How a battery changes your solar savings
A battery saves money in two ways. It stores surplus solar that would otherwise be exported cheaply, so you use it in the evening at full value. It can also charge on a cheap overnight tariff and cover daytime use. Used well, a battery is often the second-biggest saving after direct self-use.
Last updated: 5 November 2026.
Reviewed by the Scottish Energy Efficiency team.
What does a battery actually do?
A battery moves electricity in time. It captures units when they are cheap or plentiful, such as midday solar or overnight off-peak power, and releases them when power is expensive. It does not generate anything itself, so its value depends entirely on the price gap it can exploit.
Without a battery, solar you cannot use straight away goes to the grid and earns your export rate. With a battery, that unit is held until the evening, when it displaces electricity bought at the day rate instead.
Some energy is lost in charging and discharging, so a battery never returns every unit you put in. A good quotation should account for those losses.
How much can overnight charging save?
Overnight arbitrage means charging at a cheap off-peak rate and using that power during the day instead of paying the full day rate. The saving is the spread between the two prices for every unit cycled, before losses. The wider the gap, the more a battery earns.
You need a time-of-use or economy tariff for this to work. On a single flat rate, overnight charging saves nothing, and the battery relies only on storing solar surplus.
In practice you will not cycle the full capacity every night, so the real saving is well below the theoretical maximum. Ask your installer to show the cycles per year they assumed.
Does a battery help in a Scottish winter?
Yes, though mostly through overnight charging rather than solar. Winter generation in Scotland is low, so there is little surplus to store. A battery on a time-of-use tariff can still cycle cheap night units into the day, which keeps it earning through the darker months.
In summer the pattern reverses. Long days mean plenty of solar surplus, and the battery can fill from the roof rather than the grid. That year-round usefulness is why battery sizing should look at both seasons.
What size of battery makes sense?
The right size matches the electricity you use between evening and the next cheap-rate period, and the surplus your panels produce on a typical day. An oversized battery that rarely fills or empties adds cost without adding saving, so sizing should start from your usage.
Batteries are generally warrantied for around 10 years, so the saving needs to make sense within that period. Ask your installer to show the cycles per year they assumed.
To see how battery income fits into the overall sum, use the steps in our solar savings calculator guide, and compare it with export income in the Smart Export Guarantee guide.
| Without a battery | With a battery |
|---|---|
| Daytime surplus is exported at the SEG rate | Daytime surplus is stored and used in the evening at full value |
| Evening use is bought at the day rate | Evening use is covered from stored solar or cheap night units |
| No benefit from an overnight tariff | Can cycle overnight units into the day |
For more on home battery storage options across Scotland, visit Home Battery Scotland. Part of the Scottish Energy Efficiency network.
Frequently asked questions
Is battery storage worth it without solar panels?
It can be. A battery alone can charge on a cheap overnight tariff and cover daytime use. The saving depends on the gap between your night and day rates.
Can I add a battery to existing solar panels?
Usually, yes. Most systems can take a battery later, either through a hybrid inverter or a separate battery inverter. A survey confirms what your setup supports.
How long does a home battery last?
Batteries are generally warrantied for around 10 years. Capacity gradually reduces with use, so check the warranty terms on remaining capacity.
More solar savings guides
How do you get a solar savings quote?
Fill in the form and we will model the arithmetic and send a written quotation from our MCS-certified partner.