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Airport Renewable Energy Projects Inventory and Case Examples (2020)

Chapter: Chapter 2 - Considerations for Renewable Energy and Airports

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Suggested Citation:"Chapter 2 - Considerations for Renewable Energy and Airports." National Academies of Sciences, Engineering, and Medicine. 2020. Airport Renewable Energy Projects Inventory and Case Examples. Washington, DC: The National Academies Press. doi: 10.17226/25942.
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Suggested Citation:"Chapter 2 - Considerations for Renewable Energy and Airports." National Academies of Sciences, Engineering, and Medicine. 2020. Airport Renewable Energy Projects Inventory and Case Examples. Washington, DC: The National Academies Press. doi: 10.17226/25942.
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Suggested Citation:"Chapter 2 - Considerations for Renewable Energy and Airports." National Academies of Sciences, Engineering, and Medicine. 2020. Airport Renewable Energy Projects Inventory and Case Examples. Washington, DC: The National Academies Press. doi: 10.17226/25942.
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Suggested Citation:"Chapter 2 - Considerations for Renewable Energy and Airports." National Academies of Sciences, Engineering, and Medicine. 2020. Airport Renewable Energy Projects Inventory and Case Examples. Washington, DC: The National Academies Press. doi: 10.17226/25942.
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Suggested Citation:"Chapter 2 - Considerations for Renewable Energy and Airports." National Academies of Sciences, Engineering, and Medicine. 2020. Airport Renewable Energy Projects Inventory and Case Examples. Washington, DC: The National Academies Press. doi: 10.17226/25942.
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Suggested Citation:"Chapter 2 - Considerations for Renewable Energy and Airports." National Academies of Sciences, Engineering, and Medicine. 2020. Airport Renewable Energy Projects Inventory and Case Examples. Washington, DC: The National Academies Press. doi: 10.17226/25942.
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Suggested Citation:"Chapter 2 - Considerations for Renewable Energy and Airports." National Academies of Sciences, Engineering, and Medicine. 2020. Airport Renewable Energy Projects Inventory and Case Examples. Washington, DC: The National Academies Press. doi: 10.17226/25942.
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Suggested Citation:"Chapter 2 - Considerations for Renewable Energy and Airports." National Academies of Sciences, Engineering, and Medicine. 2020. Airport Renewable Energy Projects Inventory and Case Examples. Washington, DC: The National Academies Press. doi: 10.17226/25942.
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Suggested Citation:"Chapter 2 - Considerations for Renewable Energy and Airports." National Academies of Sciences, Engineering, and Medicine. 2020. Airport Renewable Energy Projects Inventory and Case Examples. Washington, DC: The National Academies Press. doi: 10.17226/25942.
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Suggested Citation:"Chapter 2 - Considerations for Renewable Energy and Airports." National Academies of Sciences, Engineering, and Medicine. 2020. Airport Renewable Energy Projects Inventory and Case Examples. Washington, DC: The National Academies Press. doi: 10.17226/25942.
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Suggested Citation:"Chapter 2 - Considerations for Renewable Energy and Airports." National Academies of Sciences, Engineering, and Medicine. 2020. Airport Renewable Energy Projects Inventory and Case Examples. Washington, DC: The National Academies Press. doi: 10.17226/25942.
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Suggested Citation:"Chapter 2 - Considerations for Renewable Energy and Airports." National Academies of Sciences, Engineering, and Medicine. 2020. Airport Renewable Energy Projects Inventory and Case Examples. Washington, DC: The National Academies Press. doi: 10.17226/25942.
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Suggested Citation:"Chapter 2 - Considerations for Renewable Energy and Airports." National Academies of Sciences, Engineering, and Medicine. 2020. Airport Renewable Energy Projects Inventory and Case Examples. Washington, DC: The National Academies Press. doi: 10.17226/25942.
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Suggested Citation:"Chapter 2 - Considerations for Renewable Energy and Airports." National Academies of Sciences, Engineering, and Medicine. 2020. Airport Renewable Energy Projects Inventory and Case Examples. Washington, DC: The National Academies Press. doi: 10.17226/25942.
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Suggested Citation:"Chapter 2 - Considerations for Renewable Energy and Airports." National Academies of Sciences, Engineering, and Medicine. 2020. Airport Renewable Energy Projects Inventory and Case Examples. Washington, DC: The National Academies Press. doi: 10.17226/25942.
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Suggested Citation:"Chapter 2 - Considerations for Renewable Energy and Airports." National Academies of Sciences, Engineering, and Medicine. 2020. Airport Renewable Energy Projects Inventory and Case Examples. Washington, DC: The National Academies Press. doi: 10.17226/25942.
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Suggested Citation:"Chapter 2 - Considerations for Renewable Energy and Airports." National Academies of Sciences, Engineering, and Medicine. 2020. Airport Renewable Energy Projects Inventory and Case Examples. Washington, DC: The National Academies Press. doi: 10.17226/25942.
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Suggested Citation:"Chapter 2 - Considerations for Renewable Energy and Airports." National Academies of Sciences, Engineering, and Medicine. 2020. Airport Renewable Energy Projects Inventory and Case Examples. Washington, DC: The National Academies Press. doi: 10.17226/25942.
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Suggested Citation:"Chapter 2 - Considerations for Renewable Energy and Airports." National Academies of Sciences, Engineering, and Medicine. 2020. Airport Renewable Energy Projects Inventory and Case Examples. Washington, DC: The National Academies Press. doi: 10.17226/25942.
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Suggested Citation:"Chapter 2 - Considerations for Renewable Energy and Airports." National Academies of Sciences, Engineering, and Medicine. 2020. Airport Renewable Energy Projects Inventory and Case Examples. Washington, DC: The National Academies Press. doi: 10.17226/25942.
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21 All airport renewable energy projects must follow a comparable path of development that includes selecting a technology, identifying an appropriate site, determining the ownership structure and funding sources, and obtaining project approvals from FAA and other regulatory jurisdictions. Numerous detailed resources are available to assist airports with this process, from tools that help identify renewable energy resources and evaluate their potential benefits and impacts, to guides and funding programs designed to facilitate their implementation. Many of these resources are listed in Appendix C of this report. This section provides fundamental infor- mation on technology, siting, ownership and financing, approvals, and operations that the project lead will draw on to develop a concept for a renewable energy project. 2.1 Renewable Energy Technology The following section briefly summarizes the renewable energy technologies currently available for airport consideration. 2.1.1 Bioenergy Bioenergy is created by harvesting organic matter and processing it into a fuel. In the renewable energy sector, bioenergy often refers to “biomass” energy, which is composed primarily of wood waste from forestry, lumber production, and paper production, as well as from other plant-based wastes from agricultural and yard activities. Biomass fuels can be burned on site as power for heating systems and for regional grid–supported electricity generation. In 2017, 44% of all biomass energy production was wood-based, reflecting the availability of wood as a feasible renewable fuel source (EIA, 2018). Airports, particularly those in forested regions, are adopting energy-efficient biomass burners fueled by wood pellets to meet on-site heating needs. Anaerobic digestion produces fuel from unused organic waste. Methane and other biogases are released when paper, food scraps, and yard waste decompose in landfills, or when sewage and animal manure are processed in special vessels called digesters (EIA, 2018). As the waste breaks down in the digester, the methane created can then be burned to generate electricity. Digesters can be custom-designed to serve the energy needs of the sites where they are located, including those in agricultural and industrial settings. Airports have the option of developing freestanding anaerobic digesters that depend not on one specific fuel source, but rather can process numerous wastes from surrounding businesses and treatment plants, thereby supporting a community’s need to reduce waste while generating renewable power for the airport. Biogases can also be harvested from landfills, where they accumulate under the landfill cap as wastes break down. In particular, methane can be collected as a renewable fuel source that C H A P T E R 2 Considerations for Renewable Energy and Airports

22 Airport Renewable Energy Projects Inventory and Case Examples can provide energy for generating electricity on a large scale, either at or near the landfill site (Figure 10). When processed and conditioned to meet regulatory and technological standards, methane and other organically created gases, referred to as renewable natural gas (RNG), can be used for heating purposes or conditioned for use as vehicle fuel (DOE, Renewable Natural Gas Production, n.d.). Several airports have contracted with Clean Energy, a supplier of compressed natural gas (CNG) to deliver RNG as a growing replacement for fossil-based CNG (Barrett, 2019). Because RNG is eligible under EPA’s renewable fuel standard to receive a fuel price subsidy, RNG is comparable in cost to CNG (when used in vehicles). Because many airports have already converted diesel-fueled buses to CNG to help improve air quality, they can now easily substitute cleaner-burning RNG as part of the fuel blend. Incorporating RNG as a ground transportation fuel furthers overall environmental benefits by both reducing carbon emissions and meeting broader airport renewable and sustainability goals. RNG can also be used as an alternative to natural gas for other airport fuel needs, particularly those associated with heating and cooling. However, because the cost of RNG is subsidized only when it is used as a transportation fuel, it is not currently as cost-competitive for heating and other nontransportation airport uses. As supplies and distribution channels improve, however, RNG may become a viable option for fueling airport heating systems in the foreseeable future. Indeed, at least one airport recently signed a contract to heat its terminal building with RNG (Port of Source: EPA. Note: MSW = municipal solid waste. Figure 10. Landfill gas delivered to customers.

Considerations for Renewable Energy and Airports 23 Seattle, 2020). A few airports have also grown bioenergy feedstock on airport property, but these efforts have been short term and do not represent bioenergy projects (Schroeder, 2011). 2.1.2 Fuel Cells Fuel cells continuously generate electricity through a chemical reaction that is catalyzed by an outside fuel source, as illustrated in Figure 11. The chemical reaction creates a flow of electricity, with heat as a byproduct (another potential energy benefit). Emissions from this type of power generation depend on the initial fuel source, with natural gas fueling most fuel cells to date. As technologies advance, however, fuel cells are increasingly using renewable and ever-present hydrogen as a catalyst. When fuel cells are powered by hydrogen, only water and oxygen are emitted as byproducts (DOE, 2017). Hydrogen fuel cells can generate both electricity and heat. Like solar, they are a modular tech- nology that can be sized to the appropriate use. Fuel cells used to power transport vehicles are sized to fit in a car or bus. Larger fuel cells are the size of storage sheds, providing a stationary electricity source for nearby energy-demand loads. As hydrogen fuel cells become more feasible sources of energy generation, the options for providing grid-independent energy for critical locations such as data centers, hospitals, and airports are growing (DOE, 2017). Currently, however, application of hydrogen fuel cells is primarily limited to vehicles, airports, and other facets of the transportation industry. One private company, FedEx, has documented its use of fuel cells to power GSE vehicles in three airport demonstration projects across the United States (Blanchard, 2018). 2.1.3 Geothermal Heating and Cooling Though geothermal energy can be produced from the heat of the Earth in specific geographic areas (e.g., geysers in Northern California, Iceland), the more common form of geothermal technology takes advantage of the constant temperatures underground for prechilling and thermal Figure 11. Fuel cell generator concept.

24 Airport Renewable Energy Projects Inventory and Case Examples storage. Geothermal heating and cooling systems (or geothermal heat pumps, GHPs) are composed of wellfields (also called bore hole fields) several hundred feet deep and a network of extending pipes that are connected to a building at the surface. Fluids are pumped through a closed-looped system from the building into the wellfield. The fluids are cooled or heated to the constant temperature of approximately 50°F, then circulated back into buildings for cooling in summer and supplemental heating in winter (EIA, 2019c). These concepts are illustrated in Figure 12. Wellfields are often constructed on lands adjacent to the recipient building. Mechanical systems associated with geothermal energy are located inside the building and are connected to the heating and cooling distribution network. However, different system types mean that not all existing buildings are easily adapted to geothermal. Therefore, while geothermal heating and cooling systems can be integrated into existing buildings as part of a major rehabilitation project, they are more common and cost-effective in new buildings. With heating and cooling systems accounting for up to 80% of energy use in airport terminals, many newly constructed or renovated terminals are turning to GHPs to meet their energy needs. Because geothermal heat pumps are the most energy-efficient, environmentally clean, and cost- effective systems for heating and cooling buildings (EIA, 2019c), airports are realizing these tangible benefits by installing GHPs beyond terminals—in hangars, towers, and other service buildings. Additionally, because airport operations include expansive outdoor areas (from runways to parking lots to pedestrian walkways), airports in cold-weather climates are exploring the potential for geothermal heating systems to help clear snow and ice from outdoor surfaces, thereby reducing the need for plows, salts, and sands, and facilitating airport operations in cold weather (Olgun and Bowers, 2016). 2.1.4 Solar Photovoltaic Solar photovoltaic modules—or panels—are designed with semiconductor material, typically silicon, that creates an electrical current when it interacts with sunlight, as illustrated in Figure 13. Figure 12. Geothermal heating and cooling concept.

Considerations for Renewable Energy and Airports 25 The electrical current that is produced must then be converted from direct current (DC) to alternating current (AC) for transmission into the local electrical infrastructure. A solar panel’s efficiency (or the amount of electricity produced by a standard solar module) has increased over time, which has improved solar PV economics (EIA, 2019b). Panels regularly include anti- reflective coating to reduce the amount of sunlight lost to reflection and to increase solar PV efficiency, a characteristic which also reduces the potential impacts of glint and glare. Because solar PV modules measure 2 feet by 3 feet, they can be laid out in a variety of ways to fit into the existing landscape, as shown in Figure 14. Panels can be mounted on top of buildings, either on sloped roofs facing south or on flat roofs. Roof-mounted arrays are a common arrange- ment for residential or commercial customers, with electricity fed directly into the building, ultimately decreasing the amount of power purchased from the utility. Panels can also be built as solar farms, where posts support rows of racking to which the panels are attached. Ground- mounted structures are often the most inexpensive design because they are easily constructed and require little engineering when attached to buildings. Costs can be further decreased on larger solar farms where economy of scale is possible. Solar panels can also be attached to canopy structures and placed over surface parking lots, where they serve the dual purpose of providing sheltered parking and generating electricity. The amount of power generated by solar PV is optimized by a design that maximizes the arrays’ exposure to the sun. In the Northern Hemisphere, this means tilting the panels to the south because the sun remains in the southern sky throughout the year. Ground-mounted projects can also be designed with single-axis tracking systems, whereby the solar panels follow the path of the sun each day and remain perpendicular to the sun. Dual tracking systems follow the sun both daily and seasonally, with a steeper tilt toward the south in winter and a Figure 13. Basic characteristics of solar PV panel. Figure 14. Different solar PV designs at airports.

26 Airport Renewable Energy Projects Inventory and Case Examples shallower tilt in summer; however, these systems are not as common because the additional efficiency gained by the seasonal adjustment is small relative to the expense of the more complex second tracking axis. Airports’ early adoption of solar power is partly attributable to (1) the amount of power they consume on site and (2) their flat, open landscape, which often provides significant and reliable exposure to the sun (Barrett et al., 2015). 2.1.5 Solar Thermal While solar PV systems generate electricity from the light of the sun, solar thermal systems capture the heat of the sun for heating buildings and generating hot water for domestic use (also referred to as solar hot water). Solar thermal systems incorporate panels with pipes that contain a fluid, such as water or another fluid mixture with enhanced capacity for heat storage. The pipes, which are designed to collect energy from the sun, circulate into the building, where they transfer the energy from the sun to the building for hot water and heating. Thermal solar panels are typically located on the roof of the building that is using the solar energy, with the panels oriented toward the south to maximize their exposure, as shown in Figure 15. Airports use solar hot water to meet terminals’ heating and hot water needs (Barrett, 2019). An alternative solar thermal design heats air instead of fluid, with hot air circulated through ducts to heat buildings. These solar thermal applications can lower the cost of energy for airports that would otherwise rely on fossil fuels. 2.1.6 Wind Power Wind turbine generators with three-bladed rotors produce electricity when wind energy turns the blades. Because winds intensify at higher altitudes, wind power is most effectively generated by large structures as tall as 500 feet. Wind farms are located in areas where wind resources are strong, including mountain passes, the Great Plains, and coastal regions. The rapid development of large wind farms across the country has significantly increased the amount of renewable energy generated in the United States (DOE, 2016). Because efficient wind power generation depends on tall structures, and because tall struc- tures close to airports represent a hazard to air navigation, wind farms are not compatible with airports. Some airports, however, still derive a limited amount of renewable energy from smaller Figure 15. Solar thermal collectors on roof of terminal at Boise Airport, ID.

Considerations for Renewable Energy and Airports 27 wind turbines. For example, the fixed base operator at Burlington International Airport in Vermont generates energy from a 125-foot-tall wind turbine located on airport property that is adjacent to the terminal building (see Figure 16). Other wind installations at airports include building- mounted wind turbines, which produce much lower amounts of electricity. Although wind energy is not a practical option for supplying large amounts of power when located on airport properties, many airports have the option to purchase wind energy from off-site providers; this supports renewable energy development and helps airports meet defined sustainability objectives. 2.1.7 Energy Storage While not a renewable energy–generating technology, energy storage is becoming an increas- ingly important component of renewable energy use. Storage enables energy managers to control when the renewable energy is distributed and consumed. Without storage, use of renewable energy is limited only to those times that the renewable resource is available (Diehl, 2015). The most common energy storage system is the lithium-ion battery, of the same type used in consumer electronics and electric vehicles. In a larger-scale configuration, lithium-ion storage is modular, with systems composed of many smaller batteries protected in a cabinet (see Figure 17). Energy storage systems have multiple benefits that enhance the capabilities of renewable energy. Storage allows the operator to control when the power is consumed, which creates a more consistent energy source. This enables operators to reduce the use of grid-supplied power during peak price periods, lowering the overall cost of on-site energy use. Storage also provides an option for expanding the capacity of renewable energy projects, as a portion of the generated power can be consumed at a later time. And, as storage stabilizes the intermittent aspect of power generated from renewable sources such as sun or wind, storage systems can serve as a foundation for integrating renewable energy technologies as a central component of airport microgrids (independent energy networks, which are discussed later). 2.1.8 Thermal Storage Thermal energy storage systems collect and retain thermal energy (either heated or cooled) in a storage medium, such as water, for future use (Sarbu and Sebarchievici, 2018). In the context of renewable energy, heat may be captured from the sun or as a byproduct of burning bioenergy and stored in a liquid contained in an insulated vessel. Figure 16. Wind turbine generator at Burlington International Airport, VT.

28 Airport Renewable Energy Projects Inventory and Case Examples Like battery storage, thermal energy storage gives energy operators flexibility to use the energy when it is most needed or when purchasing the power for heating or cooling systems is expen- sive. Thermal storage is not exclusively used with renewable energy, but it is particularly valuable to renewable energy sources that are intermittent and not constantly generating energy. Airports that use thermal storage have constructed large water storage tanks with exterior insulation to prevent cooling loss (DN Tanks, n.d.). The water in the tanks is cooled with elec- tricity and traditional refrigeration methods at night, when electricity costs are low. The cold water is stored in the tanks until the following afternoon, when electricity consumption increases and prices peak. Instead of using electricity to power cooling systems during these peak consump- tion periods when electricity is expensive, the airport diverts the cool water to its building systems to provide cooling. Thermal storage has been demonstrated in at least three airports in Texas and one in Illinois, and—although these systems are not currently used to store energy generated by renewable means—the potential exists for this storage technology to be applied on a broader scale to help maximize renewable energy projects. 2.1.9 Microgrids Uniting on-site renewable energy generation with robust energy storage enables airports to create self-contained, resilient energy networks. When these networks can run entirely inde- pendent of a regional utility grid, they become known as microgrids. Microgrids require on-site electricity generation and can be run either in tandem with the regional utility grid or as wholly independent power systems. With a microgrid in place, airports, as well as other critical services such as hospitals and data centers, can be far less reliant on an external utility’s electrical grid. In the event of a regional utility grid loss or failure, microgrids can go into “islanding mode,” providing uninterrupted airport electricity to power operational and safety systems through on-site energy generation, as illustrated in Figure 18. Because microgrids require enough on-site energy generation to keep an airport operable even in regional emergency situations, renewable energy is a key component to simultaneously Figure 17. Lithium-ion battery system at Moi International Airport in Kenya.

Considerations for Renewable Energy and Airports 29 supporting on-site power generation and alleviating reliance on external distribution networks for traditional fossil fuels. Airports are recognizing the need to plan and implement microgrids, given their potential to minimize the risks associated with regional power failure. In support of these efforts, ACRP and TCRP have published ACRP Synthesis 91–TCRP Synthesis 137: Microgrids and Their Application for Airports and Public Transit (Heard and Mannarino, 2018). Another forthcoming publication is ACRP Project 10-26: Airport Microgrid Implementation Toolkit. 2.2 Project Siting The airport landscape affords a variety of opportunities for locating renewable energy projects, as illustrated in Figure 19. The exact location of a renewable energy project on the airport campus will influence its design. Solar projects, for instance, have the greatest design flexibility when located on the ground, whereas projects located on the top of buildings or over parking areas have more limitations because they need to conform to the basic footprint and orienta- tion of those facilities. Despite constraints, there may be co-benefits of structural placement for solar depending on specific airport goals and parameters. Other renewable energy engineering considerations include issues such as wind load and subsurface geology, which, again, will vary by project location. Some technologies, such as biomass heating, can typically be connected to existing mechanical infrastructure, while geothermal heating and cooling must be incorporated into overall airport building structures. While some siting options are defined in part by the design of the technology and the use of the power produced, the following summary focuses on the airport property itself, and how airport lands might be more effectively used through implementation of renewable energy systems. Figure 18. Physical composition of airport microgrid.

30 Airport Renewable Energy Projects Inventory and Case Examples 2.2.1 Airfields Airports require a significant amount of buffer area to protect airspace and aviation activities, as well as to limit impacts on neighboring lands. Often, these surplus buffer lands offer oppor- tunities for renewable energy development. Some components of appropriate renewable energy technologies can be located within aircraft movement areas, in close proximity to runways and taxiways, when federal regulations and FAA requirements are met. Because structures must not impinge on the lower limit of airspace as defined by Federal Regulation Title 14, Part 77, solar structures no higher than 10 feet can be a viable option for renewable energy development on airfields. Like all solar projects located on airport property, however, the siting of panels on the airfield must comply with FAA’s interim solar policy and the ocular hazard standard used to protect pilots and other aviation receptors from impacts of glint and glare. A recent example of a solar facility sited close to runways exists at Columbia Metro- politan Airport in South Carolina (see Figure 20). This project avoided glare impacts because of its location south of the control tower. Projects that are located east or west of the tower have Figure 19. Different areas of airport to site renewable energy facilities. Figure 20. Solar PV project at Columbia Metropolitan Airport, SC.

Considerations for Renewable Energy and Airports 31 a higher likelihood of glare. Additionally, this project site is not directly east or west of a flight path, which further reduces its potential for glare impact. Glare that is identified in a model of a solar project near an airfield or anywhere on an airport property may be mitigated through design modifications, such as altering the tilt angle or azimuth angle of the project to direct glare away from glare receptors (Barrett, 2013). In addition to considerations regarding glare, questions have arisen about whether solar and associated structures attract wildlife, which could be a hazard if sited near airport runways. Research has shown, however, that solar projects do not attract wildlife when compared to typical airfield conditions. According to the U.S. Department of Agriculture’s Wildlife at Airports report, solar panels can actually reduce the overall incidence of wildlife on airport land by modifying animals’ natural habitat. However, solar panels, like any other structures in the airfield, should be monitored because they could provide shade or serve as perches for birds (DeVault et al., 2017). Solar panels are also considered an “allowable use” for siting within the runway protection zone (RPZ), per a 2012 FAA memorandum titled “Interim Guidance on Land Uses within a Runway Protection Zone” (FAA, 2012c). Before these specific FAA guidelines, a limited number of projects were constructed in the RPZ, including the one shown in Figure 21 at Fresno Yosemite International Airport. Since these guidelines were issued, however, FAA has instituted stricter limitations. The administration now requires that solar projects proposed for siting within the RPZ undergo an FAA Headquarters Review, at which airport representatives must demonstrate that there is no feasible alternative location for the project at the airport. Like solar project components, geothermal heating and cooling project components can be placed in the airfield, close to airport infrastructure. As illustrated in Figure 22, the geothermal wellfield at South Bend International Airport was placed in the airfield and does not impact any aircraft activities because project components are located underground, away from taxiing airplanes and other airplane activity. Because of the significant operational and safety regulations that govern airfields and their immediate buffer areas, renewable energy projects may provide unique opportunities for airports to use these areas in appropriate and beneficial ways. 2.2.2 Buildings Airports have a variety of large buildings that require energy for operations; thus, locating facilities for generation of renewable energy on or next to those buildings can make sense from both an engineering and an economic perspective. Solar PV or thermal panels can be placed on Figure 21. Solar PV project at Fresno Yosemite International Airport, CA.

32 Airport Renewable Energy Projects Inventory and Case Examples top of buildings, on roof areas that may otherwise not serve any enhanced function. Figure 23 illustrates the placement of solar PV panels on top of the rental car center at Phoenix Sky Harbor International Airport. These panels were installed in 2012 and provide 51% of the electricity necessary to run the rental car facility (City of Phoenix Aviation Department, n.d.). Geothermal heating and cooling systems, as well as biomass and biofuel systems, are building- integrated systems. Ancillary system components—such as the geothermal wellfield or the feedstock silo or tank—are located adjacent to the building. In addition, geothermal wellfields can be covered and used for surface parking in an effort to maximize airport land use, a practice completed at the Portland International Jetport in Maine in 2012. 2.2.3 Parking Surface parking, either open asphalt lots or the exposed upper level of parking garages, can cover large stretches of airport property. To increase usage of these spaces, airports can install canopy structures for solar PV panels, which provide the added benefit of covered parking for travelers and airport personnel. Solar PV panels sited on canopy structures can improve the customer parking experience, provide airport visitors with a direct view of solar technology at work, and maximize use of the parking area by creating a platform for renewable electricity generation. A review of airport solar projects shows an increasing number of canopy installa- tions in recent years. One such project was constructed in 2019 at Evansville Regional Airport in Indiana, as shown in Figure 24. Figure 22. Geothermal wellfield concourse at South Bend International Airport, IN. Figure 23. Solar PV panels on rooftop of rental car center, Phoenix Sky Harbor International Airport, AZ.

Considerations for Renewable Energy and Airports 33 2.3 Ownership and Financing The three primary ownership structures for airport renewable energy projects include airport-owned projects, privately owned projects, and utility-owned projects. Though it is feasible to apply different ownership structures to all renewable energy technologies deployed at airports, these ownership and financing variations are most common for solar PV projects. Other renewable energy projects, including geothermal, are typically owned by the airport. The availability of tax credits, which catalyze private investment in developing and owning solar projects and lower the cost of the electricity produced, is a primary driver for the private ownership model. 2.3.1 Airport-Owned Projects When the renewable energy project is owned by the airport, the airport itself must finance, build, and operate the facility. When it does, the airport owns the power that is produced by the facility and uses that energy directly on site, thereby reducing the amount of energy purchased from the utility service provider. In regard to solar PV projects that generate electricity, the airport also owns the renewable energy certificates (RECs) and other environmental attributes that are created by the project. Airports often retire these RECs to certified carbon registries as validation of their carbon footprint reduction. The airport-owned concept is illustrated in Figure 25. Project financing mechanisms for airport-owned renewable energy projects are similar to those available for other airport projects. The airport can apply for FAA’s AIP funds, which include Voluntary Airport Low Emissions (VALE) Program grants for certain nongrid technologies (e.g., geothermal heating, solar thermal) when the airport is located in an EPA-designated area of poor air quality. Airports can also apply under the AIP for funding for renewable energy initiatives (see Section 512 of the FAA Modernization and Reform Act of 2012). Projects may also be wrapped into larger capital programs funded through a municipal bond issuance. In addition, utilities have programs that provide rebates for certain technologies such as geothermal heating and cooling. In implementing its own project, the airport will go out to bid to contract with firms to design, engineer, construct, and energize the renewable energy systems. Once the project is operating, the airport will likely contract with a firm to conduct operations and maintenance, or the airport may train its staff to perform some maintenance activities internally. Figure 24. Canopy-mounted solar PV panels at Evansville Regional Airport, IN.

34 Airport Renewable Energy Projects Inventory and Case Examples 2.3.2 Privately Owned Projects In this structure, private developers (sometimes referred to as third parties) seek to lease airport land where they can build, own, and operate renewable energy projects, predominantly solar PV facilities. The airport may participate in such a project in one of three ways. First, the airport could purchase all or a portion of the electricity generated from the facility, as well as the RECs and other environmental attributes, by executing a power purchase agreement (PPA). Second, the airport could purchase all or a portion of the electricity but not the RECs, which would be sold to another buyer (e.g., the utility). Third, the developer could sell the power and the RECs to another entity, in which case the airport is simply a landlord who receives an annual lease payment for hosting the facility (see Figure 26). Some states have created community solar programs to expand the availability of renewable energy to residential or commercial customers. In this model, the developer builds and operates the solar facility and identifies subscribers to purchase the electricity. Projects often include an “anchor” subscriber, an entity with significant electricity demands that will purchase a large portion of the facility’s power. (For example, in Colorado, the anchor can purchase up to 40% of the power from a community solar project). Airports may be approached by developers to host a community solar facility on airport land, to serve as an anchor subscriber, or possibly to fulfill both roles in the project. Figure 25. Airport-owned renewable energy facility.

Considerations for Renewable Energy and Airports 35 Regardless of project origin, the process for initiating a privately owned renewable energy facility at an airport often requires public procurement to select a private renewable energy partner. A request for proposals (RFP) typically identifies the project area to be leased, specifies if the response should include a proposal and costs for providing the power to the airport, and details the expected term of the lease and PPA as applicable. Once a developer is selected, it designs, builds, owns, and operates the facility. During the development process, the developer must coordinate closely with the airport on requests for FAA approvals because, as the landowner, the airport is considered the project applicant. The developer finances the facility and backs the investment through the PPA. Developers can reduce construction costs and provide a more cost-effective PPA through incentives such as the investment tax credit. 2.3.3 Utility-Owned Projects Depending on state energy laws, a utility company may be able to own power-generation assets in addition to its primary role in owning and managing the transmission infrastructure that distributes the power. These conditions occur in regulated energy markets or in deregulated markets where some utility-generation ownership is permitted. In these markets, the utilities may be required to provide renewable energy to their customers, either by purchasing RECs from projects developed by others or by constructing, owning, and operating their own facility. The driver for utility ownership of renewable energy is often a state legislative mandate that requires a utility to provide a minimum amount of total power from a renewable source. This is also referred to as a renewable portfolio standard (RPS). Figure 26. Privately owned renewable energy facility.

36 Airport Renewable Energy Projects Inventory and Case Examples Like in the private developer model, the utility signs a lease agreement with the airport, which serves as a landlord for the facility. The utility must then collaborate with the airport on the approval process. The utility finances, builds, owns, and operates the facility and delivers a renewable energy product to its customers. 2.4 Approval Process The approval process for a renewable energy facility will depend on the type of project and its associated potential impacts. If the renewable energy project is part of a larger development initiative, such as a terminal expansion or a new parking garage, the consideration for renewable energy will be made in the context of the approval of the larger project. Projects that are proposed on their own are approved as individual projects. All projects will require review from a local municipal or county board for evaluation in accordance with local zoning and land use requirements. Projects may also trigger review by a state agency depending on project location and whether state-regulated resources, such as natural environments or state highways, may be affected by the project. The following section summarizes the specific issues associated with developing renewable energy projects in regard to federally obligated airports and their responsibilities under FAA grant assurances. These issues can be readily categorized as planning, environmental, airspace, or land use concerns. 2.4.1 Planning FAA requires that airports regularly inventory their existing operations and infrastructure and plan for future operations according to forecasts for potential aviation growth. The airport sponsor develops an ALP, which shows existing and future airport conditions, and may also develop an airport master plan to assess in more detail how the airport plans to accommodate future development activity to sustain airport business. [On October 5, 2018, H.R. 302, FAA Reauthorization Act of 2018, was signed into law (P.L. 115-254). Section 163(d) of the act, titled “Amendments to Airport Layout Plans,” reduces the scope of FAA’s review and approval authority for airport layout plans and changes to such plans.] Before approving a project, FAA will want the airport sponsor to demonstrate how a proposed renewable energy facility is consistent with the airport’s long-term planning objectives. In partic- ular, FAA will review the project to make sure that it does not displace potential aeronautical development such as runway or taxiway improvements, or aviation buildings such as terminal expansions or aircraft hangars. The airport sponsor then submits an amended ALP (referred to as a pen-and-ink change) that (1) shows the proposed project’s location and (2) demonstrates the project’s consistency with the airport’s long-term planning objectives and its mission to develop aviation-related businesses. Figure 27 provides an example of a pen-and-ink change approved by FAA for a solar project that will be constructed in late 2020 at Pontiac Municipal Airport in Illinois. The location of two solar arrays, highlighted in the figure, do not interfere with future aeronautical development. 2.4.2 Environmental FAA, as a federal agency, must act in accordance with the National Environmental Policy Act (NEPA), including in its issuance of permits and provision of funding. NEPA requires FAA, together with the airport sponsor and other proponents of the project, to assess a project’s potential effects on specified resource categories and to publish information demonstrating that impacts have been avoided, minimized, and mitigated. While all development projects subject

Considerations for Renewable Energy and Airports 37 to a federal action (e.g., permit issuance, funding support) require a NEPA evaluation, the level of evaluation varies with the size of the project and the extent of its potential impacts. For renewable energy projects being developed as part of a larger capital project, the NEPA assessment of renewable energy will often be conducted as a component of the larger development initiative. For individual renewable energy projects, the NEPA review is specific to the project. FAA has identified project types that, according to their characteristics, will not cause a signifi- cant impact and therefore qualify for a categorical exclusion, or CATEX. For renewable energy projects, these may include building-mounted facilities, additions to existing buildings, and solar PV projects covering an area of land 3 acres or smaller. If a project is eligible, the airport can file the CATEX form, and FAA confirms that the project qualifies for a CATEX, completing the NEPA review. In some instances, however, a documented CATEX may be required to provide information on consultation with other agencies and to demonstrate that the project has no extraordinary circumstances that would necessitate further NEPA evaluation. Projects that do not meet the standards of a CATEX must file an environmental assessment (EA) or an environmental impact statement (EIS). An EIS is required only for proposed projects that are likely to result in significant impacts. Most renewable energy projects are not expected to result in significant impacts; therefore, an EA is customary if the project does not qualify for a CATEX. Proponents of renewable energy projects, particularly solar PV projects, that cover more than 3 acres of land typically use a short-form or condensed EA template that provides a streamlined format for distilling information. The EA is generally prepared by the airport and its consultants Figure 27. Pen-and-ink change to ALP showing location of solar facilities at Pontiac Municipal Airport, IL.

38 Airport Renewable Energy Projects Inventory and Case Examples for an airport-owned facility, or by a private developer and its consultants for a private owner and airport lease project. In either case, the airport sponsor submits the EA to FAA (or to the state department of aviation in block grant states) for review. When the process is complete, FAA may issue a Finding of No Significant Impact or a Record of Decision to complete the process. 2.4.3 Airspace Part of FAA’s core mission is to ensure that development projects both on and off airport property do not impact airspace safety. It has developed design standards that designate setbacks from runways and taxiways for various structures, as well as boundaries extending away from runways that define the bottom limits of airspace (referred to as “imaginary surfaces” in Federal Regulation Title 14, Part 77). FAA also reviews projects to ensure that they do not impinge on airspace or affect navigational facilities such as radar. Tall structures, such as conventional wind turbines, are not appropriate near airports because of their impingement on airspace. Other renewable energy technologies, such as geothermal and solar PV, do not impinge on airspace because they have low profiles and because their components are housed within existing or proposed buildings. In addition to physical impacts such as impingement and blocking of radar signals, other nonphysical impacts are possible. For renewable energy, the most noteworthy is potential glare from solar PV panels. To address this issue, FAA published its solar policy in 2013. This policy provides the methodology and tools for assessing glare, as well as an ocular hazard standard for aviation-sensitive receptors to determine significant impact. Before solar projects located on airport property can proceed, they must assess potential glare using the SGHAT and demonstrate compliance with the FAA ocular hazard standard. Figure 28, an image of the approved and constructed solar project at Evansville Regional Airport in Indiana, shows a screenshot of the SGHAT Google Map interface, where users identify the location of the solar project, air traffic control tower, and flight paths on final descent to the airport for analysis. To complete the airspace review process, the airport sponsor must file Form 7460-1 with FAA’s office of Obstruction Evaluation and include a copy of the glare study that assesses potential impacts. 2.4.4 Land Use The land use assessment is completed in part with the review of the ALP and the issuance of the pen-and-ink change showing the proposed renewable energy project. These initial steps confirm that the area proposed for the project is consistent with the ALP, does not represent an area impor- tant for future aeronautical uses, and will not be an obstacle to growth of the aviation business. If the proposed project is owned by the airport, FAA oversight can be completed with an updated ALP, a NEPA Finding of No Significant Impact, and an airspace determination of no hazard. However, if the airport seeks to lease the property to a private entity to build, own, and operate the facility, FAA must also approve the lease agreement and, if the airport intends to buy the electricity, the PPA to verify that the contracts are in the best business interest of the long-term operation of the airport. A central part of FAA’s lease agreement review is a determination of fair market value. The airport sponsor, working with the applicant, must submit to FAA an independent appraisal of the property and the draft lease agreement between the airport and the developer, as well as the PPA if applicable. FAA evaluates the appraisal and compares it to the economic terms contained in the lease agreement and PPA. Because airport sites proposed for renewable energy projects, such as solar PV, are typically considered underused lands with little real estate value, their

Considerations for Renewable Energy and Airports 39 comparable land uses are often agricultural. When the PPA is part of the evaluation, the lease may include both a lease payment for using the land and a price for the electricity, or it may include just the price of electricity. The land use approval often constitutes a formal land release, notice of which may be required in the Federal Register during a 30-day comment period before final approval of the lease of land. 2.5 Operations Once renewable energy facilities are approved and constructed, they become integrated into overall airport operations. The level of effort associated with facility operations and maintenance varies by technology and location. For example, for renewable energy projects developed by private parties, long-term operations and maintenance are not a central concern for the airport because such projects are generally owned and operated by the private parties. Many of these projects are solar facilities, and the private owner will monitor system performance from a remote location and access the site for periodic preventative and corrective maintenance as necessary. These types of projects require close coordination between the contractor and the airport because projects may be located in secure areas. Regardless of ownership structure, however, the following maintenance, optimization, and warranty information should be considered. Figure 28. SGHAT Google Map user interface for identifying solar projects and airport receptors for analysis, Evansville Regional Airport, IN.

40 Airport Renewable Energy Projects Inventory and Case Examples 2.5.1 Maintenance All renewable energy facilities have routine preventative maintenance procedures to change out components with short operational lives. Technical staff may be required to conduct corrective maintenance on larger components if a failure occurs. As an example, solar PV facilities may require periodic changes of fuses and cables as part of their preventative maintenance program, while the failure of an inverter (a critical component that converts the DC electricity generated by the solar panels to AC for common use) would require corrective maintenance and represent a significant cost. Geothermal heat pump systems, biomass furnaces, and solar thermal systems are integrated within a building’s energy infrastructure; thus, the maintenance program and schedule for these projects would look similar to those required for conventional heating and cooling systems. 2.5.2 System Optimization A notable difference between solar and geothermal energy generation is system optimization. Because solar projects generate electricity from the sun using photovoltaic panels, the system’s performance is primarily a function of the system’s design (e.g., type and rating of panel selected, tilt and azimuth angle). Once the system is installed, little can be done to change subsequent performance unless the facility is repositioned. Geothermal systems often require adjustments to coordinate operations with the actual heating and cooling demands of the building. An optimal geothermal heating and cooling design balances heating in winter and cooling in summer. Achieving this system balance and reaching optimal operating conditions can take a full year. Such tasks are typically monitored by airport facilities staff. 2.5.3 Warranties and Useful Life Renewable energy system components include warranties that provide owners and operators with assurances on long-term performance and expected life of the facility. For example, a solar panel customarily includes a warranty that the panel will produce 90% of the rated capacity after 10 years and 80% of capacity after 25 years (EnergySage, n.d.). The inverter, a critical component of the system distribution, is typically warrantied for 10 to 12 years, though extended warran- ties can be purchased. The wells and underground piping components for geothermal systems come with warranties between 25 and 50 years (DOE, Choosing and Installing Geothermal Heat Pumps, n.d.).

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Airports have implemented a variety of renewable energy technologies since 1999—with the largest growth occurring over the past decade—in parallel with the evolution and maturation of renewable energy markets. Of the renewable energy options available to airports today, the prevailing technology is solar photovoltaic (PV), which accounts for 72% of all projects cataloged in the Renewable Energy Projects Inventory.

The TRB Airport Cooperative Research Program's ACRP Synthesis 110: Airport Renewable Energy Projects Inventory and Case Examples draws on existing literature and data to present the state of practice for airport renewable energy. It presents the integration of renewable energy projects—including solar PV, geothermal, bioenergy, solar thermal, and small wind projects—into airport development and operations and the drivers behind those efforts.

The Renewable Energy Projects Inventory in the report is also available online as a searchable database.

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