One of the world’s leading experts in energy storage systems for aircraft predicts when we will see a breakthrough in battery technology and describes NASA’s pioneering work in power systems ahead of his presentation at the forthcoming Electric & Hybrid Aerospace Technology Symposium, which takes place on November 8-9 in Cologne, Germany.
What will you talk about at the Electric and Hybrid Aerospace Technology Symposium?
My presentation will review energy storage options, including batteries, fuel cells, supercapacitors and flow batteries, for electrified aircraft. It will describe what is possible with current batteries and fuel cells and how the latest batteries can influence niche markets. Energy storage requirements for several classes of aircraft will be reviewed. Projections on advances in energy storage systems will be made based on current worldwide activities. Operational and integration challenges for application of energy storage systems in electrified aircraft will be discussed. Specific research and development requirements for electrified aircraft will be highlighted.
What will future energy storage in a large aircraft look like?
For large aircraft like 737 class, the specific energy of a battery pack needs to be five times higher compared with the current state-of-the-art batteries for a viable hybrid electric aircraft.
For fuel cells, the power density has to increase by a factor of five or so for hybrid electric large aircraft with around a 900-1000-mile range. Unless there is a breakthrough, I do not foresee use of batteries or other types of energy storage systems as part of a primary propulsion system for large (737-class) aircraft with long range until 2035 or so.
However, with a two-to-three-times increase in battery specific energy, I can see the use of batteries as part of a primary hybrid electric propulsion system for large 737 class aircraft with a 300-mile range, for which there could be a potential market.
Although it will take a long time before batteries and fuel cells can be used as part of the primary propulsion system for large aircraft, they will find application in the power management system of large aircraft with more electric architecture, maintaining the stability of the power system.
Batteries and other energy storage systems will be used as part of the primary electrified propulsion system for smaller aircraft, like four-passenger urban air mobility vehicles and 10-passenger thin haul aircraft in the near term.
What will be the main technical challenges for testing and certification as more energy storage is used in aircraft?
Commercial and developmental batteries are targeted for the automotive sector. They need to be tested under aircraft operating conditions and mission cycles for electrified aircraft applications.
The key certification challenge is assuring the safety of the aircraft due to battery fire. Li-ion batteries are known to cause a fire in electric vehicles and aircraft. Battery fire is going to remain a major concern for the next generation of high specific batteries that use liquid electrolyte.
A robust battery health management system will be required for early diagnostics and prevention of fire in batteries. In case a fire is initiated in a battery, the fire must be contained to protect the aircraft.
What is NASA’s most important work concerning hybrid electric aircraft?
NASA’s most important work related to hybrid electric aircraft is the development of megawatt-scale high-power density electrical machines and associated power electronics. These will provide a two-to-three-times increase in power density compared with current state-of-the-art power systems.
We are performing demonstrations of megawatt-scale power systems under aircraft operating conditions in the NASA Electric Aircraft Testbed (NEAT). NASA engineers are also developing foundation technologies to increase power density and weight of electrical components, and developing integrated power-propulsion-thermal management modeling tools for design of electrified propulsion system.
Are we still waiting for a battery capacity breakthrough?
There will be a continuous increase in battery capability with time. While a breakthrough that will provide five times the energy density of the state-of-the-art batteries will be wonderful, the industry is not waiting for that to happen to fly hybrid electric aircraft.
There are niche markets for small planes using the current state-of-the-art batteries. While the range will be limited for an all-electric small aircraft using the latest and best batteries, there are many more options if the hybrid electric option is pursued. Both for the urban air mobility and thin-haul market, many companies are developing aircraft that use batteries. Based on an optimistic projection, it is expected that the initial commercial introduction of such vehicles might occur around 2025.
Based on research in advanced batteries, there is an optimistic projection that the specific energy of batteries will double within the next several years. With the potential doubling of the specific energy of batteries, it is expected that the market for hybrid electric and all-electric aircraft will expand, with the capability for longer range and more passengers for urban air mobility and thin haul market segments.
All of these projections are based on the assumption that the advanced batteries meet the life, safety, and operational requirements for hybrid electric aircraft.
Increasing the specific energy of batteries by three times will enable the commercial introduction of regional hybrid electric aircraft by 2030. This will require significant R&D on batteries beyond the scope of current investment by the automotive sector.
So, yes, a battery capacity breakthrough that increases the specific energy by five times will be required for introduction of hybrid electric aircraft for the 737 class and larger aircraft.
Dr Ajay Misra is one of more than 40 experts speaking at the Electric & Hybrid Aerospace Technology Symposium, the world’s leading international conference dedicated to ultra-low-emission aircraft technology and full-electric flight, which takes place on November 8-9 in Cologne, Germany.