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

Feasibility Study of Economics 

and Performance of Solar 

Photovoltaics at Massachusetts 

Military Reservation 

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

Byron Stafford, Robi Robichaud, and 

Gail Mosey

Technical Report

NREL/TP-6A20-49417

July 2011
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.

National Renewable Energy Laboratory

1617 Cole Boulevard

Golden, Colorado 80401

303-275-3000 • www.nrel.gov

Contract No. DE-AC36-08GO28308

Feasibility Study of Economics 

and Performance of Solar 

Photovoltaics at Massachusetts 

Military Reservation 

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

Byron Stafford, Robi Robichaud, and 

Gail Mosey

Prepared under Task No. WFD5.1000

Technical Report

NREL/TP-6A20-49417

July 2011
NOTICE

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iii

Acknowledgments

The National Renewable Energy Laboratory (NREL) thanks the U.S. Environmental Protection 

Agency (EPA) for its interest in securing NREL’s technical expertise. In particular, NREL is 

grateful to the following individuals for their assistance and dedication during the preparation of 

this report: 

Desiree Moyer, U.S. EPA Region 1 

Paul Marchessault, U.S. EPA Region 1

Lura Matthews, U.S. EPA Headquarters 

Rose Forbes, Air Force Center for Engineering and the Environment/MMR

Mark Dakers, Massachusetts Department of Environmental Protection

Natalie Andrews, Massachusetts Department of Energy Resources
iv 

Executive Summary 

The U.S. Environmental Protection Agency (EPA), in accordance with the RE-Powering 

America’s Land initiative, selected the Massachusetts Military Reservation (MMR) to receive 

technical assistance from the National Renewable Energy Laboratory (NREL) for a feasibility 

study to be conducted on a superfund site located within MMR. The purpose of this report is to 

assess sites within the landfill area at MMR for suitability for possible solar photovoltaic (PV) 

installations and estimate the cost, performance, and site impacts of the different PV mounting 

options. In addition to this, the report recommends future actions that could assist in the 

procurement and implementation of a PV system. 

Four sites were considered and found suitable to incorporate PV systems at MMR—three landfill 

caps and a borrow pit. See Figure ES-1 for an aerial view of the four potential sites. The 

economics of the potential PV systems were analyzed using an electric rate of $0.159/kWh and 

incentives offered in the Commonwealth of Massachusetts, such as the solar renewable energy 

certificates (SRECs). Table ES-1 summarizes the system performance and economics of a 

typical potential system at MMR. Crystalline silicon PV modules were used in the calculations. 

Using PV modules with higher or lower efficiencies will result in significantly different results. 

In addition, different types of PV mounting systems—fixed tilt, single-axis tracking, and twoaxis tracking—were analyzed. A fixed-tilt PV system is a more likely outcome because of lower 

operations and maintenance (O&M) and ease of meeting wind-loading requirements. However, 

proposals with single-axis and two-axis PV system mounting could be considered if all of the 

MMR requirements are met and the overall project costs are reasonable. 

Any procurement should include all types of PV modules and all types of PV mounting systems. 

Table ES-1 represents reasonably sized 30-degree fixed-tilt PV systems in the range of 8 MW for 

MMR. Portions of these PV systems could be installed depending on the needs, available funds, 

and interest. Table ES-1 also summarizes job creation if the MMR sites were used for PV. 
v 

Figure ES-1. Aerial view of potential PV system sites at MMR 

Credit: AFCEE, 2011 MMR-AFCEE Data Warehouse with 2009 Aerial Photography from MassGIS

Table ES-1. PV System Performance and Economics by Sitea 

Site PV 

System

Size 

(kW)

Installed 

Cost 

($/W)

Annual 

Output 

(kWh/year) 

Annual 

O&M 

($/year)

System 

Cost ($)

Simple 

Payback 

Period

(years)

Jobsb

Created

Jobsc

Sustained

I 3,633 $5.00 4,112,548 $30,880 $18,165,000 9.4 197 0.34

II 1,356 $5.00 1,535,060 $11,527 $6,780,000 9.4 74 0.13

III 1,888 $5.00 2,137,612 $16,051 $9,442,000 9.4 103 0.17

Pit 857 $5.00 970,492 $7,287 $4,287,000 9.4 47 0.08

Total 7,735 $5.00 8,755,712 $65,745 $38,674,000 9.4 420 0.71 a Data assume a usable area of 2,062,596 ft2 and a fixed-tilt system at 30 degrees. b Job-years created as a result of project capital investment including direct, indirect, and induced jobs. c Jobs (direct, indirect, and induced) sustained as a result of O&M of the system.
vi 

Table of Contents

List of Figures ........................................................................................................................................... vii

List of Tables ............................................................................................................................................. vii

1 Study Location...................................................................................................................................... 1

2 PV Systems ........................................................................................................................................... 2

2.1 PV System Performance and Solar Resource ......................................................................3

2.2 Ground-Mounted PV Systems .............................................................................................7

2.3 PV System Components ....................................................................................................10

3 MMR Ground-Mounted PV Site Locations ....................................................................................... 12

3.1 Wind Loading ....................................................................................................................14

3.2 Typical PV-Mounting Systems ..........................................................................................15

3.3 Usable Land Area ..............................................................................................................17

3.4 MMR Electrical Distribution System ................................................................................17

3.5 Environmental Considerations ...........................................................................................17

4 Economics and Performance............................................................................................................ 20

4.1 Summary of the Sites .........................................................................................................20

4.2 Assumptions and Input Data for Analysis .........................................................................20

4.3 Incentives and Financing Opportunities ............................................................................24

4.4 Job Creation .......................................................................................................................25

5 Conclusions and Recommendations ............................................................................................... 26

Appendix.................................................................................................................................................... 27
vii 

List of Figures

Figure ES-1. Aerial view of potential PV system sites at MMR .................................................... v

Figure 1. Major components of grid-connected PV system ........................................................... 2

Figure 2. Comparison of energy production for 1 kW PV system at Otis ANGB as a function of 

tilt ........................................................................................................................................ 4

Figure 3. Estimate of monthly energy production for a 1 MW PV system at MMR ...................... 5

Figure 4. Row spacing depends on the latitude and tilt of the PV modules ................................... 6

Figure 5. Packing factor estimate versus tilt ................................................................................... 7

Figure 6. Aerial view of potential PV system sites at MMR ........................................................ 12

Figure 7. Landfill cap with relatively shallow slope..................................................................... 13

Figure 8. View of the bottom of the borrow pit ............................................................................ 14

Figure 9. A ballast-weighted system using two precast concrete weights .................................... 16

Figure 10. A ballast system similar to that used on rooftops can be adapted for a ground-mounted 

PV system ......................................................................................................................... 16

Figure 11. Statistical analysis of LCOE using ranges of values listed in Table 2 ........................ 22

Figure 12. Linear regression analysis of statistical analysis of LCOE using ranges of values listed 

in Table 2 for four different types of PV mounting .......................................................... 23

Figure A-1. Landfill cap aspect analysis ....................................................................................... 29

List of Tables

Table ES-1. PV System Performance and Economics by Site ....................................................... v

Table 1. Usable Area of Four Different Sites ............................................................................... 17

Table 2. PV System Performance and Economics by Site ........................................................... 20

Table 3. List of Parameters used in SAM for Financial Calculations .......................................... 21

Table 4. Summary of Four Different PV Mounting Options ........................................................ 24

Table A-1. Summary of PV System Calculations for a 30-Degree Fixed-Tilt PV System for All 

Four MMR Sites Using a Low SREC Estimate of $300/MWh ........................................ 27

Table A-2. Summary of Financial Calculations for Four Different 1 MW PV Mounting 

Options .............................................................................................................................. 28
1 

1 Study Location

The U.S. Environmental Protection Agency (EPA), in accordance with the RE-Powering 

America’s Land initiative, selected the Massachusetts Military Reservation (MMR) to receive 

technical assistance from the National Renewable Energy Laboratory (NREL) for a feasibility 

study to be conducted on a superfund site located within MMR. 

MMR, a military training facility, is located on the upper western portion of Cape Cod, 

immediately south of the Cape Cod Canal in Barnstable County, Massachusetts. It includes parts 

of the towns of Bourne, Mashpee, and Sandwich and abuts the town of Falmouth. MMR covers 

nearly 21,000 acres—approximately 30 mi2

.

1

The Air National Guard, located at the Otis Air National Guard Base (ANGB) [102 Intelligence 

Wing (102 IW)] on MMR, is interested in exploring opportunities for on-site generated 

renewable energy to offset the high energy costs ($0.159/kWh) and to help meet the federal 

mandate under Executive Order 13514

 

2

The ANGB property includes the main base landfill; however, the landfill is managed by the Air 

Force Center for Engineering and the Environment (AFCEE) as a superfund site under the 

Installation Restoration Program. The landfill is 100 acres, of which 60 acres consist of three

landfill caps managed under the Resource Conservation and Recovery Act (RCRA) Subtitle C 

program. The adjacent borrow pit is 5.3 acres. This report estimates the feasibility of PV systems 

on the landfill caps and in the borrow pit. 

to achieve greater energy efficiency and use of 

renewable energy at federal facilities. The main base landfill was selected as a preferred location 

for solar photovoltaics (PV). 

 

1 Massachusetts Military Reservation. http://www.mmr.org. Accessed September 2010. 2 Executive Order 13514. Federal Register. http://edocket.access.gpo.gov/2009/pdf/E9-24518.pdf. Accessed March 

2011.
2 

2 PV Systems 

Solar PVs are semiconductor devices that convert sunlight directly into electricity. They do so 

without any moving parts and without generating any noise or pollution. They must be mounted 

in an unshaded location; rooftops, carports, and ground-mounted arrays are common mounting 

locations. PV systems would be appropriate at MMR, where the average global horizontal annual 

solar resource is 3.63 kWh/m2/day.3

Figure 1

 This number, however, is not the amount of energy that can 

be produced by a PV system. The amount of energy produced by a PV system depends on 

several factors. These factors include the type of modules, the tilt and azimuth of the modules, 

the tracking of the modules, the temperature, and the level of sunlight and weather conditions. 

An inverter is required to convert the direct current (DC) to alternating current (AC) of the 

desired voltage compatible with building and utility power systems. The balance of the system 

consists of conductors/conduit, switches, disconnects, and fuses. Grid-connected PV systems 

feed power into the facility’s electrical system and do not include batteries. 

 shows the major components of a grid-connected PV system and illustrates how these 

components are interconnected.

Figure 1. Major components of grid-connected PV system

Credit: NREL

PV modules are made up of many individual cells that all produce a small amount of current and 

voltage. These individual cells are connected in series to produce a larger current. PV modules 

are very sensitive to shading. When shade falls on a module, that portion of the module is no 

longer able to collect the high-energy beam radiation from the sun. If an individual cell is 

shaded, it will act as a resistance to the whole series circuit, impeding current flow and 

 

3

 Typical meteorological year 3 (TMY3) data for Otis ANGB available from NREL, 

http://rredc.nrel.gov/solar/old_data/nsrdb/1991-2005/tmy3/. NREL’s System Advisor Model (SAM), version 

2010.11.9, summarized the annual global horizontal solar resource as 1,325.2 kWh/m2

/year, or 3.63 kWh /m2/day. 

SAM is available at https://www.nrel.gov/analysis/sam/. 
3 

dissipating power rather than producing it. By determining solar access—the unimpeded ability 

of sunlight to reach a solar module—one can determine whether an area is appropriate for solar 

panels. 

If a site is found to have good potential for a PV system, then the next step is to determine the 

size of that system, which highly depends on the average energy use of the on-site facilities. 

Providing more power than a site would use is generally not advisable due to the economics of 

most net-metering agreements. The system size would thus be determined by the economics of 

the project along with the applicable net-metering regulations or by how much land area is 

available. The PV systems will be broken down by site so the total system size can be adjusted 

based on what the utility requests, requirements by MMR, and financial incentives. 

PV module efficiencies range from high efficiency crystalline silicon PV modules with 18% 

efficiency to thin-film amorphous silicon PV modules with 6% efficiency. An efficiency of 

13.5% was used in the analysis, which is typical for crystalline silicon PV modules. For a first 

approximation, if a higher efficiency module of 18% efficiency is assumed, then the power of the 

PV system would be proportionally higher by the ratio of 18/13.5, or the area of the PV system 

would be reduced proportionally by the ratio of 13.5/18.

2.1 PV System Performance and Solar Resource

In general, a PV module facing south and tilted from the horizontal about the same number of 

degrees as the latitude of the PV module will produce the maximum annual energy output. The 

azimuth is the descriptor for the orientation of the PV module’s face with respect to the compass 

degrees. A PV module with an azimuth of 180 degrees faces south. For most installations, PV 

modules cannot be oriented or tilted for maximum annual energy production and compromises 

between energy production, total system cost, and future operation and maintenance (O&M) 

costs are made.

Most PV systems are described by the sum of the DC power ratings of all of the PV modules in a 

system. NREL has developed a Web-based software program called PVWATTS4 to estimate the 

monthly and annual energy output of a PV system based on the system size, location, tilt, and 

azimuth. NREL has also developed a software program called System Advisor Model (SAM)5

Version 2010.11.9 that incorporates PVWATTS. Solar resource data for Otis ANGB was used.6

Using SAM, the annual energy production of a 1 kW PV system was calculated for various tilts 

with an azimuth of 180 degrees. The energy production numbers are linearly scalable for larger 

PV systems—a 100 kW PV system produces 100 times more energy than a 1 kW PV system. 

Figure 2 shows the energy output as a function of the tilt. In addition, the ratio between energy 

produced and power is useful for estimating the energy production from any size PV system. For 

example, if for a given location, the tilt and azimuth ratio of kWh/W is 1.2, then a 2 MW PV 

system would produce 2,400 MWh of energy per year. 

The resource data used are from a typical meteorological year (TMY3) from 1991–2005. 

 

4 PVWATTS. www.nrel.gov/rredc/pvwatts. Accessed March 4, 2011. 5 SAM. www.nrel.gov/analysis/sam. Accessed March 4, 2011. 6 See http://rredc.nrel.gov/solar/old_data/nsrdb/1991-2005/tmy3/ for a listing of all sites and a description of the 

data.
4 

At high latitude, such as at MMR, the maximum energy production does not occur at a PV 

module tilted at latitude—41.7 degrees. Instead, the maximum energy production occurs at a tilt 

of 35 degrees. Christensen and Barker7

 suggest four reasons why this occurs: (1) clearer summer 

days when the sun is higher in the sky; (2) more diffuse scattered light on lower tilted modules; 

(3) less atmospheric attenuation when the sun is higher in the sky; and (4) lower tilt angles 

reduce the number of hours when the sun rises or sets north of east and north of west. A tilt of 30 

degrees was selected for this analysis since a lower tilt will reduce the wind loading, which will 

require less ballast weight while only reducing the performance less than 0.5%. 

Figure 2. Comparison of energy production for 1 kW PV system at Otis ANGB as a function of tilt

Data from SAM Version 2010.11.9 using PVWATTS and Otis ANGB TMY3 solar resource data

Using SAM, the monthly energy production of a 1 MW PV system was calculated for a fixed 30-

degree tilt with an azimuth of 180 degrees. See Figure 3 for a chart of the data. 

 

7 Christensen, C.B.; Barker, G.M. (2001). “Effects of Tilt and Azimuth on Annual Incident Solar Radiation for 

United States Locations.” Kleis, S.J.; Bingham, C.E., eds. Solar Engineering 2001: Proceedings of the International 

Solar Energy Conference Presented at FORUM 2001, April 21-25, 2001, Washington, D.C. NREL Report No. CP550-32966. New York: The American Society of Mechanical Engineers (ASME); pp. 225-232.

0.90

0.95

1.00

1.05

1.10

1.15

0 5 10 15 20 25 30 35 40 45 50

Energy Produced (kWh/W)

Tilt (degrees)

PV System Performance Versus Tilt

1 kW PV System Facing South at Otis ANGB
5 

Figure 3. Estimate of monthly energy production for a 1 MW PV system at MMR

Data from SAM Version 2010.11.9 using PVWATTS and Otis ANGB TMY3 solar resource data. 

For a PV system with a tilt of 0 degrees, there is no azimuth and the energy production is the 

same at all azimuths. A PV system with a 0-degree tilt is not practical on the ground. All PV 

systems need some slope to facilitate rainwater runoff. Most PV module manufacturers 

recommend a minimum of 10 degrees. In a snowy climate, such as MMR, a steeper tilt is 

desirable to encourage any accumulated snow to slide off. A distance of 3 ft from the bottom 

edge of the PV modules is a sufficient distance for snow to slide off the PV modules without 

blocking the modules. Steep module slopes necessary for snow to slide off require more ballast 

weight since the PV system would have a higher wind profile. A tilt of 30 degrees is used in this 

analysis compared to an optimal 35 degrees based solely on energy production. Commercial 

mounting hardware options are more readily available for ballast weighted systems tilted 30 

degrees or less. 

The labor cost to clear snow from PV systems is usually more than the increased production 

revenue. The PV system operator needs to determine when it would be cost effective to clear 

snow from the PV modules. As an example, it may take 32 man hours (two people, 2 days, 

8 hrs/day) at $30/hr, or a total of $960, to clear the snow from a 1 MW PV system. However, the 

sun could melt it off the PV modules in 4 days. If the energy production increase is only 20% for 

4 days in winter, the increased energy production is 1,360 kWh (1,700 kWh/day production in 

January for a 1 MW PV system at MMR), which is valued only at $231 if electricity is 

0

20,000

40,000

60,000

80,000

100,000

120,000

140,000

Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec

Monthly Energy Production (kWh)

Net Energy Output (kWh) for a 1 MW PV System,

Fixed 30-Deg Tilt at MMR
6 

$0.17/kWh. Rainfall is adequate in this location so PV module cleaning is generally not 

considered. 

As depicted in Figure 4, when PV module A is tilted at a given angle, then PV module B placed 

behind it—to the north—must be spaced so that the shadow from the top of PV module A in 

front does not shadow the bottom of PV module B in back. Usually PV modules or groups of PV 

modules are placed in rows, so this spacing is called row spacing, which can be generalized to a 

non-dimensional term called packing factor. The worst solar day occurs at the winter solstice, 

which is typically December 22. A 6-hr window of no shade on the back row is used in this 

analysis. The critical angle for MMR is a sun altitude angle of 12.75 degrees above the horizon 3 

hrs before and after solar noon on December 22. This critical sun elevation determines the row 

spacing for the latitude of MMR.

Figure 4. Row spacing depends on the latitude and tilt of the PV modules

Packing factor is the ratio of the row spacing divided by the row-to-row spacing. Figure 5 

illustrates different packing factors as a function of tilt. A packing factor of 0.30 was used in this

analysis to determine the total PV system size for a given area. The total PV system size is the 

area times the packing factor times the PV module’s power per unit area. A system designer can 

increase the packing factoring to place more PV modules in a smaller area at the expense of 

some PV production in the winter months. The majority of PV energy is produced in the spring 

and summer months so some reduction in winter months could be acceptable.
7 

Figure 5. Packing factor estimate versus tilt

Based on location, the available area, the packing factor, the tilt and azimuth of the PV modules, 

the size, and the energy production of the PV system can be estimated. It is generally not 

advisable to provide more energy than the site will use on an annual basis due to the economics 

of most net-metering agreements. Based on meter data, the base grid at MMR uses about 

2 million kWh of energy per month. In addition, another 800,000 kWh of energy per month was 

used from independent utility feeders. From July 2009 to June 2010, a 12-month period, the base 

grid at MMR used 24,792,501 kWh.8

In addition to the estimated energy production, the electrical infrastructure at MMR needs to be 

able to absorb the peak power production from the PV system. An 8 MW (DC rating) PV system 

could produce peak power around 6.2 MW (AC rating). Typically, this peak power production 

occurs during the months of May, June, July, and August. The PV system could be segmented 

such that the peak power is split between different feeders. An interconnection study is needed to 

determine the best way to interconnect any PV system on MMR. 

This is almost twice the energy that a PV system on the 

landfill caps and borrow pit could produce on an annual basis. The PV system size can be 

adjusted based on what the utility requests, financial incentives, and what MMR requires. 

2.2 Ground-Mounted PV Systems

A ground-mounted PV system can be an in-ground system using poured concrete foundations or 

metal piers driven into the ground. This is not an acceptable mounting method for a PV system 

on top of a landfill cap. However, ballast-weighted ground-mounted PV systems are possible. 

This is a common mounting method for PV systems on roofs where roof penetrations are not 

permitted or desired. Only ballast-weighted mounting methods are considered in this analysis for 

the landfill cap sites at MMR. The borrow pit site at MMR could have either an in-ground 

 

8 Base energy data supplied by Rose Forbes, AFCEE.

0.00

0.20

0.40

0.60

0.80

1.00

1.20

0 10 20 30 40 50 60 70 80 90

Packing Factor (ratio)

Tilt (degrees)

Packing Factor Versus Tilt

6 Hours of No Shade as a Function of Module 

Tilt for Latitude 41.7 Degrees on December 22
8 

mounting system or a ballast-weighted mounting system as there are no landfill materials 

underneath that may be penetrated by an in-ground mounting system. 

Ballast-weighted mounting methods rely on the weight of the PV modules, the mounting racks, 

and extra ballast to meet wind-loading design considerations. Three wind-loading 

conditionsoverturning, uplifting, and slidingneed to be considered. In most systems, sliding 

is the more critical design requirement since the friction between the ground and the ballast has 

to be estimated under all weather conditions. A steeper module tilt increases the wind loading 

and, consequently, the total ballast weight. The ballast weight can increase or decrease the point 

load depending on the area of the ballast weight in contact with the ground. The maximum total 

dead weight and individual point loads need to be determined and approved for the landfill caps. 

An engineering analysis was completed for a hypothetical ballast-weighted PV system—the 

Greenfield PV system in Greenfield, Massachusetts.

9 The calculated contact bearing pressure for 

this hypothetical PV system was always less than the landfill cap maximum load of 1,008 lb/ft2. 

The engineering analysis included a poured concrete ballast weight of 3 ft (W) x 8 ft (L) x 1.5 ft 

(H), buried 0.5 ft in the ground. Concrete slabs for transformers and inverters were also 

considered. Although the slope of the landfill cap is in the range of 2.0−3.5 degrees, the downhill 

sliding of the ballast weight was considered. The maximum bearing pressure for the MMR 

landfill caps needs to be determined for that specific cover system. The range of maximum 

bearing pressure for landfill caps in Massachusetts is in the range of 720–1,008 psf.10

Vehicle access on the landfill caps during the assembly needs to be considered. Typical delivery 

vehicles for a PV system of this size include standard tractor-trailers. Equipment is off-loaded by 

an overhead crane or by forklifts. Overhead cranes could be separate truck-mounted cranes or 

cranes mounted on the delivery vehicle. Forklifts could be either construction-type (extending 

booms) or fixed-mast forklifts. Equipment could be reloaded at MMR onto smaller vehicles 

more suitable for travel on the landfill caps. Andrews designed a temporary 18-in thick gravel 

road that could be installed and used on the landfill caps.

 In 

summary, most any commercially available ballast-weighted PV system will be less than the 

maximum weight-loading requirements of the MMR landfill caps. 

11 Alternately, portable roadways could 

be installed. An example is a product, MegaDeck,

12

The design of the ballast and PV module mounting frame needs to consider storm water runoff, 

snow load, potential local settling of the landfill cap, and the slope of the ground so that the PV 

 that could reduce the point loading to less 

than 1,008 lb/ft2

. The portable roadway is moved around a landfill cap as the PV system is 

installed. The dynamic loading of the temporary or the portable roadway when using a crane still 

needs to be evaluated. Vehicle access on the landfill caps during maintenance can be 

accomplished with low-ground-pressure vehicles such as all-terrain vehicles. 

 

9 Andrews, D. Calculations of Contract Bearing Pressure and Estimated Settlement of Foundation Footings for Axio 

Greenfield Solar. Internal report of Massachusetts Department of Environmental Protection (MassDEP), June 11, 

2010.

10 Dakers, M. Email. MassDEP, Boston, MA, 31 March 2011. 11 Andrews, D. Calculations of Contract Bearing Pressure and Estimated Settlement of Foundation Footings for 

Axio Greenfield Solar. Internal report of MassDEP, June 11, 2010. 12 Signature Flooring, MegaDeck product. www.eventdeck.com/MegaDeck.shtml. Accessed March 4, 2011.
9 

system does not gradually slide downhill. This is manageable, but it is site and manufacturer 

specific. 

A Weston & Sampson report estimates the expected settlement of the nearby Falmouth landfill 

cap.

13

For this report, three types of ground-mounted systems are considered. Fixed-tilt systems are 

installed at a specified tilt and are fixed at that tilt for the life of the system. Single-axis tracking 

systems have a fixed north-south axis and a variable tilt in the east-west direction. Two-axis 

tracking systems continually adjust the azimuth and tilt so that the PV modules always face the 

sun. Typically, two-axis tracking systems are mounted on a single pole, which requires extensive 

concrete or piers deep into the ground. While the typical two-axis tracking system should be 

okay for the borrow pit, it is unacceptable for the landfill caps. Although large-scale ballastweighted two-axis tracking systems have not been deployed, it is possible to conceive of a twoaxis tracking system similar to a fixed-tilt PV system where the individual PV modules track the 

sun.

Similar settlement may be possible at MMR but needs to be evaluated. Settlement is 

normal and expected. The following is a brief summary based on the Falmouth landfill study. 

Primary settlement of a landfill cap usually occurs in the first 1–3 months and should have 

happened years ago. Secondary settlement occurs over the life of the landfill. Weston & 

Sampson estimate a uniform secondary settlement of 0.25–0.55 ft over a 30-year period. There 

can also be differential settlement from a localized subsidence at the landfill. Two cases were 

modeled. The first case considers a refrigerator collapsing that causes a 2-ft drop on the top 

surface over an area of 6 ft x 8 ft. The second case considers a single cell or trench that was 

poorly compacted or settled faster than nearby cells or trenches. In the second case, a drop of 8 ft 

on the top surface could occur over an area 50 ft wide by the length of that landfill trench. Based 

on expected settling, the PV system design for the landfill caps should consist of separate units 

with dimensions in the range of 50 ft or less that can be separately adjusted. The separate units 

should not be physically interconnected along with some reasonable physical separation. It is 

possible to design a PV-mounting structure that will accommodate future secondary settlement. 

Settlement is not expected at the borrow pit, so the range of PV-mounting systems is expanded. 

Annual or semiannual inspections are required to check on the physical structure of any PV 

system.

14

Based on the solar resource for the MMR area, a single-axis tracking system and a two-axis 

tracking system can produce nearly 12% and 31% more energy, respectively, than a flat 30-

degree fixed-tilt system. The drawbacks to single-axis and two-axis tracking systems include 

increased O&M costs, increased ballast weight, and increased installed costs. Nonetheless, 

single-axis and two-axis tracking systems should be included in any procurement since the gain 

 In addition to fixed-tilt PV systems, single-axis and two-axis tracking systems could be 

considered for the landfill caps and for the borrow pit and should not be excluded from any 

procurement. Proposers need to meet the point-loading requirements along with the wind-loading 

requirements. In addition, all proposers should include an estimate of the O&M costs for the 

weather and ground conditions at the MMR sites. 

 

13 “Design Summary Report and Technical Specifications, Landfill Closure Design, Thomas Landers Road 

Landfill.” Weston & Sampson report to Town of Falmouth, MA, 1998. 14 Some examples are http://kdmegatech.en.ec21.com/Rooftop_Solar_Tracker_Dual_Axis--4607559_4612259.html

and http://www.sedonaenergylabs.com/storage/white-papers/SEL_ProductSheet_final5.pdf. NREL presents these 

systems as concepts and has no knowledge as to their suitability for MMR. 
10 

in energy production could balance out any drawbacks. If there is a power (kW) limitation on the 

MMR electrical distribution system, a single-axis or two-axis tracking system can produce more 

energy (kWh) for no change in the power rating (kW). 

When considering a ground-mounted system, an electrical tie-in location should be identified to 

determine how the energy will be fed back into the grid. Two different electrical feedersEast 

Feeder A and North Feederare in close proximity to the landfill site. An electrical engineering 

study is needed to determine the power capabilities of these two feeders. The PV system could 

be segmented to feed separate feeders to alleviate power limitations on a single feeder.

2.3 PV System Components

The PV system considered here has these components:

• PV arrays, which convert light energy to DC electricity 

• Inverters, which convert DC to AC and provide important safety, monitoring, and 

control functions 

• Various wiring, mounting hardware, and combiner boxes 

• Monitoring equipment

2.3.1 PV Array 

The primary component of a PV system, the PV array, converts sunlight to electrical energy; all 

other components simply condition or control energy use. Most PV arrays consist of 

interconnected PV modules that range in size from 50 peak DC-Watts to 300 peak DC-Watts. 

Peak watts are the rated output of PV modules at standard operating conditions of 25°C (77°F) 

and insolation of 1,000 W/m2. Because these standard operating conditions are nearly ideal, the 

actual output will be less under typical environmental conditions. PV modules are the most 

reliable components in any PV system. They have been engineered to withstand extreme 

temperatures, severe winds, and impacts. ASTM E1038-0515 subjects modules to impacts from 

1-in hail balls at terminal velocity (52 mph) at various parts of the module. PV modules have a 

life expectancy of 20–30 years, and manufacturers warranty them against excessive power 

degradation for 25 years. The array is usually the most expensive component of a PV system; it 

accounts for approximately two-thirds of the cost of a grid-connected system. A large choice of 

PV manufacturers is available.16

2.3.2 Inverters

Inverters are required to change the DC output of the PV modules into AC electricity. The DC 

input range of the inverter is selected to match the DC output of the PV modules. The AC output 

is selected to match the voltage of the distribution wiring where the inverter will be 

interconnected. A typical AC output is 480 V, three-phase. Transformers are used if a higher 

output voltage is required. 

 

15 ASTM International. “E1038-05 Standard Test Method for Determining Resistance of Photovoltaic Modules to 

Hail by Impact with Propelled Ice Balls," West Conshohocken, PA, 2005, DOI: 10.1520/E1038-05. 

http://www.astm.org/Standards/E1038.htm. Accessed August 2010. 16 Go Solar California, a joint effort of the California Energy Commission and the California Public Utilities 

Commission, provides consumer information for solar energy systems. See http://www.gosolarcalifornia.org/

equipment/pv_modules.php. 
11 

Large inverters are commercially available in the 100–1,000 kW AC sizes. The inverters 

synchronize to the utility so multiple inverters can be used for megawatt-sized PV systems. For 

example, a 1 MW PV system would require four 250-kW inverters or ten 100-kW inverters. All 

inverters should meet “UL Standard 1741, Standard for Static Inverters and Charge Controllers 

for Use in Photovoltaic Power Systems.”17

Warranties on inverters range 5–10 years with some manufacturers offering extended warranties 

to 20 years. While most inverters are weather proof, they should be shielded from direct sunlight 

to reduce possible thermal limiting within the inverter and help lengthen the service lifetime. 

Typical efficiencies of these inverters are 95%–98%. The California Energy Commission has a 

comprehensive listing of inverters, sizes, and weighted efficiencies.

This standard is universally recognized by most 

electric utilities in the United States for interconnecting a PV system.

18

2.3.3 Monitoring Equipment

Monitoring equipment is a requirement for any PV system. Inverters may include or have 

options for some metering and data-logging capability. 

2.3.4 Operation and Maintenance

PV panels come with a 25-year performance warranty. A typical PV module performance 

warranty states that modules will produce 80% of the initial module power rating after 25 years. 

The decrease in power can be linear over the warranty time period or can be specified by the 

year, such as 90% in the first 10 years and 80% in the remaining years. The module warranties 

are manufacturer and module specific. 

The inverters, which come standard with a 5–10-year warranty (extended warranties are 

available), would be expected to last 10–15 years. System performance should be verified on a 

vendor-provided website. Wire and rack connections should be checked at least annually and 

more frequently if specified by an equipment manufacturer. For this economic analysis, an 

annual O&M cost of 0.17% of total installed cost is used based on the O&M cost of other fixedtilt grid-tied PV systems. For the case of single-axis tracking, an annual O&M cost of 0.35% of 

total installed cost is used based on O&M costs of existing single-axis tracking systems. Twoaxis tracking systems would have a higher O&M cost than single-axis tracking systems. The 

exact O&M cost is system specific and should be specific by the system integrator or designer. 

 

17 UL 1741. “Inverters, Converters, Controllers and Interconnection System Equipment for Use With Distributed 

Energy Resources.” http://ulstandardsinfonet.ul.com/scopes/1741.html. Accessed July 2010. 18 Go Solar California. “List of Eligible Inverters per SB1 Guidelines.” 

http://www.gosolarcalifornia.org/equipment/inverters.php. Accessed February 2011.
12 

3 MMR Ground-Mounted PV Site Locations 

An NREL solar assessment site visit occurred on February 25, 2010.19 Sampson analyzed PV 

systems on landfills, and the report was used in consideration of PV systems at MMR.

20

MMR has three landfill caps and a borrow pit that are suitable for ground-mounted PV systems. 

For this report, the caps are numbered I, II, and III, from west to east (Figure 6). These caps have 

short vegetation without any trees. There are no significant shading issues on these caps—see 

Figure 7. The caps are relatively flat on top with slopes ranging from 2.0, 3.5, and 2.7 degrees 

from the top of the landfill caps numbered I, II, and III, respectively. The slopes are uniform in 

all directions based on the NREL analysis of the contour map in the Appendix—Figure A-1. As 

seen on the contour maps, the caps are relatively flat with significant slopes only at the edges of 

the caps. Only the relatively flat areas were considered for PV systems. The remaining areas of 

the landfill caps were not considered for a PV system because of significant slopes near the 

edges. 

 Figure 6. Aerial view of potential PV system sites at MMR 

Credit: AFCEE, 2011 MMR-AFCEE Data Warehouse with 2009 Aerial Photography from MassGIS 

 

19 Mosey, G,; Robichaud, R. “Site Visit Report for Solar Assessment Activities at the Massachusetts Military 

Reserve, Falmouth, MA.” Golden, CO: National Renewable Energy Laboratory, May 7, 2010. 20 Sampson, G. Solar Power Installations on Closed Landfills: Technical and Regulatory Considerations.” Bren 

School of Environmental Science and Management, Santa Barbara, CA: University of California, 2009.
13 

Figure 7. Landfill cap with relatively shallow slope

Credit: AFCEE/MMR

At the request of AFCEE, the borrow pit was also included. The borrow pit is a depression that 

has a relatively flat bottom of compressed aggregate—see Figure 8. The existing vegetation, 

consisting of primarily scrub pines, could be removed if necessary. The borrow pit has good 

drainage and is not known to hold water after a rain storm. There is no active equipment for 

draining the borrow pit. While the borrow pit is an easy site for a PV system, a back-up sump 

pump should be considered for extreme rain events or other flooding possibilities. 
14 

Figure 8. View of the bottom of the borrow pit

Credit: AFCEE/MMR

The PV system envisioned for this analysis consists of many east-west rows of PV modules that 

cross over the crowns of the landfill caps or cover the flat area of the borrow pit. There should be 

significant space to drive a vehicle (all-terrain vehicle or pickup truck) in between the rows for 

maintenance. The rows should have gaps so that any settling of the cap will have only a limited 

impact on the PV-mounting structure.

Only ballast-weighted PV-mounting systems should be considered for the landfill caps. These 

systems usually require no ground penetrations. Typically, ballast-weighted PV-mounting 

systems are placed on top of the existing soil. If allowed, the ballast weights could be partially 

buried in the top soil of the landfill caps.21

The range of PV-mounting systems for the borrow pit can be expanded to include driven or 

poured concrete piers. 

 

3.1 Wind Loading

MMR operates under the Unified Facility Criteria (UFC) system for most design and 

construction projects where appropriate.22 The most recent UFC Structural Engineering, UFC 3-

301-01, addresses wind-loading criteria.23

 

21 Andrews, D. Calculations of Contract Bearing Pressure and Estimated Settlement of Foundation Footings for 

Axio Greenfield Solar. Internal report of MassDEP, June 11, 2010.

Table E-1, Structural Climatic Loading Data – United 

States, Its Territories and Possessions, in UFC 3-301-01 lists 115 mph basic wind speed for Otis 

ANGB/Falmouth. Dr. Robert Dinan states that depending on the configuration of the PV arrays, 

22 Unified Facilities Criteria (UFC). Available from Whole Building Design Guide. 

http://www.wbdg.org/ccb/browse_cat.php?o=29&c=4. Accessed April 2, 2011. 23 UFC. Structural Engineering, with Change 2, 31 January 2011, 

http://www.wbdg.org/ccb/DOD/UFC/ufc_3_301_01.pdf. Accessed April 2, 2011.
15 

the design wind load on the PV arrays would be calculated using ASCE 7-05 Section 6.5.13, 

Equation 6-25.24,25

3.2 Typical PV-Mounting Systems

 Dinan states that even though this is not a building, the PV array would 

respond to wind in the same manner as an open building with a monoslope roof. 

This analysis presents two different types of fixed, ballast-weighted PV-mounting systems for a 

basic wind speed of 90 mph.26

The first example considers a PV-mounting system similar to Unirac’s ISYS Ground Mount 

system,

 PV system designs, including ballast-weighted systems, are 

possible with design wind speeds up to 115 mph. 

27 which uses ballast weights instead of buried supports to install the PV system to the 

ground. This system is similar to the system analyzed in Andrews’s structural report.28

Two precast concrete ballast weights are estimated at 9,000 lbs each for this location.

 Assuming 

20 PV modules (BP3225T) in a 4 module by 5 module landscape arrangement will result in a 

sub-array of 4.5 kW, which is about 30 ft long by 14 ft deep. Furthermore, assume only two 

poles will hold this sub-array at an effective angle of 30 degrees with respect to level, not 

necessarily the ground. 

29 Exact 

structural calculations are required. Snow load was the critical factor since the sub-array is 

supported in the middle and not at the corners or edges. Typical dimensions of the ballast could 

be 2 ft (W) x 10 ft (L) x 3 ft (H). This results in a contact bearing pressure of 450 lb/ft2

, which 

should be acceptable for the landfill cap. Total weight of the sub-array would be around 

20,000 lbs, including the framing and the PV modules. Over the sub-array area of 30 ft by 14 ft, 

this averages to a net 50 lb/ft2. The UFC Structural Engineering document lists the snow loading 

for Otis ANGB/Falmouth as 25 lb/ft2 in Table E-1.30

See Figure 9 for a typical sub-array using two ballast weights. This type of PV-mounting system 

has access benefits—it will be easy to walk around the system to perform maintenance and to 

realign the PV sub-array if localized settlement occurs. 

 Meeting the combined system weight 

loading and the snow loading is very doable for both the landfill caps and the borrow pit. 

 

24 Dinan, R. E-mail correspondence. Air Force Civil Engineer Support Agency, 5 May 2011. 25 American Society of Civil Engineers (www.asce.org) publishes standards, including ASCE 7-05, which covers 

wind loads.

26 While two particular mounting systems were used, these are representative and not an endorsement of any 

particular company. Non-concentrating flat-plate tracking systems are not covered in this report, but could be used 

at MMR. 

27 Unirac. ISYS Ground. http://www.unirac.com/?q=commercial/commercial-products/isys-ground-commercial. 

Accessed July 17, 2011.

28 Andrews, D. Calculations of Contract Bearing Pressure and Estimated Settlement of Foundation Footings for 

Axio Greenfield Solar. Internal report of MassDEP, June 11, 2010. 29 Lonetti, D. Telephone conversation. Unirac, 9 August 2010. 30 UFC. Structural Engineering, with Change 2, 31 January 2011, 

http://www.wbdg.org/ccb/DOD/UFC/ufc_3_301_01.pdf. Accessed April 2, 2011.
16 

Figure 9. A ballast-weighted system using two precast concrete weights

Credit: Unirac

Another option is using a ballast-weighted PV-mounting system similar to those used on 

rooftops (see Figure 10). These types of PV-mounting systems spread the weight over a wide 

area by using structural beams. On a roof, the lower edge of the PV modules can be relatively 

close to the roof membrane. For a ground-mounted system, the lower edge, hence the whole 

structure, needs to be elevated to reduce the potential of the vegetation growing high and shading 

the modules. In addition, a higher height allows room for snow to slide off the PV modules. This 

type of sub-array PV-mounting system is good if there is any localized settlement and if the subarrays are not physically connected. 

The net loading of this system will be around 4 lb/ft2.

31 Concrete blocks can be placed under the 

mounting system to elevate the whole system so that the lower edge of the PV modules is about 

36 in off the ground. The contact bearing pressure could be in the range of 500 lb/ft2 if there are 

four support blocks, each 4 ft2 in surface area.

Figure 10. A ballast system similar to that used on rooftops can be adapted for a ground-mounted 

PV system

Credit: Unirac

 

31 Lonetti, D. Telephone conversation. Unirac, 9 August 2010.
17 

3.3 Usable Land Area

Using Google Earth, polygons were drawn similar to the possible areas for PV systems at MMR

on a map similar to the one shown in Figure 6. The sum of the Google Earth polygons is 

2,062,594 ft2

—see Table 1. For the PV-sizing analysis in this report, the areas from Google 

Earth were used in Table A-1 since the areas could be broken out for each landfill cap. The 

saddles between the caps could be used as well but were neither highlighted in Figure 6, nor 

estimated in Table 1.

Table 1. Usable Area of Four Different Sites

Location Usable Area (ft2)

I 968,798

II 361,616

III 503,560

Pit 228,620

Total 2,062,594

3.4 MMR Electrical Distribution System

MMR is fed by a 25 kV distribution line from a local electric utility company, NSTAR.32

3.5 Environmental Considerations

The 

Main West Substation distributes the power around MMR through various feeders. A separate 

engineering report is required to determine the best options to interconnect a PV system onto the 

NSTAR system, the MMR distribution system, or a combination of both. 

There are several environmental considerations that need to be addressed during the design, 

construction, maintenance, and eventual end-of-life decisions for the PV systems. An 

Environmental Assessment or Environmental Impact Statements may be required depending on 

the local, state, or federal regulations. 

Landfill gas is an environmental consideration that needs to be considered. Landfill gas can pose 

a risk to public health (toxic compounds in ambient air), safety (explosion, fire, and 

asphyxiation), and welfare (nuisance odors). One concern associated with the installation of a PV 

system at almost every landfill will be worker exposure to landfill gas during installation and 

O&M. An Occupational Safety and Health Administration (OSHA) health and safety plan needs 

to be provided for installation and O&M. 

Depending on the PV modules selected and the orientation (tilt and azimuth), there may be some 

glare—that is, sunlight reflection. Typically, the glare is comparable to glare from buildings or 

lakes. At various times during the day and throughout the year, there may be some unwanted 

sunlight reflection. This may pose a risk for aircraft pilots. However, given the speed of the 

aircraft, any reflection in a pilot’s eye is short in duration. While a complete ray tracing can be 

done to determine when and where these reflections occur, it is easier to mitigate the problem 

after installation if there is one. Mitigation may be as simple as placing a sun screen to block a 

specific reflection. The Federal Aviation Administration (FAA) addresses glare in their recent 

 

32 Forbes, R. Telephone communication. AFCEE, Otis ANGB, MA, 16 August 2010. 
18 

document, “Technical Guidance for Evaluating Selected Solar Technologies on Airports.”33

At some point, the PV system will be decommissioned or repopulated with different PV 

modules. Recycling programs are still under development for PV modules. The general problem 

is that the disposal requirements of PV modules are module specific and disposal-method 

dependent. One state or county may permit PV modules to be tossed in a landfill as construction 

waste, while other jurisdictions prohibit it. What is permitted this year may not be permitted next 

year or 20 years from now. When there is a broken PV module, the decision regarding disposal 

needs to be made sooner than at the PV system’s end of life. A landfill operator can determine if 

the PV modules are considered non-hazardous based on data or results from the toxic 

characteristic leaching procedure. Also, recycling should be considered for broken PV modules 

and during the decommissioning of the PV system. At least one company, First Solar, has a 

bonded recycling program for their cadmium-telluride (CdTe) PV modules.

The 

FAA does not have specific standards for potential glare. Consultation with the FAA early in the 

PV system design is recommended.

34

With PV modules tilted at any angle, the rainwater runoff needs to be managed to prevent soil 

erosion. The use of gutters and piping to channel rainwater to the bottom of PV modules is never 

used due to cost considerations—mostly maintenance costs. Within the first several months, a 

survey of the PV system is made and corrective actions are taken on the ground, such as adding 

gravel to major drip points or regrading the soil in critical areas. The initial corrective actions 

should be part of the installation contract and in the O&M contract if third-party owned. 

First Solar’s 

program is a prefunded, extended, producer-responsibility program that is paid from a portion of 

the initial purchase price of the PV modules. Most of the PV module manufacturers have a 

voluntary program to take back broken or old PV modules for recycling. The inverters and other 

electronics have standard disposal requirements. Disposal and recycling options should be 

presented by the PV system vendor, or the options could be made a part of the evaluation criteria 

if there is a competitive solicitation.

The row spacing described earlier is ideal for PV annual performance. The rows could be placed 

closer together, improving the summer production at the expense of winter production when 

more of the rows would be shaded by the rows in front. There are other factors to consider in 

row spacing unrelated to PV performance but of importance to landfill management by MMR. 

Storm water runoff associated with the site drainage system must be analyzed as well as any 

extra erosion mitigation measures that might be necessary due to the PV system. The landfill 

cap, as it stands now, has an impervious membrane covered by topsoil that is currently fully 

vegetated with native grasses, small vegetation, and weeds. This layer of vegetated topsoil 

serves as an effective absorber for heavy rain conditions thereby preventing drainage overload 

conditions. Heavy storms are currently able to be fully absorbed with no areas of standing water 

 

33 Federal Aviation Administration (FAA). “Technical Guidance for Evaluating Selected Solar Technologies on 

Airports.” November 2010. 

http://www.faa.gov/airports/environmental/policy_guidance/media/airport_solar_guide.pdf. Accessed March 31, 

2011.

34 First Solar. “First Solar Module Collection and Recycling Program.”

http://www.firstsolar.com/Downloads/pdf/Brochure_CollectionRecyclingProgram_NA.pdf. Accessed April 5, 

2011.
19 

accumulating due to the well-designed erosion mitigation system in place. Soft saturated soil 

conditions often exist during “mud season,” which occurs most springs after there has been a 

period of freezing temperatures and precipitation. 

The PV modules themselves are impervious and contribute to accelerated runoff streams coming 

off of every module during rainstorm conditions. They also significantly reduce aspect ratio of 

absorbable land versus impervious land. The landfill surface essentially has an imperviousness 

ratio of zero. That is, there are no impervious surfaces across the entire landfill surface.

Installing the PV system will result in a significant addition to the numerator of that ratio. The 

smaller the ratio the better in terms of accelerating runoff streams. The steeper the modules, the 

smaller the ratio and the better for water runoff management. This is the opposite of the windloading consideration for MMR. Consideration for both cost and performance for each system is 

necessary.

Also of interest/concern is the vegetation—its growth and required maintenance activities. These 

two primary factors need to be included in the final row spacing analysis. Left unchecked, most 

wild grassy panels with wildflowers turn into bush habitat within a few years followed by trees. 

Regular maintenance of the vegetation will be required. It is already being done periodically. The 

issue to investigate is if the maintenance activities can be accomplished as well and as easily as 

they currently are or if the row spacing requires a new method of vegetation control be 

developed. 

PV systems generate practically zero greenhouse gases (GHGs) over the lifetime of the system. 

During manufacturing, installing, and decommissioning, some GHGs are produced. During 

operation, no GHGs are produced except by vehicles used for maintenance. For the most part, 

PV systems, on a life cycle basis of 20–25 years, do not produce GHGs. An estimate of the 

GHGs reduced can be determined by locating the GHG emissions data of the electric power that 

the PV system replaces. The exact GHG reduction is dependent on the fuel mix (coal, hydro, and 

natural gas), time of day (peaking plant or base load), and season (hydro) for the electric utility 

power that is being displaced. An estimate of the GHGs avoided in the New England area is 

890 lbs/MWh of PV energy produced.35

Installing ground-mounted PV systems will have some, but not a significant, impact on the flora 

and fauna. The vegetation under the PV modules will be shaded and different types of grasses or 

vegetation will flourish better. Similarly, the shade will provide a different type of habitat for 

animals. Overall, the impact on the flora and fauna will be minor. There will be some 

disturbance during construction. A site survey before construction and at intervals during 

operation is always recommended. Vegetation that routinely gets taller than 36 in should be 

pulled. This is not a concern on the landfill caps but is a concern in the borrow pit based on 

Figure 6. 

 

35 ISO New England. “2008 New England Electric Generator Air Emissions Report.” http://www.isone.com/genrtion_resrcs/reports/emission/2008_emissions_report.pdf. Accessed February 2011.
20 

4 Economics and Performance

4.1 Summary of the Sites 

MMR was found suitable to incorporate PV systems. The economics of the potential systems 

were analyzed using an electric rate of $0.159/kWh and incentives offered in the State of 

Massachusetts, most notably the solar renewable energy certificate (SREC) of $300–$550/MWh 

for 10 years. The 30% federal investment tax credit (ITC) could also potentially be captured. 

The calculations reflect the solar potential if the total area is utilized from Locations I, II, and III 

and the borrow pit. The results are summarized in Table 2 for a 30-degree fixed-tilt PV system

with a conservative SREC market estimate of $300/MWh. Additional information is summarized 

in Table A-1. 

Table 2. PV System Performance and Economics by Sitea 

 PV 

System 

Size 

(kW)

Installed 

Cost 

($/W)

Annual 

Output 

(kWh/year) 

Annual 

O&M 

($/year)

System 

Cost ($)

Simple 

Payback 

Period

(years)

Jobsb

Created

Jobsc

Sustained

I 3,633 $5.00 4,112,548 $30,880 $18,165,000 9.4 197 0.34

II 1,356 $5.00 1,535,060 $11,527 $6,780,000 9.4 74 0.13

III 1,888 $5.00 2,137,612 $16,051 $9,442,000 9.4 103 0.17

Pit 857 $5.00 970,492 $7,287 $4,287,000 9.4 47 0.08

Total 7,735 $5.00 8,755,712 $65,745 $38,674,000 9.4 420 0.71 a Data assume a usable area of 2,062,596 ft2 and fixed tilt system at 30 degrees. b Job-years created as a result of project capital investment including direct, indirect, and induced jobs. c Jobs (direct, indirect, and induced) sustained as a result of O&M of the system.

4.2 Assumptions and Input Data for Analysis

SAM was used to estimate the levelized cost of energy (LCOE) for different systems with 

different financial assumptions. The state or the federal government could buy the system 

outright, foregoing many incentives available to tax-paying entities, such as depreciation and 

federal tax credit. SREC payments would still be available from the state. A more likely option is 

a power purchase agreement (PPA) where a third party (a tax-paying entity) owns the PV system 

on leased land with a guaranteed energy purchase agreement—usually the land owner. The PPA 

can include an option for the land owner to purchase the PV system at a fair market value at the 

end of the PPA or even at an intermediate time during the term of the PPA. The financial 

assumptions in Table 2 assume a PPA.

See Table 3 for a list of input data used in SAM. It is assumed that the installed cost of fixed-tilt 

ground-mounted systems will be $5/W. This price includes the PV array and the balance-ofsystem components for each system, including the inverter, electrical equipment, and 

installation. In July 2010, the average sales price for a PV module was $4,180/kW.36

 

36 Solarbuzz. “Solar Module Retail Price Environment.” 

 Typically, 

the PV modules are one-half to two-thirds of the total installed system price. Therefore, an 

installed price of $6/W is reasonable for small PV systems. Large PV systems usually have lower 

prices than small PV systems so a base installed cost of $5/W was used for fixed-tilt PV systems. 

http://www.solarbuzz.com/Moduleprices.htm. Accessed 

August 2, 2010.
21 

Slightly higher system costs of $5.50/W and $6.00/W were used for the single-axis and two-axis 

tracking systems. The actual installed price is dependent on many factors, such as installation 

difficulty, local labor prices, and equipment availability. The best price estimate is a response 

from a vendor to a request for a quote for a specific system.

Table 3. List of Parameters used in SAM for Financial Calculations

Parameter Value(s). Values with a range were varied in the SAM 

statistical analysis

Energy price $0.159/kWh 

Size 1 MW

Cost $5/W fixed, $5.5/W single-axis, $6/W two-axis (range 

$3.50–$7.00/W)

O&M costs Fixed at $8.50/kW/year for all systems

Inverter replacement $300,000 at year 12 

PV system degradation 1%/year

Inflation rate 2% (range 1%–3%)

Debt fraction 50% (range 20%–60%)

Loan rate 8% (range 4%–12%)

Minimum required IRR 12% (range 9%–14%)

Real discount rate 12% (range 4%–12%)

DSCR No minimum DSCR 

PPA escalation rate 0.5%/year 

Loan term 25 years

Analysis period 25 years

System lifetime 25 years

Financial incentives Federal 30% ITC

State incentives SREC, low case of $300/MWh/year and high case of 

$550/MWh for 10 years, taxable

Federal, state, property 

tax

35%/year, 8%/year, 2%/year

Depreciation MACRS mid-quarter convention 

The economics of grid-tied PV depend on incentives, financing, the cost of electricity, and the 

solar resource including panel tilt and orientation. For this analysis, it was assumed that the cost 

of electricity was $0.159/kWh. See Figure 11 for a statistical analysis of LCOE with varying 

PPA financial parameters of system cost, inflation rate, debt fraction, loan rate, minimum 

required internal rate of return (IRR), and real discount rate. The LCOE is strongly dependent on 

the system cost ($/W) and the debt fraction.37

 

37 See the SAM website for an explanation of the different financial terms. 

 A linear regression line is shown. For a given 

system cost, there is a range of possible LCOE depending on the other financial assumptions. 

Depending on the present financial conditions, not all data points are necessarily possible but are 

instructive to show the importance of those parameters. 

www.nrel.gov/analysis/sam. 
22 

Figure 11. Statistical analysis of LCOE using ranges of values listed in Table 2

Similar analyses were made for 10-degree fixed-tilt, single-axis, and two-axis tracking systems.

Another analysis was made for a 30-degree fixed-tilt PV system using a high estimate of 

$550/MWh for the SRECs. Figure 12 shows only the linear regression lines for all four PV 

system mounting types, plus a high estimate of $550/MWh for a fixed 30-degree tilt system. 

Analysis of Figures 11 and 12 indicate that single-axis and two-axis tracking systems may be 

economically possible (based on assumptions in this analysis) if favorable system costs are 

available and if the systems can meet the point-loading and wind-loading requirements and 

weather conditions of the different MMR sites. Also, a 30-degree tilted system will be more 

economical than a 10-degree tilted system if both systems cost the same since there is more 

energy production with the higher tilt. 

The value of the SREC clearly influences the LCOE as seen by the difference between the two 

curves for a fixed 30-degree tilt system with SRECs of $300/MWh (low case) and $550/MWh 

(high case). The SRECs favor energy production compared to other states’ incentive programs 

based on the power rating of the system. Depending on the additional costs for tracking systems, 

which increase the energy production without increasing the system power rating, tracking 

systems could be economically more favorable in Massachusetts. However, the load-bearing 

pressure constraints of the landfill caps may preclude placing a tracking PV system on the 

landfill caps. A tracking PV system in the borrow pit is feasible. 

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0.45

0.50

3.50 4.00 4.50 5.00 5.50 6.00 6.50 7.00

LCOE Real ($/kWh)

Total Installed PV System Cost ($/W)

LCOE Real - Fixed 30-Deg Tilt

Analysis with Different System Costs, Loan Rates, Debt Fractions, 

Inflation Rates, Minimum IRR, and Real Discount Rates.

LCOE Real - Fixed 30-Deg Tilt

Linear (LCOE Real - Fixed 30-Deg Tilt)
23 

Figure 12. Linear regression analysis of statistical analysis of LCOE using ranges of values listed 

in Table 2 for four different types of PV mounting

Table 4 is a summary of the results for the four different 1 MW PV system mounting options, 

along with a high SREC case. See Table A-2 in the Appendix, which also includes the SREC 

income and the energy cost savings. 

0.00

0.05

0.10

0.15

0.20

0.25

0.30

0.35

0.40

0.45

0.50

3.50 4.00 4.50 5.00 5.50 6.00 6.50 7.00

LCOE Real ($/kWh)

Total Installed PV System Cost ($/W)

LCOE Real

Linear Regression Analysis With Different System Costs, Loan Rates, Debt 

Fractions, Inflation Rates, Minimum IRR, and Real Discount Rates.

Linear (LCOE Real - Fixed 10-Deg Tilt)

Linear (LCOE Real - Fixed 30-Deg Tilt)

Linear (LCOE Real Fixed 30-Deg Tilt, $550/MWh State Incentive)

Linear (LCOE Real - Single-Axis)

Linear (LCOE Real - Two-Axis)
24 

Table 4. Summary of Four Different PV Mounting Options 

PV System Type

(1 MW)

Annual 

Production 

(kWh/year)

Energy/ 

Power 

Ratio 

(kWh/W)

Capacity 

Factor 

(%)

Cost 

($/W)

Total 

System 

Cost

($)

LCOE 

Real 

($/kWh)

Simple 

Payback if 

Only SREC 

Income and 

Energy Cost 

Savings

(years)

Fixed 10-deg tilt—low 

SREC $300/MWh 1,039,000 1.039 11.9 $5.00 $5,000,000 $0.202 10.7

Fixed 30-deg tilt—low 

SREC $300/MWh 1,132,000 1.132 12.9 $5.00 $5,000,000 $0.173 9.6

Single-axis tracking—low 

SREC $300/MWh 1,273,000 1.273 14.5 $5.50 $5,500,000 $0.163 9.4

Two-axis tracking—low

SREC $300/MWh 1,484,000 1.484 16.9 $6.00 $6,000,000 $0.143 8.8

Fixed 30-deg tilt—high 

SREC $550/MWh 1,132,000 1.132 12.9 $5.00 $5,000,000 $0.050 6.2

Note: LCOE was determined from Figure 12 for the relevant system cost for each PV-mounting option.

A net system DC to AC conversion of 77% was assumed. This includes losses in inverter

efficiency, wire losses, PV module losses, and losses due to temperature effects. A breakdown of 

the DC to AC conversion rate is available on the PVWATTS website.

38

It is assumed for this analysis that federal incentives are received. It is important to find state 

incentives or grants to make PV cost effective. A private, tax-paying entity that owns PV 

systems can qualify for a 30% federal ITC and accelerated depreciation on the PV system. In lieu 

of the 30% ITC, companies can apply for a U.S. Treasury Department grant of 30% of the 

system cost under the 1603 program.

 

39

4.3 Incentives and Financing Opportunities

 In addition, Massachusetts offers a SREC based on the 

energy produced. The price of the SREC is market-based and can vary from a floor price of 

$300/MWh to a ceiling of $600/MWh. The total potential tax benefits to the tax-paying entity are 

significant. A PPA with a third party could be an attractive contractual instrument for MMR to 

pursue. Given the changing credit markets and interest rates, a third-party financing estimate 

cannot be provided with any degree of certainty. A general recommendation is to issue a request 

for interest, qualifications, or quote to determine potential companies. 

The Database for State Incentives for Renewable Energy (DSIRE) provides a summary of 

incentives and programs within Massachusetts and the federal government.40

 

38 National Renewable Energy Laboratory. “PVWATTSTM Version 1 Calculator.” 

 DSIRE provides a 

http://rredc.nrel.gov/solar/calculators/PVWATTS/version1/derate.cgi. Accessed February 2011. 39 U.S. Treasury Department, Program 1603, Payments for Specified Energy Property in Lieu of Tax Credits, 

http://www.treasury.gov/initiatives/recovery/Pages/1603.aspx. Accessed April 6, 2011. 40 Database for State Incentives for Renewable Energy (DSIRE). www.dsireusa.org. Accessed September 2010.
25 

summary of net metering, interconnection rules, and incentives available to Massachusetts utility 

customers.

41

Renewable energy systems, including commercial solar PV, are subject to interconnection rules 

promulgated at the state level. In Massachusetts, there is no set limit for the amount of PV power 

that can be interconnected. However, the 6 MW limit on the Massachusetts SREC program may 

effectively limit the PV system based on financial considerations.

 The power from the MMR system can be used directly at MMR. 

4.4 Job Creation

The implementation of this project would represent a large amount of money entering the clean 

energy industry of the United States. The Council of Economic Advisors (CEA) calculated the 

number of jobs created due to federal spending using economic models developed with realworld data. CEA found that $92,000 in federal spending is equivalent to one job-year.

42 This 

means that for every $92,000 of federal money that is spent, there is a job created that can be 

sustained for 1 year. See Table 2 for an estimate of job creation if MMR installs solar PV. The 

jobs created column refers to the number of job-years that would be created as a result of the 

one-time project capital investment. This means that the jobs will be created and sustained for 

1 year. The jobs sustained column refers to the number of jobs that would be sustained as a 

result of the O&M of the system. These jobs will be sustained for the life of the system, due to 

the annual costs to keep the system operating. 

 

41 DSIRE. http://www.dsireusa.org/incentives/index.cfm?re=1&ee=1&spv=0&st=0&srp=1&state=MA. Accessed 

September 2010.

42 Council of Economic Advisors, Executive Office of the President. “Estimates of Job Creation from the American 

Recovery and Reinvestment Act of 2009.” May 2009, 

http://www.whitehouse.gov/sites/default/files/microsites/Estimate-of-Job-Creation.pdf. Accessed September 2010.
26 

5 Conclusions and Recommendations 

MMR is a promising area in which to implement a PV system. MMR can easily place 8 MW of 

ground-mounted PV systems on the crowns of the three landfill caps and the borrow pit with 

fixed PV modules tilted at 30 degrees. A fixed-tilt PV system is the more likely outcome, but 

proposals with single-axis and two-axis should be considered if all of the MMR requirements are 

met and the overall project costs are reasonable.

While the Massachusetts SREC program has a cap of 6 MW per system, MMR may be able to

have multiple systems with different owners. Potential negative consequences such as settlement 

on the landfill caps will need to be addressed in the design of the PV system. 

MMR should issue a request for proposal or qualifications for the purchase of PV systems and 

for third-party PPAs. While estimates of PV system size and price were made in this analysis, a 

vendor’s proposal will be more accurate.

This site has existing transmission lines and road access in place for this renewable energy 

project. This site is an ideal candidate for a PV system and an ideal candidate to help the United 

States further its goal of increasing clean energy use and reducing environmental impact. 
27 

Appendix 

Table A-1. Summary of PV System Calculations for a 30-Degree Fixed-Tilt PV System for All Four MMR Sites Using a 

Low SREC Estimate of $300/MWh 

Location

Usable 

Area (ft2)

PV 

System 

Size

(kW)

Annual 

Production 

(kWh/year)

Total 

Installed 

Price

($1,000)

Annual Cost 

Savings 

($/year)

SREC 

Credits 

($/year)

Annual 

O&M 

($/year)

Real LCOE 

($/kWh)

I 968,798 3,633 4,112,548 $18,165 $699,133 $1,233,764 $30,880 $0.173

II 361,616 1,356 1,535,060 $6,780 $260,960 $460,518 $11,527 $0.173

III 503,560 1,888 2,137,612 $9,442 $363,394 $641,284 $16,051 $0.173

Pit 228,620 857 970,492 $4,287 $164,984 $291,148 $7,287 $0.173

Total 2,062,594 7,735 8,755,712 $38,674 $1,488,471 $2,626,713 $65,745 $0.173

Note: The usable area of 2,062,594 ft2 is about 47.4 acres, resulting in 6 acres/MW of installed PV. This is consistent with other large-scale PV 

systems that range from 5–10 acres/MW of installed PV.
28 

Table A-2. Summary of Financial Calculations for Four Different 1 MW PV Mounting Options

PV System Type

(1 MW)

Annual 

Production 

(kWh/year)

Energy/ 

Power 

Ratio 

(kWh/W)

Capacity 

Factor 

(%)

Cost 

($/W)

Total 

System 

Cost

($)

LCOE 

Real 

($/kWh)

Annual 

SREC 

Income 

($)

Annual 

Energy 

Cost 

Savings 

($)

Simple Payback 

if Only SREC 

Income and 

Energy Cost 

Savings 

(years)

Fixed 10-deg tilt—

low SREC 

$300/MWh 1,039,000 1.039 11.9 $5.00 $5,000,000 $0.202 $311,700 $165,201 10.7

Fixed 30-deg tilt—

low SREC 

$300/MWh 1,132,000 1.132 12.9 $5.00 $5,000,000 $0.173 $339,600 $179,988 9.6

Single-axis 

tracking—low 

SREC $300/MWh 1,273,000 1.273 14.5 $5.50 $5,500,000 $0.163 $381,900 $202,407 9.4

Two-axis 

tracking—low 

SREC $300/MWh 1,484,000 1.484 16.9 $6.00 $6,000,000 $0.143 $445,200 $235,956 8.8

Fixed 30-deg tilt—

high SREC 

$550/MWh 1,132,000 1.132 12.9 $5.00 $5,000,000 $0.050 $622,600 $179,988 6.2
29 

Figure A-1. Landfill cap aspect analysis

Note: The slopes of the landfill caps vary from 2.0–3.5 degrees. 

Credit: Aspect analysis was performed by CH2M Hill and slope analysis was performed by NREL