New Compressor Makes Fuel Cell Aircraft Viable

Green aviation has been a focus of the aircraft industry for the past several years, but taking the carbon out of flying is easier said than done. Batteries—the popular choice for cars—are heavy and not terribly energy dense, while hydrogen fuel cells have been plagued with complications.

An announcement from Anglo-American startup ZeroAvia may tip the scales toward hydrogen: The company said it has developed the world’s first high performance compressor for hydrogen fuel cell aviation powertrains. The technology would enable a bank of fuel cells to operate with a single compressor rather than many, saving weight.

A fuel cell uses hydrogen to produce electricity by separating the proton and electron of a hydrogen atom on one side of a membrane and recombining them on the other. While the protons pass through the membrane, the electrons run through an external circuit to power devices. A catalyst on the cathode side combines protons and electrons with oxygen atoms to produce water and heat.

“All hydrogen fuel cells need a compressor of some kind to increase the pressure of the air going into the fuel cell and help with the electric chemical reaction,” said Rudolf Coertze, head of research and development at ZeroAvia. “The higher-pressure air enhances the performance of the fuel cells themselves.”

To generate enough electricity to operate an aircraft, the ZeroAvia system stacks several fuel cells together. The fuel cells operate in unison to increase the electrical power generated. A silicon carbide inverter converts DC power generated by the fuel cell to AC power when required.

ZeroAvia designed its hydrogen fuel cell system with a single compressor to provide oxygen to all the stacks. Traditional fuel cell systems have separate compressors for each stack—powered independent from the propulsion motor—requiring additional motors, inverters, and power electronics. By combining all the fuel cell stacks to one compressor and running this compressor from the main propulsion motor, the system architecture is optimized and reduces both weight and complexity.

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To further reduce weight, ZeroAvia does not rely on high voltage batteries, similar to those in an electric car. However, onboard electronics require a low voltage battery to provide power for redundancy and safety.

The system stores hydrogen in pressurized tanks in the plane’s cargo pod and wings. The ZA600 fuel cell, expected to deploy in 2025, can produce up to 750 kW of continuous power over 300 nautical miles, enough to power turboprop planes such as the Cessna Grand Caravan. The ZA2000 fuel cell can produce up to 5 MW of continuous power over 1,000 nautical miles, enough for an 80-passenger plane.

The company sees its fuel cells as a retrofit to replace conventional aircraft propulsion systems.

“For a pilot licensed to operate a Cessna Caravan for example, the hydrogen fuel cell retrofitted powertrain will have some differences with the man-machine interface in the cockpit, instrumentation, and how the plane will handle, when compared to a traditional turbine engine,” Coertze said.

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The fuel cell electric motor is quieter than traditional turbines, but propeller noise, which is usually heard over the engine noise, would still be present.

The ZeroAvia compressor was designed with aircraft certification in mind. With the ZA600 being the first hydrogen fuel cell powertrain for aircraft, ZeroAvia reviewed existing standards for turbine engines and worked with certification authorities to ensure they understood the requirements for new technology. While more work is required before large aircraft outfitted with hydrogen fuel cells can complete long haul flights, significant progress has been made in design development and proof of concept.

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The new compressor doesn’t even remotely make fuel cell aircraft viable.

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Sounds like a single point of failure. Not the best option at thirty thousand feet

Jk

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Are you claiming that all the single engine airplanes are a big mistake with their single point of failure?

Why do you make such a claim?

Just riskier. Not the best choice

Jaak,

It depends on how large the craft is and how many people are onboard.

Hydrogen is extremely expensive and has low energy density. Which means you can only fly short distances at high cost.

During the dot con era there were a lot of companies trying to overcome how to store H.

The costs can come down with massive investments and usage. Europe is going that route.

US is also masking massive investment in Hydrogen Hubs.

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Here is the basic problem with hydrogen (one of them): To make hydrogen, typically you start with a feedstock, usually methane, and then you need an energy input. That means hydrogen will always be more expensive than natural gas.

Or you can make it by electrolysis. But that’s very energy intensive, so again, expensive.

In this case, the airplane is electric. So you are taking hydrogen fuel and processing it again to make electricity, which is only about 60% efficient which makes the fuel costs even higher. Then of course you still have the energy density problem.

If you want an electric airplane, instead of using energy to make hydrogen, you could take the energy and store it in battery and use it directly. That brings the energy cost way down. The problem is that batteries are heavy, which is not good for airplanes. That limits the range, but fuel cell airplanes are range limited too.

Bottom line is that an electric commercial-size aircraft requires tech that hasn’t been invented yet.

There is a credible hope that in the future when there is lots of wind and solar power, you could take energy that would normally be curtailed (that is, wasted) and use it to make hydrogen. If the fuel is free, the costs come down a lot. But we are not there yet.

It is not that far in the future to have green, white and gold hydrogen. Already Hydrogen Hubs are in the plans in US, Germany and other countries. Nuclear power plants can also be used for hydrogen production when there is excess generation at night. New more efficient electrolizers are being developed. Cheap hydrogen is the future.

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That light bulb in the room you are in right now is only using 8% of the energy needed to get the electricity to the bulb.

Modern gasoline engines have a maximum thermal efficiency of more than 50% , but most road legal cars are only about 20% to 40% when used to power a car.

We are going towards renewables. Making hydrogen by day with solar or at times with wind is a good way to have power at night or on a calm day.

Fuel cells in a sense are batteries.

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Yes, I’m sure it will be too cheap to meter.

The use of nuclear power for hydrogen might be a little different than expected. The old frame of reference need not apply.

Smaller reactors for larger industrial plants would do the trick.

By its nature, nuclear works better on a big scale. SMRs have great branding, but they are not particularly small or particularly modular, and we’re finding out on a per MW basis they might not be any cheaper than conventional large nuclear. The recently canceled NuScale SMR was projecting subscriber power at $89/MWh, which includes a $30/MWh subsidy, plus generous grants from DOE funding the construction. Costs probably need to be a third of that.

The DOD is working on microreactors (1 MW) but those are still years in the future.

As an aside, one advantage that large scale nuclear has is that most nuclear sites in the US were designed to accommodate multiple reactors, so there is an abundance of existing locations that don’t have to go through the siting process.

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Yes it is too cheap to meter. Nuclear plants already are doing it:

Particularly in hours of (predictable) high renewable power supply (lots of wind and sun), power producers offer their electricity for negative prices on the exchange . This is often done by marketers of renewable power but also by conventional power stations like nuclear and lignite plants.