H2OME

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How many days can you last on stored power?

The honest answer is: it depends on how much is stored and how much you use. Anyone who quotes a single number without asking about your house is guessing.

Two numbers decide it

Days of backup equals usable stored energy divided by daily use. On the storage side there is the 30 to 40 kWh battery plus whatever is held as hydrogen in the buffer, converted back at the fuel cell's 45 to 55% efficiency. On the use side, a careful household running essentials uses far less per day than the same household running heat pumps, a dryer and an electric oven. The second number is the one you control.

What it would keep running

  • Fridge and freezer around the clock
  • Water pump on demand
  • Modem and lighting
  • One heat pump for a few hours
  • Phone and laptop charging

Recharging changes everything

If you have a wind turbine or a micro-hydro scheme, the question changes from how many days to whether charging can keep up with use. A steady micro-hydro feed may cover essentials indefinitely while the grid is down. Wind is patchier, so storage bridges the calm spells. Without any off-grid source, stored hydrogen is a finite tank that only refills when the grid returns.

Hydrogen keeps for weeks in the buffer without losing charge, so a full store set aside before storm season is still full when the storm finally arrives. A battery on its own slowly drifts down and is usually topped up by its charger, which makes hydrogen the better place to park energy for an outage you cannot predict.

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.

Working out your own answer

Look at your power bill or smart meter data for a typical winter day, then list what you would actually run in an outage. Most households find their essential daily use is a fraction of their normal use. Storage sizing for pilot homes will be done against real loads like these, so we will not quote a number of days until that sizing is done for your house.

Questions

Why will you not just give me a number of days?

Because it depends on your loads, the storage fitted and whether you can recharge from wind or micro-hydro. A number quoted without those would be invented. We would rather size it properly for your house in the pilot and give you an honest figure.

Does the hydrogen leak away while waiting for an outage?

It is designed to keep for weeks in the low-pressure buffer without losing charge. That is one of the main reasons to store energy as hydrogen rather than only in a battery.

Can I extend backup by cutting use?

Yes, and it is the most powerful lever you have. Turning off heating in unused rooms, skipping the dryer and cooking on gas can stretch the same stored energy over many more days.

More in outages, weather and how it works

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