Backup power for a house
Twelve hours without power, with the boiler, the borehole, the lights and the internet running, takes about 3,8 kWh. Add a fridge and a freezer and it is 6 kWh. Answer a few questions and we will pick a system for you, with a price.
How long does one outage last?
Move the slider to see what each extra hour costs.
Answer a couple more questions and your options will appear here
Back to the questionsHow much battery a house needs
The capacity for each set of appliances and each length of outage. On the right, the start the inverter has to survive. It is set by the borehole pump, not by the boiler.
| What is running | 8 h | 12 h | 24 h | Start |
|---|---|---|---|---|
| Boiler, borehole pump, lights and internet | 2,6 kWh | 3,8 kWh | 7,6 kWh | 2,9 kW |
| The same plus a fridge and a freezer | 4 kWh | 6 kWh | 11,9 kWh | 3,3 kW |
| The whole house: a washing machine, a TV and a laptop as well | 5,5 kWh | 7,5 kWh | 13,4 kWh | 4,1 kW |
Switch everything on at once and it comes to 2 kW. But the pump runs in bursts, the washing machine heats water only at the start of a cycle and the fridge is on about a third of the time, so the average is 773 W. The figures already include about 37% for inverter losses, an incomplete discharge and battery ageing.
What matters when you back up a house
Why a house usually means an inverter
A power station runs whatever you physically plug into it. While that is a boiler, a router and a few lamps, it is enough. But the borehole pump, the water heater and the lights in the rooms are wired into the consumer unit, and you cannot reach them with an extension lead.
A hybrid inverter with batteries is wired into the consumer unit once. The power goes, it switches over by itself in a fraction of a second, and nothing in the house changes. The hob and the water heater are usually not connected to it: they eat capacity faster than everything else put together.
The borehole sets the start
The pump draws about 800 W while it is pumping, but for a moment at start-up it pulls three times that. That is why the table shows a start of 2,9 kW when everything running together is under a kilowatt.
An inverter that cannot take that start trips and shuts down. It looks as though the pump has failed, even though the battery is full. So read the peak power in the specification, not only the continuous rating.
How much battery to buy
A full day without power takes 7,6 kWh for the boiler, the borehole, the lights and the internet. With a fridge and a freezer it is 11,9 kWh, and for the whole house 13,4 kWh.
This is where portable stations run out. Very few of them hold that much, and the ones that do cost more than an inverter with separate batteries. You can also add batteries one at a time, where a station would have to be replaced outright.
One phase or three
If the supply is three-phase there are two ways to go. The cheaper one keeps a single-phase inverter, and an electrician moves the boiler, the borehole, the fridge and the lights onto one phase, which is the phase the inverter holds. The dearer one is a three-phase inverter that holds the house as it is, sockets and all.
A three-phase system is genuinely needed only if something in the house is three-phase: a deep-well pump on 380 V, a heat pump, a machine in the workshop. Otherwise the first arrangement is cheaper and works just as well.
Who installs it
The inverter goes between the meter and the house, which means work inside the incoming consumer unit: its own breakers, earthing, and splitting the wiring into what keeps working during an outage and what does not. Half a day for an electrician, and a few thousand hryvnias on top of the equipment.
Budget for that from the start. Equipment bought in autumn and left unconnected until spring because nobody is available is a thing that happens every winter.
What else to bear in mind
- Boiler rooms and garages get cold. A lithium iron phosphate battery will not charge below freezing, so the room has to be at least a little warm.
- Start with an inverter that has power to spare and add batteries later. Adding batteries is cheaper than replacing an inverter that turns out to be too small.
- Solar panels make sense here: there is a roof, there is space, and a hybrid inverter works with them out of the box. They give little in winter, but in summer they cover almost everything the house uses.
- A generator and batteries do not replace each other. A generator gives you power through long outages; batteries give you a quiet night and switch over on their own while you are away.
If it is a flat rather than a house, everything gets simpler and cheaper: a station for a flat needs neither an electrician nor work in the consumer unit.
Common questions about backing up a house
A station or an inverter with batteries?
A station, if what you need is the boiler, the internet and the fridge, and the rest of the house can wait. An inverter, if the lights have to work everywhere and the borehole has to run. Twelve hours for the whole house takes 7,5 kWh, and portable stations that large barely exist.
How far does 1 kWh go?
Backing the whole house, a kilowatt-hour lasts about 0,5 h: that load averages 773 W. Cut back to the boiler, the borehole, the lights and the internet and the same kilowatt-hour lasts 3 h.
Will it run a fridge and a freezer?
Yes. With the boiler, the borehole and the lights for 12 hours that is 6 kWh, and the compressors starting are no trouble for an inverter of this class. A freezer kept shut holds its cold for most of a day, so on a short outage you need not power it at all.
Can I install it myself?
No. The inverter is wired into the incoming consumer unit, which means breakers, earthing and splitting the wiring. That is an electrician's job and an unsafe one to take on yourself. What you can do yourself is stand a power station in the house and plug appliances into it.
I have three phases. Do I need a three-phase inverter?
Usually not. It is cheaper to keep a single-phase inverter and move everything that has to keep working during an outage onto one phase. You need three phases if something in the house is three-phase: a deep-well pump on 380 V, a heat pump, a machine tool.
What does a whole-house system cost?
Most of the money goes on batteries, so the price follows the number of hours you want to last. Eight hours takes 4 kWh, a full day 11,9 kWh, and the gap between them is real money. The quiz above shows specific kits at current prices, and it already knows this is a house.