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EV charging and home hydrogen: the honest version

People often ask whether a home hydrogen system means free EV charging. It does not. Here is what it can genuinely do for an electric car, and what it cannot.

The efficiency problem

Turning grid power into hydrogen and back into electricity loses most of the energy along the way. Round-trip efficiency is 30% or less, so a kilowatt-hour that reaches the car through the hydrogen store cost more than three to buy. Charging the car straight from the grid on a night rate is far cheaper. Anyone who tells you storing power as hydrogen to charge an EV saves money is leaving that loss out.

What it would keep running

  • Home EV charger at a reduced rate in outages
  • Heat pump and kitchen
  • Garage door and lights
  • Router and phones

Where it does help

An outage can arrive the night before a long drive, or last several days in a rural area where the nearest public charger is also down. In that case the system is designed to keep the home charger running from stored hydrogen through the battery and inverter, so the car gets enough to reach town, the hospital or work. It is a reliability tool for the days the grid is not there.

It also means the house does not have to be sacrificed to charge the car, within 15 kW continuous. The heat pump, fridge and lights keep running while the car takes what it needs at a gentle rate, rather than the household going cold so the car can charge.

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.

Sizing and timing

A home EV charger is one of the largest loads in a house. Running it alongside the oven, heat pump and dryer during an outage can push towards the 15 kW limit, so the sensible approach is to charge in a quieter part of the day or at a reduced rate. Day to day, the car should charge directly from the grid off-peak, and the system should be left full for the outage that needs it.

Questions

Can I charge my EV on hydrogen for free?

No. The system charges from the grid off-peak, or from wind or micro-hydro, and round-trip efficiency is 30% or less. Charging the car directly from the grid is far cheaper. Hydrogen backup is for outages, not daily driving.

Will it charge my car during a long outage?

It is designed to keep the home charger running from stored hydrogen through the battery and inverter. Charging at a reduced rate while the house is also running keeps you within 15 kW continuous.

Can it charge two EVs at once?

Two fast chargers plus a home can exceed 15 kW. During an outage you would charge one at a time or at reduced rates. Larger needs would be looked at in pilot sizing.

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