Can a Home Battery Take You Off Grid?

It comes up at almost every survey where someone has already done their reading. If a battery can run the house all evening and the panels can fill it again by lunchtime, why stay connected to the grid at all?

It is a fair question, and the honest answer is that going fully off grid is technically possible and almost never worth doing on a normal English home. The reason has very little to do with the battery and everything to do with December.

Off grid and backup are not the same thing

Worth separating two ideas that often get mixed up. A battery with backup capability keeps some or all of your circuits running when the grid fails, then hands back to the grid when supply returns. Going off grid means disconnecting permanently, with no supply behind you and no standing charge, which also means no second chance when your own generation falls short.

The first is a sensible option to specify on a new install. The second changes the whole design, because the system now has to cover your worst week of the year rather than your average day.

The winter problem

Solar output in this country is heavily seasonal. The same array that comfortably overfills a battery on a June morning produces a small fraction of that in late December, and in the North West you can get a run of genuinely dull, still days where output stays low from one end of the week to the other.

A grid connected system shrugs that off. You import what you need at around 24p per unit, the battery still does useful work shifting cheap overnight power, and nothing in the house notices. An off grid system has to ride it out on stored energy alone, which means sizing storage for days of autonomy rather than a single evening.

Our batteries run from 5 kWh up to 60 kWh in stackable modules, so the capacity is available. The question is what you would pay to cover a week that happens once a year, and whether that money would do more good spent elsewhere.

Power, not just energy

The second constraint is one people meet less often. A battery has a capacity in kWh and a power rating in kW, and off grid the inverter has to meet every peak on its own. An electric shower, an oven and a kettle together can ask for more at once than a modest system can deliver, and there is no grid underneath to absorb the difference. Homes that genuinely run off grid usually end up with a larger inverter, a bigger stack, and sometimes a generator for the awkward weeks.

Add a heat pump, which does its hardest work on exactly the cold, dark days when the panels contribute least, and the sums get harder again rather than easier.

Why staying connected usually pays better

There is also a financial case for the grid, which surprises people who think of it only as a bill. Export matters: surplus you cannot use is worth around 12p per unit under the Smart Export Guarantee, and an off grid system simply wastes that generation once the battery is full. Cheap overnight rates matter too, because a battery that can buy low and run your house through the expensive hours earns money all winter, when the panels cannot.

Set against a standing charge, keeping the connection is normally the better deal by a comfortable margin. Typical solar payback of five to eight years assumes that connection, and systems generate for 25 years or more.

The version that does make sense

What most people actually want is not disconnection, it is independence from the expensive hours, and that is well within reach. A well designed system with high self consumption, a battery sized to your evening and overnight usage, a smart tariff and a backup circuit for the freezer, the router and a few sockets gets you most of the practical benefit without betting your heating on the weather.

For reference, 12 panels with a 10 kWh battery starts from around £7,770, and the install itself takes two to three days. We use subcontractors for parts of some installs, as is normal in this industry, and the design, the specification and the handover remain ours to manage and ours to answer for.

If you would like to see what proportion of your own electricity a system could realistically cover, based on your usage and your roof rather than a national average, our survey is free and carries no obligation.