydraulic barrier layer. It also helps drain the overlying areas and 

reduces seepage forces in the upper layers of the landfill, which improves slope stability.

• The hydraulic barrier, identified as the 20-mil flexible membrane layer (FML) or 60-mil high-density 

polyethylene (HDPE) layer in Figure 4-4, is designed to prevent percolation into the waste by impeding 

infiltration and promoting storage and lateral drainage in the overlying components of the cap. Materials 

most commonly used to construct the hydraulic barrier include compacted clay liners (CCLs), geosynthetic 

clay liners (GCLs), geomembranes (GMs), and combinations of these materials.18

• In some cap systems, a gas venting layer, consisting of material with high gas transmissivity, is included to 

help convey gas to passive gas vents, active gas wells, and/or trenches. 

• The foundation layer, identified as the low-permeability flexible membrane layer (FML)/soil layer in Figure 4-

4, provides grade control for the cap, adequate bearing capacity for overlying layers, a surface for 

 

18 Bonaparte, R.; Gross, B.; Daniel, D.; Koerner, R.; Dwyer, S. (2004). Technical Guidance for RCRA/CERCLA Final Covers. EPA/540-R-04-007. Washington, 

DC: U.S. Environmental Protection Agency, Office of Solid Waste and Emergency Response. Accessed April 23, 2012: 

http://nepis.epa.gov/Exe/ZyPURL.cgi?Dockey=P10074PP.txt. 
Best Practices for Siting Solar Photovoltaics on MSW Landfills February 2013

25

installation of geosynthetics, and, in some cases, a buffer to help control for the effects of differential 

settlement (EPA 2004).

4.2.2.2.2 Age and Thickness 

The age and thickness of a landfill can be an indicator of settlement potential. The rates of both uniform and 

differential settlement are largely a function of the composition of the waste material and the age of the landfill cap.19

The rate of settlement will usually diminish over time, though settlement rates can increase at later stages due to 

shifts in biological or other processes over time. In general, landfills that have been capped in recent years will 

experience higher rates of settlement than landfills that were capped a decade or more ago.

Records for the landfill may provide insight on settlement and landfill cap construction. For example, the post-closure 

plan generally provides detailed information on the landfill design, maintenance plan, as well as on-going 

requirements or restrictions. Where records may be incomplete regarding past landfill operations, age can be 

combined with other information (e.g., site visits and field investigations) to provide an indication of landfill 

construction and waste composition. Knowledge of the age and composition of the waste in the landfill may provide 

insights into the potential for settlement on the landfill surface. Both of these factors can impact the selection, design, 

and construction of PV technologies on landfill surfaces.

4.2.2.3 Slope and Stability

The collection and analysis of the slope and soil stability characteristics of a landfill property is a critical element of a 

feasibility assessment of landfill PV projects. These characteristics play a significant role in the selection of PV 

technology components and in the design and layout of the solar arrays decision. Topographic maps, site surveys, 

site engineering drawings, and soils engineering studies that may be included in the landfill post-closure plan typically 

contain the information necessary to complete a slope and stability assessment. 

Landfills that have minimal grades are often the best candidates for solar development as they simplify the design 

requirements of a PV system, minimize site preparation activities and costs, and may reduce the costs of PV system 

foundation and structural components. For this reason, the plateau or top of the landfill may present the best option 

for siting solar at some landfill sites. These areas generally have minimum grades of 2-3 percent to minimize the 

rainwater infiltration through the cap, reduce erosion, and avoid ponding. These gradual slopes are ideal for PV 

system installation, especially when constructed to face south, thereby increasing sunlight exposure. 

Many landfills are composed of large mounds of capped waste with steep slopes (3:1 slope or 30+ percent grade). 

Most solar developers place an upper limit of 5-10 percent grades in considering the feasibility of installing a PV 

system on a slope. As the grade increases, the complexity of the design increases as well, often resulting in a 

commensurate increase in system price. Installing PV arrays on steep slopes can lead to system design challenges 

associated with wind loading, erosion concerns, stormwater management issues, and foundation stability 

requirements. These challenges often lead to increased system costs for ballasted or anchored PV systems, or the 

selection of an alternative mounting system such as a PV-integrated geomembrane on the sloped portions of the 

landfill. While the sides of these landfills generally have steep slopes, the relatively flat top portion of the site may 

provide sufficient acreage for a PV system while not increasing costs associated with accommodating steep slopes.

The orientation (or azimuth20) of the slope is equally important as the grade, since it can have a significant impact on 

the energy production of a PV system. The slope orientation determines the angles that the sun’s rays hit the PV 

modules. Developers generally prefer south facing slopes, or those within 20-30 degrees of due south to provide 

sufficient exposure to the sun over the course of the year. Slope orientations outside of the 20-30 degree range of 

due south will typically result in lower annual energy production from the PV system, and may necessitate additional 

design work and system layout modifications to address row-to-row shading issues. Sometimes developers seek to 

 

19 El-Fadel, M.; Khoury, R. (2000). “Modeling Settlement in MSW Landfills: a Critical Review.” Critical Reviews in Environmental Science and Technology (30:3); 

pp. 327-361. Print.

20 The azimuth angle is the compass bearing towards which the modules are pointed.
Best Practices for Siting Solar Photovoltaics on MSW Landfills February 2013

26

address slope orientations outside of the preferred range by bringing in additional fill material, or grading the existing 

slope to change its orientation. However, this approach may add cost to the project, and/or present challenges in 

complying with applicable landfill post-closure care requirements, including landfill cap integrity requirements. For 

these reasons, it may be preferable to only consider development on landfill areas that have slope orientations within 

the range of +/- 20-30 degrees of due south. 

The soil stability of sloping areas or side-slope stability is another relevant engineering consideration, and it is 

recommended to include a review of appropriate soils engineering studies and geotechnical data regarding the cap 

material during the feasibility assessment. Of particular importance is consideration of the caps’ ability to withstand 

both the construction and long-term operation of the PV system. The installation of solar arrays on steep side slopes 

can be particularly challenging, as the weight of the system places additional force on the cap compared to systems 

that are mounted on flat surfaces, and can result in failure of the side slope if the system is not properly designed. 

Building on side slopes typically results in a higher cost system, as the system is typically designed with stronger 

foundations while balancing the need to manage or control erosion, stormwater runoff, wind, snow, and/or seismic 

loading, and impacts to the PV system from differential settlement. Based on these considerations, the landfill 

plateau or buffer areas may offer the greatest potential for installation of a PV system.

4.2.2.4 Settlement 

Another important element in assessing the feasibility of a landfill solar project is the collection and review of 

information on the potential for settlement of the landfill cap. All landfills are prone to settlement, but the type and 

magnitude of the settlement needs to be investigated during the decision-grade feasibility assessment phase of the 

project. 

There are two types of settlement that occur in landfills: uniform and differential. Uniform settlement refers to a 

process where the waste material in the landfill decays evenly and results in the level of the landfill cap settling at 

similar or uniform rates over large areas. Uniform settlement is typically not a significant concern in planning for a PV 

installation on a landfill. 

Differential settlement refers to the process where the waste material decays at different rates throughout the landfill, 

resulting in uneven settlement of the landfill cap. Differential settlement may result for a variety of reasons and is 

often a function of the waste material composition. For example, some areas of the landfill may have more organic 

waste that is prone to a higher rate of decay and settlement than other areas which may contain a higher volume of 

non-organic materials that have lower rates of decay or natural settlement. As a result, some areas of the landfill may 

settle at different rates resulting in an uneven cap surface. 

Differential settlement is a significant concern for landfill solar projects, as it may place uneven stresses on the 

mounting systems and cause uneven settlement of the array foundations, which may result in the misalignment of the 

array configurations and significantly decrease energy production. If the alignment of the PV arrays is impacted, then 

the modules will not be in their optimum orientation and reductions in system energy output may occur. Depending 

on the degree and location of settlement, differential settlement may also cause structural damage to the PV 

mounting system.

The rates of both uniform and differential settlement are largely a function of the composition of the waste material 

and the age of the landfill cap. Landfills that have been capped in recent years may experience higher rates of 

settlement than landfills that were capped a decade or more ago. As the age of landfill cap increases, the rate of 

settlement is likely to diminish or become negligible. Landfill solar developers generally avoid projects on landfills that 

have been capped for less than two or three years due to the high rate of settlement expected during the early years 

after landfill closure. It is recommended to monitor settlement and evaluate actual settlement data, since some 

landfills may continue to experience high rates of settlement for more than five years.

Many landfill operators have conducted forecasts that estimate the potential for uniform and differential settlement 

throughout the site. If a forecast has not been conducted, consideration should be given to conducting one. A 

settlement forecast can be useful to assess the potential magnitude of uniform and differential settlement, and may 

provide information on areas of the landfill to avoid placement of solar arrays in the context of a feasibility 
Best Practices for Siting Solar Photovoltaics on MSW Landfills February 2013

27

assessment. A settlement forecast can also be leveraged in the design phase of the project in order to project effects 

of PV system weight on landfill cap settlement.

4.2.2.5 Erosion Control and Vegetative Cover 

A vegetative cover strategy and erosion control management plan is usually included in a landfill post-closure plan. 

The vegetative cover on the landfill cap is usually a critical component of the erosion control management plan. The 

vegetative cover is designed to absorb some stormwater runoff and also allows for infiltration of runoff through the 

cover to an underlying soil layer where it is directed to holding ponds or other suitable containment locations. In 

addition, the vegetative cover is designed to hold the surface layer of the landfill cap together and minimize soil 

erosion due to stormwater runoff. 

As part of the decision-grade feasibility assessment, it will be important to obtain and review the erosion control 

management plan and vegetative cover specifications to help ensure that PV system options under consideration will 

be compatible with any post-closure plan provisions. Certain PV system options may also necessitate modifications 

to the erosion control management plan, vegetative cover strategies, and/or the post-closure plan. The costs and 

timing of these modifications may impact the feasibility of the project. 

If a landfill is developing erosion control plans and vegetative cover strategies as part of the closure and post-closure 

planning process, the owner or operator should consider integrating PV options into those plans. For ballasted or 

shallow poured concrete footer PV foundation systems, the design and specification of erosion control measures 

might incorporate the placement of PV foundations and support structures. Alternatively, the use of a PV-integrated 

geomembrane can be investigated as a replacement for conventional erosion control and vegetative cover systems 

and, if available, incorporated into the closure and post-closure plans. 

4.2.2.6 Control of Leachate and Landfill Gas

Landfill leachate is the result of water filtering through the waste material that settles near the bottom of the landfill. 

The composition of landfill leachate is dependent on the type of waste contained in the landfill and may present risks 

to human health and the environment. Nearly all landfills use leachate collection and treatment systems. Typical 

leachate collection and conveyance systems comprise a network of piping in the waste material that allows drainage 

of the leachate to a sump area at the bottom of the landfill cell. The leachate is then pumped from the sump to an 

above ground on-site site storage and treatment facility. 

Landfill gas collection and production systems are somewhat similar to leachate collection systems, in that they 

typically consist of a network of pipes that are embedded throughout the waste material in the landfill cell to collect 

and transport landfill gas generated by decaying waste. The collected landfill gas is typically transported through 

pipes to a collection area where it is either flared or scrubbed and used for on-site electricity generation. 

Several key factors to consider in assessing the feasibility of PV systems on landfills with respect to leachate and 

landfill gas systems include weight loading and PV positioning relative to these systems. The weight bearing capacity 

of the piping and collection systems should be considered during the feasibility study. While there is already an 

enormous amount of weight resting on top of the leachate and gas collection systems, consideration should be given 

to the impacts on these systems of additional weight loading resulting from the PV system, as well as the weight of 

trucks and equipment that will be utilized in the site preparation and construction phases of PV installation. 

The feasibility assessment should also consider the location of leachate and gas piping systems, leachate and gas 

storage facilities, gas monitoring wells, and gas flaring and generation facilities. The location of these facilities may 

impact the design layout of the PV system, to the extent that the PV system may affect the operation and 

maintenance of piping, collection, or monitoring systems. In addition, locating PV arrays a safe distance away from 

landfill gas collection, monitoring, storage, flaring, and other energy generation systems is an important 

consideration. Landfill gas is explosive, and if a PV system is sited too close to landfill gas operations the potential of 

sparking from the PV system could present an explosive hazard. For these reasons, it is important that enclosed 

structures and subsurface conduits used for the management of landfill gas be designed to prevent concentration or 

conveyance of explosive gas. Therefore, a review of leachate and landfill gas systems should be conducted as part 
Best Practices for Siting Solar Photovoltaics on MSW Landfills February 2013

28

of the decision-grade feasibility assessment to evaluate weight loading on these systems from the PV arrays and 

construction equipment, as well as to assess the impacts of these systems on the design layout of the PV arrays. 

4.2.2.7 Stormwater Management

Stormwater management considerations are closely tied to erosion control and vegetative cover systems. Landfill 

covers are typically designed to absorb some stormwater runoff in the vegetative cover layer of the cap, while 

providing for additional run off to infiltrate into an underlying soil layer where it can be conveyed to retention ponds or 

other discharge areas. Landfill caps are also typically designed to allow for surface conveyance of stormwater that is 

not absorbed into the sub-surface conveyance system via uniform sheeting. This function is typically accomplished 

by incorporating a slight slope into the cap to direct water into stormwater collection areas and to prevent channeling 

of stormwater runoff, which can lead to erosion and fissures in the landfill cap. 

Stormwater discharges from active and closed landfills are subject to National Pollutant Discharge Elimination 

System (NPDES) permitting under the Clean Water Act (CWA) as stormwater discharges associated with industrial 

activity (see 40 CFR 122.26(b)(14)(v)). These discharges are typically covered by general permits, e.g., EPA’s multisector general permit (MSGP).21 In general, landfill operators are required to develop and implement a stormwater 

pollution prevention plan (SWPPP), which describes best management practices (BMPs) and controls to minimize 

discharge of pollutants in stormwater runoff from these facilities. 

To assess the feasibility of a PV system on a landfill surface, it will be important to understand these and other 

applicable storm water management requirements. It will also be important to understand how the PV system 

components could interact with the existing stormwater management system, and to limit feasible design alternatives 

to those that comply with regulatory requirements.

In addition, the CWA requires separate permits for stormwater discharges from active construction. Information 

should be collected on stormwater permitting requirements during the construction process, as well as operations 

and maintenance requirements of the stormwater management system resulting from the placement of PV modules

on the landfill cap. The cost and schedule of stormwater permitting should also be assessed as part of the overall 

decision-grade feasibility assessment. 

The landfill operating status may affect considerations associated with stormwater management during the feasibility 

analysis. If a landfill is not closed, a re-design of the stormwater management system in the existing closure and 

post-closure plans may be possible in order to ensure compatibility between the PV and storm water management 

systems. The construction of a co-designed stormwater management and conventional foundation-based PV system 

may save time and money in the long-run, even if the PV system is not built until several years later while waiting for 

the initial settlement of the landfill to occur. Alternatively, a PV-integrated geomembrane can be investigated as the 

primary stormwater management system on areas of the landfill cap, and if available, can be incorporated into the 

landfill closure plan.

In addition, on-site recovery and reuse of stormwater may be considered in order to clean PV modules if appropriate, 

especially in regions with limited precipitation or water resources. In this case, a water treatment system could be 

used to remove minerals from the stormwater, thereby avoiding leaving residue on the PV modules. Refer to Section 

7.2 Panel Washing and Water Management Plan or Natural Cleansing for additional information.

4.2.3 Institutional controls

Institutional controls (ICs) may be established for the landfill and should be taken into account as part of a feasibility 

analysis. In general, institutional controls are non-engineered instruments, such as administrative and legal controls, 

that help minimize the potential for human exposure to contamination and/or protect the integrity of a landfill. 

 

21 Specific applicable requirements may vary depending on whether EPA or the state is the NPDES permitting authority. The MSGP is available in states and 

Indian country where EPA is the permitting authority. All but five states have been authorized by EPA to administer the NPDES program, and most states 

issued general permits similar to the MSGP for industrial stormwater discharges. For more information on the MSGP, see 

http://cfpub.epa.gov/npdes/stormwater/indust.cfm. Landfills are classified in Sector L of the MSGP, and more information on requirements for this sector may 

be found at http://www.epa.gov/npdes/pubs/sector_l_landfills.pdf.
Best Practices for Siting Solar Photovoltaics on MSW Landfills February 2013

29

ICs are typically designed to work by limited land and/or resource use (e.g., uses of ground water) or by providing 

information that helps modify or guide human behavior at a site. ICs may also specify requirements for inspections 

and monitoring (e.g., to ensure that landfill wastes and contaminated media are not migrating from the site).

Examples of institutional controls that may be applicable to contaminated sites include but are not limited to: 

• Proprietary controls, such as easements or covenants, prohibiting activities that may compromise the 

effectiveness of the landfill in containing wastes;

• Governmental controls, such as zoning, building codes, ground water use regulations, and 

sports/recreational limits imposed by federal, state and/or local resources and/or public health agencies;

• Enforcement and permit tools with IC components, such as landfill closure permits that limit certain activities 

and/or require activities, such as inspections and monitoring, to ensure effectiveness of engineering and/or 

institutional controls; and

• Informational devices, such as deed notices, that provide information or notification to local communities 

that residual or contained contamination remains on site.

It is recommended that the feasibility study identify institutional controls applicable to the landfill, their type, and 

evaluate any impact(s) on whether a PV system can be developed, and/or any implications for the layout of the PV 

system components and usable area of the landfill.

4.2.4 Long term maintenance requirements

Many landfills have specific maintenance requirements to ensure the integrity of the landfill cap and other systems. 

Maintenance requirements typically go hand-in-hand with inspection requirements and can include, but may not be 

limited to: 22,23

• Routine maintenance of vegetative cover and re-vegetation;

• Inspection, routine maintenance, and repairs to the:

o Leachate collection and treatment systems;

o Landfill gas collection and treatment systems;

o Stormwater collection and treatment systems;

• Routine inspection and cap repairs; and

• Inspection, routine maintenance, and repairs to gas, ground water, and other monitoring systems.

These maintenance activities generally require access for personnel and equipment to the landfill systems. Similarly, 

maintenance of vegetated covers may require mower access. Thus, these activities may affect the layout of the PV 

system and PV system structures. 

4.3 PV Technology Selection and Technical Design 

The following sections review information on the selection of PV technology components for landfill applications, as 

well as the development of a preliminary or “conceptual” system design to assist in the decision-grade feasibility 

assessment. It also reviews additional feasibility considerations such as predicting the energy output of the system 

and assessing the economic characteristics of potential projects.

4.3.1 Matching Appropriate PV Technology to Landfill Characteristics

Once the landfill site characteristics have been reviewed and analyzed for their impacts on the feasibility of a PV 

system, the next step in a typical decision-grade feasibility assessment is to select appropriate PV technology 

 

22 Solid Waste Disposal Facility Criteria: Technical Manual. (1993). EPA/530-R-93-017. Washington, DC: U.S. Environmental Protection Agency, Office of Solid 

Waste and Emergency Response. Accessed April 23, 2012: http://www.epa.gov/waste/nonhaz/municipal/landfill/techman/index.htm. 23 Stormwater O&M Fact Sheet: Preventative Maintenance. (1999). EPA/832-F-99-004. Washington, DC: U.S. Environmental Protection Agency, Office of 

Water. Accessed April 23, 2012: http://www.epa.gov/npdes/pubs/prevmain.pdf.
Best Practices for Siting Solar Photovoltaics on MSW Landfills February 2013

30

applications based on site characteristics and landfill system requirements. While the information is presented as 

sequential steps, it is likely that the process of selecting appropriate PV technologies will be an iterative process that 

examines trade-offs among technology components. 

Often, an initial step is the selection of the type of PV module to be used, which may be based upon obtaining the 

desired system size (kW) within the available land area. Modules are typically evaluated in combination with 

compatible mounting systems and foundations. Each integrated PV system (modules, mounting system, and 

foundations) is assessed with respect to compatibility with site conditions. 

Source: PV Navigator

Figure 4-5: Sample solar PV and landfill integrated system design

When reviewing options for foundation supports, the choices are typically ballasted, shallow poured concrete 

footings, an auger/helical pier anchoring system, or a PV-integrated geomembrane. Each of these foundation types 

are described in more detail in Section 5.2 "Anchoring Systems". 

Next, options for the mounting system and array orientation are evaluated. Typically, fixed-tilt mounting systems are 

selected for landfill applications. Fixed-tilt systems are typically oriented due south and titled at an angle equal to or 

less than the latitude of site location. In some instances, it may be desirable to lower the tilt angle in order to 

maximize the output for summer production, to reduce row-to-row shading impacts, and/or to allow for more modules 

to be placed in a fixed amount of area. 

Single- and dual-axis trackers are largely avoided on landfill surface areas for several reasons. First, single-axis 

tracking systems are typically designed with driven pile or post and pier foundations, which are rarely used in landfill 

applications; while dual-axis trackers typically require large concrete foundations that are typically too heavy for use 

on landfills and also require penetration. However, tracking systems with ballasted foundations may be viable. 

Second, and perhaps more importantly, differential settlement of the landfill cap may result in the single- and dualaxis tracker arrays going out of alignment; even small alignment issues can have significant negative impacts on 

energy production. Differential settlement may also impact alignment along the tracking axis, which may cause 

damage to structural members or the actuators that rotate the arrays to track the sun and, in turn, impact energy
Best Practices for Siting Solar Photovoltaics on MSW Landfills February 2013

31

production. However, some developers have considered developing a combined or hybrid system of fixed-tilt arrays 

on the landfill surface with single-axis tracking systems on the buffer areas around the landfill. 

In addition, for landfills that have not completed the closure process, it may be desirable to select a PV-integrated 

geomembrane. Since the geomembrane can be substituted as the final cap cover for a similar price to a conventional 

cover, it may be a cost-competitive PV solution. Several geomembrane PV technologies are available in the market, 

ranging from thin film PV laminates that are flush mounted with the landfill surface, to geomembranes incorporating 

mounting frames that allow for modules to be mounted at fixed tilt angles of up to 20 degrees. New membrane 

materials have been recently introduced to the market with 30- and 35-year limited warranties, which matches or 

exceeds the typical warranty periods for PV systems. 

4.3.2 Conceptual Design of Major System Components

Development of a conceptual design of the PV system is usually one of the final steps in a feasibility assessment. 

Conceptual designs are typically thought of as an initial estimate of the PV system’s components and characteristics, 

but do not usually go into the level of detail of an engineering design. A conceptual design generally includes the 

selection and sizing of the potential components of the PV system, a preliminary layout or calculation of the footprint 

size of the system, and cost estimates for the system.

The following system components and high-level specifications typically in a conceptual design include: 

• Foundation type: typically ballasted, shallow poured concrete footings or helical pier

• Mounting system: fixed tilt, single- or dual-axis tracking or geomembrane

• PV module type: mono- or poly-crystalline or thin film

• PV module efficiency 

• Inverter type and efficiency 

Determining the size of the PV system is a function of whether the system is designed to meet on-site energy needs 

for a net-metering application, or whether it is intended to be an exporter of power to the grid. In the case of the PV 

system being designed to meet on-site loads, the system can be sized to meet up to 100-120 percent of the annual 

energy requirements of the facility based on the PV system’s projected output on a kilowatt-hour/kW basis, 

depending on local net-metering laws. However, if the objective is to size the PV system to be as large as possible 

based upon the available space, then an initial system layout (i.e., preliminary design footprint) may be created to 

determine the potential energy production for a given site. At a minimum, some preliminary calculations would be 

necessary to determine the spacing distance between rows of arrays based on module size and system support 

structure height, and then to determine how many rows (or partial rows) can fit in the available landfill space, 

excluding areas previously identified in the site characterization phase that are not suitable for PV. Such calculations 

will result in an approximate value for the resulting system size based on the objective of maximizing its size based 

on the available land areas suitable for PV development. 

The third major component of a typical conceptual design is an estimate of the installed cost of the system. There are 

several ways to obtain cost estimates. The system costs can be estimated based on a comparison to similar projects 

completed in the region (usually on a $/Watt basis), or an installer/developer can be contacted and requested to 

provide indicative pricing, or component manufacturers/distributors and local contractors can be called for price 

estimates for each component of the system. However, this last method can be time consuming and may be no more 

accurate than doing a comparative analysis to other recently completed systems in the area in terms of size, type, 

and application. 

Once complete, the conceptual design is generally used to determine the technical and economic feasibility of the 

project in terms of its expected system output (annual MWh), and economic value metrics such as its levelized cost 

of energy, payback period, net present value, and internal rate of return, all of which are discussed in the sections 

that follow. 
Best Practices for Siting Solar Photovoltaics on MSW Landfills February 2013

32

4.3.3 Energy Prediction

Based on the siting considerations outlined above, the useable acreage for the PV system can be estimated using 

aerial maps, drawings, or actual measurements from a site visit. Table 4-2 outlines the energy density values that 

can be expected from each type of system and can be used to estimate total system capacity for a ground mounted 

system.24 

Table 4-2: Energy Density by Module and System Type for Ground-mounted PV

Module Type 

System Type

Fixed-tilt Single-axis Tracking

Crystalline Silicon

2.9 - 5.5 DC-Watts/ft2 

(31.2 - 59.2 DC Watt/m2) 

2.4 - 4.5 DC-Watts/ft2 

(25.8 - 48.4 DC Watt/m2) 

Thin Film 

1.7- 2.9 DC-Watts/ft2 

(18.3 - 31.2 DC Watt/m2) 

1.4 - 2.4 DC-Watts/ft2 

(15.1 – 25.8 DC Watt/m2) 

Estimated system capacity can be used as one of the inputs for tools to estimate energy production, such as Solar 

Advisor Model (SAM) and PVWatts. Please refer to Appendix B for additional information on these tools. 

4.3.4 Economic Considerations

PV systems will produce energy anywhere there is sun and will produce more where there is a lot of sun. However, 

economic viability depends not only on the solar resource but also on economic factors pertaining to the site. 

Economic incentives for PV, such as state renewable electricity requirements with specific solar targets, increase the 

value of solar-produced electricity. The Database of State Incentives for Renewable Energy (DSIRE) is a 

comprehensive source of information on state, local, utility and federal incentives and policies that promote 

renewable energy and energy efficiency.25

Because landfill sites generally have smaller loads (e.g., a couple of lighting systems or small appliances) when

compared to the total PV production, most systems will likely sell electricity through a Power Purchase Agreement 

(PPA) with the local utility, making collaboration with the utility vital. For sites with larger loads, a “net metering” 

option through the local utility may be sufficient to drive project economics by offsetting the retail rate of electricity 

with the production from the PV system. Other key economic factors that can improve a PV system’s viability are high 

electricity rates or time-of-use (TOU) electricity rates that are high during the sunny parts of the day, solar feed-in 

tariffs, and other solar incentives associated with Renewable Portfolio Standards (RPS) or sales of Solar Renewable 

Energy Credits (SRECs). Additional discussion on financing and deal structures is provided in Appendix C.

Most projects will need to select a financing mechanism, which can be a complex decision since solar projects tend 

to have long paybacks and necessitate long-term contracts, unless high energy or system repayment costs can be 

accommodated in the short run. 

4.4 Other Potential Feasibility Factors

The following sections present information on additional factors might be considered in assessing the feasibility of 

landfill PV system including potential visual impacts and mitigation strategies, utility interconnection requirements, 

and utility policies for net-metered systems.

 

24 Energy densities are intended to be used for assessing initial potential PV capacity during a feasibility study phase. Actual design may vary. Data based on 

information from large-scale PV systems using a range of different module technologies and efficiencies. This table does not provide energy density information 

for solar geomembranes. 

25 Database of State Incentives for Renewable Energy: www.dsireusa.org
Best Practices for Siting Solar Photovoltaics on MSW Landfills February 2013

33

Highlight 4-2: Examples of Community Engagement 

Seek input from community stakeholders early and 

often during project planning and implementation to 

understand their interests and concerns. It is especially 

important to provide information about the project in 

ways that all parts of the community can understand. 

Consider engaging the community by: 

• Creating a project-specific website with project 

information, architectural renderings, and project 

contacts

• Hosting on-site demonstrations to allow the public 

to view a life-size system

• Holding a solar education day at a local school

4.4.1 Community Engagement & Support

Communities may have a strong interest in the long-term reuse of the MSW landfill. Many community groups may not 

only want to take part in discussions about solar energy on MSW landfills, but in some cases may want to learn more 

about solar technology in general, to provide additional support as community advocates for the project, and to 

provide local insight into specific community needs or considerations that may be relevant to the solar development. 

With this in mind, the RE-Powering initiative promotes reuse of MSW landfills for renewable energy projects when 

they address community concerns, interests, and land use plans. The EPA promotes active community engagement 

in all land revitalization efforts, including reuse of landfills through solar energy projects. The EPA’s vision is that the 

end use of a site should be determined through a combination of the community’s vision, key site characteristics, and 

community assets and should be protective of human health and the environment. 

MSW landfills are subject to varying federal, state, and/or 

local level regulatory requirements and authorities as is 

noted in Chapter 1 and 2 of this document. Although the 

requirements for public notice and involvement may vary, 

this section focuses on general considerations for 

community engagement that may be important in siting 

PV on closed landfills. 

4.4.1.1 Benefits of Community Engagement

Involvement of surrounding communities is important to 

the success and timeliness of projects, including large 

scale renewable energy projects such as siting solar PV 

on MSW landfills. When it is appropriate, community input 

about site reuse should be obtained early in a project. 

Continued engagement can help not only to inform the 

community about project plans, but also to gather 

information about the general setting for the project and ways it can be designed to be consistent with the community 

vision and benefit the community. Key community stakeholders can share insight into the community’s vision as well 

as potential concerns or issues that community members may have regarding reuse of the landfill. For example, 

there may be active community groups working to reuse the closed landfill as a park and recreation area, which may 

not be compatible with a PV installation at the site. 

4.4.1.2 Openness and Transparency

Open dialogue with the community, actively listening and responding to community concerns or requests, and 

transparent decision-making processes can help to foster proactive relationships between stakeholders and 

developers. These actions can also help to build trust and credibility. Failure to be transparent and open with 

communities could result in delays or other impacts to project progress. 

4.4.1.3 Facilitating Community Engagement

There are multiple ways that a developer can facilitate community engagement on renewable energy projects. 

During the “decision-grade” feasibility assessment (outlined in Chapter 4), developers typically discuss future land 

use options with local planning authorities, local officials, and community members. Directly involving the community 

through informational and town hall sessions can provide valuable community insight and a provide forum for 

addressing community concerns. In some cases community groups may be interested in partnering with the 

developer on projects.26

Communities may be interested in a wide range of topics, which may vary by site and situation. Community or 

stakeholder questions and concerns may include:

 

26 “Hartford Solar Landfill Project.” Center for Public Environmental Oversight, Accessed January 18, 2013: http://www.cpeo.org/pubs/HartfordSolar.pdf
Best Practices for Siting Solar Photovoltaics on MSW Landfills February 2013

34

• What are the benefits or costs of solar energy to the community? 

• How does a solar energy system work?

• How does a solar energy system differ from a coal- or natural gas-fired power plant?

• How will solar reuse affect site access?

• What will be the duration of site construction?

• How will the solar system be installed to maintain landfill cap integrity?

• What are the greater environmental impacts of solar reuse on the landfill?

• How reuse will impact future landfill upkeep and maintenance?

• What are the visual, aesthetic and economic impacts to the site and neighboring communities?27

• What are the job opportunities during construction and operation of the solar energy system? 

For effective community engagement, the credibility and rapport of the developer’s representative can be a critical 

element to the success of the project. Collaborative partnerships between communities, various stakeholders, and 

developers can facilitate successful reuse and development projects by taking into account community interests and 

supporting community participation in the decision making process.

4.4.2 Visual Impacts and Mitigation Strategies

Solar PV projects may, at times, raise concerns or face opposition due to perceived or real visual impacts of the 

arrays and support structures. During the permitting and public comment process, concerns may be raised as to the 

type of fencing around the perimeter of facility, or the aesthetic impacts of the solar facility on the surrounding 

community. In nearly all cases, issues and concerns related to visual impacts of a solar facility can be addressed 

easily and cost-effectively. In some instances, mitigation strategies can be as simple as not using barbed- or razor 

wire on the tops of fencing in areas that are visible to the public, or ensuring that security lighting is motion-activated 

so that the lights are not on all night, thereby disturbing nearby residents. Other mitigation strategies that may be 

deployed in response to visibility concerns include building earthen berms or planting trees around the perimeter in 

such a manner that the view of the solar arrays is blocked from view, but the berms or trees do not obstruct the sun’s 

rays from hitting the PV panels. 

4.4.3 Interconnection

All grid-connected PV systems require an interconnection agreement, and there are no specific conditions for landfillbased systems. An interconnection agreement specifies the terms, conditions, and equipment requirements for a 

grid-interactive PV system. Interconnection agreements are typically handled through the local distribution utility 

serving the site. 

Depending on the size of the PV system and the utility processing the interconnection agreement, the interconnection 

process can be time consuming and incur costs. For smaller, net-metered systems, the process can be as simple as 

a one-page contract. For larger PV systems that are exporting power to the grid, the process is likely to be more 

detailed and costly. For larger PV systems in general, the system owner will be required to submit an interconnection

application typically to the local utility, which typically includes a nominal fee for the utility to conduct an initial study 

on the impacts of the PV system on the local distribution systems. If the proposed PV system passes the utility’s 

initial screening process, then typically a more detailed power flow analysis study will be conducted by the utility for 

an additional cost to the applicant. This study will typically include an analysis of the impact of the PV system on the 

utility grid and whether local line upgrades or additional interconnection equipment is required for interconnection. 

 

27 “Amherst, Massachusetts: Impediments to Solar Installations on Closed Landfills.” Center for Public Environmental Oversight. Accessed January 18, 2013: 

http://www.cpeo.org/pubs/AmherstSolar.pdf
Best Practices for Siting Solar Photovoltaics on MSW Landfills February 2013

35

Increasingly, utilities are requiring system upgrades as part of the interconnection contract approval, and the upgrade 

costs are borne by the applicant. The entire interconnection review and approval process can take from 6-12 months 

depending on utility review and analysis periods, and the number of interconnection requests they are processing. 

During the decision-grade feasibility assessment phase of the project, it will be useful to contact the local distribution 

utility and obtain information on the interconnection application requirements, costs, and anticipated schedule. 

4.4.4 Net Metering

Net metering is a utility policy incentive that encourages development of PV and other renewable energy systems by 

its customers to offset on-site energy requirements. There are several variations among utility net metering policies, 

but the most common approach allows customers to receive full credit for every kilowatt-hour generated by the onsite renewable energy system. With respect to PV, when the system is generating energy, it offsets the customer 

consumption behind the meter. If the PV system is generating more energy than the on-site load, then the excess 

energy is exported to the utility grid and spins the meter backwards, in essence generating a credit or banking the 

excess energy with the utility. Then, as the energy generated by the PV system drops below the on-site energy 

requirements, the credits banked with the utility are drawn back. Thus, customers receive a one-to-one credit for PV 

generated on-site whether or not it was consumed by on-site loads at the time of generation. When monthly PV 

energy generation exceeds the on-site monthly energy consumption, the credits for the kilowatt-hours generated are

carried forward to the next month. Typically, at the end of the year there is a “true-up” period where the annual 

energy consumption and PV energy generation are compared. If there is excess generation at the end of the year, 

then depending on the utility, the customer may: 

• Receive compensation for the excess generation at the utility’s avoided cost of energy (i.e., at a rate 

significantly lower than the customer’s retail rate);

• Lose the excess generation credit and receive no compensation from the utility; or 

• Carry the excess generation credit forward into the next year’s billing cycle. 

If a net-metered PV project is being considered for a landfill site, it will be important to contact the local distribution 

utility and obtain a copy of its net-metering policy. Net metering policies vary widely, with some being extremely PVfriendly, while others are not. 

Net metering is limited to off-setting the energy requirements of on-site loads. In landfill settings, on-site loads 

typically tend to be small, consisting largely of leachate sump pumps, landfill gas well pumps and monitoring 

systems, and ground water monitoring systems. As a result, unless the landfill is part of a larger facility served by a 

utility master meter, net-metered PV systems on landfills will tend to be moderate in size. 

4.4.5 Virtual Net Metering

Some states and utilities allow for virtual net metering (VNM) or remote net metering. This arrangement can allow 

certain entities, such as a local government, to install renewable generation within its geographic boundary and to 

generate credits that can be used to offset charges at one or more other locations within the same geographic 

boundary. Virtual net-metered systems are typically subject to a system-capacity cap, which varies at the state or 

utility level. 

As there is typically a mismatch between on-site electrical demands and the potential for PV system size based on 

usable acreage, virtual net metering may be an important vehicle for many PV systems installed at landfills. In this 

scenario, the energy produced at the landfill offsets energy consumed by “subscribers” offsite. This arrangement may 

improve the economic feasibility of the PV project. Refer to Appendix C the discussion of Community Solar Gardens 

for an example of virtual net metering.
Best Practices for Siting Solar Photovoltaics on MSW Landfills February 2013

36

Highlight 5-1: Major Considerations Impacting 

Solar PV Project Design on Landfills

• Landfill Cap Characteristics 

• Site Slope, Stability and Orientation

• Waste Composition and Differential Settlement 

• Selection of Anchoring System

• Selection of Mounting System

• Selection of Modules

• PV System Weight Considerations 

• Stormwater Management 

• Wind and Snow Loading Criteria

• Cover Material Management 

• Site Security 

• Integration with Landfill Gas Monitoring and 

Production Systems 

• Institutional Controls

5. Design Considerations Unique to Building PV Projects 

on Landfills

Specific elements of the solar project are designed to meet the 

specific performance objectives identified for the project, 

including the performance objectives of the PV system and the 

landfill. Information gathered during the feasibility analysis can 

be used as a starting point for the solar project design.

The following chapter outlines the key landfill characteristics to 

consider when designing a solar project on a landfill, including 

cap characteristics, waste composition and settlement 

forecasts, PV system layout and component system designs, 

and considerations regarding the integrated PV-landfill system. 

A summary of the design considerations unique to building PV 

projects on landfills discussed in Chapter 5 is provided in 

Chapter 8, Table 8-1. Note that this is not an exhaustive list of 

design considerations. Project stakeholders should consider 

whether different or additional approaches are appropriate in 

light of site specific conditions.

5.1 Landfill Characteristics

Landfill characteristics will influence PV system design choices. Where there is little room to modify specific landfill 

components without compromising their function, these components will represent a design constraint. Where landfill 

components can be modified, the PV system designer will have greater flexibility. In all situations, the designer 

should consider not only the landfill characteristics as they exist prior to construction of the PV system but also how 

the PV system may alter those characteristics. Ultimately, the design should seek to optimize the performance of an 

integrated PV-landfill system.

5.1.1 Cap Characteristics

Characteristics of the landfill cap that will likely influence PV system design choices include:

• Landfill slope and slope orientation

• Thickness of cap, depth to specific cap components, and cap component function

• Post-closure, monitoring, maintenance, and use requirements

These characteristics will affect the selection and design of foundation types, mounting systems, PV module types, 

and effective area for the PV system installation. The design of the PV systems should consider how to account for 

these factors in a way that maximizes the output that can be achieved by the PV system while not compromising the 

safe, effective, and compliant operation of the landfill. Table 5-1 provides several key characteristics of the landfill 

cap and their implications for the PV system design. The inter-relationships among cap characteristics and PV 

system design considerations and choices are discussed in Chapters 5.2 through 5.13.

Table 5-1: Inter-relationships Between Landfill Cap Characteristics and PV System Design

Cap Characteristics Design considerations

Slope • Steeper slopes generally require lighter-weight solar arrays and/or heavier foundations to 

anchor the system. 

• Materials and methods used to construct steeper slopes can limit the design of PV 

systems, which can increase static and dynamic loading and affect side slope stability. 
Best Practices for Siting Solar Photovoltaics on MSW Landfills February 2013

37

Table 5-1: Inter-relationships Between Landfill Cap Characteristics and PV System Design

Cap Characteristics Design considerations

Orientation • Slope orientations outside of +/- 20o-30o from due south typically result in lower annual 

energy production from the PV system. These slopes are generally either modified 

through grading to adjust orientation or not included in the useable acreage for the PV 

system. 

Cap depth • The depth of the cap may limit compatible foundation types and design and, thus drive 

selection of PV mounting systems and PV module technologies. For example, foundation 

designs may be limited to ballasted foundation types, which may not be compatible with 

many single- or dual-axis tracking systems.

Cap components • Any cap modifications should ensure that there is no increase in potential threat to 

human health and the environment, and, if applicable, must comply with the closure and 

post-closure care requirements in 40 CFR 258 Subpart F. Additional federal, state, local

and/or tribal requirements may apply.

• Foundation types and designs may be limited due to regulatory requirements for the final 

cover system. Refer to 40 CFR 258 Subpart F and other applicable federal, state, local

and/or tribal requirements for additional information. 

• PV system wiring may need to run through above-ground conduits and not in 

underground trenches to preserve cap function. 

• Where shading could affect the presence and function (e.g., evapotranspiration, erosion 

control) of vegetative cover, cap may necessitate compensating design considerations. 

• Structures and capacity of stormwater collection systems (e.g., location of swales, size of 

detention basins) may limit the layout of PV systems, limit the amount of impermeable 

area, or necessitate compensating design considerations. 

• Depth and materials used for cap components designed for high transmissivity (e.g., 

drainage layer, gas venting layer) may limit the bearing capacity to prevent compression 

and loss of function.

• Location and depth of waste collection piping (e.g., gas, leachate) can affect the layout of 

the PV system. 

5.1.2 Waste Composition

The following sections examine the importance of examining the composition of waste material in the landfill as part 

of the PV system design process. The composition of landfill waste may have a significant impact on the PV system 

design process as a result of potential differential settlement as well as the location and function of landfill gas and 

leachate collection systems located within the waste material. 

5.1.2.1 Differential Settlement

Differential settlement occurs when waste material decays at different rates throughout the landfill, resulting in 

uneven settlement of the landfill cap. Differential settlement can be the result of many factors (e.g., operational 

practices, moisture composition), and is often the result of spatial variation and/or inhomogeneity in waste 

composition. Settlement results from mechanical, physiochemical, and biological processes, and the effects of these 

processes in terms of total settlement and rate of settlement, differs for different types of wastes. Settlement rates 

usually decrease with time, though they may increase as a landfill undergoes changes in active biological processes.

5.1.2.1.1 Differential Settlement Forecasts

Many landfill operators have conducted forecasts that estimate the potential for uniform and differential settlement 

throughout the site. If a forecast has been completed for a landfill property being considered for solar development, a 

copy of the forecast should be obtained and assessed for the potential magnitude of uniform and differential 
Best Practices for Siting Solar Photovoltaics on MSW Landfills February 2013

38

settlement. If a forecast has not been conducted, consideration should be given to conducting one. El Fadel and 

Khoury28 and EPA29 have published information on methods used for settlement monitoring and forecasting.

Pre- existing settlement forecasts should also be reviewed to assess the potential that the PV system will affect the 

forecast. Where a forecast is being conducted as part of the PV system design, it should consider the effect of the 

integrated PV-landfill system on uniform and differential settlement.

In general, differential settlement will be of greater concern for the design of PV systems on landfills containing more 

inhomogeneous waste.30

This is a critical consideration in the design of landfill solar projects, as differential settlement can place uneven 

stresses on support structures and cause them to fail, and it can create uneven settling of support structures, with the 

potential to impact array alignment, long-term structural integrity of the PV system, and energy output. Differential 

settlement is a particularly important consideration in the design of single- and dual-axis tracker arrays, but even 

small alignment issues associated with other designs can negatively impact energy production.

5.1.2.1.2 Differential Settlement – System Design Considerations 

As discussed throughout this document, differential settlement on landfills is a major consideration in the design of a 

PV system. There are three design factors that should be considered when addressing differential settlement:

• PV system component selection 

• Siting of the PV system 

• Engineering measures to mitigate settlement

The selection of components for conventional ground-mounted PV systems may have a significant impact on the 

occurrence of differential settlement or correcting for differential settlement. PV technology components that result in 

higher dead weight loads may increase the probability of the differential settlement. Extremely heavy dead weight 

loads, such as those found in concrete slab foundations, can cause or exacerbate immediate differential settlement

during the construction of the project, and can increase differential settlement concerns over the long-term. Even if 

the dead weight load of the PV system is within the acceptable design range based on the cover material weight 

bearing criteria, local variations in cap depth or waste material composition may make some areas of the landfill more 

susceptible to differential settlement. Therefore, minimizing the weight characteristics of a PV system is one potential 

design strategy for addressing differential settlement concerns. 

Another factor in the selection of PV system components is to consider mounting systems that can respond to 

differential settlement occurrences. With fixed tilt PV systems, minor incidents of differential settlement typically do 

not have sizeable impacts on PV energy production. However, if more substantial differential settlement occurs, it 

may impact the alignment of the array and reduce energy production. To correct for differential settlement after it 

occurs, it may be desirable to specify mounting systems that allow the use of shims or spacers to raise the array 

height to its pre-existing levels. Alternatively, mounting systems can be considered that have adjustable racking 

systems that allow for raising or lowering of the array height to correct for the localized differential settlement. 

PV-integrated geomembranes have fewer design considerations related to differential settlement than conventional 

ground-mounted systems. Since they are lightweight, they do not have dead weight loading concerns with respect to 

differential settlement. Minor occurrences of differential settlement may not be a large concern for geomembranes 

since the PV laminate is flush mounted with the cover surface of the landfill, and its energy production would not 

 

28 El-Fadel, M.; Khoury, R. (2000). “Modeling Settlement in MSW Landfills: a Critical Review.” Critical Reviews in Environmental Science and Technology (30:3); 

pp. 327-361. Print. 29 Bonaparte, R.; Gross, B.; Daniel, D.; Koerner, R.; Dwyer, S. (2004). Technical Guidance for RCRA/CERCLA Final Covers. EPA/540-R-04-007. Washington, 

DC: U.S. Environmental Protection Agency, Office of Solid Waste and Emergency Response. Accessed April 23, 2012: 

http://nepis.epa.gov/Exe/ZyPURL.cgi?Dockey=P10074PP.txt. 30 Sharma, H.D.; De Ariban, M. (2007). “Municipal Solid Waste Landfill Settlement: Postclosure Perspectives.” Journal of Geotechnical and Geoenvironmental 

Engineering (133:6); pp. 619-629. Print.
Best Practices for Siting Solar Photovoltaics on MSW Landfills February 2013

39

generally be impacted by minor settlement. In the event of more extensive differential settlement that impacts PV 

energy production and/or stormwater runoff patterns, the geomembrane cover material has the ability to be cut, 

tightened, loosened, or repositioned as necessary and reattached to the adjacent cover material.

The strategic placement of the PV system on specific areas of the landfill is another design strategy to mitigate the 

impacts of differential settlement. First, consideration should be given to siting the PV system on the oldest capped 

areas of the landfill first. The areas of the landfill that have been capped for the longest period of time have likely 

settled the most and will likely have the lowest rates of settlement in the future. On this basis, PV arrays could be 

sited on the oldest capped area first, followed by the next oldest area and so on. Second, differential settlement 

forecasts should be reviewed and revised to account for the additional weight of the PV system to determine areas 

more prone to differential settlement based on waste characteristics. For example, if the composition of waste 

materials is known throughout the site, the placement of the PV arrays over areas of waste known to have lower 

concentrations of organic waste material that is subject to natural decay from biochemical degradation may serve to 

lessen the effects of settlement on the PV system. Thus, an area containing construction, demolition, and/or

industrial wastes may be preferable from a settlement standpoint to other areas known to contain household wastes. 

Engineering solutions on the landfill cap to reduce the probability and/or impacts of settlement may be considered as 

another possible strategy for addressing differential settlement. These include the use of soil tamping equipment to 

compact the soil in the landfill cover. Compaction of the soil increases its density and stability. Note that compaction 

activities, like other strategies, must comply with landfill post-closure management requirements and adhere to 

engineering specifications to avoid damage to the function of cap components below the surface. Compaction may 

be more suitable for landfills in the closure process, as soil compaction activities are often performed as part of the 

final cap installation. Additionally, the use of geo-grid reinforcement systems, while adding additional cost to a 

potential project, may be able to be incorporated into the landfill cover to provide increased soil stability and tensile 

strength, and protect against cracking and fissures caused by differential settlement.

5.1.2.2 Landfill Gas and Leachate

Waste composition also influences landfill gas and leachate control requirements. The PV system design may need 

to consider the gas and leachate typically found with the types of waste in the landfill. Mitigation or avoidance of gas 

or leachate releases is a consideration that may drive the selection of the PV mounting system and overall layout of 

the PV system. For example, foundation selection may be constrained in order to avoid creating preferential 

migration pathways, and changing the water balance in the landfill.

5.2 Anchoring Systems 

Selecting the appropriate anchoring system for the PV array is one of the most critical steps in the design phase, as 

the anchoring system is the building of the PV system and is the interface between the PV system and the landfill 

cap. Building upon the information collected and initial decisions made in the decision-grade feasibility assessment, 

the selection and final design of the anchoring system involves balancing a number of design factors specific to 

landfills, including system weight requirements, differential settlement, and wind and snow loading. 

Five types of anchoring systems are commonly used to support PV systems in landfill applications: 

• Shallow poured concrete footers/ pre-fabricated concrete footings;

• Concrete slabs; 

• Auger / helical pier supports;

• Ballasted systems; and

• PV-integrated geomembranes. 

As mentioned in Section 3.2.3.1, while driven pile foundations are widely used in conventional PV projects, they are 

not typically suitable for landfill applications. Since landfill caps are not always uniform in depth, there is a risk with 
Best Practices for Siting Solar Photovoltaics on MSW Landfills February 2013

40

post foundations that the cap and waste material may be pierced by the post and compromise the integrity of the cap 

which may increase the potential threat to human health and the environment. 

5.2.1 Shallow Poured Concrete Footers and Pre-fabricated Concrete Footers 

Shallow poured concrete footers and pre-fabricated concrete footers are similar anchoring systems for PV 

installations, with the former being constructed on-site, and the latter off-site. The concrete footers are set in shallow 

holes in the landfill cap, and hold the mounting system in place and support the load of the PV system. The size and 

weight of the concrete footers are determined by weight bearing characteristics of the landfill cap, as well as by the 

design criteria established by the wind and snow loading requirements. Concrete footers tend to be heavier than 

other anchoring systems on a pounds-per-square-inch basis than other anchoring systems, but they may provide 

more stability compared to other anchoring systems for applications on steep slopes. 

Source: Oldcastle Precast

Figure 5-1: Precast ballast foundation for fixed tilt PV on a landfill 

5.2.2 Concrete Slabs 

Concrete slabs have also been used to support PV systems in landfill applications. The slabs are poured on the 

landfill cap over the area of the footprint where the mounting system will be placed. Once the concrete is cured, the 

mounting system is bolted to the slab. This configuration allows for more equal distribution of the weight of the PV 

system across the landfill cap; however, due to the weight of the slab this anchoring system may result in much 

higher dead weight loads than concrete footers. In addition, concrete slabs are prone to cracking from both uniform 

and differential settlement, which can result in uneven stress on the mounting system, misalignment of the PV arrays, 

and loss of the uniform distribution of dead weight loading. 

Source: NREL 

Figure 5-2: Slab foundation for PV system at Boulder, Colorado 
Best Practices for Siting Solar Photovoltaics on MSW Landfills February 2013

41

5.2.3 Augers or Helical Piles 

Augers or helical piles are a type of post support with an auger configuration at the base of the pier. Unlike driven 

piles, they are screwed into the ground typically with the use of a hydraulic torque motor. The advantages of a helical 

pile anchoring system include quick installation, high stability and structural support, and low cost. The potential 

disadvantage is that like a driven pile foundation, it penetrates the landfill cap and presents risk of piercing the cap 

and entering the waste layer if shallow landfill cap depths are encountered. However, once the pile is set, it is less 

likely to sink further over time. This anchoring solution is more applicable to landfills with deeper and known cap 

depths, as well as in side slope applications, where additional support and stability is necessary, and buffer zones. 

See Section 6.3 for additional discussion on penetrations of the landfill cap and associated regulatory requirements

that may be applicable. 

5.2.4 Ballasted Systems 

Ballasted systems are the most common anchoring method for PV systems on landfills. A ballasted system is 

typically composed of a flat tray or large concrete block that is placed on the landfill cap, with the array support 

structure attached to the tray or concrete block. In tray-based systems, the ballast material—usually pre-cast 

concrete blocks—are then placed on top of the tray. The weight of the ballast material holds the PV system down and 

protects it from wind uplift and sliding. The advantages of a ballasted anchor system are that: the system (i) does not 

penetrate the landfill cap; (ii) requires minimal site prep or disturbance to the vegetative cover; (iii) can be installed 

quickly; and (iv) can provide good structural support for the PV array. The key factor in designing a ballasted system 

is the selection of the proper weight of the ballast material to balance the dead weight loading requirements of the 

landfill cap while protecting against wind uplift and horizontal sliding. As ballasted anchoring systems become more 

commonplace for PV systems, an increasing number of manufacturers are offering pre-packaged ballast and racking 

solutions that are designed for site-specific conditions. Ballasted systems may be good candidates for flat landfill 

surfaces, but become more difficult to install as the slope of the landfill surface increases.

Source: SunDurance Energy LLC

Figure 5-3: Ballasted anchoring system at Landfill 1A project at New Jersey Meadowlands

5.2.5 PV Integrated Geomembranes 

PV integrated geomembranes are an emerging PV technology solution for landfill applications. A PV-integrated 

geomembrane is a landfill cover, typically comprising a thermoplastic polyolefin (TPO) material, which can be used in 

place of a vegetative or other final cover on the landfill. PV-integrated geomembranes are usually only considered 

prior to beginning the landfill closure process, as they may be largely redundant if placed on top of a final landfill 
Best Practices for Siting Solar Photovoltaics on MSW Landfills February 2013

42

cover, and/or may require modification of the landfill closure and/or post-closure plan. However, these systems may 

also have applications on landfills for which an existing final cover is being considered for refurbishment or 

replacement. 

A PV-integrated geomembrane is anchored by means of an anchor trenching system. This system consists of 

trenches that are dug into the landfill cap, and the geomembrane is laid out on the landfill cover and into the trench. 

Once the membrane has been set to its desired position, soil is placed in the trenches. The weight of the soil in the 

trenches anchors the membrane to the landfill cover. The spacing between trenches is determined by the design 

wind speed in the geographic area. Horizontal anchors are also utilized to weigh the system down in areas that are 

more exposed to the forces of wind and weather. 

The cost of the PV-integrated geomembranes is similar to that of the final landfill cover that it replaces with the added 

benefit of solar power production. It also weighs less than other anchoring systems and is not subject to the loading 

restrictions of other anchoring systems. Compared to a conventional landfill cover, the geomembrane provides good 

cover stability, reduces maintenance costs of the landfill cover, reduces erosion and soil maintenance costs, and 

decreases rainwater intrusion of the landfill cover. However, PV geomembranes are largely limited to landfills in the 

closure process, and are available only through a small number of manufacturers in the marketplace with limited 

options for solar panel technology. That said, additional suppliers are beginning to enter the market offering a 

selection of tilt angles integrated into the membrane material, as well as additional choices of solar panel technology. 

Source: Republic Services, Inc.

Figure 5-4: Hickory Ridge Road Landfill – Geomembrane solar cover

5.3 Mounting Systems

The PV mounting systems are attached to the anchor system and provide structural support to the racking 

assemblies and PV modules. As noted in the introduction in Section 3.2.3.1, with respect to landfill applications, the 
Best Practices for Siting Solar Photovoltaics on MSW Landfills February 2013

43

most common type of mounting system is the fixed-tilt mounting system. As discussed previously, single- and dualaxis tracking systems are not typically specified for use on landfill covers for a variety of reasons, and are not 

discussed in this chapter on design considerations. An alternative mounting system applicable to landfill applications 

is the PV-integrated geomembrane, which is addressed in this chapter. 

5.3.1 Fixed-tilt Mounting Systems

Fixed-tilt mounting systems consist of structural supports that hold the racking system and PV array at a fixed angle 

for the life of the system. The angle at which the fixed-tilt system is set is part of the design process and is dependent 

on a number of factors. Determining the tilt angle of the mounting system may require a dynamic modeling process to 

optimize the design based on:

• Economic price signals from the utility or power off-taker;

• Wind and snow loading criteria;

• Row-to-row shading impacts;

• Desired system size and available land area; and

• Other site-specific factors. 

A general rule of thumb is that the angle of a fixed-tilt system is set to the latitude of the site to maximize annual 

energy output. However, this is not always valid, and using a simple model such as PVWATTS will assist in 

determining the optimal tilt angle for a particular site to optimize annual energy production from the system. This rule 

of thumb is less valid as the latitude increases (i.e., in the northern regions of the US). However, it may not always be 

desirable to maximize the annual energy production from a PV system due to economic or site specific design 

criteria. 

One factor in assessing the angle of a fixed tilt PV system is to review the price signals being sent by the utility or the 

off-taker of the solar power. If the PV system is net-metered, then the applicable rate tariff for the site should be 

reviewed to determine the value of energy being offset by solar production. If the rate tariff is a fixed price per 

kilowatt-hour over the course of the year, the tilt angle should be set to maximize annual energy production. If the 

applicable rate tariff is, for example, a seasonal rate with higher rates in the summer months, then consideration 

should be given to lowering the tilt angle to maximize for summer production (i.e., 10-15 degrees below the latitude of 

the site). Similarly, if the solar energy is being exported off-site for sale to a utility or other off-taker, then the tilt angle 

should be optimized to maximize the revenue of the system based on the structure of sales price whether that is a 

flat price for every kilowatt-hour produced or higher priced energy during the summer months. 

Wind and snow loading also impact the determination of the tilt angle. With fixed tilt systems, higher tilt angles will 

experience increased wind loading and may necessitate additional foundation support. The impacts of wind loading 

on systems with higher tilt angles will be multiplied in areas with high wind design speeds. However, wind loading 

may need to be balanced with snow loading design criteria in areas prone to heavy snow and/or ice loads, and these 

criteria may be at odds with one another. For example, higher tilt angles may be desired to allow for snow to slide off 

the panels, but the higher tilt angle will likely result in increased wind loading on the system. 

Another aspect of determining the tilt angle is the row-to-row shading factor. Higher tilt angles result in increased 

array height. The higher the height of the array, the longer the shadow it casts, and the larger the space between 

rows needs to be to avoid shading of the modules on the row behind it. The distance between rows is determined by 

the “design day” when the sun is at its lowest angle above the horizon and casts the longest shadow, which is the 

winter solstice. As a result, higher tilt angles necessitate a larger distance between rows of modules, and lower tilt 

angles require a shorter distance between rows. The row-to-row shading factor may also be related to meeting PV 

system size criteria if the objective is to maximize the system size based on the available area of land. Since lower tilt 

angles require smaller spacing between rows, more PV modules can fit in a finite area of land and allow for larger 

systems, while higher tilt angles with increased row spacing requirements will reduce the potential system size. 
Best Practices for Siting Solar Photovoltaics on MSW Landfills February 2013

44

As can be seen from the above discussion, selecting the optimal tilt angle may not be as simple as setting it to the 

local latitude to maximize the annual energy production of the PV system. Additional factors, such as economic price 

signals, wind and snow loading requirements, row-to-row shading factors, foundation requirements, and other landfill 

specific design criteria need to be assessed as part of the system design process. 

5.3.2 PV Integrated Geomembranes 

PV-integrated geomembranes provide an alternative to conventional mounting systems. They may also demand a 

less stringent design analysis than conventional PV systems, since geomembranes are usually considered as part of, 

and integrated with, the landfill closure process. As a result, they can be designed as part of the final landfill cap 

cover and are not as impacted by pre-existing landfill structures that may not have been built with PV generation in 

mind. While the design process should incorporate criteria for stormwater management, differential settlement, and 

other site specific factors, it is likely to be less arduous than the design process for a conventional PV system on an 

existing landfill. PV-integrated geomembrane products are available as a laminate material with the PV mounting 

systems either flush with the landfill cover or mounted at low tilt angles (up to 20 percent tilt angle), which minimizes 

the design analysis related to optimal tilt angles for the PV array. For example, by default, the annual energy output is 

optimized for summer production (unless placed on a highly sloping surface), wind loading is not a significant design 

consideration as the membrane is installed flush with the landfill cover and anchored by a trenching system with sitespecific trench spacing based on local design wind speeds, nor is system weight a concern as the geomembrane 

comprises lightweight TPO material. Snow loading is not a significant design factor either, although snow removal 

may be required if moderate- to long-term accumulation builds up over the PV components and impedes energy 

production. 

5.4 Modules

The selection of PV modules to utilize for a landfill solar process may also require an iterative design review. There 

are a wide variety of modules available to choose from, requiring a decision-making process to determine the optimal 

balance among such factors as efficiency, weight, and cost. There are three main categories of PV modules, namely 

mono-crystalline silicon, poly-crystalline silicon, and thin film. Silicon-based modules continue to dominate with 

approximately 86 percent marketshare, compared to thin-film PV at approximately 14 percent.

31 The trade-offs 

between each of these PV products are addressed below. 

5.4.1 Mono-crystalline 

Mono-crystalline PV modules are the highest efficiency products available on the commercial market with conversion

efficiencies nearing 20 percent. Due to their high power density (power output per unit area), they are particularly 

applicable in applications where available land is limited and maximizing the overall size of the system is desired.

Mono-crystalline panels weigh approximately the same as poly-crystalline panels, but more than thin film 

technologies with the exception of Cadmium Telluride thin film modules. In addition, mono-crystalline modules tend to 

be the most expensive of module technologies on a dollar per watt basis. 

5.4.2 Poly-crystalline 

Poly-crystalline silicon modules have efficiencies of up to 17 percent, in the middle range between mono-crystalline 

and thin film technologies. Due to decreased poly-crystalline silicon prices (poly-crystalline silicon is the raw material

used in manufacturing poly-crystalline PV modules), and increased manufacturing efficiencies, poly-crystalline silicon 

module prices have dropped considerably over the last several years to a level where they are nearly competitive 

with many thin film products. While product characteristics vary by manufacturer, poly-crystalline silicon modules may 

offer a middle ground option for balancing weight, efficiency, and cost factors for landfill applications. 

 

31 Agrawal, M., Bolman, C. et. al. (2012) Photon Consulting. Solar Annual 2012: The Next Wave; p. 24. Print.
Best Practices for Siting Solar Photovoltaics on MSW Landfills February 2013

45

5.4.3 Thin Film PV Products 

Thin film PV products offer a wide range of technology and product solutions. The two main technology options most 

prevalent in the market today are amorphous silicon and cadmium telluride products. In addition to these 

technologies, there are also thin-film PV modules that use copper indium gallium (di)selenide (CIGS), among other 

semiconductor materials, but represent a smaller portion of commercially available product.

Amorphous silicon products are available in two forms, modules and laminates. Amorphous silicon has one of the 

lowest efficiencies in the PV marketplace, with efficiencies of up to 9 percent. They are also the lightest weight 

modules on the market, and may be low cost when compared to the crystalline silicon products. The trade-offs with 

amorphous silicon modules are that when used in fixed tilt applications, they require additional balance of system 

(BOS) materials (foundations, support structures, racking systems) due to their low power density. Additionally, they 

require significantly more land area to achieve the same power output compared to other technologies (i.e., 

approximately twice as much as a poly-crystalline silicon module system). These factors may significantly outweigh 

the cost savings seen at the module level, when evaluating the overall system cost. From a weight perspective, due 

to the additional balance of system requirements, they may place more overall weight across its footprint on the 

landfill surface, although dead weight point loading will be low compared to other technologies. In addition to module 

products, amorphous silicon is also available in laminates and is often used in PV-integrated geomembranes due to 

their flexible properties and low cost. Because they are placed directly on the cap surface, these PV-integrated 

geomembrane laminate solutions do not present the same BOS material concerns as amorphous modules. 

The other main thin film technology option is Cadmium Telluride (CdTe). CdTe modules have efficiencies of up to 12

percent. The main advantage of CdTe products are that they are some of the least expensive modules available on 

the market, while offering moderate efficiencies. Similar to the amorphous silicon thin film modules, CdTe modules 

also require additional BOS materials and typically require additional land area to obtain the same level of power 

output compared to the crystalline silicon options (although not as much land as the amorphous silicon modules). 

The biggest concern with CdTe modules in landfill applications is that they are some of the heaviest on the market. 

Due to this heavy module weight, as well as the additional BOS materials required, the resulting dead weight point 

loads could be an issue on landfill caps with low weight bearing capacity. 

As illustrated in the above discussion, the choice of PV modules for landfill applications typically involves an analysis 

of the trade-offs among energy production needs, available area, efficiency, cost, and weight, as well as the impacts 

of various modules on system dead weight loads and overall system costs. The analyses presented above are based 

on a comparison of the general characteristics of the various technologies, and when conducting a site-specific 

design analysis, PV module information should be reviewed based on technology specifications provided by 

individual manufacturers in terms of product efficiencies, weights, and costs. 

5.5 System Weight Considerations

The overall weight of a conventional PV system, as determined by the aggregate weight of the anchoring system, 

mounting system, and PV module selected is a key design criterion for landfill PV projects. Based on the weight of 

the system and the anchoring system design, dead weight point loads can be calculated, which is the force the 

system weight places on the landfill cover. The dead weight loading of the PV system needs to be compared to the 

weight bearing capacity of the landfill cover, which is a function of landfill cap depth and composition and the makeup 

of the waste material in the landfill cell. Typically, the weight bearing capacity of landfill covers can handle dead 

weight point loads of up to 7 pounds per square inch (psi), although point loads of up to 5 psi are preferred by some 

landfill solar developers. Alternative PV technology applications such as the geomembrane are lightweight and serve 

as part of the final cover, and while their weight considerations still need to be assessed as part of the design 

process, they are not a significant issue.
Best Practices for Siting Solar Photovoltaics on MSW Landfills February 2013

46

5.6 Stormwater Management 

Stormwater discharges from active and closed landfills are subject to NPDES permitting under the CWA because

stormwater discharges are associated with industrial activity (see 40 CFR §122.26(b)(14)(v)). These discharges are 

typically covered by general permits, e.g., EPA’s Multi-Sector General Permit (MSGP).32 In general, landfill operators 

are required to develop and implement a Stormwater Pollution Prevention Plan (SWPPP), which describes BMPs 

and controls to minimize discharge of pollutants in stormwater runoff from these facilities. The PV project design 

should consider the interaction between the PV system components and the existing stormwater management 

system. Depending on the design of the cap, the existing stormwater management system could include, among 

other controls:

• The vegetated surface layer of the landfill cap and landfill buffer area;

• A drainage layer above the hydraulic barrier used to collect and direct runoff off of the cap and help control 

infiltration;

• Vegetated and/or rock-lined swales used to collect surface and drainage layer and convey the runoff for 

further control and/or discharge;

• Underground piping and other conveyance system components (e.g., catch basins) used to collect and 

convey runoff for control and/or discharge;

• Stormwater detention and retention ponds used to contain and/or control the rate of discharge of the runoff 

off-site; and

• Stormwater treatment systems.

The components of the stormwater management system are often specified in an erosion control management plan 

and vegetative cover strategy in the landfill post-closure management plan. The design basis for the stormwater 

management system, including design storm and runoff and stage-storage calculations, should be understood before 

proceeding with the design of the PV project. If this information is not available, it should be reproduced to 

understand the incremental impact of the PV system on stormwater runoff in accordance with regulatory

requirements. Also prior to PV system design, information should be collected on stormwater permitting requirements 

during the construction process (i.e., NPDES), as well as operations and maintenance requirements of the 

stormwater management system resulting from the placement of PV panels on the landfill cap.

In addition to the requirements for stormwater discharges from the landfill, the CWA also requires separate permits 

for stormwater discharges from active construction. PV system design should take into account requirements 

associated with NPDES stormwater permitting, in addition to stormwater management during the operation and 

maintenance phase. 

In most cases, the PV system will affect the operation of the stormwater management system. The PV system will 

increase the impervious surface area of the landfill and will create localized changes in rainfall infiltration and runoff 

patterns. The magnitude and nature of these impacts will depend on the meteorological setting and specific landfill 

and PV system characteristics. The following should be considered when designing the PV project:

• Overall and localized changes in rates and timing of stormwater runoff during design storm events and 

capacity of existing drainage systems, including the drainage layer, swales, piping, ponds, and treatment 

systems (e.g., constructed wetlands, tanks) to effectively direct, contain, and treat the runoff; and

 

32 Specific applicable requirements may vary depending on whether EPA or the state is the NPDES permitting authority. The MSGP is available in states and 

Indian country where EPA is the permitting authority. All but five states have been authorized by EPA to administer the NPDES program, and most states 

issued general permits similar to the MSGP for industrial stormwater discharges. For more information on the MSGP, see 

http://cfpub.epa.gov/npdes/stormwater/indust.cfm. Landfills are classified in Sector L of the MSGP, and more information on requirements for this sector may 

be found at http://www.epa.gov/npdes/pubs/sector_l_landfills.pdf.
Best Practices for Siting Solar Photovoltaics on MSW Landfills February 2013

47

• Localized effects of PV arrays and foundation systems on rainwater infiltration, surface flows patterns and 

potential erosion, and the functioning of the drainage layer.

Where system-wide and/or localized changes are predicted, changes to the stormwater management systems to 

meet landfill permit and other local, state, and/or federal requirements for runoff control and discharge requirements 

should be included in the design of the integrated landfill-PV system. Design considerations could include 

construction of drainage features to collect and direct runoff from PV foundations and arrays, resizing drainage 

swales and/or relining drainage swales to control erosion, resizing detention and retention ponds, and resizing and/or 

upgrading stormwater treatment systems. 

If a landfill is in the closure process, the stormwater management system for the closed landfill can be designed in 

tandem with the PV system to ensure compatibility of both designs.

5.7 Wind/Snow Loading and Frost Protection

There are a number of design considerations associated with wind and snow loading on PV systems in landfill 

applications. Many of these concerns have been addressed previously in this chapter including the interactive effects 

of wind loading with various support structure tilt angles and the impacts on foundation structures, as well as the 

balancing of design criteria between wind and snow loading requirements. 

PV systems on landfills should be designed to meet the local maximum wind speed design criteria. One source for 

determining the design wind speed is the American Society of Civil Engineers Standard 7-05, Chapter 6 pages 32-

33, Figure 6-1. The local building department will also have information on local design wind speeds. Design wind 

speeds are based on 50-year, 3- second gust speeds, and typically range from 80-120 mph throughout most of the 

country, with design wind speeds as high as 130-140 mph in hurricane prone regions. 

Designing a PV system to local design wind speeds requires considerations related to interactive effects of wind 

loading on PV array tilt angles, structural supports, and foundation systems. The consideration of design wind speed 

also should factor in the impacts of additional system design criteria such as landfill maintenance and snow loading 

factors. For example, landfill cover maintenance may require raising the arrays higher to allow for access of mowing 

equipment underneath the panels, and similarly, in areas prone to long-term snow accumulation, the panels may 

need to be raised two or three feet off the ground so that snow does not accumulate on the panels. In both of these 

instances, a raised PV array will be subject to higher wind forces and require a design review relative to tilt angle, 

structural support strength, and foundation requirements. 

In addition, landfill-based PV systems should be designed to incorporate frost protection measures for anchoring 

systems in cold weather climates. 

5.8 Lightning Protection and Grounding 

Electrical grounding is a standard design consideration for all PV systems. Proper grounding protects the PV system 

from electrical surges and lightning strikes. The National Electric Code (NEC) provides safety standards for 

grounding of electrical equipment (Article 250), as well as specifics related to wiring and grounding of PV systems 

(article 690). In landfill applications, PV systems should be grounded into the soil either in buffer areas or into the 

landfill cap material if it is determined that the material and thickness of the cap is sufficient to dissipate the electrical 

charge. If the PV system is grounded to the landfill cap, grounding rods should not be installed vertically such that 

they penetrate the landfill cover and protrude into the waste material, as this poses a fire and explosion hazard due to 

the presence of landfill gas. 

5.9 Cover Management 

In designing a PV system on an existing landfill, it is important to consider how to integrate the PV system with the 

existing closure and post-closure plan provisions for maintaining the landfill cap, including any vegetative cover 

present. For example, for landfills with vegetative covers, PV systems should provide for adequate row spacing to 
Best Practices for Siting Solar Photovoltaics on MSW Landfills February 2013

48

allow access for mowing equipment. If a vegetative cover exists beneath the PV arrays, then the arrays may need to 

be raised for mowing and other maintenance equipment to gain access. Additionally, low-growth vegetative covers 

should be selected to reduce required maintenance.

Another design consideration is the age of the landfill cover and its expected remaining life. PV systems have an 

expected life of 25-30 years. Thus, if the remaining life of the cover material is expected to be only 10 years, then 

installing a PV system with a 25-30 year expected life on top of it would be problematic, as it would be nearly 

impossible to replace the landfill cover with the PV system in place. In these instances, it may be preferable to 

replace the landfill cap during the PV construction phase to avoid landfill cap replacement issues after the PV system 

has been installed. 

The above discussion on cover materials is specific to conventional PV systems with ballasted or similar foundation 

supports. For landfills entering the closure process that utilize a PV-integrated geomembrane, the geomembrane 

serves as the cover system, and design considerations specific to existing cover materials and vegetative 

management are not an issue. 

5.10 Security 

Security concerns also should be addressed in the design phase of a solar project to protect against the threat of 

theft and vandalism and to prevent unauthorized entry into the area by individuals who may be exposed to safety 

hazards resulting from the presence of high voltage equipment. For example, some landfill locations may be popular 

destinations for ATV and snowmobile riders, and they should be kept out of the area containing PV arrays for their 

own protection and safety. The most common, and often required, security measure is perimeter fencing around the 

footprint of the PV system. Design criteria of fencing systems include type, height, and required set back distances 

from the solar arrays. Some solar project sites also employ the use of security cameras. Security lighting is typically 

not employed as security measure, as they consume a significant amount of energy, and they may also face 

opposition from local residents due to visual impact concerns. However, the use of motion-activated security lighting 

along the fence perimeter may warrant consideration. 

5.11 Integration with Landfill Gas Monitoring and Production Systems 

One of the final design considerations for a landfill PV system is to ensure the system layout is compatible with existing 

landfill gas collection, monitoring, and generation systems. The main impact of the landfill gas systems on PV system 

design is that PV system components should be set back a safe distance from landfill gas system components. Siting 

PV systems away from landfill gas equipment is a safety precaution against isolated incidents of sparking from the PV 

system potentially igniting landfill gas. In addition, the further the PV system is away from landfill gas (and leachate 

collection) systems at or near the landfill surface, the less likely that heavy maintenance vehicles or equipment are to 

inadvertently hit above ground equipment or run over and damage below grade piping systems. 

Another design element of the landfill gas and PV system integration is whether there is an on-site landfill gas fueled 

electric generation facility. If a landfill gas generator exists, then consideration should be given to whether the two 

systems will operate separately or as a hybrid system. Typically, PV and landfill gas generation units are operated 

independently and in isolation from one another. In this instance, consideration should be given to electrical metering 

requirements, particularly if power from the two systems is being exported through the same interconnection point. If 

the PV system is planned to be net-metered, this can be problematic, as utilities will generally not allow a PV system 

to be net-metered when an independent power producer (i.e., landfill gas generator) is on-site and exporting power to 

the grid. In these instances, it will be necessary to work with the local utility to determine whether a new 

interconnection point will be required for either the net-metered PV system or the landfill gas generation, or whether 

sub-metering options are available to account for each source of generation. 

An emerging PV / landfill gas generation strategy is to operate the generating units as a hybrid system. This strategy 

can maximize the economic value of both systems and eliminate some of the concerns over sub-metering and 

interconnection requirements. With a PV / landfill gas hybrid system, the landfill gas generation can be used to “firm” or 
Best Practices for Siting Solar Photovoltaics on MSW Landfills February 2013

49

shape the output of the solar power system. For example, if the PV system output drops during the day, the landfill gas 

generation can be ramped up to compensate for the drop in PV output. The output of the hybrid system can also be 

shaped to match the needs of local utilities, if power is sold to them, and capture a higher sales price due to the ability of 

the hybrid system to provide firm power when it is needed. If a landfill generation unit is already operational on-site, this 

strategy would likely reduce the interconnection requirements and costs of a PV-only system, as much of the 

interconnection equipment and permitting requirements are already in place. Additionally, as landfill gas production 

decreases, more PV can be deployed to take advantage of existing transmission capacity at the site. Utility approval 

would still be required for interconnection of the PV system, but it is typically easier to have an existing interconnection 

agreement reviewed for additional capacity than it is to apply for a new interconnection agreement. 

5.12 PV System Engineering Design and Layout 

The final phase of the design process is to develop the PV system design and overall layout based on the design 

considerations presented in this chapter. The first step of this process is the PV system design based upon the 

selected components. Weighing such design factors as site characteristics, regulatory requirements, and preferred 

characteristics of system components, the final technology components are selected and integrated into the design. 

This design includes schematics of the integrated system (foundations, racking, modules). Once the schematics of 

the integrated components are complete, then basic characteristics of the array are known, e.g. array height and row 

length. This then serves as the building block for the site layout. 

The next step in the design process is to create a system layout. The layout is based on the development of a 

footprint for the PV system based on areas determined to be suitable to build on, as well as areas identified to avoid 

due to existing landfill gas/leachate systems, steep slopes, and other site specific requirements. Then, typically 

starting with oldest capped area of the landfill within the PV system footprint, the rows of PV arrays are laid out in the 

desired orientation. Then, allowing for the required spacing between rows based upon shading and PV system and 

landfill cover maintenance access requirements, adjacent rows are laid out within the footprint until the desired 

system size is achieved, or the footprint is maximized. 

This is a simplified description of the engineering design process, and is presented as a framework for how PV 

technology components are selected and the considerations that factor into the overall layout of a system on a landfill 

property. Additional civil engineering design work will be required for site preparation and grading requirements of the 

site, and additional electrical engineering design work will be required for wiring schematics, code compliance, 

inverter placement and interconnection equipment design and specification, integration with system monitoring 

equipment, and other electrical design elements. 
Best Practices for Siting Solar Photovoltaics on MSW Landfills February 2013

50

Highlight 6-1: Major Construction 

Considerations for Building PV Projects 

on Landfills

• Site Preparation and Grading Requirements 

and Constraints

• Site Compaction

• Avoidance of Penetrating Landfill Cap

• Avoidance of Landfill Gas Monitoring, Piping, 

and Production Equipment

• Dust Control

• Stormwater Management

• Site Security

6. Construction Considerations Unique to Building PV 

Projects on Landfills 

The following chapter discusses site preparation, grading, site compaction, working around landfill features, and 

other site-specific issues that should be considered. A summary of the construction considerations unique to building 

PV projects on landfills discussed in Chapter 6 is also provided in Chapter 8, Table 8-1. Note that this is not an 

exhaustive list of construction considerations. Project stakeholders should consider whether different or additional 

approaches are appropriate in light of site specific conditions.

Proposed modifications to an existing cap or planned cap design, and closure and post-closure plans should be 

discussed with, and necessary approvals obtained from, the appropriate permitting authority, which is typically the 

director of an approved state. In addition, financial assurance to cover costs may be adjusted if changes are made to 

the closure plan or post-closure plan.

6.1 Site Preparation and Grading Considerations 

Construction of a PV system on a closed landfill will require 

site preparation and may require grading. Site preparation and 

grading may include (i) removal and replacement of vegetation 

and topsoil and/or (ii) excavation to prepare the site for setting 

foundations and to address modifications to other landfill 

systems (e.g., to create/reconstruct stormwater collection 

swales). It could also include the construction of temporary 

access roads and staging areas for PV system materials and 

equipment, construction vehicles, and other construction 

equipment. Staging areas and access roads should be located 

to not interfere with landfill operation, inspection/monitoring, 

and maintenance activities. Access roads should be designed 

to avoid impacts to the functioning of the landfill cap and other 

systems by limiting the travel of heavy equipment to 

specifically designated areas.

Grading of the landfill cap should be avoided and/or minimized in order to ensure that there is no increase to the 

potential threat to human health and the environment. Grading of the landfill cap must comply with any applicable 

federal, state, and/or local closure, post-closure, and other requirements. For landfills that are regulated under 40 

CFR Part 258, any modifications to the cover system must comply with the requirements outlined in 40 CFR 258 

Subpart F at landfills where this regulation is applicable; see Section 4.2.2.2 for additional information on cover 

systems. Among other things, final grading must meet minimum final cover requirements or, for alternative final cover 

designs, be approved by the director of an approved state. In addition, all modifications to the final cover system 

must comply with post-closure care requirements under 40 CFR 258.61. Note that additional federal, state, tribal, and 

or/local requirements may also apply. 

Furthermore, areas exposed by site preparation and other construction activities (e.g., areas with new fill or where 

the topsoil or subsoil has been exposed) should be stabilized and managed to minimize erosion in accordance with 

post-closure care and NPDES permitting requirements (see Section 5.6).

6.2 Site Compaction 

Site preparation, grading, and construction activities will add temporary and/or permanent loads to the landfill cover, 

which could result in secondary differential settlement in the areas affected. Where new fill is placed on the landfill 

cover (e.g., to create a uniform surface for PV system foundations), the possibility of secondary settlement should be 
Best Practices for Siting Solar Photovoltaics on MSW Landfills February 2013

51

considered in the engineering design.33 Where settlement is expected, fill may be initially placed to a grade above the 

final proposed grade, and compaction and/or a period to allow for settlement may be required. If the new fill material 

is to be compacted, compaction methods and testing should strictly adhere to engineering specifications to avoid 

damage to the function of cap components below the surface layer.

6.3 Penetrations of the Landfill Cap 

In general, penetrations of the landfill cap should be avoided or minimized in order to ensure that there is no increase 

in potential threat to human health and the environment. At typical MSW landfills, there are penetrations in the landfill 

cap for monitoring wells, leachate collection systems, and gas collection systems. These penetrations are designed 

and constructed in order to avoid creating preferential paths for methane or other gases by isolating penetrations 

from the final cover system. Typically, this isolation is achieved through an engineered combination of membrane 

layers, gas venting layers, and other layers designed specifically to block potential gas pathways near penetrations in 

the final cover system. 

Penetrations associated with the installation of a PV system should be designed and constructed in the same way. 

Penetration isolation systems are generally approved as part of the final cover system by the permitting authority. 

Note that the landfill continues to be subject to applicable regulatory requirements under 40 CFR 258 and/or other

federal, state, local, and/or tribal requirements after PV system installation. 

Depending on the status of the landfill closure, designing for or modifying the final cover system to accommodate 

penetrations may not be cost effective. Post-closure care requirements under 40 CFR 258.61(a)(1) call for 

maintaining the integrity and effectiveness of the final cover, while 40 CFR 258.61(c)(3) requires that post-closure 

use of the property not disturb the integrity of the final cover. 

6.4 Avoidance of Landfill Gas Monitoring, Piping, and Production Equipment

As discussed in previous sections, the PV system should be designed to avoid landfill gas monitoring, piping, and 

production equipment and ensure the long-term effectiveness and safety of these systems. Any temporary enclosed 

structures installed at the site should be monitored for explosive levels of landfill gas. During construction of the PV 

systems strict site control should be maintained to prevent inadvertent damage to these systems and to avoid 

hazardous situations (e.g., potential sparking near landfill gas). Site control can be maintained by fencing or 

otherwise restricting access to areas containing gas monitoring and control equipment and areas where construction 

personnel could be exposed to elevated gas concentrations. In addition, clearly designated access roads should be 

established to limit the movement of construction vehicles and equipment.

6.5 Dust Control 

Dust control is typically a requirement for all ground-mounted PV systems during the construction process, 

particularly during the site preparation and grading phase. Control of dust is usually accomplished with the use of 

water trucks that spray recently disturbed ground to prevent winds from dispersing loose fine dirt throughout the area. 

The use of water trucks for dust control is a common practice during construction activities. In landfill applications, the 

main concern is that the weight of the water truck is not too heavy for the load-bearing characteristics of the landfill 

cover. The use of overly heavy water trucks could induce landfill settlement or pose a threat to landfill gas or leachate 

collection systems. 

 

33 Sharma, H.D.; De Ariban, M. (2007). “Municipal Solid Waste Landfill Settlement: Postclosure Perspectives.” Journal of Geotechnical and Geoenvironmental 

Engineering (133:6); pp. 619-629. Print.
Best Practices for Siting Solar Photovoltaics on MSW Landfills February 2013

52

6.6 Stormwater Management 

Stormwater discharges from construction activities disturbing one or more acres of land are generally subject to 

NPDES stormwater permitting requirements (see 40 CFR §122.26(b)(14)(x) and (15)). Construction site discharges 

are typically permitted under general permits, e.g., EPA’s Construction General Permit (CGP).34 In general, 

construction site operators are required to develop and implement a SWPPP, which describes BMPs and controls to 

minimize discharge of pollutants in construction stormwater discharges. These sites and smaller sites may be subject 

to local stormwater control requirements as well. 

In addition, in some cases, components of the landfill stormwater management system under its industrial stormwater 

permit will be temporarily impacted by the installation of a PV system. Site preparation could remove vegetation and 

temporarily expose soil to rainfall prior to construction of overlying structures and/or final stabilization of the area.

Overland flow and swales could be temporarily interrupted by the staging of construction materials and equipment 

and by temporary excavations, rutting, or access roads. Controls should be put in place and maintained to prevent 

excess erosion and permanent damage to these systems and the surrounding environment. When the installation of 

the PV system requires modification to the stormwater collection system, construction should follow engineering 

specifications and good construction practice, including specifications for trenching, inverts and elevations, materials 

(e.g., rip rap, drainage matting, stormwater piping), bedding requirements, etc. Standards for good construction 

practice have been developed by the American Society of Civil Engineers35,36 and may also be specified in state and 

local rules and regulations. Construction equipment used for modifications and/or installation of stormwater 

management systems and the operation of construction equipment should conform to engineering specifications 

designed to prevent excess live loads on the landfill cap and compaction. As with other construction activities, 

erosion controls should be installed and maintained according to engineering specifications and local, state, and/or 

federal requirements. 

Construction of stormwater management systems should be inspected and overseen by a competent inspector and 

engineer and testing of materials and installed systems should meet specified requirements. Modifications to the 

original design to address unforeseen field conditions should be reviewed with the design engineer and government 

personnel with oversight authority. 

6.7 Security

As with any construction project, the threat of theft and vandalism is a major concern, and security safeguards should 

be employed to protect against those threats. Since a security fence will be required around the perimeter of the final 

installation, it is recommended that the permanent fence be erected early on in the construction process and prior to 

the delivery of PV panels and other balance of system equipment. In many cases, the landfill may already have 

security fence in place, negating the need for a new fence to be erected. 

The project developer may even consider the use of temporary lockable storage sheds to secure valuable PV system 

equipment prior to installation, as PV panels and copper wire spools are an easy target for thieves. If theft or 

vandalism is of particularly high concern, the developer may want to consider hiring a security patrol during the 

construction process. 

 

34 Specific applicable requirements may vary depending on whether EPA or the state is the NPDES permitting authority. The CGP is available in states and 

Indian country where EPA is the permitting authority. All but five states have been authorized by EPA to administer the NPDES program, and most states 

issued general permits similar to the CGP for construction stormwater discharges. For more information on the CGP, see 

http://cfpub.epa.gov/npdes/stormwater/const.cfm 35 Task Committee of the Urban Water Resources Research Council of the American Society of Civil Engineers and the Water Environment Federation. (1993). 

Design and Construction of Urban Stormwater Management Systems. ASCE Manuals and Reports on Engineering Practice No. 77, WEF Manual of Practice 

FD-20. New York, NY: American Society of Civil Engineers. Print. 36 Standard Guidelines for the Installation of Urban Stormwater Systems. (2006). ASCE Standard No. 46-05. Reston, VA: American Society of Civil Engineers. 

Print.
Best Practices for Siting Solar Photovoltaics on MSW Landfills February 2013

53

Highlight 7-1: Major Considerations and

Best Practices

• Adherence with landfill post-closure operation, 

maintenance, and monitoring plans

• Panel washing and water management plan or 

natural cleansing

• Stormwater management 

• Cover material management 

• System monitoring and troubleshooting 

7. Operations and Maintenance Considerations for PV 

Projects on Landfills 

The following chapter outlines the types of long-term actions (e.g., adherence with post-closure plans, water 

management, panel cleaning) that should be taken to ensure continued safe and effective operation of the PV 

system once it is established. Routine operations and maintenance of PV systems are usually minimal in cost, 

ranging from $10-15/kW on an annual basis. A summary of the operations and maintenance considerations for PV 

projects on landfills discussed in Chapter 6 is also provided in Chapter 8, Table 8-1. Note that this is not an 

exhaustive list of operations and maintenance considerations. Project stakeholders should consider whether different 

or additional approaches are appropriate in light of site specific conditions.

7.1 Adherence with Landfill Post-Closure Operation, Maintenance, and Monitoring 

Plans 

Following the successful installation of the PV project, 

continued compliance with applicable regulations is required 

for the landfill post-closure operation, maintenance, and 

monitoring plan, including modifications to the plan approved 

for the integrated landfill-PV system. Following installation of 

the PV system, opportunities should be sought to integrate 

landfill and PV system operation, maintenance, and monitoring 

requirements. For example, routine cap and PV system 

inspections could be conducted at the same time and certain 

equipment maintenance and/or material supply contracts could 

be combined.

In addition, opportunities for combining maintenance scheduling and operational monitoring data systems could be 

explored, not only to identify operational efficiencies but also to enable integrated analysis of monitoring data. For 

example, settlement and PV production output data could be combined and analyzed to determine possible 

interactions between cap settlement and output. Such systems could be used to identify and/or rule out potential 

sources of operational inefficiencies and enable appropriate responses.

7.2 Panel Washing and Water Management Plan or Natural Cleansing

The washing of PV panels is the main routine maintenance activity undertaken for PV systems. Removing dust and 

silt from the PV panels increases their performance and may be required on a periodic basis, depending on the 

frequency of rainstorm events at a given site. In some areas of the country that receive frequent and abundant 

rainfall, there is not a need to wash the solar panels as they are cleansed naturally. In drier areas of the country, and 

during times of drought, panel washing may be required. In determining the need to wash panels, it may be beneficial 

to perform a benefit-cost analysis to compare the estimated reduction in PV system output without panel washing to 

the cost of washing panels (primarily labor costs) to the estimated reduction in system output (reduction on kilowatthours multiplied by the value of each kilowatt-hour). In a number of cases, PV system owners have found that it is 

more cost-effective to rely on natural cleansing than to pay for panel cleaning. 

Panel washing is water-intensive, and the use of water to clean panels may not be allowed in some waterconstrained jurisdictions. However, particularly in landfill applications, PV module washing should not use cleaning 

fluids that contain harmful chemicals, as these chemicals could leach into the landfill cover and underlying layers, 

and/or may runoff during stormwater events. Attention should also be given to the weight of water trucks on the 

landfill if water-based cleaning is used and there is no on-site water available. 
Best Practices for Siting Solar Photovoltaics on MSW Landfills February 2013

54

7.3 Stormwater Management 

Routine and corrective maintenance of stormwater management systems will be required to ensure that they 

continue to meet aesthetic and functional requirements. Aesthetic maintenance can include grass trimming in areas 

around stormwater management components, weed control, etc. Functional maintenance can include preventive 

maintenance (e.g., maintenance of vegetative cover, removal of sediment from swales and ponds, maintenance of 

mechanical equipment) and corrective maintenance (e.g., erosion and embankment repairs and mechanical

equipment repairs).37

7.4 Vegetation and Cover Management 

In landfill solar applications, the maintenance of the landfill cover is typically negotiated in the contract between the 

system owner and landfill owner. In some instances, maintenance is the responsibility of the PV system owner, and 

in others the responsibility falls to the landfill owner. Cover maintenance activities are rather straightforward and 

largely consist of periodic mowing if there is a vegetative cover. Remaining maintenance activities are largely 

inspection and repair related. Typically, inspections are conducted on a quarterly or half-yearly basis to look for 

cracks or fissures in the cover material, erosion or channeling from stormwater runoff, or occurrences of differential 

settlement. If damage to the cap is identified, then this damage is repaired and corrected. 

The cover management process is even simpler with geomembrane systems, as the membrane is examined 

periodically for tears in the cover material or slumping of the cover material due to differential settlement. In these 

cases, the cover material is repaired if tears are found or repositioned to correct for differential settlement. 

7.5 System Monitoring and Troubleshooting 

Most PV systems come equipped with remote monitoring systems to allow the system operator to monitor the 

system’s performance. Often, small weather stations are installed at the site to allow a comparison of predicted 

system output based on recent weather data versus the actual output of the system. This allows for identification of 

problems with the system if the actual output is less than predicted. Typically, the larger the PV system, the more 

complex the monitoring system becomes, as it becomes more important to identify modules or strings of modules 

that are underperforming in a timely manner. PV monitoring systems are useful for providing real-time cumulative 

data on system performance that can be used in public displays, such as kiosks, to highlight a project to the local 

community. 

7.6 System Security

As discussed above, solar PV systems consist of expensive components such as PV modules and inverters, which 

make onsite security an important consideration. The permanent fencing installed during the construction phase may 

be sufficient. However, more sophisticated security measures may be appropriate for remote or unsupervised 

facilities. 

 

37 Livingston, E.H.; Shaver, E.; Skupien, J.J. (1997). Operation, Maintenance, & Management of Stormwater Management Systems. Work performed by 

Watershed Management Institute, Inc., Ingleside, MD. Washington, DC: U.S. Environmental Protection Agency, Office of Water. Accessed April 23, 2012: 

http://www.stormwater.ucf.edu/research/stormwaterOMM/stormwateromm.pdf.
Best Practices for Siting Solar Photovoltaics on MSW Landfills February 2013

55

8. A Summary of Best Practices for Siting Solar PV Projects 

on Landfills

The best practices for siting solar PV projects on landfills discussed in this document are summarized in Table 8-1. 

This table provides an overview of best practices and is not an exhaustive list. Project stakeholders should consider 

whether different or additional approaches are appropriate in light of site specific conditions. As indicated in Chapter 

1, solar installations on landfills are a relatively new redevelopment approach. Since PV technology is rapidly 

developing and changing, as future projects are brought on line and as PV technology continues to evolve, EPA and 

NREL intend to update the information contained in this document. 

Table 8-1: Summary of Technical Considerations, Challenges, and Best Practices 

Technical Considerations Challenges Best Practices

Design 

Steep Slopes • Stability of foundation/anchoring 

system

• High wind loads

• Stormwater management

• Increased erosion

• Lighter weight PV modules and balance of 

system (BOS) components

• Fixed tilt mounting systems

• Heavier, more robust foundation/anchoring 

systems (i.e., ballasted foundations, helical 

piles)

• PV Integrated Geomembrane

• Re-grading to minimize slope 

Waste Composition and Settlement • Differential settlement 

• Water ponding 

• Stormwater management 

• Misalignment of arrays

• Use of settlement forecasts in the design 

phase

• Strategic siting of PV arrays (i.e., use older 

landfill areas and areas containing 

construction waste)

• Lighter weight PV modules, anchoring 

systems, and BOS components 

• Fixed tilt mounting systems that can 

accommodate future use of spacers/shims to 

correct for differential settlement

• Adjustable fixed tilt mounting systems 

• PV integrated geomembranes

• Cover compaction / soil tamping

• Geogrid reinforcement

Cap Characteristics • Compliance with closure and 

post-closure care requirements 

as described in 40 CFR 258 

Subpart F and other laws as 

applicable

• Areas of thin cover material

• Compatibility with stormwater

management system

• Import fill to increase thickness of cover

• Lightweight and/or non-invasive anchoring 

systems (i.e., ballasted, shallow-poured

concrete footers, pre-cast concrete footers)

• Fixed tilt mounting systems

• PV integrated geomembranes

• Strategic layout of PV arrays to accommodate 

stormwater management system

• Use of rain gutters on PV arrays to channel 

stormwater runoff
Best Practices for Siting Solar Photovoltaics on MSW Landfills February 2013

56

Table 8-1: Summary of Technical Considerations, Challenges, and Best Practices 

Technical Considerations Challenges Best Practices

Stormwater Management • Compatibility with stormwater

management system

• Ensure “sheeting” of stormwater 

runoff to avoid erosion

• PV integrated geomembranes

• Strategic layout of PV arrays to accommodate 

stormwater management system

• Use rain gutters on PV arrays to channel 

stormwater runoff to swales and retention 

ponds

• Coordinate with state waste management 

office and update the SWPPP under the 

industrial stormwater permit to address 

discharge from PV arrays, if necessary

Wind and Snow Loading • Ensure that PV system is 

compliant with localized wind 

speed design criteria

• Ensure that PV system is 

designed to handle localized 

snow loads

• Wind: 

o Minimize the height of the array

o Utilize heavier, more robust anchoring 

systems (i.e., ballasted, concrete slabs, 

shallow-poured concrete footers/precase concrete footers) 

o PV integrated geomembranes

• Snow: raise the height of the module 2-3 feet 

off the ground to minimize impacts from snow 

accumulation on the ground

• Combined: Consider both wind and snow 

loads to establish tilt angle, i.e. higher tilt 

angles will allow snow to slide off, but will 

result in increased wind loading on the 

system

Cover Material Management • Ensure consistency with landfill 

post-closure management plan 

• Access to cover for maintenance

• Allow adequate distance between rows of PV 

arrays to allow for access of maintenance 

equipment 

• Raise array height, if needed, to provide 

access to cover material beneath PV arrays

Site Security • Prevent unauthorized access to 

PV system 

• Protect against theft and 

vandalism

• Perimeter fencing

• Security cameras

• Security lighting with motion sensors

Integration with Landfill Gas 

Monitoring and Production / Leachate 

Collection Systems 

• Ensure compatibility of PV 

system with landfill gas and 

leachate systems

• Ensure weight of PV system is 

compatible with load bearing 

capacity of landfill gas and 

leachate piping systems

• Strategic layout of PV systems with setbacks 

from landfill gas and leachate systems

• Avoid use of heavy equipment over landfill 

gas and leachate systems

• Lightweight PV systems

• Explore opportunities to operate the landfill 

gas production and PV generating units as a 

hybrid system
Best Practices for Siting Solar Photovoltaics on MSW Landfills February 2013

57

Table 8-1: Summary of Technical Considerations, Challenges, and Best Practices 

Technical Considerations Challenges Best Practices

Construction 

Site Preparation and Grading 

Requirements and Constraints 

• Compliance with closure and 

post-closure care requirements 

as described in 40 CFR 258 

Subpart F and other laws as 

applicable

• Ensure compliance with 

engineering design and 

specifications of the landfill cover 

with landfill post-closure 

management plan

• Avoidance of landfill cap 

penetration

• Determine whether applicable regulatory 

requirements allow for grading and obtain 

necessary approvals for any modifications

• Minimize grading requirements 

• Bring in fill material, if necessary, to ensure 

cover characteristics are compliant with 

landfill cover requirements

• Revegetate the landfill cover if any vegetation 

was removed in the grading process; explore 

opportunities for low growth vegetation using 

native species

• Alternative final cover system designs are 

subject to approval through a director of an 

approved state

Site Compaction • Prevent or minimize differential 

settlement 

• Bring in fill material and use soil tamping 

equipment to stabilize and compact the 

material, or allow for a settlement period of 

the imported fill material

Penetrations of Landfill Cap • Compliance with final cover 

system requirements as 

described in 40 CFR 258 Subpart 

F and other laws as applicable 

• Avoid penetrating landfill cap 

• Determine whether applicable regulatory 

requirements allow for penetrations and 

obtain necessary approvals for any 

modifications 

• Avoid or minimize any cap penetration 

• Design isolation systems for areas 

surrounding any penetrations in the final 

cover system to avoid creation of preferential 

paths for methane or other gases

• Use fixed tilt mounting systems with nonpenetrating or minimally penetrating 

anchoring systems (i.e., ballasted systems, 

pre-cast concrete footers, shallow poured 

concrete footers, concrete slabs) 

• Alternative final cover system designs are 

subject to approval through a director of an 

approved state

Avoidance of Landfill Gas Monitoring, 

Piping, and Production Equipment

and Leachate Collection Equipment 

• Avoid landfill gas and leachate 

systems 

• Install temporary fencing around landfill gas 

and leachate systems to prevent contact with 

construction equipment

• Ensure that roads are set back from landfill 

gas and leachate equipment and that vehicles 

stay on designated roads 
Best Practices for Siting Solar Photovoltaics on MSW Landfills February 2013

58

Table 8-1: Summary of Technical Considerations, Challenges, and Best Practices 

Technical Considerations Challenges Best Practices

Dust Control • Minimize dust generation during 

the construction process

• Use water trucks to water site during 

construction

• Ensure water trucks are not too heavy for the 

load bearing capacity of the landfill and 

landfill gas/leachate piping systems

Stormwater Management • Ensure stormwater management 

system is not impacted or altered 

during the construction phase 

• Obtain NPDES permit prior to construction

• Minimize disturbances to the stormwater 

management system during construction

• If the existing stormwater management 

system is altered during the construction 

phase, ensure that the system is remediated 

and is compliant with the engineering 

requirements and design in the landfill postclosure management plan

Site Security • Prevent unauthorized access to 

construction site 

• Protect against theft and 

vandalism

• Install permanent perimeter fencing prior to 

construction

• Consider use of temporary, lockable storage 

sheds to secure PV modules and BOS 

equipment

• Consider hiring security patrol service

Operations & Maintenance

Adherence with Landfill Post-closure 

Operation, Maintenance, and 

Monitoring Plans

• Ensure compliance with landfill 

post-closure plans

• Consider combining landfill maintenance and 

PV system maintenance inspections to obtain 

operational and cost efficiencies 

• Use PV system monitoring and analysis to 

identify potential settlement issues on the 

landfill

Module Washing and Water 

Management Plan or Natural 

Cleansing

• Clean modules to remove dust 

and silt to maximize PV system 

output

• Consider natural cleansing from storm events 

• Avoid use of chemical cleansers in landfill 

applications

• If water cleansing is used and no on-site 

water is available, ensure that water trucks 

are not too heavy for the weight bearing 

capacity of the landfill

Stormwater Management • Ensure long-term functionality of 

stormwater management 

systems

• Conduct routine maintenance of landfill cover 

and landfill cover materials

• Conduct preventive maintenance on 

stormwater management system (i.e., 

removal of sediment from swales and ponds, 

maintenance of mechanical equipment)

• Conduct corrective maintenance (i.e., erosion 

and embankment repairs and mechanical 

equipment repairs)
Best Practices for Siting Solar Photovoltaics on MSW Landfills February 2013

59

Table 8-1: Summary of Technical Considerations, Challenges, and Best Practices 

Technical Considerations Challenges Best Practices

Cover Material Management • Ensure long-term functionality of 

landfill cover and/or vegetative 

cover

• Conduct routine maintenance of landfill cover 

(i.e., grass mowing, weed control)

• Conduct periodic inspections of landfill cover 

to identify cracks or fissures in the cover 

material, erosion or channeling from 

stormwater runoff, or occurrences of 

differential settlement

• Perform repairs to landfill cover as identified

System Monitoring and 

Troubleshooting 

• Ensure optimal performance of 

PV system

• Use remote monitoring system in conjunction 

with on-site weather station to identify system 

performance anomalies and to trouble shoot 

and isolate potential PV system problems 
Best Practices for Siting Solar Photovoltaics on MSW Landfills February 2013

A-1 

Appendix A: Solar PV on Landfill Projects 

This list includes PV systems installed at landfills as of February 2013. This list is for informational purposes only. 

The information in this list was gathered from public announcements of renewable energy projects in the form of 

company press releases, news releases, and, in some cases, conversations with the parties involved. It may not be a 

comprehensive list of all projects completed on landfills.

Table A-1: Completed Solar Landfill Projects 

Project Location Size Completion PV Technology

Bee Ridge Landfill/ Rothenbach Park Sarasota, FL 250 kW 2008 Crystalline 

Camp Pendleton San Diego, CA 1.4 MW 2011 Crystalline

East Hampton Landfill Easthampton, MA 2.2 MW 2011 Crystalline

Evergreen Landfill Canton, NC 550 kW 2010 Crystalline

Fort Carson AFB Landfill Ft Collins, CO 2 MW 2008 Thin Film

Greenfield Solar Farm Greenfield, MA 2 MW 2012 Crystalline

GROWS Landfill38 Bucks Co, PA 3 MW 2010 Crystalline

Hickory Ridge Atlanta, GA 1 MW 2011 Thin Film

Islip/Blydenburg Hauppauge/Islip, NY 50 kW 2011 Crystalline

Madison County Lincoln, NY 50 kW 2011 Thin Film

NC State University – Agricultural 

Pesticide Landfills

Raleigh, NC 76.5 kW 2007 Crystalline

Nellis Air Force Base Las Vegas, NV 14.2 MW 2007 Crystalline

Paulsboro Terminal – Gypsum Landfill Paulsboro, NJ 276 kW 2002 Crystalline

Pennsauken Landfill Pennsauken, NJ 2.1 MW 2008 Crystalline

Tessman Road San Antonio, TX 135 kW 2008 Thin Film

 

38 Solar PV system was constructed on buffer land adjacent to the GROWS Landfill.
Best Practices for Siting Solar Photovoltaics on MSW Landfills February 2013

B-1 

Appendix B: Tools and Resources

EPA’s RE-Powering America’s Land Initiative, Renewable Energy Interactive 

Mapping Tool

The Google Earth mapping tool developed through EPA’s RE-Powering America’s Land Initiative and screening 

criteria decision trees developed by the U.S. Department of Energy (DOE) NREL are examples of two tools that 

developers and landfill owners can use to conduct a pre-site visit or preliminary screening assessment. 

EPA's Renewable Energy Interactive Mapping Tool, a Google Earth KMZ file, makes it possible to view EPA's 

information about siting renewable energy on contaminated land and mine sites, alongside other information 

contained in Google Earth. It enables the user to search by renewable energy type or by contaminated land type. In 

addition to the site's location, it also provides: site name and identification information; EPA Region and program 

managing the site; a link to the site's cleanup status information; and specific acreage and renewable energy 

resource information as illustrated in Figure B-1. 

Source: EPA 

Figure B-1: Google Earth Interactive Mapping Tool

For more information on EPA’s Interactive Mapping Tool, including directions on how to use the tool, please see: 

www.epa.gov/renewableenergyland/mapping_tool.htm. 
Best Practices for Siting Solar Photovoltaics on MSW Landfills February 2013

B-2 

Siting Renewable Energy on Contaminated Properties: Addressing Liability Concerns 

Fact Sheet 

This fact sheet provides answers to some common questions that developers of renewable energy projects on 

contaminated properties may have regarding potential liability for cleaning up contaminated properties. To view the 

fact sheet, please visit: www.epa.gov/enforcement/cleanup/documents/superfund/re-liab-2012-fs.pdf

Please see: www.epa.gov/renewableenergyland/tools.htm for more information on the tools and resources available 

to address liability concerns. 

NREL System Advisor Model

NREL System Advisor Model (SAM) is a performance and economic model designed to facilitate decision making for 

people involved in the renewable energy industry, ranging from project managers and engineers to incentive program 

designers, technology developers, and researchers. 

SAM makes performance predictions for grid-connected solar, solar water heating, wind, and geothermal power 

systems and makes economic calculations for both projects that buy and sell power at retail rates, and power 

projects that sell power through a power purchase agreement.

SAM consists of a performance model and financial model. The performance model calculates a system's energy 

output on an hourly basis (sub-hourly simulations are available for some technologies). The financial model 

calculates annual project cash flows over a period of years for a range of financing structures for residential, 

commercial, and utility projects. 

LCOE – levelized cost of energy

IRR – internal rate of return

NPV – net present value

Source: NREL SAM General Presentation

Figure B-2: SAM block diagram

SAM makes performance predictions for grid-connected solar, small wind, and geothermal power systems and 

economic estimates for distributed energy and central generation projects. The model calculates the cost of 

generating electricity based on information you provide about a project's location, installation and operating costs, 

type of financing, applicable tax credits and incentives, and system specifications. SAM also calculates the value of 

saved energy from a domestic solar water heating system. Figure B-3 shows the sample of PV system inputs.
Best Practices for Siting Solar Photovoltaics on MSW Landfills February 2013

B-3 

Source: NREL SAM PV Presentation

Figure B-3: PV system inputs

SAM is based on an hourly simulation engine that interacts with performance, cost, and finance models to calculate 

energy output, energy costs, and cash flows. The software can also account for the effect of incentives on project 

cash flows. SAM's spreadsheet interface allows for exchanging data with external models developed in Microsoft 

Excel. The model provides options for parametric studies, sensitivity analysis, optimization, and statistical analyses to 

investigate impacts of variations and uncertainty in performance, cost, and financial parameters on model results. 

SAM models system performance using the TRNSYS39, building energy and system component simulation software 

developed at the University of Wisconsin combined with customized components. TRNSYS is a validated, timeseries simulation program that can simulate the performance of PV, concentrating solar power, water heating 

systems, and other renewable energy systems using hourly resource data. TRNSYS is integrated into SAM so there 

is no need to install TRNSYS software or be familiar with its use to run SAM. Figure B-4 shows the sample of 

simulation results. Visit the SAM40 website (http://www.nrel.gov/analysis/sam) for more details and software 

download. 

 

39 TRNSYS, http://sel.me.wisc.edu/trnsys/ 40 SAM, www.nrel.gov/analysis/sam 
Best Practices for Siting Solar Photovoltaics on MSW Landfills February 2013

B-4 

Source: NREL SAM PV Presentation

Figure B-4: Sample of SAM simulation results

NREL PV Watts

NREL's PVWatts calculator determines the energy production and cost savings of grid-connected PV energy

systems throughout the world. It allows homeowners, installers, manufacturers, and researchers to easily develop 

estimates of the performance of hypothetical PV installations. 

PVWatts is the energy simulation engine used by DOE’s Solar Advisor Model. The PVWatts calculator provides 

users with a more basic user interface and provides only energy prediction information.

The PVWatts calculator works by creating hour-by-hour performance simulations that provide estimated monthly and 

annual energy production in kilowatts and energy value. Users can select a location and choose to use default values 

or their own system parameters for size, electric cost, array type and efficiency, tilt angle, and azimuth angle. The 

azimuth angle is the compass bearing toward which the modules are pointed. A system facing true north has an 

azimuth of 0°, due east 90°, south 180°, and west 270°. In addition, the PVWatts calculator can provide hourly 

performance data for the selected location.

PV systems should ideally be designed and installed with an azimuth within 45° of true south (for the northern 

hemisphere) to maximize electricity production. Modules typically produce the most energy if tilted at an angle equal 

to the latitude of the location, but system design economics may dictate a more cost-optimal orientation. 

Using typical meteorological year weather data for the selected location, the PVWatts calculator determines hourly 

performance data for the system and adjusts it for losses—both in production of energy and the conversion from DC 

to AC power. Hourly values of AC energy are then summed to calculate monthly and annual AC energy production.

The PVWatts output is particularly useful in matching seasonal loads to output of the PV system. Running PVWatts 

with different scenarios is also helpful in understanding the variations in output from design changes to the system 

such as size, angle, and orientation.
Best Practices for Siting Solar Photovoltaics on MSW Landfills February 2013

B-5 

Source: rredc.nrel.gov/solar/calculators/PVWATTS/version1/US/code/pvwattsv1.cgi

Figure B-5: Example of input and output of PVWatts
Best Practices for Siting Solar Photovoltaics on MSW Landfills February 2013

B-6 

Solar Decision Tree 

The Solar Decision Tree is designed to guide users through a three-phase process to assess sites, including 

Municipal Solid Waste (MSW) landfills for redevelopment with solar PV. Users navigate the decision tree by 

responding to questions in the "Evaluation" boxes. Depending on the response, the user is directed to the next 

criteria or alerted to a potential obstacle by the "Flags." The user is directed to the next process step by "Arrows." 

The solar PV decision tree is located at: http://epa.gov/renewableenergyland/docs/solar_decision_tree.pdf. See 

Section II.5 for landfill-specific considerations.

Source: EPA

Figure B-6: Solar Decision Tree
Best Practices for Siting Solar Photovoltaics on MSW Landfills February 2013

C-1 

Appendix C: Financing and Procurement Options

Owner and Operator Financing

The owner/operator financing structure is characterized by a single entity with the financial strength to fund all of the 

solar project costs and, if a private entity, sufficient tax appetite to utilize all of the project’s tax benefits. Private 

owners/operators typically establish a special purpose entity (SPE) that solely owns the assets of the project. An 

initial equity investment into the SPE is funded by the private entity using existing funds and all of the project’s cash 

flows and tax benefits are utilized by the entity. This equity investment is typically matched with debt financing for the 

majority of the project costs. Project debt is typically issued as a loan based on the owner/operators’ assets and 

equity in the project. In addition, private entities can utilize any of federal tax credits offered. 

For public entities that choose to finance, own and operate a solar project, funding can be raised as part of a larger, 

general obligation bond, as a stand-alone tax credit bond, through a tax-exempt lease structure, bank financing, grant 

and incentive programs, internal cash or some combination of the above. Certain structures are more common than 

others and grant programs for solar programs are on the decline. Regardless, as tax-exempt entities, public entities 

are unable to benefit directly from the various tax credit based incentives available to private companies. This has 

given way to the now common use of third party financing structures such as the Power Purchase Agreement (PPA) 

described below. 

Third Party Developers with Power Purchase Agreements (PPA)

Since many project site hosts do not have the financial or technical capabilities to develop a capital intensive project, 

many times they turn to third-party developers (and/or their investors). In exchange for access to a site through a 

lease or easement arrangement, third-party developers will finance, develop, own and operate solar projects utilizing 

their own expertise and sources of tax equity financing and debt capital. Once the system is installed, the third-party 

developer will sell the electricity to the site host or local utility via a power purchase agreement (PPA), a contract to 

sell electricity at a negotiated rate over a fixed period of time. The PPA typically will be between the third-party 

developer and the site host if it is a “behind the meter” retail transaction or directly with an electric utility if it is a 

wholesale transaction. 

Site hosts benefit by either receiving competitively priced electricity from the project via the PPA or land lease 

revenues for making the site available to the solar developer via a lease payment. This lease payment can take on 

the form of either a revenue sharing agreement or an annual lease payment. In addition, third-party developers are 

able to utilize federal tax credits. For public entities, this arrangement allows them to utilize the benefits of the tax 

credits (low PPA price, higher lease payment) while not directly receiving them. The term of a PPA typically vary from 

20-25 years.

Third Party “Flip” Agreements

The most common use of this model is a site host working with a Third Party Developer who then partners with a taxmotivated investor in a special purpose entity that would own and operate the project. Initially, most of the equity 

provided to the SPE would come from the tax investor and most of the benefit would flow to the tax investor (as much 

as 99 percent). When the tax investor has fully monetized the tax benefits and achieved an agreed upon rate of 

return, the allocation of benefits and majority ownership (95 percent) would “flip” to the site host (but not within the 

first five years). After the flip, the site host would have the option to buy out all or most of the tax investor’s interest in 

the project at the fair market value of the tax investor’s remaining interest. 

A “flip” agreement can also be signed between a developer and investors within an SPE, where the investor would 

begin with the majority ownership. Eventually, the ownership would flip to the developer once investors’ return is met.
Best Practices for Siting Solar Photovoltaics on MSW Landfills February 2013

C-2 

Hybrid Financial Structures

As the solar market evolves, hybrid financial solutions have been developed in certain instances to finance solar 

projects. A particular structure, nicknamed “The Morris Model” after Morris County, New Jersey, combines highly 

rated public debt, a capital lease and a PPA. Low-interest public debt replaces more costly financing available to the 

solar developer and contributes to a very attractive PPA price for the site hosts. New Markets Tax Credits have been 

combined with PPAs and public debt in other locations, such as Denver and Salt Lake City. 

Solar Services Agreement and Operating Lease

The Solar Services Agreement (SSA) and Operating Lease business models have been predominately used in the 

municipal and cooperative utility markets due its treatment of tax benefits and the rules limiting Federal tax benefit 

transfers from non-profit to for-profit companies. Under IRS guidelines, municipalities cannot enter capital leases with 

for-profit entities when the for-profit entities capture tax incentives. As a result, a number of business models have 

emerged as a work around to this issue. One model is the “Solar Services Agreement” wherein a private party sells 

“solar services” (i.e., energy and RECs) to a municipality over a specified contract period (typically long enough for 

the private party to accrue the tax credits). The non-profit utility typically purchases the solar services with either a 

one-time up-front payment equal to the turn-key system cost minus the 30 percent Federal tax credit, or may 

purchase the services in annual installments. The municipality may buyout the system once the third party has 

accrued the tax credits, but due to IRS regulations, the buyout of the plant cannot be included as part of the Solar 

Services Agreement (i.e., the SSA cannot be used as a vehicle for a sale and must be a separate transaction).

Similar to the SSA there a variety of lease options that are available to municipalities that allow the capture of tax 

benefits by 3rd party owners, which result in a lower cost to the municipality. These include an operating lease for 

solar services (as opposed to an equipment capital lease), and a complex business model called a “sales/leaseback”. Under the sales/lease-back model, the municipality develops the project and sells it to a 3rd party tax equity 

investor who then leases the project back to the municipality under an operating lease. At the end of the lease period, 

and after the tax benefits have been absorbed by the tax equity investor, the municipality may purchase the solar 

project at Fair Market Value.

Sale/Lease Back

In this widely accepted model, the public or private entity would install the PV system, sell it to a tax investor and then 

lease it back. As the lessee, they would be responsible for operating and maintaining the solar system as well as 

have the right to sell or use the power. In exchange for use of the solar system, the public or private entity would 

make lease payments to the tax investor (the lessor). The tax investor would have rights to federal tax benefits 

generated by the project and the lease payments. Sometimes, the entity is allowed to buy back the project at 100

percent fair market value after the tax benefits are exhausted. 

Community Solar Gardens 

The concept of “Community Solar” is one in which the costs and benefits of one large solar project are shared by a 

number of participants. A site owner may be able to make the land available for a large solar project which can be the 

basis for a community solar project. Ownership structures for these projects vary but the large projects are typically 

owned or sponsored by a local utility. Community Solar Gardens are distributed solar projects wherein utility 

customers have a stake via a pro-rated share of the project’s energy output. This business model is targeted to meet 

demand for solar projects by customers who rent/lease homes or business, do not have good solar access at their 

site, or do not want to install solar system on their facilities. Customer pro-rated shares of solar projects are acquired 

through a long-term transferrable lease of one or more modules, or they subscribe to a share of the project in terms 

of a specific level of energy output or the energy output of a set amount of capacity. Under the customer lease option, 

the customer receives a billing credit for the number of kWh their pro-rated share of the solar project produces each 

month; it is also known as “virtual net-metering”. Under the customer subscription option, the customers typically pay 
Best Practices for Siting Solar Photovoltaics on MSW Landfills February 2013

C-3 

a set price for a block of solar energy (i.e., 100 kWh per month blocks) from the community solar project. Other 

models include monthly energy outputs from a specific investment dollar amount, or a specific number of modules. 

Community solar garden and customer subscription-based projects can be solely owned by the utility, owned solely 

by Third Party Developers with facilitation of billing provided by the utility, or may be a joint venture between the utility

and a Third Party Developer leading to eventual ownership by the utility after the tax benefits have been absorbed by 

the Third Party Developer.

There are some states that offer solar incentives for community solar projects, including Washington State 

(production incentive) and Utah (state income tax credit). Community Solar is known as Solar Gardens depending on 

the location (e.g. Colorado). 
Best Practices for Siting Solar Photovoltaics on MSW Landfills February 2013

D-1 

Appendix D: References

Chapter 1

EPA, Municipal Solid Waste in the United States: 2009 Facts and Figures. EPA530-R-10-012. December 2010. 

http://www.epa.gov/osw/nonhaz/municipal/pubs/msw2009rpt.pdf

EPA OSWER Center for Program Analysis. Siting Clean and Renewable Energy on Contaminated Lands and Mining 

Sites. Factsheet. Undated.

EPA. RE-Powering America’s Land: Siting Renewable Energy on Potentially Contaminated Land and Mine Sites. 

Anywhere the Sun Shines: Developing Solar Energy on Contaminated Land. October 2009.

Suflita, J.M., Gerba, C.P., Ham, R.K., Palmisano, A.C., Rathje, W.L., Robinson, J.A. The World’s Largest Landfill: A 

Multidisciplinary Investigation. Environmental Science and Technology 26.8 (1992): 1486-1495.

US. Department of Energy, National Renewable Energy Laboratory. 2006. Power Technologies Energy Data Book, 

Fourth Edition. Table 12.1. Available at: http://www.nrel.gov/analysis/power_databook. Annual Electricity Generation 

(kWh) Based on 1 MW Capacity: U.S. Department of Energy, National Renewable Energy Laboratory. 2009. A 

Performance Calculator for Grid‐Connected PV Systems. Data accessed for average annual solar radiation 

(kWh/m2/day) for Portland, OR (Class 3), Minneapolis, MN (Class 4) Los Angeles, CA (Class 5), and Alamosa, CO 

(Class 6). Available at: http://www.nrel.gov/rredc/pvwatts/

Chapter 2

Commission File Number 1-14267. Annual Report Pursuant to Section 13 or 15(d) of the Securities and Exchange 

Act of 1934, for the fiscal year ended December 31, 2009. Republic Services, Inc..

Department of Health and Human Services, Agency for Toxic Substances and Disease Registry. Landfill Gas Primer: 

An Overview for Environmental Health Professionals. November 2001.

RCRA Orientation Manual 2008: Resource Conservation and Recovery Act. (2008). EPA. p II-11.

Solid Waste Disposal Facility Criteria: Technical Manual. (1993). EPA530-R-93-017. EPA. Accessed April 22, 2012: 

http://www.epa.gov/waste/nonhaz/municipal/landfill/techman/index.htm

Solid Waste Disposal Facility Criteria: Technical Manual (Subpart F: Closure and Post-Closure). (1993). EPA530-R93-017. EPA. Accessed April 22, 2012: http://www.epa.gov/waste/nonhaz/municipal/landfill/techman/index.htm. 

Waste – Non-Hazardous Waste – Municipal Solid Waste.” EPA. Accessed April 22, 2012: 

http://www.epa.gov/osw/nonhaz/municipal/landfill.htm. 

Chapter 3

US Solar Market Insight 2010 Year-end Review.” Solar Energy Industries Association. Accessed November 15, 

2011: www.seia.org/cs/research/SolarInsight

Chapter 4

Bonaparte, R.; Gross, B.; Daniel, D.; Koerner, R.; Dwyer, S. (2004). Technical Guidance for RCRA/CERCLA Final 

Covers. EPA/540-R-04-007. Washington, DC: U.S. Environmental Protection Agency, Office of Solid Waste and 

Emergency Response. Accessed April 23, 2012: http://nepis.epa.gov/Exe/ZyPURL.cgi?Dockey=P10074PP.txt. 

Denholm, P.; Margolis, R.M. (2008). “Land Use Requirements and the Per-Capita Solar Footprint for Photovoltaic 

Generation in the United States.” Energy Policy (36); pp. 3531–3543

“Hartford Solar Landfill Project.” Center for Public Environmental Oversight, Accessed January 18, 2013: 

http://www.cpeo.org/pubs/HartfordSolar.pdf
Best Practices for Siting Solar Photovoltaics on MSW Landfills February 2013

D-2 

“Amherst, Massachusetts: Impediments to Solar Installations on Closed Landfills.” Center for Public Environmental 

Oversight. Accessed January 18, 2013: http://www.cpeo.org/pubs/AmherstSolar.pdf

El-Fadel, M.; Khoury, R. (2000). “Modeling Settlement in MSW Landfills: a Critical Review.” Critical Reviews in 

Environmental Science and Technology (30:3); pp. 327-361. Print.

Institutional Controls: A Guide to Planning, Implementing, Monitoring, and Enforcing Institutional Controls at 

Contaminated Sites (Interim Final). (2010). EPA/540-R-09-001. Washington, DC: U.S. Environmental Protection 

Agency, Office of Solid Waste and Emergency Response. Accessed April 23, 2012: 

http://www.epa.gov/superfund/policy/ic/pdfs/PIME-IC-Guidance-Interim.pdf. 

“Solar Map.” National Renewable Energy Laboratory. Accessed August 24, 2011: www.nrel.gov/gis/solar.html. 

Solid Waste Disposal Facility Criteria: Technical Manual. (2003). EPA/530-R-93-017. Washington, DC: U.S. 

Environmental Protection Agency, Office of Solid Waste and Emergency Response. Accessed April 23, 2012: 

http://www.epa.gov/waste/nonhaz/municipal/landfill/techman/index.htm. 

Solid Waste Disposal Facility Criteria: Technical Manual. (1993). EPA/530-R-93-017. Washington, DC: U.S. 

Environmental Protection Agency, Office of Solid Waste and Emergency Response. Accessed April 23, 2012: 

http://www.epa.gov/waste/nonhaz/municipal/landfill/techman/index.htm.

Stormwater O&M Fact Sheet: Preventative Maintenance. (1999). EPA/832-F-99-004. Washington, DC: U.S. 

Environmental Protection Agency, Office of Water. Accessed April 23, 2012: 

http://nepis.epa.gov/Exe/ZyPURL.cgi?Dockey=200044A0.txt. 

Agrawal, M., Bolman, C. et. al. (2012) Photon Consulting. Solar Annual 2012: The Next Wave; p. 24. Print.

Chapter 5

Bonaparte, R.; Gross, B.; Daniel, D.; Koerner, R.; Dwyer, S. (2004). Technical Guidance for RCRA/CERCLA Final 

Covers. EPA/540-R-04-007. Washington, DC: U.S. Environmental Protection Agency, Office of Solid Waste and 

Emergency Response. Accessed April 23, 2012: http://nepis.epa.gov/Exe/ZyPURL.cgi?Dockey=P10074PP.txt. 

El-Fadel, M.; Khoury, R. (2000). “Modeling Settlement in MSW Landfills: a Critical Review.” Critical Reviews in 

Environmental Science and Technology (30:3); pp. 327-361. Print.

Sharma, H.D.; De Ariban, M. (2007). “Municipal Solid Waste Landfill Settlement: Postclosure Perspectives.” Journal 

of Geotechnical and Geoenvironmental Engineering (133:6); pp. 619-629. Print.

Chapter 6

Sharma, H.D.; De Ariban, M. (2007). “Municipal Solid Waste Landfill Settlement: Postclosure Perspectives.” Journal 

of Geotechnical and Geoenvironmental Engineering (133:6); pp. 619-629. Print.

Standard Guidelines for the Installation of Urban Stormwater Systems. (2006). ASCE Standard No. 46-05. Reston, 

VA: American Society of Civil Engineers. Print.

Task Committee of the Urban Water Resources Research Council of the American Society of Civil Engineers and the 

Water Environment Federation. (1993). Design and Construction of Urban Stormwater Management Systems. ASCE 

Manuals and Reports on Engineering Practice No. 77, WEF Manual of Practice FD-20. New York, NY: American 

Society of Civil Engineers. Print.

Chapter 7

Livingston, E.H.; Shaver, E.; Skupien, J.J. (1997). Operation, Maintenance, & Management of Stormwater 

Management Systems. Work performed by Watershed Management Institute, Inc., Ingleside, MD. Washington, DC: 
Best Practices for Siting Solar Photovoltaics on MSW Landfills February 2013

D-3 

U.S. Environmental Protection Agency, Office of Water. Accessed April 23, 2012: 

http://www.stormwater.ucf.edu/research/stormwaterOMM/stormwateromm.pdf.