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3 Power outages occur due to aging infrastructure, extreme weather events, and other causes ranging from animal-related outages to physical and cyberattack.3,4 The grid is also susceptible to disruption from human activities, including accidents, errors in operations, and political sabotage. The consequences of power losses are more significant in the computer age because the briefest interruption in electricity supply can result in loss of data and require system restarts that may damage equipment or delay activities. Many risk factors are increasing, and recent experiences have trended toward a higher frequency of disruptions. Between 2000 and 2015, the number of power outages doubled every 5 years. In 2015, reported outages increased to over 3,500 in the United States, according to the annual Blackout Tracker report.5 The impacts of these events are estimated to cost the economy over $150 billion in annual losses. Airports are not immune. Atlanta HartsfieldâJackson International Airport, the busiest air- port in the world, experienced a power supply disruption on December 17, 2017. During the 11 hours that the power was out, the Airport Authority had to cancel nearly 1,200 flights, and tens of thousands of passengers were stranded at HartsfieldâJackson or waiting at connecting airports. Burlington International Airport lost power 10 days later due to an electrical fire. More recently, Cleveland Hopkins International Airport (CLE) experienced a four-hour power outage on January 23, 2018, that caused flight delays and cancellations. Each potential flight by a narrow-body aircraft can represent over $100,000 in ticket sales, and cancellations can cause the loss of this revenue while more broadly lowering consumer confidence in reliable and on-time air travel. The purpose of this report is to provide background on the rationale for microgrids and what the Airport Microgrid Implementation Toolkit provides. Airport users can visit the toolkit directly if they are already moving forward with energy resilience actions and seek an interactive resource. The toolkit is available at https://acrpmicrogridtoolkit.xendee.com/. Microgrids for Airports Microgrids can be designed to compete economically with grid-purchased electricity by reducing utility and fuel bills and by generating new sources of revenue. Microgrids can also create broader societal benefits by contributing to grid reliability, supporting economic develop- ment, contributing to environmental goals, and enhancing public safety by protecting critical infrastructure.6 The number of microgrids is projected to increase tenfold globally to 5 gigawatts (GW) of capacity over the next decade.7 In the US, a number of government and industry sectors have implemented microgrids as a solution to achieve their power reliability objectives. Universities have achieved significant accomplishments, including a microgrid system at the University of Microgrid Overview
4 Airport Microgrid Implementation Toolkit Texas, Austin, that can generate 135 megawatts (MW) of power via a combined heat and power (CHP) system and fully provide for all energy needs. University of California at San Diego obtains over 90 percent of its energy from its microgrid, which is powered via biogas fuel cells and solar photovoltaics (PV). Princeton University maintained its power during and after Hurricane Sandy with wise planning and its on-campus microgrid. Some health care facilities, such as Tampa General Hospital, have invested in microgrids to ensure there are no disruptions to their patientsâ care. The US military has supported microgrid pilot projects on domestic installations across the country in order to meet Department of Defense energy resilience and mission assurance objectives.8 Microgrid Solutions Airports are excellent candidates for microgrids. Similar to hospitals and military operations, airports support mission-critical activities to protect lives and provide emergency relief. Besides keeping passengers and tenants physically safe in terminals, airportsâ role in the National Air- space System is to ensure that aircraft can land in both routine and contingency conditions. In the aftermath of regional disasters and extreme weather, airports provide crucial response and recovery functions. Emergency operations centers are often based at airports, and the land within the fence line is often used as a logistical staging area. Several active duty military airfields and close to 70 Air National Guard units are co-located with civilian airports across the country. To sustain these critical functions, Detroit Metro- politan Wayne County Airport (DTW) installed two microgrid systems to cover 100 percent of their electricity load. Other airports such as San Diego International Airport (SAN), Pittsburg International Airport (PIT), and Denver International Airport (DEN) are implementing micro- grids. SAN has installed a 12 kilovolt system that reduces operational energy costs. PIT will install a 22.5 MW microgridâfive gas-fired generators (20 MW) and 7,800 solar panels (2.5 MW). In Denver, at the Peña rail station, DEN partnered with the local utility provider and Panasonic to deploy a $10 million system that includes solar generation and battery storage. Other airports have redundant power for emergency situations; however, they are not set up to realize the full range of energy resilience benefits. Airports could be positioned for a dramatic energy trans- formation via microgrids, but there are significant challenges. Stakeholder Involvement Stakeholders need confidence that an airport microgrid will deliver sufficient benefits to justify changes to the status quo. Airport employees have existing priorities and pre-established job roles, and they may legitimately view microgrid implementation as a distraction. Airlines and other businesses located on the airport also have limited resources to participate in new initiatives. Even if there is consensus among airport staff and tenants, external party participa- tion and decisions can make or break the initiative. While the FAA, as an agency, has a strong commitment to microgrids, regional representatives may need to be convinced that imple- mentation will not impact safety. Utility and grid-operator traditional business models rely on continuous facility demand for externally produced electricity. Neighboring communities also require briefings and communication about microgrids to feel confident in airport energy transformation. Microgrid Components Microgrids can be configured to accomplish a broad range of objectives using a range of system architectures at different scales. System configuration should be based on a clear under- standing of the critical loads being supported on airport property as well as interaction with the
Microgrid Overview 5 broader utility system. The toolkit provides airport project proponents with an overview of the microgrid configuration process as well as education about key technical issues, questions, and decision points. Electricity and Thermal Loads Microgrids can be deployed to serve single facilities, campuses, or entire communities. Airports need to identify the critical loads that need to be supported (i.e., the critical energy requirements) and assess the adequacy of current capabilities to meet these requirements (e.g., determine whether diesel generators are in place). Technology Integration Once the loads have been assessed, airports can develop high-level assumptions about poten- tial technology architectures. In some cases, the gap between requirements and resilience capa- bilities may require that new technologies be installed to serve vulnerable and high-priority loads. In some cases, the gap can be closed by tying together existing assets (e.g., linking existing diesel generators) and/or integrating new and existing systems (e.g., linking existing generators with new solar PV and battery storage systems). In other cases, the objective of the microgrid may be to secure the entire airport and back up both critical and non-critical loads. Controls Airports must understand the controls and communication functions that enable a microgrid to dispatch generation and storage resources both in islanded and grid-connected mode. To maintain mission-critical functions, switching from grid to non-grid power must be seamless. Controls are essential for potential transactive actions that equip airports to improve peak load performance and reduce operational costs on-site (see Figure 1). Such controls also enable Figure 1. Island electricity dispatch analysis tool: Islanded scenario from XENDEE Corporation.
6 Airport Microgrid Implementation Toolkit microgrids to participate in markets that support the functionality of the wider electricity grid. There is a wide range of hardware and software approaches to microgrid control, with new solutions entering the market at a rapid pace. Utility Interconnection Airports need to meet microgrid utility technical requirements for equipment and opera- tion. Connection of distributed electric production resources with the grid creates technical challenges for both the regional utility and the airport microgrid operator. The airport must be able to connect safely to the grid at the correct power frequency and phase, provide elec- tricity of sufficient quality to meet utility requirements, disconnect quickly from the grid when disruption occurs, and reconnect (either automatically or via operators) at the end of an event. The following interconnection challenges need to be discussed with an airport utility service provider: ⢠Frequency and voltage controlâairports need to achieve power quality to deliver electricity back to the grid. ⢠Dispatchabilityâutilities and airports need to coordinate so that the microgridâs power to the larger grid can be activated when necessary for autonomous off-grid switching. ⢠Islandingâthere are some protective devices that need to be in place to enable shedding excess load and other functions required for functioning off the grid. ⢠Generator interconnection considerationsâa range of generators have their own charac- teristics and power needs. ⢠Power relay requirementsâmicrosystems require protective relays to prevent damage to the system from changing loads. Clean Energy Sources Wind turbines, fuel cells, PV cells, solar thermal arrays, geothermal energy, biomass, and heat recovery can all function within microgrids. Solar PV has been the most successfully deployed on-site renewable energy generation technology at airports primarily because it can easily be integrated into the existing airport landscape. Geothermal and biomass have been used where resources are available and cost-effective. CHP is also already part of many airport systems. Wind turbines that are small and building-integrated have limited capacity to provide reliable electricity supply and are generally not recommended for airport applications. Other generation technologies are dependent on delivery of a fuel supply, which limits their reliability. Many airports have backup diesel generators that are activated if the grid power shuts down. Fuel cells are a more efficient alternative for reliable backup power, though most units currently in use require a fuel catalyst in the form of natural gas. Future designs include hydrogen power with water as the catalyst. In the interim, more sustainable fuels such as landfill gas and liquid biofuel are increasingly available but still require off-site delivery, which may be dis- rupted in the event of a regional outage. Geothermal is an option for space heating/cooling. The technology may reduce consumption of fossil fuels for building thermal usage; however, since it relies on additional electricity to power heat pumps, geothermal heat pumps do not directly reduce grid dependence by themselves. Siting Solar has been deployed in flat, managed airfield areas that do not support aeronautical or other commercial uses, on building rooftops (see Figure 2), and on canopy structures associated
Microgrid Overview 7 with surface parking. A key siting criterion is the avoidance of adverse glare on the airport traf- fic control tower and aircraft on final runway approach. Some small-scale wind turbines up to 250 kW have been installed on airport property. The challenge with wind technologies is that they are most efficient when located on tall towers with long blades, design elements that increase the potential to impinge on navigable airspace. Other technologies, like geothermal and biomass, may present siting issues based on design and infrastructure support components. Energy Storage Energy storage is critical to balance periods between high power generation and high power use (see Figure 3). Besides the diesel fuel for engine generators, the two most common storage solutions are battery banks and ice-based thermal energy storage. Mobile storage options with vehicles may be a possibility in the future. The toolkit provides more in-depth recommenda- tions, including taking advantage of multiple revenue streams for battery deployments (i.e., âvalue stackingâ), which can allow for cost-effective battery project deployment. Figure 2. Rooftop solar installation at San Diego International Airport (Courtesy of Stephen Barrett). Figure 3. Battery energy storage system data model from XENDEE.
