Home battery storage without solar: does it pay?

A battery does not generate anything. It moves electricity from a cheap moment to an expensive one. Panels are one way to make electricity cheap at a particular moment, but they are not the only way: a time of use tariff does the same thing with no roof involved.

So yes, a battery can pay without solar. Whether it does comes down to one number, and you can put real rates into it today.

The number that decides it

The spread between your cheap rate and your expensive rate, per kilowatt hour.

Every unit the battery shifts earns you that spread, less what is lost in the round trip of charging and discharging. The spread on offer right now is not hypothetical: an EV tariff like Intelligent Octopus Go charges 8p per kilowatt hour off peak, while the capped standard rate is 26.11p. With a round trip efficiency near 87%, a kilowatt hour bought at 8p overnight returns about 0.87 kilowatt hours at 26.11p the next evening: 22.7p of value for 8p of cost, roughly 14.7p of net gain per unit cycled. Older two rate tariffs such as Economy 7 offer the same mechanism with a narrower spread.

Three things follow immediately:

• A wide spread makes storage attractive. A narrow one does not, however good the battery is.
• The return scales with how much you can actually shift, which is capped by your consumption during expensive hours.
• Round trip losses are a real deduction. Not all the energy you put in comes back out, which is why the sum above multiplies by 0.87 before comparing rates.

Working out what you could shift

The honest way is with your own data rather than a rule of thumb.

1. Get your half hourly consumption from your smart meter data.
2. Identify which hours fall in the expensive band on the tariff you are considering.
3. Add up your consumption in those hours across a typical fortnight, and scale to a year.
4. Cap that by the battery’s usable capacity multiplied by how many times a day it can realistically cycle.

Whichever of those two is smaller is what you can shift.

A worked example. A household uses 3,000 kilowatt hours a year outside the cheap window, and is considering a battery with 10 kilowatt hours usable. The battery could cycle up to 3,650 kilowatt hours a year at one full cycle a day, so consumption is the binding cap: 3,000 kilowatt hours shifted, at the 14.7p net gain worked out above, is about £440 a year. Against an illustrative £5,000 installed price that is a simple payback around eleven and a half years, before allowing for capacity fade over the battery’s life, which lengthens it. On a narrower spread the same battery earns proportionally less: halve the spread and you roughly halve the return.

That is the whole model. Everything else is detail around those two caps.

Where this works well

High evening and overnight consumption. Electric heating, an electric car charged at home, or simply a household that is busy after dark. The more consumption sits in expensive hours, the more there is to shift, and the closer the battery gets to a full daily cycle actually earning.

A tariff with a genuinely wide spread. The 8p against 26.11p example above is an 18p gross spread. Some time of use tariffs are barely differentiated, and the arithmetic collapses with the spread.

A battery that can charge from the grid. This sounds obvious and is not. Some solar oriented systems are configured to charge only from generation. If grid charging is not available, arbitrage is not available either. Ask explicitly, in writing, before you sign.

Where it does not

A flat tariff. No spread, no arbitrage, no return. The whole model depends on rates differing through the day, and on a single rate tariff the battery would buy and sell the same priced unit while paying round trip losses for the privilege.

Low consumption. A battery that cannot find enough expensive units to displace will sit part cycled, and you paid for the whole thing. In the worked example, a household with only 1,500 expensive hour kilowatt hours earns about £220 a year, and the payback stops making sense.

Consumption concentrated in the cheap window already. If you are already charging the car and running the laundry overnight, a battery is competing with a habit you have, and only the remainder counts.

The things people buy it for that are not returns

Two common motivations, both legitimate, neither a financial case:

Backup during a power cut. Most systems do not provide this unless specifically configured for it, and doing so costs more. If this is why you want it, confirm it is included rather than assuming.

Reducing grid draw on principle. A perfectly reasonable thing to want. Just do not let it be scored as payback.

It also changes the case for panels later

If you add solar afterwards, a battery already in place raises how much of that generation you keep rather than export, and stored solar has its own per unit value that adds to the arbitrage. The two reinforce each other, which is why the order you buy them in is worth thinking about rather than defaulting to panels first.

If solar is likely, specifying a hybrid inverter now avoids paying for conversion twice.

Check it against your own tariff

Take your spread, your consumption in expensive hours, and a realistic usable capacity, and work out the annual figure before looking at any manufacturer’s payback claim. Storage economics are dominated by your tariff, so a generic answer cannot be right for your house. The ROI calculator models battery only configurations as well as combined ones, applies the round trip and degradation deductions for you, and keeps the whole projection in today’s money, which is the honest way to look at a purchase that pays back over a decade.