Solar panels generate most of their electricity in the middle of the day. Most households use most of theirs in the evening. A battery connects the two, and whether it is worth adding comes down to how big that gap is in your home.
What happens without a battery
Any electricity your panels make that you do not use straight away goes to the grid. You get paid for it through the Smart Export Guarantee, but export rates are usually well below what you pay to import. So you sell your surplus cheaply at lunchtime and buy power back at full price at teatime. A typical home without storage uses around a third of what its panels generate.
What a battery changes
A battery stores that daytime surplus and releases it in the evening. Self-consumption can rise to 70% or more, so far less is bought from the grid. In winter, when panels generate less, a battery can also charge overnight on a cheaper time-of-use tariff and run the house through the expensive evening peak.
When it is worth it
A battery tends to pay off if:
- You are out during the day and use most of your energy in the evening
- Your system regularly produces more than you use
- You are on, or willing to switch to, a time-of-use tariff
- You drive an electric car and charge it at home
When it might not be
If someone is home all day running the washing machine, dishwasher and heating, you may already use most of your solar as it is generated. A small system with little surplus has less to store. In those cases the extra cost takes longer to earn back.
Adding one to an existing system
You do not need to fit panels and a battery at the same time. If your system is already running, an AC-coupled battery can be added without replacing the inverter. If you are installing new panels and think storage is likely, a hybrid inverter makes adding one later simpler. Batteries added to existing systems also qualify for 0% VAT until 31 March 2027.
Getting the size right
Bigger is not always better. A battery sized to your evening use, often 5 to 10kWh for a typical family home, will empty and refill most days. One sized well beyond that spends much of its time half full, and you have paid for capacity you rarely use.
The right answer depends on your usage, not a rule of thumb. Experienced solar panel installers in Bristol will look at your consumption pattern and smart meter data before recommending a battery, and should tell you plainly if one will not pay for itself in your home.
