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

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16 Preparing Your Airport for Electric Aircraft and Hydrogen Technologies Successfully implementing electrified aircraft hinges on not only the technical feasibility and production capability of the aircraft in isolation, but also on broader support infrastructure for these aircraft to be implemented at scale. Given transportation’s large energy requirements, broadly, growth in the capacity of electricity generation is needed, either on-site or across a national grid. Additional factors also include several items within airport planning related to space, ground sup- port equipment (GSE), service personnel, and technicians, and power and energy delivery capacities. These considerations must also be further developed to truly realize growth in electrified aircraft. 2.3 Integral Electric Aircraft Components Energy Storage Energy storage technologies, such as batteries, are key components of all-electric vehicles. A battery is an individual cell that converts chemical energy to electrical energy through electro- chemical reactions. When a current is sent into the battery, this chemical reaction can be reversed. A battery pack is a collection of two or more cells connected in a series or parallel configuration. The design and performance of battery packs are crucial components of electric vehicles. In these types of vehicles, battery packs are the main source of energy and contribute significantly to the overall vehicle weight. Common parameters to describe the performance of the many types of batteries are as follows: • Specific Energy (Watt-hours per kilogram or Wh/kg) is the most commonly used battery performance parameter and is used in estimating electric-vehicle endurance. It describes the amount of electrical energy stored per unit of battery mass. • Specific Power (Watts per kilogram or W/kg) is the amount of power delivered per unit mass of the battery. This parameter can be used to describe how fast a battery can take in energy and release it. These two parameters are most commonly used when comparing battery technologies. A bat- tery’s capacity decreases as the discharge time increases. A vehicle that operates at a high-power setting will quickly deplete its batteries. Likewise, a vehicle with high specific energy batteries will have low specific power characteristics. Charge capacity is another important battery parameter that affects the performance of electric aircraft. How quickly a battery is discharged will affect the total energy the battery can provide. The slower the current draw is, the more energy can be extracted from the battery. Figure 9. Propulsion equivalent energy costs for jet fuel and electricity.

What Are Electric Aircraft? 17   Additional battery considerations that affect the performance and operations of electric vehicles include the following: • Specific Power: 1 kW/kg for most applications, although some applications might require 2 to 3 kW/kg. • Cycle Life: The number of discharge charge cycles the battery device can experience before it fails to meet specified performance criteria. The number of battery cycles depends on the type of operations. • Cold Weather Performance: Lithium-ion batteries show faster degradation outside accept- able temperature ranges. Rechargeable battery technology has a relatively low energy density compared to fossil fuels (Figure 10), which limits the range and scope of operations for electric aircraft. However, energy density of batteries is increasing and has grown by 8 percent each year in recent years (Figure 11). Battery technology performance is projected to continue to grow. A 2017 NASA Battery Technologies Workshop provided the following industry projections on battery technologies: • Specific energy is expected to increase by 5 to 8 percent per year. • Implementation of innovative concepts that can improve packing and integration, such as the following: – Lightweight container structure (e.g., cellular, lattice block); – Multifunctional structures with load-carrying capability for packaging materials; – Advanced thermal management techniques (e.g., phase change materials if the cost is not a factor, high conductivity materials); – Integrated thermal management system to cool battery packs; – Polymer heat exchangers; and – Larger cells. Figure 10. Volume and mass-specific energy characteristics of different energy storage systems.

18 Preparing Your Airport for Electric Aircraft and Hydrogen Technologies • Innovation in battery health management, such as moving to a software-based battery health management system for state-of-charge and state-of-health estimation. The U.S. Department of Energy, the battery industry, academia, and National Labs have raised their performance expectations to 300 Wh/kg at pack level (approximate 400 Wh/kg at cell level) for automotive and industrial applications but have not focused on electric aircraft applications. Electric aircraft will need to verify their performance, safety, and integration to bolster battery-related research. Beyond this approximate 400 Wh/kg capability at the cell level, the aeronautics community can focus on developing batteries with 600 Wh/kg specific energy at the cell level (400 to 500 Wh/kg at pack level), which is believed to be an achievable target. Higher levels of specific energy, on the order of greater than 700 Wh/kg at the pack level, are almost impossible to achieve at the short- term horizon, assuming current technologies (Figure 12). Figure 11. Roadmap for lithium-ion battery technology. Figure 12. Battery requirements for different classes of vehicles.