The short answer
A solar battery is a home energy store that holds the electricity your panels generate during the day so you can use it in the evening, rather than exporting the surplus to the grid. Most home batteries use lithium-ion chemistry and are rated by usable capacity in kWh — a common UK domestic size is around 5 to 10 kWh. The point of a battery is to raise self-consumption: solar generation peaks at midday when many homes use little, so without storage that surplus is exported. A battery captures it for use at night, cutting how much you buy from the grid. Many systems also let the battery charge from cheap off-peak grid electricity. A battery adds cost, so it suits homes that use a lot of electricity in the evening.
Solar generation and household demand rarely line up — the panels are busiest at midday, but most homes use most power in the morning and evening. A battery bridges that gap. This page explains how.
Key facts
- What it isA home store for solar electricity
- Common chemistryLithium-ion
- Typical UK home sizeAround 5–10 kWh usable
- Main benefitHigher self-consumption of your solar
- Also can charge fromCheap off-peak grid tariffs
Why storage matters with solar
The mismatch between when solar is generated and when a home uses electricity is the whole reason batteries exist. Panels generate most around the middle of the day. Many households, though, use the least electricity then — people are out, and the big draws (cooking, lighting, TV, charging) come in the evening when the panels have wound down.
Without a battery, the midday surplus is exported to the grid, earning a modest payment under the Smart Export Guarantee, and the home then buys electricity back at a higher rate in the evening. A battery breaks that pattern: it stores the daytime surplus and releases it later, so you use more of your own solar and buy less from the grid. The measure of this is self-consumption — the share of your generation you use yourself rather than export — and a battery can raise it substantially, because the surplus that would otherwise leave the home at midday is instead kept on hand for when the household actually draws power.
Capacity, power and how it connects
Two numbers describe a battery. Usable capacity (in kWh) is how much energy it can store and release — this is the headline size. Power rating (in kW) is how fast it can charge or discharge, which determines how many appliances it can run at once. A typical UK home battery offers around 5 to 10 kWh of usable capacity, sized to cover a good share of evening use.
A battery connects through an inverter. A hybrid inverter handles both the panels and the battery in one unit, while a separate battery (AC-coupled) inverter can be added alongside an existing solar inverter to retrofit storage to a system installed earlier. Most modern batteries also accept charge from the grid, so on a time-of-use tariff they can fill up overnight on cheap electricity and discharge during expensive peak hours — a benefit that works even in winter when solar generation is low.
| Term | What it means | Typical UK home figure |
|---|---|---|
| Usable capacity | Energy it can store (kWh) | Around 5–10 kWh |
| Power rating | How fast it charges/discharges (kW) | Around 3–5 kW |
| Chemistry | Battery type | Lithium-ion |
| Round-trip efficiency | Energy kept after a charge/discharge cycle | Around 85–95% |
Indicative figures for guidance only. Source: Energy Saving Trust.
Is a battery worth it?
A battery suits a household whose electricity use is concentrated outside daylight hours, or one that wants to store cheap overnight electricity to use during peak times. The more of your own solar (or cheap off-peak power) you can shift to when you actually need it, the more a battery earns its keep.
It is, however, an extra cost on top of the panels and inverter, and like the inverter it has a finite life — lithium-ion home batteries are commonly warranted for around 10 years. Whether the savings justify that outlay depends on your tariff, how much electricity you use in the evening, and the size of your solar array. Many homeowners fit solar first and add a battery later once they have seen their own generation and usage patterns, which a hybrid inverter or an AC-coupled retrofit makes straightforward.
How a battery affects your export and bills
Adding a battery changes the shape of your solar economics. Without storage, midday surplus is exported and earns a Smart Export Guarantee payment, then you buy electricity back at a higher rate in the evening. A battery captures that surplus instead, so you export less but buy less — and because imported electricity usually costs more per kWh than the export rate pays, shifting that energy to your own evening use is generally worth more than exporting it.
There are a few practical points to weigh:
- Round-trip losses. A battery does not return every kWh it stores; typical round-trip efficiency is around 85 to 95%, so a small amount is lost in each charge-and-discharge cycle.
- Cycle life. Batteries are rated for a large number of charge cycles, and warranties commonly run to around 10 years, so it is a component you should expect to replace eventually.
- Off-peak charging. On a time-of-use tariff, the battery can fill overnight on cheap electricity and discharge during expensive peak hours, which adds value year-round, not only in sunny months.
For a household with high evening use or a favourable tariff, these factors stack up in a battery's favour. For one with low evening demand, the surplus is better simply exported. The honest position is that a battery improves how much of your generation you keep for yourself, but it is an optional addition whose worth depends on your own usage and tariff rather than a must-have for every solar home.
Frequently asked questions
How big a solar battery do I need?
Most UK homes are fitted with around 5 to 10 kWh of usable capacity, sized to cover a good share of evening electricity use. The right size depends on how much you use after dark, your solar array size and your tariff. Oversizing beyond what you can fill and use each day brings diminishing returns.
Can I add a battery to existing solar panels?
Yes. An AC-coupled battery with its own inverter can be retrofitted alongside an existing solar inverter without replacing the panels. Alternatively, if the inverter is being replaced anyway, a hybrid inverter can manage both. Retrofitting is common because many homeowners fit solar first and add storage later.
Does a solar battery work in winter?
Solar generation is low in winter, so there is less surplus to store from the panels. But a battery on a time-of-use tariff can still charge from cheap off-peak grid electricity overnight and discharge during expensive peak hours, so it can save money year-round, not only when the sun is strong.
Sources & further reading
Figures on this page are typical UK ranges drawn from published sources and depend on your specific home. They are guidance, not a quotation or guaranteed saving.