How much backup power you actually need
Answer a few questions and get a specific system with prices. We don't sell anything, so we won't recommend something that doesn't suit you.
Where will the equipment go?
The location determines what kind of equipment can go there.
Answer a couple more questions and your options will appear here
Back to the questionsFrom “what has to keep running” to a specific model
- 1
You say what has to keep running
You pick from everyday things like lights, the fridge or the heating. No need to count watts.
- 2
You get the numbers
How much battery you need and how much power the system has to hold. With headroom, so it still covers you after the first year.
- 3
You see specific models
With prices and an explanation of why they suit you.
Why these numbers can be trusted
Three things most calculators get wrong.
A fridge averages 53 W, not 150
A fridge is plugged in around the clock, but its motor only runs about a third of that time. If you use the figure from the sticker on the back, you get three times more than you actually need.
We size the peak by one start, not the sum of all of them
When a pump or a fridge starts, it draws several times more than it does while running, for a second or two. But appliances don't all start at once, so we count the heaviest single start rather than the sum. Otherwise the system would cost twice as much.
The headroom you cannot see
Some energy is lost along the way, a battery shouldn't be drained to zero, and it holds less as it ages. Together that adds about +37%. Without this headroom the system will start falling short within a couple of years.
Frequently asked questions
Is this really free? What is the catch?
There is no catch. The site doesn't sell anything or take money from shops, so we have no reason to recommend something more expensive than you need. The buy button takes you to the product page, and from there you deal with the shop, not with us.
Where do the prices come from and how fresh are they?
We take prices from public sources and update them periodically, so they may differ slightly from what the shop is charging right now. The product page the button links to always shows the exact price.
Why is a fridge counted as 53 W when the sticker says 150?
The sticker shows the compressor's power while it's running. But it only runs about a third of the day, and the rest of the time the fridge is simply keeping cold. If you size by the sticker, the system comes out three times bigger and three times more expensive than you need.
What is the difference between a power station and an inverter with batteries?
A power station works like a big battery with sockets. Set it down, plug in what you need and it just works. An inverter with batteries is wired into your home and powers the whole house, including things without a plug, such as the boiler, the pump and the lights. We suggest a station for as long as one is enough, and a fixed system once it isn't.
Do I need an electrician?
Not for a station, it simply plugs into a socket. For a fixed system you do. The inverter is connected to the consumer unit, and that isn't a job to do yourself.
I have three phases. What does that change?
A single-phase system backs up part of the consumer unit, not all of it. That is usually enough for the lights, fridge, boiler and internet, but heavy three-phase equipment won't run from it. If you tell us you have three phases, we say so clearly in the result instead of quietly suggesting something that won't work.
How accurate is the calculation?
It gives you the right ballpark, not a figure accurate to the watt. Real consumption depends on your appliances and how you use them, which is why we build in 37% of headroom. That is enough to make a purchase. To design a fixed system you need an installer who can take measurements on site.