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

Renewable Energy Applications 

for Existing Buildings

Preprint

Sheila J. Hayter and Alicen Kandt

To be presented at the 48th AiCARR International Conference

Baveno-Lago Maggiore, Italy

September 22-23, 2011

Conference Paper

NREL/CP-7A40-52172

August 2011
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1 

Renewable Energy Applications for Existing 

Buildings

Applicazioni dell’energia rinnovabile su edifici esistenti

SHEILA J. HAYTER, PE, FASHRAE – ALICEN KANDT

U.S. Department of Energy’s National Renewable Energy Laboratory – Integrated Applications Center

SUMMARY

This paper introduces technical opportunities, means, and methods for incorporating renewable 

energy technologies into building designs and operations. This paper provides an overview of renewable 

energy resources and available technologies used successfully to offset building electrical and thermal 

energy loads. Methods for applying these technologies in buildings and the role of building energy 

efficiency in successful renewable energy projects are addressed. Tips on implementing effective

renewable energy projects are also provided.

RIASSUNTO

Questa memoria considera le opportunità tecniche, i mezzi e i metodi per incorporare le tecnologie 

ad energia rinnovabile (RE) nei progetti e nel uso degli edifici. La memoria fornisce una panoramica delle 

risorse RE e delle tecnologie disponibile utilizzate con successo per ridurre i carichi elettrici e termici degli 

edifici. Vengono considerati anche metodi per applicare queste tecnologie negli edifici ed il ruolo 

dell’efficienza energetica nell’edificio per progetti RE riusciti. La memoria offre anche suggerimenti per 

implementare progetti RE ben riusciti. 

1. INTRODUCTION

Buildings account for approximately 40% of the worldwide annual energy consumption (WBCSD 

2009). Total global energy consumption in 2007 was 495 quadrillion British thermal units (Btu), meaning 

the buildings sector consumed about 198 quadrillion Btu. According to the Energy Information Agency, 

worldwide energy consumption is expected to increase 1.4% per year through 2035, implying that 

buildings will consume 296 quadrillion Btu by the year 2035 (EIA 2010). 

Fossil fuels meet a majority of world energy needs and because buildings are a large energy 

consumer, they are also a major contributor to global carbon emissions and greenhouse gas (GHG) 

production. It is now largely recognized that addressing energy use in buildings can reduce total fossil fuel 

consumption and associated GHG emissions. Benefits such as decreased building operational energy costs 

have prompted growing interest among policy makers, the technical community, and the general public in 

addressing building energy issues and investigating solutions for decreasing building energy consumption.

While energy efficiency is being incorporated into new construction, existing buildings account 

for a majority of the building stock that will be in place in the foreseeable future. In his 2009 presidential 

address, American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) 

presidential member Gordon Holness stated that 75% to 80% of the buildings that will exist in 2030 already 

exist today (ASHRAE 2010). This statistic suggests that there is an opportunity for reducing the building 

sector’s contribution toward global energy consumption through reduction of energy use in existing 

buildings.

Reducing existing building energy consumption consists of two synergistic approaches: (1) to 

reduce the need for energy through implementation of energy efficiency measures and (2) to offset the 

remaining building energy needs through use of renewable energy systems (Figure 1). It is important to 

note that building energy efficiency measures should be considered first, as the cost to invest in efficiency 

measures is approximately half the cost of installing renewable energy generating capacity equal to what 
2 

the efficiency measures offset (IEA 2006). It is advised that all energy efficiency opportunities are explored 

and as many are implemented as is feasible before or in conjunction with renewable energy projects for 

existing buildings. It should be noted that this paper focuses only on the opportunities and issues 

surrounding implementing renewable energy projects for existing buildings.

Figure 1. Demonstration of how combining energy efficiency and 

renewable energy strategies significantly reduce total building conventional energy use.

Source: National Renewable Energy Laboratory

National and local policy is being implemented in both developed and developing countries that 

require greater amounts of energy to come from renewable energy resources. For example, the 2009/28/EC 

Renewable Energy Sources (RES) Directive requires that 20% of energy produced within the European 

Union is from renewable energy systems by 2020 compared to 2010 (European Union 2009). Also, the 

2002/91/ED Energy Conservation in Buildings Directive requires building energy labeling and sets 

standards for energy performance, including application of renewable energy resources (European Union 

2002). As policies such as these are enacted, incentives for installing renewable energy systems are also 

being developed and regulatory barriers are being removed. The use of renewable energy systems for 

meeting building energy needs is also becoming a means for demonstrating leadership in environmental 

sustainability and resource conservation, increasing the reliability of on-site electrical and thermal energy 

supplies, addressing energy security issues, and other benefits. These actions are encouraging those who are

making decisions regarding existing building retrofit projects to seek out ways to use renewable energy 

systems to meet sustainable building goals. In addition, these actions encourage those who are paying for 

the energy use associated with these buildings to explore using renewable energy systems as a means to 

reduce utility costs, and in many cases, the building’s carbon footprint.

2. RENEWABLE ENERGY RESOURCES AND TECHNOLOGIES

Renewable energy resources commonly used for building applications include solar, wind, 

geothermal, and biomass. Before selecting an appropriate renewable energy technology to apply to an 

existing building retrofit project, it is important to first consider a number of factors. Examples of these 

factors include:

• Available renewable energy resource at or near the building site

• Available area for siting of the renewable energy technology

• Cost of energy purchased from the electrical or thermal energy provider for the building

• Available incentives for offsetting the installation cost of the renewable energy system

• Local regulations affecting renewable energy systems

• Desire to preserve or not alter existing architectural features

• Characteristics of the energy profiles to be offset by the renewable energy installation.
3 

European renewable energy resource data are available through organizations such as the Global 

Energy Network Institute (GENI 2007). Renewable energy resource maps are a starting point to determine 

if a building site is located in an area with acceptable amounts of renewable energy resource. However, 

other factors such as the cost of alternative energy sources and available local incentives for renewable 

energy installations often make installing renewable energy systems cost effective even if the resource is 

not ideal. For example, Germany leads Europe in solar electric system installations with 5,351,000 

megawatts peak (MWp) of cumulated installed capacity in 2008, yet, most of the country has a modest 

average annual solar resource of less than 1,000 kilowatt hours per square meter (kWh/m2

). Italy, on the 

other hand, has a solar resource ranging from modest to very good (between 900 and 1,800 kWh/m2

) and 

has 317,500 MWp installed solar electric capacity as of 2008 (EurOberv’ER 2009). See Figure 2 for a 

comparison between solar resources in Germany and Italy. This example illustrates how factors other than 

renewable energy resource influence decisions to install solar electric systems.

Figure 2. Solar resource maps for Germany and Italy. 

Source: GENI 2007 (GIS PV/© European Communities)

Examples of renewable energy technologies that can be incorporated with building energy systems 

include:

• Solar electric, or photovoltaic (PV), systems

• Solar thermal, including solar hot water (domestic water heating and space heating), and solar 

ventilation air preheating

• Geothermal heat pump 

• Wind turbines

• Biomass systems. 

More information on each technology is provided in the following sections.

2.1. Solar Electric PV

PV arrays convert sunlight to electricity. Systems are made up of modules assembled into arrays 

that can be mounted on or near a building or other structure (Figure 3). A power inverter converts the direct 

current (DC) generated by the system into grid-quality alternating current (AC) electricity.
4 

Figure 3. The Williams Building in downtown Boston, Massachusetts. 

372 modules were installed for a total system capacity of 31 kW. 

Source: Photo from SunPower, NREL/PIX 08466

Traditional single crystal solar cells are made from silicon, are usually flat-plate, and are generally

the most efficient (the solar cell efficiency is an indicator of how well it converts sunlight to direct current 

electricity). Multi-crystal solar cells are a similar technology but slightly less efficient. Thin-film solar cells

are made from amorphous silicon or non-silicon materials such as cadmium telluride. Thin-film solar cells 

use layers of semiconductor materials only a few micrometers thick. See Table 1 for an overview of 

module efficiencies for each type of solar cell. 

Table 1. Typical Efficiency of Different Types of PV. 

Module Efficiencies

Single crystal 14–19%

Multi-crystal 13–17%

Thin film 6–11%

Building-integrated photovoltaic (BIPV) products may be appropriately suited for applications on 

existing buildings during major renovations. These technologies can double as rooftop shingles (single-ply 

membrane, standing seam metal roofs, and others.) and tiles, building facades, or the glazing for skylights

(NREL 2009). Figure 4 shows an example of this technology integrated into shingles. In some cases, BIPV 

can add cost and complexity to a project and may not be universally available, but may help enhance 

acceptance of a project on a visible surface.

Figure 4. Thin-film solar PV shingles. 

Source: Photo from United Solar Ovonic, NREL/PIX 13572
5 

Most PV systems installed today are in flat-plate configurations, which are typically made from 

solar cells combined into modules that hold about 40 cells. A typical American home will use about 10 to 

20 solar panels to power the home. Many solar panels combined together to create one system is called a 

solar array. For large electric utility or industrial applications, hundreds of solar arrays are interconnected to 

form a large utility-scale PV system (NREL 2009). These systems are generally fixed in a single position 

but can be mounted on structures that tilt toward the sun on a seasonal basis or on structures that roll East to 

West over the course of a day (NREL 2011) Figure 5 shows the components of a typical PV system.

Figure 5. PV system components. 

Source: Illustration by Jim Leyshon, NREL

There are typically three scales of solar installations: utility-scale, commercial, and residential.

• Utility-scale installations are very large arrays located on open lands, and provide power for 

hundreds or even thousands of homes and businesses.

• Commercial systems are smaller and may provide power for multiple or single commercial or 

municipal buildings on campuses, in complexes, neighborhoods, or other special districts.

 Commercial-scale systems offer potential advantages for locating solar PV. Rather than attempting 

to find appropriate locations for solar panels on individual structures, a commercial-scale system 

might be located in a less visible or impactful location, such as above a parking structure or on an 

open lot. Power can be lost in transmission from these arrays to the end-use location, however, so 

distances need to be minimized.

• Residential-scale PV systems produce power for use on a single property.

The major challenge with siting solar PV technologies is ensuring appropriate siting for maximum 

electricity production. An ideal solar installation would be situated in an unshaded, south-facing location 

with an optimum tilt angle, and would supply electricity to a site where there is a demand for the electricity 

being produced. Not all sites are suitable for solar technologies, however. The following guidelines may be 

helpful in determining when solar technologies are appropriate for a site: 

• Identify an unshaded area for solar PV installation, particularly between peak sun hours occurring 

during the middle part of the day, for example between 9:00 and 15:00. Shade will reduce the 

output of a solar panel and is commonly caused by trees, nearby buildings, and roof equipment or 

features (such as chimneys).

• Orient fixed-mount panels due South in the northern hemisphere and due North in the southern 

hemisphere. Siting panels so that they face East or West of due South/North will decrease 

efficiency. However, that effect varies by location, and could be minimal.

• Maximize the annual energy production from a fixed-mount PV system by tilting the array to 

approximately match the lattitude of where the system is located. For example, a system located 

at 40° north latitude shoud be tilted at approximately 40° for maximum annual efficiency.

• Install fixed-mount solar panels on roofs (flush- or tilt-mounted), or on the ground, (polemounted), or integrate into building materials, such as roofs, windows, and awnings. However, a 

desired tilt angle is not always feasible because of factors such as roof pitch, wind, or snow 
6 

loading considerations. It is possible to install panels at a different angle. The impact of a nonideal tilt angle varies by location, and could be minimal.

• Obtain a thorough understanding of the size and nature of an electric load to properly select and 

size a PV system. PV systems can be designed to provide power simultaneously with the utility 

(grid-connected); independent of the utility (stand-alone, with batteries); or to do either (dual 

mode). The systems can be designed to power any percent of an electric load, from a very small 

percentage to over 100% of the load, depending on available area for the panels, sun availability, 

and allowances provided by utility policy to sell the energy back to the utility. When considering a 

system that will be tied to the utility grid, or grid-connected, it is essential to understand the

applicable standards and rules for the serving electric utility company.

• Keep in mind the difference in efficiency of various PV modules. Efficiency is more important to 

consider than the available or required area of the PV system. Fewer modules made of a higher 

efficiency cell (such as single crystalline) would be needed for approximately the same power 

output as more modules made of a lower efficiency cell (such as thin film). Therefore, if a project 

location has limited space, then a higher efficiency, and potentially higher cost, module may make 

the most sense. However, if a project has an abundance of space, then a lower efficiency, less 

costly module may be more practical.

2.2. Solar Thermal

Solar water heating can be a cost-competitive way to generate hot water or air and eliminate both 

the cost of electricity or fossil fuel as well as the associated environmental impacts.

Solar Hot Water Systems. Solar hot water systems use a collector to absorb and transfer heat from 

the sun to water, which is stored in a tank until needed. These systems are categorized by the temperature at 

which heat is most efficiently delivered and the collector type that is best suited for that delivered 

temperature, including low-temperature (unglazed collectors), mid-temperature (flat-plate collectors), and 

high-temperature (evacuated tube collectors). See Figure 6. 

Figure 6. From left to right, examples of unglazed, glazed, and evacuated tube solar hot water systems 

Sources: Photos by (from left) Albert Nunez,, NREL/PIX 10651; Todd Spink, NREL/PIX 10050; Alan Ford, NREL/PIX 09501 

In general, solar water systems are reliable and low maintenance because they have few moving 

parts. The primary components of a solar water heating system are the collectors and heat transfer systems, 

which include a heat exchanger, pumps, hot water storage, and controls.

The guidelines previously provided for siting solar electric systems are also applicable to siting 

solar thermal systems. Carefully considering siting issues will help increase the efficiency and cost 

effectiveness of solar thermal system installations.

Solar Ventilation Preheating Systems. Solar ventilation preheating systems heat ventilation air 

for applications needing high volumes of ventilation air. In principle, the sun warms the collector surface, 

where heat is then conducted from the surface to a thermal boundary layer of air. Fans then draw the 

boundary layer though holes in the collector before the heat can escape by convection (Figure 7).
7 

Figure 7. Solar ventilation preheating collector operation. 

Source: National Renewable Energy Laboratory

Solar ventilation preheating collectors can be added to an existing building in a retrofit project. 

Factors to consider when determining whether solar ventilation preheating is a good option for a facility 

include: relatively high utility rates for heating, a relatively long heating season, and the building’s southfacing wall has enough surface area to mount the collector (Figure 8). Methods for liking the solar 

ventilation preheating system to the buildings heating, ventilating, and air-conditioning system should also 

be considered. These systems are low cost, reliable (no moving parts other than the fan), low maintenance, 

high efficiency (up to 80% efficient), and have no storage requirements.

Figure 8. Solar ventilation preheating system installed on the U.S. Department of Energy’s 

National Renewable Energy Laboratory Research Support Facility.

Source: Photo by Patrick Corkery, NREL/PIX 17412

2.3. Geothermal

Geothermal technologies use the heat from the center of the earth. Geothermal resources include 

the heat retained in shallow ground, hot water and rock found a few miles beneath the earth's surface, and 

extremely high-temperature molten rock called magma located deep in the earth. Almost everywhere, 

shallow ground, or the upper 3 meters of the earth's surface, maintains a nearly constant temperature of 

10°–16°C. Using geothermal heat pumps, this heat can be tapped to provide heating and cooling for homes 

and buildings. Deeper and warmer geothermal reservoirs can be tapped directly for heat or through 

advanced technologies for heat and electricity generation (DOE 2011a). Building applications for 

geothermal technologies include geothermal heat pumps and direct use of the geothermal resource. 

However, because geothermal heat pumps are the most common geothermal energy technology used in 

buildings, this is the only geothermal technology discussed further in this paper.
8 

Geothermal heat pumps use the constant temperature of the earth as an exchange medium for heat. 

Although many parts of the world experience seasonal temperature extremes—from scorching heat in the 

summer to sub-zero cold in the winter—the ground a meter or so below the surface remains at a relatively 

constant temperature.

Geothermal heat pumps are able to heat, cool, and, if so equipped, supply homes and buildings 

with hot water. A geothermal heat pump system consists of a heat pump, an air delivery system 

(ductwork), and a heat exchanger—a system of pipes buried in shallow ground. In the winter, the heat 

pump removes heat from the heat exchanger and pumps it into the indoor air delivery system. In the 

summer, the process is reversed, and the heat pump moves heat from the indoor air into the heat 

exchanger. The heat removed from the indoor air during the summer can also be used to provide a free 

source of hot water.

There are four types of geothermal heat pump systems. Three of these—horizontal, vertical, and 

pond/lake—are closed-loop systems. The fourth type of system is open-loop. Which system is best for a 

particular site depends on the climate, soil conditions, available land, and local installation costs. All of 

these approaches can be used for residential and commercial building applications (DOE 2011b). 

Installing geothermal heat pumps in building retrofit projects impose an added level of complexity 

of locating the loops on site and tying the geothermal heat pump system to the existing building heating, 

ventilating, and air-conditioning system. These and other design factors should be carefully considered 

early in the process when geothermal heat pump systems are being considered to determine if installing 

such a system can be done cost effectively.

2.4. Wind

Wind energy is created by uneven solar heating of the Earth’s surface. This wind flow, or motion 

energy, can be harnessed by modern wind turbines to generate electricity. Wind turbines use rotating 

propeller-like blades to harness the energy in the wind and drive a turbine that generates electricity.

Before installing a wind turbine, it must be established that the wind resource in a specific location 

is adequate. Wind resource is classified according to its potential to produce electricity over an annual basis 

(Table 2). Wind resource maps can determine if an area of interest should be further explored, but wind 

resource at a micro level can vary significantly. Therefore, it is important to evaluate the specific area of 

interest before deciding to invest in wind systems.

Table 2. Wind Resource Classifications.

Wind Power Class Resource Potential Wind Speed at 50m (m/s)

1 Poor <5.6

2 Marginal 5.6–6.4

3 Fair 6.5–7.0

4 Good 7.0–7.5

5 Excellent 7.5–8.0

6 Outstanding 8.0–8.8

7 Superb >8.8

If the site has a class 3 wind resource, consider small wind turbine (100 kW or less) or large, lowwind speed turbine opportunities. If the site has a class 4 or greater wind resource, wind may be a good 

option and even larger, utility-scale turbines may provide economic options.

Lower wind resources are less likely to be economically feasible, but should be reviewed if the 

site is in a class 2 area and there are nearby pockets of class 3 resources (DOE 2011c). 

Most wind turbines are designed for an operating life of up to 20 years and require little 

maintenance during this period. Wind turbines require land area, so on-site wind power generation usually 

occurs for projects having space for installing the turbines (Figure 9). Roof-mounted wind systems are 

beginning to be used in some building projects. However, building designers should carefully consider 

issues such as maintaining the building’s structural integrity, noise, and the added cost before determining 

if building-mounted systems are appropriate for a specific project.
9 

Figure 9. The City of Medford, Massachusetts, USA owns a 

Northern Power Systems Northwind 100 wind turbine sited 

at McGlynn Elementary and Middle School.

Source: Photo from Northern Power Systems, NREL/PIX 16729

2.5. Bioenergy

There are many types of biomass—organic matter such as plants, residue from agriculture and 

forestry, and the organic component of municipal and industrial wastes—that can be used to produce fuels, 

chemicals, and power. Wood has been used to provide heat for thousands of years. This flexibility in 

materials has resulted in increased use of biomass technologies (DOE 2011d). 

Biomass technologies break down organic matter to release stored energy from the sun. The 

process used depends on the type of biomass and its intended end use. For example, biofuels and biopower 

can be used to provide heat or electricity for buildings.

Biofuels are liquid or gaseous fuels produced from biomass. Most biofuels are used for 

transportation, but some are used as fuels to produce electricity (DOE 2011e). Biofuels include ethanol and 

biodiesel.

Biopower is the production of electricity or heat from biomass resources. Biopower technologies 

include direct combustion, co-firing, and anaerobic digestion (DOE 2011f). 

2.6. Connecting to the Electrical Grid

Building-sited renewable energy systems generating electricity and connected to the electrical 

utility grid (known as “grid-tied” systems) are known as distributed generation (DG) systems. It is 

important to consider all issues of connecting the DG system to the grid when such systems are part of a 

building project. Project leads should communicate with the utility on topics such as technical design 

requirements, which the utility may mandate for interconnection and net metering agreements, including 

rates the utility will pay for excess renewable energy power generations supplied back to the grid.

Net metering allows for the flow of electricity from a grid-connected DG system both to and from 

the customer typically through a single, bi-directional meter. When a customer’s generation exceeds usage, 

electricity flows back onto the grid. This effectively offsets electricity consumed by the customer at a 

different time during the same billing cycle or is carried over as a credit on future billing cycles. Net 

metering policies vary widely. Some net metering programs reimburse customers for excess generation at 
10

the wholesale rate, while others reimburse at the retail value. Some policies specify a limit on the capacity 

of renewable energy systems that can participate in the net metering program.

Interconnection standards specify the technical and procedural process by which a customer 

connects a renewable energy system to the grid. Such standards include the technical and contractual 

arrangements by which system owners and utilities must abide.

Utilities can be reluctant to allow interconnection of DG systems. The reasons for this are often 

associated with concerns over ensuring high-quality, reliable power to all customers, load management 

when considering the intermittency of renewable energy power generation, safety of those maintaining the 

utility distribution systems, and other similar issues. Even with the increased number of DG systems being 

added to grid systems, many utilities still have limited experience with these systems. As a result, these 

utilities address the interconnection questions on a case-by-case basis, which can result in a significant 

amount of time needed to develop interconnection agreements.

For those pursuing grid-connected renewable energy systems for buildings projects, consider the 

following steps to ensure effective relations and solutions with the utility: 

• Meet up-front and often with utility representatives and develop a strategy for potential rate 

structure changes as well as taking advantage of incentives the utility may be offering for 

renewable energy system installations

• Work with a reputable installer/contractor with proven interconnection experience

• Size the DG system to be less than the minimum electrical load so there is no back feeding onto 

the grid

• Ensure anti-islanding capabilities, which means the renewable energy system stops providing 

power to the electrical grid when power from the electrical utility is no longer present (depending 

on application)

• Undertake engineering studies and negotiate who pays for utility line upgrades

• Submit the interconnection proposal early. 

3. INTEGRATING RENEWABLE ENERGY SYSTEMS IN HISTORIC BUILDINGS

Maintaining the architectural aspects of existing buildings, especially historic buildings, is often a 

priority of existing building retrofit projects. In addition, reusing historic and existing buildings is 

considered by many to be a sustainable design strategy, especially when renewable energy technologies are 

included with the project. The embodied energy of a building—the energy consumed by all of the processes 

associated with the production of building materials and components—is equal to approximately 20% of 

the energy that the building consumes, on a life-cycle basis (UNEP 2007). Grants, tax credits, or other 

incentives are available to encourage historic preservation in many areas, which further urge investment 

into existing building retrofit projects. However, without proper planning, installing a renewable energy 

system on or near the building can comprise both the architectural aesthetics and structural integrity of the 

building.

Historic preservation entities from the national to the local levels exist in many nations. These 

entities are often responsible for designating historic properties, providing guidance and resources for 

historic preservation projects, and imposing regulatory restrictions with which historic projects must 

comply. Therefore, it is important to understand what regulations apply to historic building projects before 

investigating renewable energy installation options.

In general, when embarking on an historic building project, it is advised to first determine what 

energy efficiency features included in the building’s original design can be rehabilitated, such as 

daylighting, natural ventilation, and thermal storage features. The next step is to consider how to 

incorporate on-site renewable energy installations. Some technologies can be hidden from view, such as 

installing a bio-fuel generator or geothermal heat pump. Solar electric and solar thermal systems can be 

integrated into the building “skin”, such as the roofing material or shading devices (Figure 10). These 

systems can also be installed out of the view of building visitors, such as on a roof, facing away from where 

visitors view the building, behind roof parapets, on other structures located on the site such as a parking 

structure, or ground-mounted away from the historic building.
11

Figure 10. Building-integrated solar water heating array incorporated into the historically correct,

teme-coated copper, standing-seam roof of the U.S. White House in Washington, DC. 

Source: Photo from Solar Design Associates, Inc., NREL/PIX 15663

4. IMPLEMENTATION PROCESS

The process for implementing renewable energy projects for existing buildings is described in the 

following steps (Figure 11). 

Figure 11. Process for implementing energy efficiency and renewable energy projects. 

Source: (NREL 2011)

4.1. Step 1: Identify Potential Stakeholders and Projects

When considering a renewable energy project for an existing building, it is essential to identify 

relevant stakeholders and potential project locations.

Identifying Stakeholders. Early identification and engagement of all relevant stakeholders is a 

large determinant of project success. Stakeholders may include facilities engineers and renewable energy 

system installation companies who can assist with the implementation of the project. Easement holders and 

private and commercial property owners will be important stakeholders due to their control over the 

property or land where renewable energy installations might be possible. Other stakeholders include 

• Identify potential stakeholders and 

projects

• Engage stakeholders

• Follow appropriate review requirements

• Implement projects

• Evaluate impact of completed project
12

government organizations that may have funding and renewable energy targets that need to be met, as well 

as financiers with knowledge of rebates, grants, third-party financing, and tax credits.

The project goals, type, and financing mechanism dictate the type of people who should be 

involved as stakeholders. Although not an exhaustive list, stakeholders may include the following:

• Adjacent property owners

• Technical assistance providers such as equipment vendors

• Public recipients of grants or funding

• Planners

• Contractors

• Engineers

• Property owners

• Federal agencies

• Non-profit preservation and environmental groups

• Local government.

Entities in the construction process, such as manufacturers, contractors, and others with a vested 

interest in the promotion, sale, or installation of energy efficient or renewable energy products may be 

consulted for technical information relevant to the discussion, but not labeled as stakeholders.

Identifying Projects

High costs of energy combined with the incentives and rebates for renewable energy installations, 

along with legislation and the need for energy security, are all drivers for considering installing renewable 

energy projects on existing properties. Alternate solutions for siting the renewable energy system should be 

considered such as installing solar on a carport over a parking area or a ground-mounted array elsewhere on 

the property instead of limiting solutions to just available roof area. There will be times when it is not 

possible to roof-mount a solar system without negatively impacting a building’s character-defining 

features, so one of these out-lying locations may be a viable alternative or another renewable energy 

technology should be considered.

. The identification of potential projects ideally begins with an initial goalsetting exercise. Determining, with appropriate stakeholders, what the motivations for and goals of the 

project are will help define and drive the project development throughout the entire implementation 

process. Goals could be related to municipality energy reduction or renewable energy use goals, building or 

neighborhood environmental requirements, and building owner or tenant motivations, for example. Project 

identification may include an analysis of building stock to determine which buildings have the most 

feasible renewable energy installation potential, an assessment of the potential impact to the building’s 

character-defining features, consideration of electricity costs or incentives available for energy projects, 

and understanding energy efficiency measure that have been implemented as part of previous building 

retrofit projects.

Siting renewable energy systems may not be limited to locating the systems on a single site or 

structure. There is potential for “district renewable energy” and/or more distant locations than the site 

allows. These types of systems could make sense in some district situations, such as grouping solar 

installations on a large institutional rooftop, open field, or over a parking lot, where locating the system in a 

hidden area could be a better solution than placing all the systems on visible rooftops. It should be noted

that there are technical issues related to distance, as well as legal and regulatory issues when more than one 

property is involved.

4.2. Step 2: Engage Stakeholders

After stakeholders and projects have been identified, it is important to engage stakeholders to 

ensure that requirements of architectural preservation are met, resources are fully utilized, and more 

informed decisions are made. This will ultimately increase the likelihood of project success.

The process for engaging stakeholders depends on the project location and scale. Different 

stakeholders will be involved in different phases of the process. Legal requirements or local code could 

partially stipulate which stakeholders are involved. The process of engagement could be done through 

third-party advocates, public notices, statutes and mandates, Web announcements, conferences, workshops, 

awards, newsletters, solar advertisements, funding announcements, or public hearings. By exploring all 

available avenues and considering various entities and stakeholders, a project will have a greater chance for 

success. 
13

4.3. Step 3: Follow Appropriate Review Requirements

The review process for renewable energy installations will vary according to the type of project and 

the property. Properties that have been designated as historic may be protected through local historic 

preservation or landmark preservation ordinances. As a result, review processes can differ greatly 

depending on local and national policies for historic buildings and/or districts. To acquire more information 

regarding the review process for a specific project, contact local historic building authorities for guidance.

Locally applicable environmental protection processes should also be examined. For example, 

some properties are protected by preservation or conservation easements. The easement holding entity 

should be involved in the renewable energy installation from the earliest phase.

4.4. Step 4: Implement Project

The project is ready to be implemented once stakeholders have been engaged, the project location, 

renewable energy technology, and renewable energy system size have been identified, and all requirements 

have been considered and met. Implementation may involve a number of stakeholders and will require 

open communication between the installers of the renewable energy system, the stakeholders, and the local 

community. Consideration should be given to the impact of project implementation and construction on the 

function of the building or district and its occupants. Also, renewable energy projects must be implemented 

in a way that not only maintains structural and architectural integrity, but ensures maximum energy

generation.

4.5. Step 5: Evaluate Project Effects

Evaluating a renewable energy project can help to increase the rate of success of future projects. 

Review is recommended of what was successful in the project implementation process as well as what 

could have been done differently. This review should take place during the process and after installation to 

analyze the coordination of planners, installers, property owners, utilities, and energy bill payees. The 

review should also consider impacts on policies, neighbors, appeal boards, and the like. Case studies or best 

practices can be created to share the experiences with other entities trying to replicate similar projects as 

well as with the public.

CONCLUSION

European studies suggest that buildings are responsible for around 45% of global carbon dioxide

emissions over the entire life cycle (UNEP 2007). Given this large contribution to global emissions, 

buildings are ripe for retrofits that result in reduced energy consumption and associated emissions. There 

are many synergies between existing buildings and energy-efficient and renewable energy technologies. 

Conserving and rehabilitating existing buildings to operate more efficiently and cleanly can reduce energy 

use, energy cost, and GHG emissions. Retrofitting an existing building rather than building a new building 

also optimizes the energy previously expended that is associated with the embodied energy in the 

building’s materials and past construction. Many existing buildings are prime candidates for energy 

efficiency and renewable energy technologies. In fact, older, historic buildings often have energy-efficient 

features, such as natural daylighting, ventilation, and thermal storage, included in the building design.

ACKNOWLEDGEMENT

This work was supported by the U.S. Department of Energy under Contract No. DE-AC36-08-

GO28308 with the National Renewable Energy Laboratory. 

REFERENCES

ASHRAE 2010. “Sustaining Our Future by Rebuilding Our Past” – President’s Address. American Society 

of Heating, Refrigerating, and Air-Conditioning 

Engineers. http://www.slideshare.net/ashrae6/presidents-address. 
14

DOE 2011a. “Geothermal Technologies.” U.S. Department of Energy Office of Energy Efficiency and 

Renewable Energy 

(EERE). http://www.eere.energy.gov/basics/renewable_energy/geothermal.html. Accessed 17 July 

2011.

DOE 2011b. “Geothermal Heat Pumps.”

EERE. http://www.eere.energy.gov/basics/renewable_energy/geothermal_heat_pumps.html. 

Accessed 17 July 2011.

DOE 2011c. “Integrating Renewable Energy in Federal Construction.” 

EERE. http://www2.eere.energy.gov/femp/reconstructionguide/preliminary_screening.html. 

Accessed 17 July 2011.

DOE 2011d. “Biomass Technologies.”

EERE. http://www.eere.energy.gov/basics/renewable_energy/biomass.html. Accessed 17 July 

2011.

DOE 2011e. “Biofuels.” EERE. http://www.eere.energy.gov/basics/renewable_energy/biofuels.html. 

Accessed 17 July 2011.

DOE 2011f. “Biopower.” EERE. http://www.eere.energy.gov/basics/renewable_energy/biopower.html. 

Accessed 17 July 2011.

EIA 2010. International Energy Outlook 2010, World Energy Demand and Economic Outlook. Energy 

Information Agency. Report #DOE/EIA-0484(2010). Release Date: July 27, 

2010. http://www.eia.gov/oiaf/ieo/world.html. 

EurOberv’ER. (2009). “Photovoltaic Barometer.” Le Journal du photovoltaique. Updated 

11/05/2009. http://www.eurobserv-er.org/pdf/baro190.pdf. 

European Union 2009. Directive 2009/28/EC of the European Parliament and of the Council of 23 April 

2009 on the promotion of the use of energy from renewable sources and amending and 

subsequently repealing Directives 2001/77/EC and 2003/30/EC. The Official Journal of the 

European Union. May 2009. http://www.energy.eu/directives/pro-re.pdf. 

European Union 2009. Directive 2002/91/EC of the European Parliament and of the Council of 16 

December 2002 on the energy performance of buildings. The Official Journal of the European 

Union. April 2003. http://ec.europa.eu/energy/efficiency/buildings/buildings_en.htm. Accessed 

25 July 2011.

GENI 2007. Renewable energy resource maps. Global Energy Network 

Institute. http://www.geni.org/globalenergy/library/renewable-energy-resources/index.shtml. 

Accessed 17 July 2011.

IEA 2006. The World Energy Outlook 2006 Maps Out a Cleaner, Cleverer and More Competitive Energy 

Future. Press Release. International Energy Agency. November 7, 2006, 

London. http://www.iea.org/press/pressdetail.asp?press_rel_id=187. 

NREL 2009. Learning About Renewable Energy, Solar Photovoltaic Technology. National Renewable 

Energy Laboratory. http://www.nrel.gov/learning/re_photovoltaics.html. Accessed 17 July 2011. 

NREL 2011. Kandt, Walker, Hotchkiss. Implementing Solar PV Projects on Historic Buildings and in 

Historic Districts. NREL. Draft Technical Report. NREL/TP-7A40-51297. May 2011.

UNEP 2007. Buildings and Climate Change. Status, Challenges and Opportunities. United Nations 

Environment Programme. ISBN: 978-92-807-2795-

1. http://www.unep.fr/shared/publications/pdf/DTIx0916xPA-BuildingsClimate.pdf.
15

WBCSD 2009. Energy Efficiency in Buildings. World Business Council for Sustainable 

Development. http://www.wbcsd.org/DocRoot/Ge2Laeua8uu2rkodeu7q/91719_EEBReport_WEB

.pdf. Accessed 17 July 2011.

____________________

NOTE: The Alliance for Sustainable Energy, LLC (Alliance) is the manager and operator of the National Renewable Energy 

Laboratory (NREL). Employees of the Alliance, under Contract No. DE-AC36-08GO28308 with the U.S. Dept. of Energy, have 

authored this work. The United States Government retains and the publisher, by accepting the article for publication, acknowledges 

that the United States Government retains a non-exclusive, paid-up, irrevocable, worldwide license to publish or reproduce the 

published form of this work, or allow others to do so, for United States Government purposes.