Preparing Your Airport for Electric Aircraft and Hydrogen Technologies (2022)

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115   Power Generation and Management 13.1 Power Management The advent of low-cost computing has helped improve power and building management tech- nologies. However, according to extensive study by James Dice from Nexus, technology in buildings is decades behind other industries. This report will attempt to tease out ways for airports to apply the best available technologies to maximize the efficiency and use of their existing elec- trical assets and reduce energy bills. Why Power Management? The real price to produce electricity can swing wildly throughout the day and across different seasons. Not all of these cost differences are always passed along to customers. However, utilities are allowed to charge differential prices in several different ways: • Demand Charges: The utility measures the peak electric use over any 15-minute period during the month and charges a specific cost per kilowatt of demand. • Time-of-Use Rates: These rates are usually voluntary, sometimes mandatory for large cus- tomers. As implied by the name, the cost of electricity varies throughout the day. • Demand Response: This program rewards customers for shifting their energy use away from times of high electricity demand (traditionally hot summer afternoons). • Global Adjustment: Some utilities measure the demand on a single peak hour, or several peak hours throughout the year and charge additional costs per kilowatt. Generally, variable prices are lower because the customer is taking on some of the risk from the utility. When prices spike, airports must manage their energy use to avoid very high bills. Emerging Power Management Technologies New hardware and software tools can help airports manage their electricity use and con- trol bills. This technology will become more important as airport demands increase. One key to enabling large-scale advances in electric transportation use is to defer distribution system upgrades by shifting loads to lower-use times. Advanced metering and management combine hardware and software that can measure real- time power flows, display them for action by operators, and control circuit breakers for some advanced users. The costs of metering hardware have decreased in recent decades, and there are more options for monitoring smaller loads in real time. Some providers suggest monitoring down at the smallest branch circuit levels. Other providers suggest focusing on bigger loads and controllable loads that can be scheduled for different times of the day. C H A P T E R   1 3

116 Preparing Your Airport for Electric Aircraft and Hydrogen Technologies Building management systems have been traditionally used to control HVAC loads within buildings. These systems are getting more sophisticated by using digital twins, fault detection and diagnostics, machine learning, data lakes, and cloud computing. Load management for demand response/grid interactivity, which has not been a traditional use of building manage- ment systems, is a new trend. Charge management systems have been built specifically for managing the electricity used to charge electric vehicles. The largest current use case is to manage energy costs for electric-vehicle fleets, which are quite price-sensitive. There are not many options yet for large public parking facilities, such as airport short- and long-term parking lots. New options will likely emerge for airport-specific use cases in the next few years. Battery energy storage technology was introduced in Chapter 10, Electric Industry Trends. These systems can help shift loads from times when power is expensive to times when power is cheap. In addition, there are other benefits to the utility and to the transmission system that can produce additional revenue streams to the airport. Rocky Mountain Institute estimates that there are 13 different services to customers (including airports), distribution utilities, and regional transmission organizations. Distributed energy resources refer to a wide variety of technologies that could be controlled by a utility to manage the grid. For example, if an airport has a microgrid, the utility could send a request for the airport to export power to the grid or to cease all exports. Utilities are investing in distributed energy resources management systems that allow them to communicate in robust ways with more end customers and loads. Future Energy Delivery Roadmap As part of integrating electric aircraft with airport operations, the industry should develop a roadmap on energy delivery for any future fuels. The National Renewable Energy Laboratory has been assisting the move toward electric Class 8 heavy trucks to identify gaps and timing concerns with the standardization of protocols and electrical capacity. Similar roadmaps will ideally be prepared for the future electric loads in the United States. Several countries have looked into this subject, especially Norway, one of the pio- neer countries. Avinor, Norway’s main airport operator, carried out a study that indicates that it will be able to accommodate charging a capacity of 2 MW at its smallest airports, up to 10 MW at larger airports, and up to 30 MW at Oslo Air- port given a planning horizon of 5 years. 13.2 Power Generation and Backup Overview This section of the report discusses the need for backup power generation for the airport industry, given the possibility of electric aircraft emerging as a technology option. The rationale for emergency backup power and a high-level evaluation of three backup power technologies— diesel, natural gas, and hydrogen—were conducted as part of this report. Not all air service can be replaced by electrically powered aircraft, because batteries are heavy and significantly less energy-dense compared with conventional aviation fuels, and electric

Power Generation and Management 117   aircraft may have different flight characteristics; however, in certain applications (e.g., short-haul and cargo service), electric power may be more efficient than jet engines that use fossil fuel. Implementation of some electrically powered aircraft is considered for this report. Documenting the risks associated with a part-electric fleet will enable certain informed decisions to be made on vital infrastructure and holistic planning for new and emergent technologies. Rationale for Grid Resiliency Utility power outages that effect an airport for just a few hours can cause thousands of flight delays and cost millions of dollars. Airports have already invested billions of dollars in both redundant sources of utility power and backup power systems that are expected to perform in rare, but impactful outage situations. Table 21 highlights the impact of power outages at various U.S. airports over the past few years. Table 21. Recent airport power outages. Date Airport Name 3-Letter FAA Code Country Duration Operational Impacts 02/21/2021 Dallas-Fort Worth Intl. DFW USA Several hours A severe winter storm hit North Texas, causing a power grid failure. Approximately 4.4 million Texans lost power for several days, as well as DFW for a few hours. DFW said it was experiencing delays and cancellations until the next day. 8/2/2019 John Wayne SNA USA About 12 hours An issue in an electrical transformer in Irvine, CA, caused an overnight power outage causing the cancellation of all flights until the next morning. 9/8/2018 Orlando Intl. MCO USA About 12 hours Some flights were delayed because the jet bridges temporarily lost power after a local outage. The airport used its backup generators to restore power and maintain operations until power was restored. 8/15/2018 Washington– Ronald Reagan Natl. DCA USA 1 hour Minor impact on flight operations but difficulties for passengers to recover their bags and move around in the terminal because it was plunged into darkness. 3/6/2018 Hamburg HAM Germany Several hours Airport suspended flight operations due to a power outage. 12/17/2017 Hartsfield- Jackson Atlanta Intl. ATL USA 11 hours A fire in a substation of the energy provider resulted in a power outage, causing about 1,200 flight cancellations and an estimated loss of up to $50 million for Delta Air Lines. 8/18/2016 Barranquilla –Ernesto Cortissoz Intl. BAQ Colombia Unknown One flight in short final approach made a go around because the runway lighting stopped due to a power outage. These lights are supported by an emergency generator, but it took about 10 seconds for the system to start. 3/27/2015 Amsterdam Schiphol AMS Netherlands 90 minutes Significant flight delays due to a regional power outage. (continued on next page)

118 Preparing Your Airport for Electric Aircraft and Hydrogen Technologies Date Airport Name 3-Letter FAA Code Country Duration Operational Impacts 7/30/2012 Delhi Indira Gandhi Intl. DEL India Several hours Despite a multistate outage due to a massive failure of the northern grid of the country, 95% of the airport activity was preserved. Airport used its backup system to maintain essential services. 2/8/2012 São Paulo– Guarulhos Intl. GRU Brazil 13 minutes The airport was able to run on its own generator during the whole power outage. 9/28/2011 Mexico– Benito Juarez Intl. MEX Mexico Overnight Diversions to Veracruz, Guadalajara, and Monterrey. 8/8/2011 Delhi Indira Gandhi Intl. DEL India 5 hours Unknown. 2/26/2014 São Paulo– Guarulhos Intl. GRU Brazil 20 minutes The airport went out of power after a failed electric test at a substation. 12 flights were delayed and 1 inbound flight diverted. 10/13/2013 O.R. Tambo International Airport JNB South Africa Several hours Power cables were stolen nearby the airport, creating a power outage that affected the pumps of the hydrant system. Several flights were delayed because they were unable to refuel. 3/25/2013 Pointe-à-Pitre PTP France 2 days Multiple flight cancellations. 3/3/2013 Brasília Intl. BSB Brazil 2 hours Of all the flights scheduled on that day, 55% were significantly delayed and 6% were cancelled. 12/26/2012 Rio de Janeiro– Galeão Intl. GIG Brazil 1 hour Unknown. 12/7/2012 Budapest Ferenc Liszt Intl. BUD Hungary Unknown Airport temporarily closed due to a power outage affecting the air traffic control tower. Table 21. (Continued). When transitioning to electric aircraft, it is also important to consider scenarios in the event of a sustained power outage, such as climate-related or natural disaster emergencies. Although reliability has improved in recent years, many types of natural disasters are expected to increase as the climate continues to change. Airports may have new responsibilities to provide services even during a power outage. The following section highlights the impact of natural disasters as well as the role of emergency preparedness. Natural Disasters The airport industry has experienced different disasters over past years, including numerous earthquakes, floods, wildfires, energy shortages, landslides, and severe storms. However, increased frequency and intensity of weather events will continue to adversely affect aviation, causing route changes, increased flight times, disruption to ground transport access, and loss of utility power supply. Looking specifically at the future security of utility supplies: • Heat waves can increase load requirements that can lead to equipment failure. • Rising temperatures could lead to decreasing thermal efficiencies, meaning that more fuel will be required to generate the same amount of power.

Power Generation and Management 119   • Storms can damage electric distribution facilities and electric generation facilities. • Droughts and high winds across the West, especially in California, are increasing the wildfire risk, which has led to pre-emptive Public Safety Power Shutoff events. Although some airports have already conducted climate change vulnerability assessments and resiliency studies, moving forward, it is imperative that the airport industry continue to ensure planned-response efforts in the event of a large-scale natural disaster. Financial firms and the U.S. government are now focusing more on “climate risk disclosure,” which helps asset owners understand their vulnerabilities. 13.3 Utility Power Reliability Reliability Indices Power reliability is a vital factor when considering the transition to increased electrification. Without an understanding of existing reliability, it will be difficult to properly understand the value of resiliency and the costs of mitigation. Utility companies generally monitor reliability for regulated, investor-owned utilities around a state to ensure that performance is upheld. Table 22 contains the four major reliability indices that are measured and tracked by regulators throughout the United States. Reliability metrics oscillate from year to year based on large, but infrequent power outage events. Therefore, a 10-year rolling average is generally used to show improvements over time. Reliability is the average performance as measured by the four reliability indices. For all four metrics, lower numbers indicate more reliability. For example, if a customer average interruption duration is experienced, the number represents the number of minutes of the outage, so an outage of only 10 minutes shows a more robust system than an average outage of 45 minutes. Regulations mandating strict performance requirements and technological changes have improved overall reliability over the past 20 years across most utilities. 13.4 Backup Power Options The following section outlines potential emergency backup power technologies that could provide airports with adequate supply in the event of an extended disruption or disaster. Options are discussed with a primary focus on potential feasibility. Index Measure Units System Average Interruption Duration Index Average outage duration per customer Minutes per outage (per customer) System Average Interruption Frequency Index How often a customer can expect to experience an outage Number of outages a year (average) Customer Average Interruption Duration Index Average outage duration if an outage is experienced, or average restoration time Minutes per year (per customer) Momentary Average Interruption Frequency Index The frequency of momentary interruptions Number of instantaneous outages per year (average) Source: Electric Power Research Institute. Table 22. Electric power distribution reliability indices.

120 Preparing Your Airport for Electric Aircraft and Hydrogen Technologies Roughly 95 percent of generators used today by commercial buildings and critical facili- ties are powered by either diesel or natural gas. Apart from differences in costs, an important distinction between the two fuels is that diesel is supplied by truck deliveries and stored on-site, while natural gas is supplied by pipeline. As storage is generally not an option for natural gas, any event that disrupts the natural gas supply will disrupt the operation of a natural gas-fueled generator. Natural gas generators are further constrained to locations with access to natural gas pipelines. On the other hand, diesel generators require fuel resupply to continue operating, which can prove difficult in the event of a long outage. Natural gas generators face the risk of a loss of gas pressure, while diesel generators face the risk of running out of fuel. Both risks are greatest for large, long outages. Emerging technologies could disrupt these established industries in favor of alternative fueling sources, such as hydrogen fuel-cell backup power generation and on-site battery storage. Those technologies in their current nascence are defined in the following sections. Diesel Fuel Generators Diesel generators convert fuel energy (diesel or biodiesel) into mechanical energy by using an internal combustion engine and then converting it into electric power by using an elec- tric generator. Diesel generators are the most common electricity generator used in building- integrated microgrids because of their size, initial cost, simplicity, and ease of buying the fuel. A diesel generator is composed mainly of an internal combustion engine, an electric generator, mechanical coupling, an automatic voltage regulator, a speed regulator, a support chassis, a battery for starting the motor that permits the diesel generator start-up, a fuel tank, and a com- mand panel. Diesel generators are classified as compression-ignition engines because the air that flows into the compressor is compressed to a temperature sufficiently high for autoignition. The combustion chamber then mixes the heated air with fuel and burns it. Diesel generators convert some of the chemical energy contained by the diesel fuel to mechanical energy through combustion. This mechanical energy then rotates a crank to produce electricity. Electric charges are induced in the wire by moving the latter through a magnetic field. In an electric generator application, two polarized magnets usually produce the magnetic field. A wire is wound around the crankshaft of the diesel generator that is placed between the magnets in the magnetic field. When the diesel engine rotates the crankshaft, the wires are then moved throughout the magnetic field, which can induce electric charges in the circuit. Natural Gas Generator Unlike diesel engines that only use the heat from compression and the injection of fuel to start the combustion process, natural gas engines will need an external spark to begin the process and are classified as spark-ignition engines. In a spark-ignition engine, the fuel is mixed with air and then inducted into the cylinder during the intake process. Whereas in a diesel engine, only air is admitted at this stage. In the simplest case, this spark plug is located at the top of the cylinder and directly ignites the mixture within the cylinder (Figure 54). After the piston compresses the fuel-air mixture, the spark ignites it, causing combustion. The expansion of the combustion gases pushes the piston during the power stroke. Stationary Battery Storage Stationary batteries are not an alternative energy source but are merely a mechanism to store electrical energy. They can store power when loads are low and power is cheap, such as

Power Generation and Management 121   nighttime, and release that energy when power is expensive. Unlike generators, batteries have a limited time duration and get more expensive the longer they are required. Batteries can be integrated with a solar photovoltaic system and used as a source of emergency backup power. Batteries also play a key buffering role in a microgrid to help stabilize the loads seen by the primary generator. Hydrogen Fuel-Cell Generator There is increasing interest and research into using hydrogen for power generation to achieve a completely carbon-free energy ecosystem. Hydrogen is a clean-burning fuel that does not produce any carbon emissions because it does not include any carbon molecules. In a complete and balanced reaction, hydrogen would mix with oxygen in the air to produce only water and thus would not emit hazardous air pollutants or GHG. When used in a generator, hydrogen produces power by using fuel-cell technology, which is a chemical reaction and does not contain any combustion. A fuel cell is constructed much like a typical battery with an anode, a cathode, and an electrolyte membrane. A fuel cell works by passing hydrogen through the anode (negative charge) of a fuel cell and oxygen through the cathode (positive charge). At the anode side, the hydrogen molecules have the electron separated, leaving the hydrogen molecule with a positive charge. The positively charged hydrogen ion passes through the electrolyte membrane, while the electrons are forced through an electrical circuit, generating an electric current and excess heat. At the cathode, the hydrogen ions, electrons, and oxygen combine to produce water (Figure 55). Fuel cells are more efficient than combustion technology. Note that most fuel cells in use today use natural gas instead of hydrogen in the fuel cell. The process is the same, but the additional carbon molecules also end up producing CO2 as a Source: Martinez et al. (2017). Figure 54. Spark-ignition engine.

122 Preparing Your Airport for Electric Aircraft and Hydrogen Technologies by-product. However, unlike a natural gas combustion generator, a natural gas fuel-cell gen- erator avoids the production of NOx and particulate matter air pollutants. The major fuel-cell manufacturers are moving toward offering hydrogen, and the following section describes the options for a full hydrogen fuel-cell system. There are some drawbacks to fuel-cell generators. The immediate concerns are the fuel source and the space required to store the fuel and fuel cells. There are four general choices for how hydrogen can be sourced: • Hydrogen gas delivery via a high-pressure tube trailer or mobile refueler. • Liquified hydrogen delivery via a tanker. • Pipeline delivery of hydrogen gas. • On-site production via steam methane reforming (SMR) or electrolysis. Access to inexpensive hydrogen fuel remains a significant challenge, although many compa- nies are trying to crack this challenge across the globe. Therefore, long-term costs for hydrogen sourcing should be considered carefully. In addition, contingency and redundancy should be considered for all technologies in case of equipment failure. Despite the source, all hydrogen (whether gaseous or cryogenically liquified), must have ade- quate and safe on-site storage. Hydrogen has a lower energy content per volume compared to compressed natural gas, requiring larger storage containers to deliver the same energy. Figure 56 depicts the layout example for fuel cells that can give 3-MW power for 48 hours by using 10,000 kilograms of liquid hydrogen. An additional concern that must be considered when using hydrogen fuel is the overall safety of the facility. Hydrogen flame has high heat and low luminosity and therefore is hard to see. A flame detection system specifically configured for hydrogen flames must be installed on the maintenance facility. Adjustments to the maintenance facility’s safety code and safety zones might also be needed in the case of a hydrogen leak, because hydrogen is more flammable and more prone to seepage compared to natural gas. Source: Sciencescene. Figure 55. Electricity generation in fuel cell.

Power Generation and Management 123   Microgrids and Other Options Microgrids are an emerging solution set that may help airports save on operating costs while still providing the backup power discussed in this report. Microgrids consist of on-site power generation sources that can run during blue-sky operations, but also run in full “island mode” during power outages (i.e., serving as the sole source of power for the local user). They often feature more than one type of power generation source, with one of the most common configu- rations as solar, battery, and a natural gas generator. This provides some flexibility in operations. Usually. the natural gas generator is clean enough to run regularly. This combination of assets can have a good return on investment, and some companies specialize in financing and operating these assets to improve returns. When considering solar power, reflection from the solar photovoltaic arrays is a big con- cern for airport stakeholders. Solar installations must comply with FAA glare policy and standards. Traditional backup power options are not able to be used for revenue or energy bill manage- ment. However, cleaner sources of power could be run to reduce costs or provide revenue. For example, due to their clean nature, fuel cells (both hydrogen and natural gas) can be run 24/7 and may produce a strong payback. Natural gas generators could be built that can help airports meet fast-ramping markets in the evening hours when power prices are highest. This could be a reliable source of revenue in certain markets, especially California currently. Battery energy storage systems can participate in wholesale markets and earning revenue from the operator of the transmission system. One additional benefit from batteries could be reduced interconnection costs from the utility company. Costs Among the considerations for determining the best-fit backup power strategy to support operations are lifecycle costs. This analysis focuses on the following primary costs associated with each backup power strategy to support in evaluating the cost-benefit of each option: (1) power unit costs, (2) fuel storage costs, (3) installation costs, (4) maintenance costs, and (5) energy costs. Table 23 summarizes the anticipated costs for each backup power option. Battery energy storage system costs are not calculated here because they operate in a fundamentally different way (no fuel input). In addition, battery configurations can vary quite widely and do not lend themselves to a cost per kilowatt calculation. Hydrogen Fuel Cells Hydrogen Storage Power Conditioning Radiators Source: Ballard Figure 56. Hydrogen generator layout example.

124 Preparing Your Airport for Electric Aircraft and Hydrogen Technologies Capital Costs Included in the considerations for determining the capital cost of each backup power strategy are the costs associated with procuring the unit itself, fuel storage costs, and installation costs. In this analysis, each item cost is broken down by cost per kilowatt to provide a standard metric of evaluation. Costs used in this analysis were sourced from several references, including direct manufacturer quotes, past purchase agreements, and scholarly reports. As the most mature technology option, at $580 per kilowatt, the diesel component costs are lower than the natural gas and hydrogen fuel cell. This cost assumes the diesel generator includes any additional equipment required to meet the EPA’s most stringent air quality standards, classified as Tier 4. The installation costs associated with diesel generators are also the lowest at approximately $150 per kilowatt. Component costs and installation costs for natural gas generators are comparable to diesel at $725 and $160 per kilowatt, respectively. The most expensive option (albeit cleanest), with the highest component and installation costs as well as an addi- tional consideration for fuel storage, is the hydrogen fuel-cell option, requiring an investment of $1,500 per kilowatt for the components and an additional $337 per kilowatt for installation and on-site fuel storage. The on-site hydrogen fuel storage costs assume a direct procurement of the liquid hydrogen tank; alternatively, airports may elect to lease out, which would also alleviate responsibility to maintain the equipment. The capital costs for natural gas exclude the cost of upgrading pipeline infrastructure at each site, which could be substantial and would need to be discussed with the utility. Operating Costs Costs associated with operating backup power units include fuel costs for a full day of service and ongoing maintenance costs. Fuel costs (Table 24) were estimated per kilowatt-hour by multiplying current regional fuel costs by the fuel consumption per hour of the associated technology. A 2,000-kW diesel generator operating at full load has an approximate fuel con- sumption of 141 gallons per hour. At the current regional price of diesel ($3.40 as reported by the U.S. Energy Administration), the anticipated diesel fuel cost is $0.24 kWh. A typical commercial gas rate is approximately $1.17 per term, resulting in an estimated cost of $0.12 kWh. The cost of delivered hydrogen fuel can vary depending on supplier location and local supply; however, current rates average around $9 per kilogram, resulting in an estimated cost of $0.20 kWh. Beyond the cost of fuel, the ongoing operating costs for maintaining backup power include periodic tests and repairs to the unit. If the unit primarily serves emergency situations with Fuel Type Diesel Natural Gas Hydrogen Generator $580 $725 $1,500 On-Site Fuel Storage $2 $4 Installation $150 $160 $333 Table 23. Estimated capital costs per kilowatt of power. Fuel Type Fuel Cost Fuel Cost Diesel $3.40/gallon $0.24 kWh Natural Gas $1.17/term $0.12 kWh Hydrogen $9.00/kilogram $0.20 kWh Table 24. Estimated fuel costs.

Power Generation and Management 125   low operational hours, it can be assumed that the majority of the maintenance performed will be scheduled maintenance and testing. The maintenance costs (Table 25) used in this analysis were sourced from the National Renewable Energy Laboratory and are applied equally to all backup power options. The operating costs included in this analysis do not explicitly account for permitting. Emissions Emergency and non-emergency generators using common combustion sources can have a significant impact on air quality and public health. If located in a metropolitan or urban area, generators increase the risk of exposing communities to dangerous air pollutants and GHGs. Particulate matter, SOx, and NOx are the major air pollutants that can cause serious health risks. Particulate matter is a complex mixture of microscopic particles and liquid droplets that get into the air. Once inhaled, these particles can affect the heart and lungs and cause serious health effects. SOx and NOx contribute to acid rain, and if inhaled, can harm the heart, irritate airways, and aggravate respiratory diseases. Particulate matter and NOx are the leading causes of reduced visibility (haze) in parts of the United States. GHGs retain heat in the atmosphere, thus increasing global temperature, altering the climate, and changing weather patterns at the global and regional levels. The main GHGs are water vapor, CO2, methane, ozone, nitrous oxide (N2O), and chlorofluorocarbons. Emissions levels vary dramatically by generator configuration and fuel type. Figure 57 illus- trates the different levels of significant air pollutant emissions released on-site based on a natural gas fuel cell, natural gas generator, and diesel generator. The emission calculations do not account for the extraction of natural gas and diesel. Based on the figure, fuel-cell-powered Item Diesel Natural Gas Hydrogen 1-Year Maintenance Costs (Per MW) $35,000 $35,000 $36,750 Table 25. Estimated yearly maintenance costs. Note: The daily emission calculation was assumed for a 150 kW-rated generator and 24-hour operation. Source: Minnesota Pollution Control Agency. Figure 57. Air pollutants and GHG daily emission based on generator fuel type.

126 Preparing Your Airport for Electric Aircraft and Hydrogen Technologies generators emit the least pollutants in total. In contrast, the operation of diesel generators has the highest daily total emission for GHGs, SOx, and particulate matter, while natural gas gen- erators emit the most NOx daily. While current diesel generators pollute significantly less than older models, they still present potential health risks. To anticipate these risks, the EPA implements a tier system for diesel generators based on the engine’s power and year. Based on this regulation, all new diesel generators must comply with the strictest standard of allowed emissions (Tier 4). For backup generators that are used only during grid outages, Tier 3- and Tier 2-compliant engines are permitted. The engine particulate matter emission rate will also affect the allowed operating hours for reliability-related activities, such as hours used for testing and maintenance. Per Airborne Toxic Control Measures (ATCM) standard, diesel engines with less than 0.15 grams per brake horsepower-hour (g/bhp-hour) particulate matter emission rate can operate for a maximum of 50 hours for reliability-related activities. Meanwhile, engines with less than 0.01 g/bhp-hour particulate matter emission rate can operate for a maximum of 100 hours for reliability-related activities. Emissions from natural gas engines are less than those from Tier 2 diesel generators and mostly on par with those of the Tier 4 diesel system. Based on EPA Stationary Combustion Emission Factors, natural gas engines emit approximately 28 percent less CO2, 67 percent less methane, and 83 percent less nitrous oxide compared to diesel-fueled engines. Because natural gas engines emit significantly fewer emissions than comparable diesel engines, they can meet air quality requirements easier, which results in a more straightforward permitting process. Natural gas and liquified petroleum gas generators do not have an ATCM or trigger Health Risk Assess- ment requirements. However, some jurisdictions (e.g., those within California) are implementing or evaluating natural gas bans. It is possible that some of the current natural gas supply could be replaced with renewable natural gas. However, there is not currently a large supply of renewable natural gas, and it is more expensive compared to traditional natural gas. Due to the nascency of fuel-cell-powered engines, no significant regulations directly pertain to hydrogen generators. However, considering that it emits even fewer pollutants than natural gas-powered generators, it likely will be easier to meet the permitting requirements related to air quality standards. Although hydrogen-powered generators produce the least emissions on-site, there are still concerns with the emissions resulting from the production of hydrogen and hydrogen leakage. Figure 58 illustrates the amount of emissions produced during the production, processing, and delivery of each fuel (well-to-tank emissions). Hydrogen generation from fossil compressed natural gas SMR produces the most carbon dioxide equivalent emissions compared to other fuel production. Hydrogen production through the electrolysis of water, on the other hand, produces only hydrogen and water as by-products. However, it requires a large amount of energy and water and is still not commonly used by commercial hydrogen suppliers due to the nascency of the technology. Solutions have been considered to achieve greener hydrogen production, such as using renewable natural gas or carbon capture and sequestration technologies for SMR, and the use of renewable energy sources for electrolysis. The numbers show, using landfill biomethane SMR can reduce GHG emissions. Moreover, using zero-carbon intensity electricity sources, such as solar, wind, or wave panels, to produce hydrogen through electrolysis will reduce emissions even further.

Power Generation and Management 127   Sources: NREL. (2015). Natural gas for cars. https://www.nrel.gov/docs/fy16osti/64267.pdf and Lajunen, A. & Lipman, T. (2016). Lifecycle cost assessment and carbon dioxide emissions of diesel, natural gas, hybrid electric, fuel cell hybrid and electric transit buses. Energy. 106: 329-342. https://doi.org/10.1016/j.energy.2016.03.075. Figure 58. Maximum potential well-to-tank emission for different types of fuel. Note: EV stands for electric vehicles Source: Lajunen and Lipman, 2016. Figure 59. CO2 emissions for vehicles with different fuel types. Even though the hydrogen generation through SMR produces more emissions compared to the production of other fuels, the operation of the fuel-cell engine itself will generate zero emissions. Hydrogen is a clean-burning fuel that does not include any carbon in its balanced combustion reaction and only produces water as a by-product. From Figure 59, it can be con- cluded that fuel-cell vehicles produce the most emissions from well-to-tank hydrogen produc- tion, but ends up with a lower total emission compared to diesel, compressed natural gas, or diesel-compressed natural gas hybrid vehicles. Generators are assumed to have comparable emission proportions with the internal combustion engines used in vehicles.

128 Preparing Your Airport for Electric Aircraft and Hydrogen Technologies Research also shows that significant hydrogen leakage could have negative effects on the atmosphere, such as increasing the lifetime of methane, increasing climate effects, and causing some depletion of the ozone layer. The research found that overall air quality in the lower atmosphere will still improve if hydrogen is introduced to the future mix of energy sources due to the reduction of fossil fuel use. However, hydrogen could also potentially act as a GHG itself under high levels of leakage. Therefore, safety measures to prevent leakage must be put in place and are essential to achieve a green hydrogen use. Another sustainable option for backup power is using battery energy storage systems. Much like fuel-cell generators, battery energy storage systems only generate emissions during elec- tricity production. Therefore, the level of emissions will vary based on the source of electricity. 13.5 Future Planning As electric aircraft and “electrifying everything” become more common, airports will need to continue to invest in electric reliability, redundancy, and backup power. Comparing the various fuel sources, costs, and availability (in 2020 dollars), diesel-fueled power generation has the fewest barriers to entry from a capital and operating costs perspective. However, diesel has significant negative externalities. It has the highest emissions due to fossil fuel combustion and is already the target of increased government regulation and cannot be run during blue-sky events to control energy costs. Natural gas generators are seen as more reliable than diesel generators, although these con- clusions are based on estimates from small data sets and significant assumptions. Thus, natural gas provides the largest reliability premium compared to diesel for regions that face high risks of long outages. Natural gas is a viable solution in the medium term when located adjacent to a pipeline and has significantly lower emissions than diesel. Hydrogen fuel-cell backup power generation is currently significantly more expensive than established technologies. However, informed decisions based on airport strategic goals will support the overall transition to zero-emission operations. It is therefore recommended to continue researching technological possibilities in terms of backup power generation. For example, fuel cells can run on natural gas today easily and then can be converted to hydrogen when it makes sense to do so. Due to the nascence of emergent technologies, such as hydrogen fuel-cell technology, it is suggested to observe industry trends, disruptions, and advancements that appear on the horizon over the next decade. Vested interests, existing infrastructure, and political support continue to enable fossil fuel technologies’ costs to remain artificially low. However, what is feasible in the years ahead will be drastically different than the solutions presented in this 2020 study. Specifically, in the realm of zero-emission operations, a “tipping point” is forecast to occur in the coming 5 to 7 years, when technological advances in terms of batteries and alterna- tive and renewable fuel sources will be financially competitive in the marketplace. Systemic disruption allows for economies of scale to emerge for these new systems and technological opportunity to emerge.