By Bjorn Fehrm
January 10, 2025, ©. Leeham News: We do a Corner series about the state of developments to replace or improve hydrocarbon propulsion concepts for Air Transport. We try to understand why the development has been slow.
We listed the different projects in the second Corner of the series that have come as fast as flying a functional model or prototype. In Part 3, we went through some of the causes of the slow growth. It was a mix of inexperienced startup managments, all wanting to be the new Elon Musk but lacking elementary knowledge in the aeronautical field, to what is the real hard part of an alternative propulsion concept.
Many startups developed new electric motors for eAirplane or eVTOL use, a relatively straightforward development when the real hard part is the batteries. We described how batteries differ significantly from fuel as an energy source in Part 3.
Now, we add a market aspect that is poorly understood by most players.
Figure 1. The Pipistrel Velis Electro trainer. Source: Pipistrel.
Aeronautical battery market
In Part 3, we described how batteries are a very troublesome energy source, as these weigh a lot once they are at the system level, wear if used to more than 60%-70% of capacity, and don’t like fast charging or discharging. Their cost is also way higher than all players have assumed. Here’s why.
A very important aspect that is poorly understood by the players is the difference in market dynamics of battery markets that consume large quantities, like the car market, and the small quantities of the aeronautical market of today and tomorrow.
The batteries in our handheld devices, such as phones, computers, tools, and electric vehicles, are made up of cells that are serial and parallel connected to get the needed Voltage and Current capacity. A laptop or tool battery could have four to six cells connected, while an electric car battery has up to 10,000 cells connected to get the instantaneous and long-term power needed.
A challenging production
These cells require a very sophisticated production process as the electric capacity comes from electrodes living very close to each other, separated by a thin electrolyte separator. Any fault in the separator where the electrodes touch each other causes the cell to start a thermal runaway.
Figure 1. Cross section of a lithium-ion cylindrical cell[. Source: batteryuniversity.com
The battery cell industry spends vast R&D sums on developing new, better cell chemistries that increase energy capacity, charge and discharge currents, and cell longevity (the number of charges/discharges before the cell loses capacity).
In the 10 years of debate since 2015 about battery-electric aircraft or hybrids, optimists have constantly cried out that new chemistries have been developed that now increase the capacity by X%.
What these persons ignore is the very long and costly process of taking a chemistry from the lab to reliable and economical production at scale. It can take up to five years.
For a battery player to do this, it must see a sizeable market for its new cells. There is a lot about the battery cell market that the eAircraft or eVTOL startups need to understand, or there can be major hiccups late in their programs.
A minuscule market
Too often, the marketing materials and even investor prospects from these startups take data for battery capacity and cost from the e-car market and project it on the aeronautical case. This is making a multi-dimensional fault:
- As we have described several times, aeronautical cells need higher C-rates than car cells. For aircraft cells, the double, and for eVTOLs, we talk about four to five times the C-rate. It requires cells that have a different design from the car cells.
- These cells are, therefore, not part of the gigantic production volumes and, thus, low costs of car cells. The annual production of cells for the car industry was 2024 around 800,000,000 kWh (you measure cell production in capacity as there are different form factors where the cells have different capacities).
- The annual production of cells for the aeronautical industry during 2024 can be estimated as less than 1,000 kWh or less than 0.0001% of the car industry.
The problem is that this difference in production volumes will not change anytime soon. The industry with the highest ambitions for yearly production of battery electric aircraft is the eVTOL industry.
Joby described in its Reinvent investor presentation 2021 that it would produce 350 eVTOLs per year during 2025. It now expects to reach a production volume of one eVTOL per month by the end of 2025. With a 100kWh battery system per eVTOL, we will need 1,200kWh for Joby during 2026 if the rate is realized.
On the aircraft side, we have serial production of the Pipistrel Velis with a 25kWh battery system. The production rate is around 25 aircraft per year, which equals 625kWh needed annually. The next aircraft with a yearly need of around 1,000kWh will be the Beta Aircraft CX300, presumably for 2026.
So we talk about a market of 0.0001% of the car industry, with cells with a different build-up and, therefore, with a different production. There is no way these cells’ prices can be compared with the car industry’s prices.
The reality is even harsher than the different costs for the cells. With minuscule volumes continuously moved to the right, the aero industry faces disinterest and, thus, disinvestment from the cell industry as its internal business plans are continually adjusted to the right and down.
For an eAircraft or eVTOL player, it’s imperative to plan their battery side so the venture is immune from battery cell providers who decide to stop the project with their special high-capacity cell. Otherwise, the project’s battery modules must be redesigned, affecting the battery system and, in turn, the module certification.
When there is no longer a supply of cells for the aircraft’s battery modules, a project’s final years of development or the start of production can become a nightmare for the startup or its customers. Redesigning and re-certifying the battery modules can be a major disruptor for projects using that extra-capacity, special cell.
Prudent players, therefore, opt for less capacity cells with a secured alternative market and thus will be available when the eAircraft or eVTOL is in production and later when customers need battery module replacements during operation use.
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