Developers and prospective operators of eVTOL aircraft remain hostage to multiple complex challenges as they seek to launch commercial services. Battery performance is high on that list, according to power technology specialist About:Energy, which is seeking to guide the ambitious advanced air mobility sector through a complex path to making the best of what is available and what yet might become available.
In the early years of eVTOL development, the most audible concern around batteries related to their safety. “The bigger challenge now is their commercial viability,” Yashraj Tripathy, About:Energy’s head of product, told AIN. “At one point there was the idea that ‘one battery accident could take down the whole industry,’ but there is now clearer understanding with the regulators on harmonizing standards, albeit there will also be a further push for safer batteries.”
The bigger wake-up call for the industry has been around the real limits of battery performance not just in terms of energy density but also recharge performance and useful life. According to Tripathy, big expectations that companies had in the heady days around 2018 and 2019 have had to be tempered by the realization that current batteries will probably not be able to sustain a range of 100 miles or so throughout their life. “They should probably expect more like 10 to 20 miles,” he said, suggesting that those seeking greater range will, for now, need to turn their attention to hybrid-electric propulsion.
“To a large extent, there is now an understanding that 20 to 30% of energy reserves are untouchable because a lot of power is needed to land the aircraft and that has to be maintained throughout the life of batteries,” Tripathy explained. “So, there will need to be multiple batteries available through life to run multiple electric motors.”
That poses challenges for manufacturers and operators over how to manage battery usage in a way that supports commercially viable services, such as high-density air taxi flights. “Ideally, batteries would all be around the same age and gradually run down together,” Tripathy said. “This is really an electric propulsion challenge, rather than just a battery challenge. For eVTOL aircraft, the batteries will probably keep running up to around 85 to 90% of the end of their life. In fact, the end of life isn’t just on the energy side, but also in terms of how much peak power performance you are losing at that point.”
This is where About:Energy is trying to help the industry make sense of complex considerations around batteries. The UK-based company conducts advanced prototyping to reduce the time and cost of developing batteries and can also accurately model battery performance to assess factors such as degradation during their life cycle.
How to Get the Most from Battery Life
When manufacturers are seeking proposals for the purchase of batteries, useful life and timelines for changing them out are burning questions. “Depending on how you manage the batteries, the answers are different,” Tripathy explained. “The aircraft use case is a big part of the answer. For instance, it can be better to recharge batteries at a slower rate, but that impacts the number of missions you can do each day.”
These are key points for which About:Energy can provide illuminating modeling that can analyze the performance of each cell and the battery’s internal electrochemistry, which can govern the sustainable level of operations. Its team uses simulation and data modeling to avoid the need to repetitively test and rebuild batteries.
According to Tripathy, operators could be looking at replacing batteries every three to 12 months. And he said these could be five to 10 times more expensive than automotive batteries and even those now being used in motorsports. In his view, this reality makes the case for the industry to operate some kind of power-by-the-hour or battery-as-a-service model so that operators aren’t shouldering this burden individually.
At the end of their useful life in AAM service, batteries will still be relatively new and so could well have a second life in some other application. Their auxiliary components could even have three or four new owners over time.
The industry won’t be stuck with the current level of battery technology forever, with breakthroughs being claimed all the time by companies such as MagniX. The question is what is coming next, when will it be available, and what will be the right time and circumstances to upgrade.
“It is difficult to know when to upgrade batteries, and that will largely depend on how long the certification process for these will be,” concluded Tripathy. “We might be looking at a five- to 10-year horizon, depending on whether it involves a chemistry shift or a form factor shift. Companies are using cylindrical cells for now, but the new chemistries are tending to be in pouches.”
This presents yet more seemingly intractable dilemmas that About:Energy is seeking to help the high-expectations AAM pioneers wrestle with.