The short answer
- You can add a battery to almost any existing solar panel system, whatever its age or make.
- Most retrofits use an AC-coupled battery with its own inverter, so your existing solar inverter stays in place.
- For an average home, 6–10 kWh is usually the most economical size. All-electric homes and EV owners may need more.
- Batteries fitted in homes are zero-rated for VAT until 31 March 2027, including those added to existing solar panels.
Can you add a battery to existing solar?
Yes. Without a battery, solar electricity you don't use straight away is exported to the grid, usually for much less than you pay to import it. A battery stores that surplus so you can use it in the evening instead.
At the survey, we check:
- the make, age and rating of your existing solar inverter
- space in your consumer unit and the condition of your wiring
- where the battery can go, such as a garage, utility room or outside wall, depending on the model
- how much electricity you use, and when
- whether you're on the Feed-in Tariff, which affects how the battery is wired
AC-coupled or hybrid?
There are two ways to connect a battery to an existing solar system:
| Feature | AC-coupled | Hybrid (DC-coupled) |
|---|---|---|
| How it connects | Battery has its own inverter and connects to your home's wiring | One hybrid inverter runs both the panels and the battery |
| Existing solar inverter | Stays in place | Replaced by the hybrid inverter |
| Efficiency | Slightly lower, as solar power is converted more times | Slightly higher when charging from the panels |
| Best for | Most retrofits, especially with a working inverter | Older systems whose inverter is due for replacement |
If your solar inverter is working well, an AC-coupled battery is usually the simplest and most cost-effective option. If it is old or failing, replacing it with a hybrid inverter solves both jobs at once.
What size battery you need
Battery capacity is measured in kilowatt hours (kWh). Ofgem's typical figure for a medium-use home works out at around 7 kWh of electricity a day, though homes with a heat pump or an electric car use far more. The part that matters most is how much you use in the evening peak, from about 4pm to 9pm, when electricity is often most expensive.
Over the years we've found the most economical size for an average home is 6–10 kWh. All-electric homes, homes with a heat pump and those with an EV charger often benefit from more. Oversizing adds cost without adding savings, so we size the battery from your usage and your panels' output.
VAT and costs
Since 1 February 2024, batteries installed in homes have been zero-rated for VAT. That includes batteries added to existing solar panels and standalone batteries that charge from the grid. The zero rate runs until 31 March 2027, after which VAT goes back to 5%.
The Boiler Upgrade Scheme doesn't cover batteries, so the VAT saving is the main financial support. Your price depends on the battery's capacity, whether you need a hybrid inverter and how much wiring is involved, and we give you a fixed quote after the survey.
Telling the network operator
Every battery has to be notified to your local network operator, which in Hampshire and Dorset is SSEN (Scottish and Southern Electricity Networks). We handle this for you:
- If your solar and battery inverters together are rated at no more than 16 amps per phase, about 3.68 kW on a typical home supply, we notify SSEN within 28 days of commissioning under the G98 process.
- Most solar-plus-battery systems are bigger than that, so we apply for permission under the G99 process before installation. The network operator can approve it, ask for an export limit or, rarely, ask for network upgrades.
Feed-in Tariff and export payments
If your panels are on the Feed-in Tariff, you need to tell your FIT supplier when a battery is connected. Your generation meter must still measure only the electricity from your panels, so we wire the battery to keep your FIT payments accurate.
With a battery, you'll export less, because you use more of your own electricity. You can still earn Smart Export Guarantee payments for what you do export, and some tariffs pay more for electricity exported at peak times.
A recent battery retrofit
We added a battery to an existing solar PV system for a homeowner in the Hedge End area, near Southampton (SO30). In their Checkatrade review, posted in October 2024, they scored the job 10/10:
“James and Dan were friendly, knowledgable and courteous. The work was expedited in an efficient manner…”
Read the full review on Checkatrade, or see our battery storage installation page and the work we do in Southampton.
Common questions
Will a battery keep my power on during a power cut?
Not automatically. For safety, most battery systems switch off when the grid goes down. Some batteries offer a backup supply to selected circuits, which needs extra wiring, so tell us at the survey if that matters to you.
How long do home batteries last?
Most modern home battery systems last 10–15 years or more, depending on how hard they're used. The manufacturer's warranty sets out how much capacity the battery should keep over that time.
Can I charge my battery from the grid at night?
Yes. On a time-of-use tariff, most batteries can charge from cheaper overnight electricity and use it in the evening peak. That's useful in winter, when your panels generate less.