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How a fuel cell turns hydrogen back into electricity

A fuel cell runs electrolysis in reverse. Hydrogen and oxygen recombine into water, and the energy released comes out as electricity rather than a flame.

No flame, no engine

People often picture a fuel cell as a kind of engine that burns hydrogen. It is not. There is no combustion, no pistons and no spark. Hydrogen is fed to one side of a membrane and air to the other. A catalyst strips electrons off the hydrogen, those electrons flow through the external circuit as useful current, and the reaction finishes on the air side, where hydrogen ions, electrons and oxygen form water.

What it would keep running

  • Battery top-up during a long outage
  • Steady power behind the inverter
  • Overnight essentials when the grid is down
  • Water returned to the loop
  • Quiet running near bedrooms

Efficiency and heat

The system's PEM fuel cell is 45 to 55% efficient, meaning roughly half the energy in the hydrogen comes out as electricity. The rest leaves as heat, which is why fuel cells have cooling systems. A combustion generator wastes heat too, through its exhaust and radiator, but also needs fuel delivered and makes noise and fumes.

The fuel cell's output is direct current. The hybrid inverter converts it to the alternating current your appliances use, and the battery smooths the flow so the house sees steady power whatever loads switch on or off. The fuel cell can then run at an even, comfortable rate rather than chasing every jug and pump.

How it works →
The H2OME loop: an electrolyser splits water into hydrogen, the hydrogen is stored in a tank for weeks, a fuel cell turns it into electricity for your home, and the water returns to the loop.

The water comes back

The only by-product at the point of use is water. In this design, that water is captured and goes back into the loop to be used again by the electrolyser. So of the roughly 9 litres it takes to make a kilogram of hydrogen, the fuel cell gives most of it back. That closed loop matters most in dry country where every litre in the tank is counted.

Questions

Does a fuel cell wear out?

Fuel cell stacks degrade gradually with operating hours and conditions. How long this system's stack will last in home use is something pilot homes will show. We will not quote a lifespan before that data exists.

Is the water from the fuel cell drinkable?

The design returns it to the electrolyser loop rather than to your taps. It is not presented as drinking water and is not plumbed or treated for that use, so you should not plan to drink it. Keep your own stored drinking water for emergencies.

Why not just use a fuel cell without a battery?

A fuel cell responds smoothly but not instantly to sudden large loads. The battery and inverter cover start surges and give instant switch-over in UPS mode, while the fuel cell runs at a steady rate in the background.

More in outages, weather and how it works

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