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Glossary: home hydrogen power terms in plain words

Hydrogen power comes with its own vocabulary. Here are the words you will meet on this site, explained without jargon.

Making and using hydrogen

Electrolyser: the machine that splits water into hydrogen and oxygen using electricity. Fuel cell: the device that recombines hydrogen with oxygen from the air to make electricity, heat and water. PEM: proton exchange membrane, the thin polymer sheet at the heart of both. Stack: many cells built together to reach a useful power. De-ioniser: the water treatment stage that removes dissolved minerals before water reaches the electrolyser.

What it would keep running

  • Electrolyser and fuel cell
  • PEM stack
  • Hydrogen buffer at 30 bar or less
  • LiFePO4 battery
  • Hybrid inverter in UPS mode

Storing and switching

Buffer: the vessel that holds hydrogen, here at 30 bar or less. Bar: a unit of pressure, with one bar roughly the air pressure around us. LiFePO4: lithium iron phosphate, the battery chemistry used for its stability and long cycle life. Hybrid inverter: the unit that converts between battery DC and household AC and manages the grid connection.

UPS mode: uninterruptible power supply mode, where the inverter switches to battery so fast that nothing in the house resets. Backfeed: power flowing out of a house into the grid during an outage, which endangers line workers and which the inverter is designed to prevent by isolating the house.

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.

Measuring energy

kW, or kilowatt: a rate of power at a moment, like the speed on a speedometer. kWh, or kilowatt hour: an amount of energy, like the distance travelled. Continuous output: the power the system can supply steadily, 15 kW here. Round-trip efficiency: the share of energy you get back after storing it, 30% or less for hydrogen storage. Off-peak or night rate: cheaper electricity offered overnight on some plans.

Questions

What is the difference between AC and DC?

Direct current, DC, flows one way and is what batteries, electrolysers and fuel cells use. Alternating current, AC, reverses many times a second and is what the grid and household sockets supply. The inverter converts between the two.

What does designed to a standard mean?

It means the system is engineered to follow that standard's requirements. It is not the same as certified, which means an independent body has tested and approved it. While in development, we say designed to.

What is surge or start-up load?

Motors in pumps, fridges and compressors draw a short burst of extra power when they start. The battery and inverter handle these bursts instantly, which is something a fuel cell on its own could not do.

More in outages, weather and how it works

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