H2OME

Home / Uses / Why round-trip efficiency is 30% or less

Round-trip efficiency: why only 30% or less comes back

Put 10 kilowatt hours of electricity into hydrogen storage and you get roughly 3 or less back out. That is not a flaw we hide. It is physics, and it shapes how the system should be used.

Where the energy goes

Energy is lost at every step. Grid or wind power is converted to direct current for the electrolyser, which loses a little. The electrolyser turns part of that electricity into hydrogen and the rest into heat. Storage at low pressure costs little extra. Then the fuel cell, at 45 to 55% efficiency, turns hydrogen back into electricity, losing roughly half as heat. Finally the inverter converts it to household power. Multiply those steps and the total is 30% or less.

What it would keep running

  • Long-outage backup where any energy beats none
  • Surplus wind that would otherwise be wasted
  • Overnight micro-hydro flow
  • Battery for efficient daily cycling
  • Weeks of storage without losing charge

It is not free energy

Anyone selling hydrogen storage as free power is wrong. Every kilowatt hour you take out of storage cost about three or more to put in. If you charge on night-rate grid power, the cost per stored kilowatt hour is the night rate multiplied by that factor. Whether that is cheaper than daytime power depends entirely on your tariff, and often it will not be.

Compared with a battery, which returns most of what you put in, hydrogen looks poor on this measure, and we will not dress that up. The case for it rests on something else entirely, which is storing a large amount of energy for weeks without losing charge, ready for the outage nobody saw coming.

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.

When it still makes sense

For daily shifting of power from night to day, a battery is more efficient. For riding out a week-long outage, or bridging a long calm spell on a wind-powered property, low efficiency matters less than having energy at all. Surplus wind or micro-hydro that would otherwise be wasted also changes the sums. The system uses its battery for daily cycling and keeps hydrogen for the long haul, which is where its strengths lie.

Questions

Will it lower my power bill?

Probably not, and we will not claim it will. With round-trip efficiency of 30% or less, stored energy costs more than the electricity used to make it. The value is resilience, not savings.

Will efficiency improve?

Electrolysers and fuel cells are improving across the industry, and better heat use can help. We will only publish efficiency figures for this system once bench testing and pilots measure them. For now, plan on 30% or less.

Why is the fuel cell only 45 to 55% efficient?

Converting chemical energy to electricity always releases some heat, and no real device avoids it. Fuel cells convert hydrogen more efficiently than most small combustion generators manage with their fuel, but around half the energy still leaves as heat.

More in outages, weather and how it works

Elsewhere

Every use →

Join the pilot list

Pilot installs go to people on this list first. Rural homes, farms and remote sites especially. No spam, no payment.