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Power for the granny flat and the main house

Granny flats are where parents age in place, adult kids save for a deposit, or a carer lives on site. When the power goes, the flat is usually the coldest building on the property.

Who lives in the flat matters

Many minor dwellings are built for an older parent, often with a heat pump, a small kitchen and an electric bed or recliner. Small, often lightly insulated buildings lose heat fast, and the person in them may be the least able to cope with a cold night. If anyone in the flat relies on medical equipment, keep their power company's medically dependent registration and their clinician's plan; this system is a backup to those, not a replacement.

What it would keep running

  • Heat pump in the flat
  • Electric bed or lift recliner
  • Flat kitchen and fridge
  • Main house heating and hot water

One system, two buildings

A granny flat is usually supplied from the main house switchboard or a sub-board off it. The system is designed for 15 kW continuous, enough for an average home with headroom for peaks. A main house and a modest flat together can fit within that, but two full households with heat pumps, ovens and dryers all running at once may push it, and that would be sized honestly in the pilot. The battery and inverter run in UPS mode, so both buildings switch over at the same instant.

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.

Planning it into a new build

If the flat is still being planned, the best time to think about backup is before the trench goes in. Wiring the flat's sub-board so it is covered from day one is much easier than retrofitting. The hydrogen store sits outside at 30 bar or less, with leak sensors, automatic shutdown and venting, and the design is to AS/NZS 60079 and ISO 19880. Placement on the section is part of pilot planning.

Questions

Can one system cover both buildings?

It is designed for 15 kW continuous output, which can cover a house and a modest flat together in many cases. If both run big loads at once, a larger or multi-unit setup may be needed, sized in the pilot.

Mum uses a hospital bed. Is this enough?

Keep her power company's medically dependent registration and her clinician's plan. The system is designed to keep the bed powered through outages, but it is not a hospital-grade supply and does not replace a medical plan.

Is it better to plan this before building the flat?

Yes. Wiring the flat's sub-board and planning where the store sits on the section is easiest before construction. Pilot planning would cover where the store sits, cabling between the buildings and how the loads add up.

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