A Californian company says its new “turbo air-cooled” fuel cell design can deliver three times the power and four times the lifespan of a regular cell, opening the door for high-speed, long-range, hydrogen-powered electric VTOL aircraft. Hypoint, a start-up formed in 2018 and run by three Sergeys and an Alex, have created “turbo air-cooled fuel cells” which promise huge range and power for hydrogen-powered eVTOLs.
HyPoint set out to create low-temperature proton exchange membrane (LTPEM) fuel cell systems for industrial-grade drone systems, but since moving to Silicon Valley and being accepted into the Alchemist Accelerator program, the company began looking at a bigger target.
“When we arrived in the United States we saw a huge potential market in urban air mobility,” says CEO Alex Ivanenko, PhD. “The main drivers of this market are mobility, compactness and energy density. Now, the main powertrains are built on lithium batteries, which have a fundamental technical barrier. Such batteries have a low energy density, while existing fuel cells have low specific power. The air transport market requires both high specific power and high energy density. There’s no power source that can satisfy both requirements at the same time. Not lithium, not fuel cells.”
Forecasting that suitable lithium battery technology might be as much as 15 years away, the HyPoint team began focusing its efforts on a fuel cell design specifically targeted at eVTOLs. To keep things lightweight, it would have to be an air-cooled design; liquid-cooled fuel cells, says Ivanenko, which work well in the automotive world, but the associated coolant tanks and pumps add parasitic mass that literally isn’t going to fly in the aviation world.
“Today’s available air-cooled fuel cells have limited power capacity and lifespan, and they only work in temperatures between -5 and 30 °C (23 and 86 °F),” continued Ivanenko. “So we set out to develop something faster and hardier, and came up with what they call the “turbo air-cooled fuel cell.
“We boost the power of the fuel cell stack by placing it inside an air duct, where pressurized, humidified and thermally stabilized air is circulated by fans,” he explains. “The compression of air is maintained about 3 bars inside by a compression system, and the air with reduced oxygen content is charged through a control valve, and replaced with fresh compressed air with normal oxygen content.”
This extra oxygen on the cathode side of the fuel cell stack, in conjunction with a new High Temperature Proton Exchange Membrane (HTPEM) technology HyPoint has developed, allows you to force three times as much hydrogen through the fuel cell as a traditional design, tripling its specific power output without adding any parasitic cooling mass that might weigh a VTOL aircraft down.
With the entire system taken into account, the HyPoint system delivers 2,000 watts of power per kilogram (2.2 lb) of mass. The best of the liquid-cooled fuel cells deliver between 150-800 W/kg, and other air-cooled fuel cells sit at about 800 W/kg.
The energy density of the full system comes in at around 960 Wh/kg, where lithium batteries typically sit at about a third of that figure and other air- and liquid-cooled fuel cell systems come in a little over half – all according to HyPoint’s own figures.
“The system has some other huge benefits as well”, he continues. “It accepts dirty hydrogen that’s only 99 percent pure, which is a fraction of the cost of the 99.999 percent purified hydrogen you need for an LPTEM system.” Adding, “That’s a huge decrease in a significant operational parameter for a commercial eVTOL operation.”
While it’s still in the lab at this stage, the team projects these fuel cells will last some 20,000 hours without maintenance, where LTPEM systems typically last around 5,000 hours – another very significant factor for a commercial operator.
“HyPoint has been in touch with a number of major players in the emerging eVTOL market from the US and Europe to Australia,” said Ivanenko. It is alleged two companies are ZeroAvia and Bartini.
“We’re seeing big interest from many companies,” he continues. “We believe we’ve found a solution for them. Many of these companies are asking for us to validate our technology with a prototype, because we’ve only validated it in the lab. So our development plan for 2020 is to build a 15- to 20-kW prototype, to validate the technology. Then a full scale, say 150-200-kW system in 2022.”
Ivanenko explains that moving from the present lithium-powered prototype to a hydrogen powertrain, shouldn’t require a total redesign of most eVTOL airframes, so the opportunity to achieve long-range flights with fast refueling is open to more or less any of the contenders if they’re willing to change some details of the inner aircraft design.
The question of safety is paramount. Ivanenko immediately rolls his eyes, grins and mimes shooting himself in the head when asked.
“That’s a common question from consumers,” he smiles. “And that’s OK, because I think most consumer technology will be too difficult to switch over to hydrogen technology anyway. That’s one of the reasons why we’re focused on B2B with large companies that care about efficiency. But yes, ‘it’s a hydrogen bomb! Remember the Hindenburg!’ That was in 1938, almost a hundred years ago. What people need to understand is that hydrogen, oxygen, propane and natural gas are all in the same group of dangerous flammable gases. The propane bottle you use on your BBQ has the same warning certificate, it’s in the same class as hydrogen.
“There’s no special hazard class for hydrogen. Moreover, hydrogen is the lightest gas in the universe, and it can’t be concentrated in the field to achieve the kinds of dangerous concentrations that might cause a big boom. Of course, you should follow special safety rules, but you shouldn’t be afraid of hydrogen gas. Oxygen is much more dangerous.”
Meanwhile, HyPoint’s hydrogen powertrains are compact, lightweight and very powerful. Ivanenko points out that he drives a Toyota Mirai hydrogen-powered car. “It’s been thoroughly crash-tested for safety. Any manufacturer of hydrogen powertrains understands what steps to take to get an appropriate safety certificate for a given application, and we’ll be no different.”
It is possible that lithium battery technology may make a quantum leap in energy density during the next five years, which is roughly when most eVTOL companies are projecting they’ll be ready to start commercial air taxi flights. Perhaps, the batteries of 2025 will have huge capacities, light weight, ultra-fast charging and they’ll meet all the right safety criteria. But it is also very possible they won’t, and if that’s the case, hydrogen innovators like HyPoint could well find themselves in a highly advantageous position.
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