Meet the SuperStack - The Fuel Cell Power Generation System for ZeroAvia’s 600kW Powertrains - ZeroAvia

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    July 27, 2023

    Meet the SuperStack – The Fuel Cell Power Generation System for ZeroAvia’s 600kW Powertrains

    by Rudolf Coertze, CTO Hydrogen

    In this blog post, we’re going to walk you through how our power generation system will work for powering the first commercial, zero-emission aircraft in flight. 


    In our ISO Clean Lab at Cotswold Airport in the UK we are building fuel cell systems for ZA600


    The ZA600 is a 500 to 750 kW continuous-class hydrogen-electric powertrain and the first commercial product from ZeroAvia. It will deliver zero-emission flight for thousands of 9-19 seat regional turboprops, including the Cessna Grand Caravan, Twin Otter and Dornier 228 popular airframes, which will receive supplemental type certification for retrofit and linefit of the popular airframe. 


    The first ZA600 equipped commuter platform will be ready for service in 2025, fueled by gaseous hydrogen tanks and capable of carrying passengers up to 300 NM plus reserves. You may have seen our own breakthrough flight of our Dornier 228 testbed and other recent demonstrations – these demonstrations were all using hydrogen-electric powertrains in this power class. To go beyond 20 seat aircraft, we need more powerful engines, and we will cover these technologies in a future blog post.


    First let’s walk through how the system works overall as part of the overall powertrain architecture.  Our system is made up of four distinct parts – a Hydrogen Management, Power Generation, Power Distribution, and electrical propulsion. In this post, we’re most interested in the power generation system – how do we take the compressed hydrogen stored in tanks and use fuel cell systems to create as much electrical power as possible to power the electric propulsion systems? 


    Let’s begin with how a fuel cell works in principle. Fuel cells generate electricity through an electro-chemical reaction using hydrogen and oxygen (with water and heat as by-products) create water Hydrogen fuel from our onboard storage is fed into the anode, compressed air (to supply oxygen) is fed into the cathode. 


    A catalyst separates hydrogen atoms into protons and electrons, which take different paths to the cathode. Protons pass through the membrane, while electrons are being conducted in an external circuit to create the required flow of electricity. The byproducts of this process are water vapor and heat and the average operating temperature is around 80 degrees celsius. 


    To maintain the functioning of fuel cells, we need a “balance of plant” 

    For these Low Temperature PEM fuel cells, it consists of:

    • Compressors to deliver the quantities of oxygen needed to the cathode
    • Humidifiers to control the humidity and ensure the fuel cells do not dry out or flood
    • Liquid cooling/heat exchangers to prevent overheating 
    • Pumps and sensors

    The low operating temperature of fuel cells creates one of its chief advantages – it means low wear and tear of the systems and thus enhanced durability and lower maintenance costs. For larger systems flying at higher altitude, lower temperatures will also mean we can distil and manage water vapour exhaust to prevent contrail impacts. 


    At the same time, these lower operating temperatures also create a significant challenge. As the total amount of heat rejected increases with the amount of power produced, rejecting the heat becomes challenging, because the temperature difference between the operating fuel cell and ambient temperatures is smaller than in typical combustion processes. Heat exchangers are critical, and along with the compressors and humidifiers, add weight to the system and thus affect the power density of the system. 


    In a typical configuration for automotive, the system level density is around 0.7 kW/kg – less of a concern, of course, when the vehicle does not need to take off!


    Our challenge as pioneering fuel cell engineers in aviation, is to get the system level density to around 1.5 kW/kg. Enter the SuperStack, ZeroAvia’s proprietary configuration to deliver the necessary fuel cell system for a type certified 600kW hydrogen-electric engine. 

    ZeroAvia’s “SuperStack” - developed in conjunction with partner PowerCell

    We have developed one of the highest power-dense multi-stack modules available. The “SuperStack” module is capable of generating 400kW continuously, encapsulates many of the latest aviation fuel cell componentry technologies, and offers an industry-leading scalable power block with specific power in excess of the targeted 1.5 kW/kg.


    While the precise system architecture of the SuperStack remains IP sensitive at this point, what we have designed is a system that can make the most efficient use of a shared compressor, humidifiers and optimised cooling systems.

    From our first 250kW powertrain system for a six seat aircraft we have come a long way to flight testing the fuel cell systems in our prototype ZA600 design. We’re moving at speed towards certification. It’s a lot of hard work for the team, but we’re motivated by the idea that these systems could be flying passengers and cargo in commercial operations in less than three years – a totally game-changing outcome for the future sustainability of aviation. 


    Learn more about ZeroAvia’s 600kW system for the Cessna Caravan in our white paper here.

    Watch ZeroAvia's Tech Deep Dive on the ZA600: