Battery vs Solar Panels: Which Actually Saves You More?

How a battery captures most of the value

This is the key point that most solar+battery marketing overlooks. Without a battery, your daytime electricity costs 33.5p/kWh. With a battery, it effectively costs 9.5p/kWh. The battery has already done the heavy lifting.

When you add solar panels on top of an existing battery setup, the solar power doesn't displace 33.5p grid electricity. It displaces 9.5p battery-stored electricity. The value per solar kWh drops from 33.5p to roughly 10p.

The marginal value problem

Think of it this way:

The battery has already captured ~23p of the 33.5p. Solar can only capture the remaining ~10.5p. That's a 69% drop in the marginal value of every solar kWh.

This doesn't mean solar is worthless. It means the return per pound spent is much higher on a battery than on solar panels, assuming you don't already have a battery.

Three scenarios compared

Here's how the numbers break down for a typical UK household on Octopus Go (9.5p off-peak, 33.5p peak), comparing an 11.5 kWh battery (like the Habo Energy system at £4,600) and a 4kW solar array (~£7,000 installed standalone, or ~£5,000 if added to an existing Habo Energy battery with hybrid inverter).

Even at typical market prices, a battery pays for itself faster than solar. At Habo Energy's price, it's almost half the payback. But the key row is the last one: once you have a battery, the incremental value of adding solar drops sharply. The range depends on how much double-cycling occurs, where solar recharges the battery midday for a second discharge in the evening.

Use our savings calculator to run the numbers for your own tariff and battery size.

How the savings are calculated

Battery alone

An 11.5 kWh battery with 90% round-trip efficiency delivers 10.35 kWh of usable energy per cycle. On Octopus Go:

This works every day of the year, rain or shine. The off-peak rate is available 365 nights a year.

Solar alone (no battery)

A 4kW solar system in the UK generates roughly 3,400 kWh per year. Without a battery, a typical household self-consumes about 50% and exports the rest.

Adding solar to an existing battery

With a battery already in place, solar power during the day displaces battery-stored electricity, not peak-rate grid electricity. The battery energy cost 9.5p/kWh to charge overnight. And because the battery absorbs excess solar instead of exporting it, self-consumption rises to around 80% (compared to ~50% without a battery).

That's less than half the value of solar without a battery. Higher self-consumption actually works against you here: more solar gets stored at 9.5p value instead of exported at 15p. The battery has already captured the spread between peak and off-peak. Solar can only capture the off-peak rate itself.

What about double-cycling?

In theory, the second cycle is charged for free (from solar instead of 9.5p grid), adding up to £3.47 per day in savings. But this only works when solar generation is high enough to fully recharge the battery. In the UK, that's roughly May through August. For the rest of the year, there isn't enough solar to fully recharge, and many winter days produce almost nothing.

This is what drives the range in the table above. The lower end (~£350/year, 14-year payback) is the base case where solar only displaces cheap battery power. The upper end (~£600/year, 8-year payback) reflects realistic partial double-cycling on sunny days. Even at the optimistic end, the payback is still notably longer than a standalone battery at £4,600.

Solar generation is seasonal. Tariff arbitrage is not.

A key advantage of battery-only arbitrage is consistency. The off-peak rate is available every night, all year round. A battery on Octopus Go saves roughly the same amount in December as it does in June.

Solar output in the UK varies dramatically by season:

December production is roughly a sixth of June. Yet December is when energy demand is highest and when you most need savings. A battery delivers consistent value regardless of weather or season. Solar does not.

When solar does make sense

This analysis assumes you're on a time-of-use tariff with a cheap overnight rate. If that's not your situation, the picture changes.

What could change this

The battery-first argument depends on a wide spread between off-peak and peak rates. If that spread compresses, solar's relative value grows. This could happen if off-peak rates rise faster than peak rates, or if peak rates fall due to increased renewable generation on the grid. In recent years, off-peak rates have been creeping up, so this is worth watching.

Export tariffs also matter. If export rates rise well above 15p/kWh, solar's export revenue improves and the case for panels alongside a battery gets stronger. Conversely, if export rates fall (as they did with changes to the Smart Export Guarantee), solar's numbers get worse.

None of this changes the conclusion today. But it's worth revisiting the maths as tariff rates shift.

The bottom line

For UK households on a time-of-use tariff with meaningful electricity consumption, the question isn't "battery or solar?" It's "where does my money do the most work?"

A standalone battery saves more per pound invested, works year-round, and pays for itself in around five years. Solar is a good technology, but when cheap overnight rates already exist, the battery captures the biggest saving. Solar picks up the remainder.

If you're considering a home battery, try our savings calculator to see what you could save. Or read our guide to battery storage without solar for a full overview of how standalone batteries work.