Battery retrofit guide
Can I add a battery to my existing solar panels?
Yes — you can add a battery to most existing solar panel installations. A retrofit battery stores your daytime solar generation for evening use and lets you buy cheaper off-peak electricity overnight. A typical 9-10kWh battery costs from £5,500 including 0% VAT, and most retrofits take 1-2 days.
Compatibility
Is my solar system compatible with a battery?
Most solar PV systems installed in the last 10 years can have a battery added. The installer checks your inverter type, panel array, and wiring during the survey.
There are two main ways to add a battery:
AC-coupled battery
A separate battery and inverter unit installed alongside your existing solar inverter. Works with almost any existing solar system and is the most common retrofit approach.
DC-coupled battery
A hybrid inverter that manages both solar panels and battery in one unit. More efficient but may require replacing your existing solar inverter — best for new installations.
Your surveyor inspects your existing inverter, panel array and wiring to recommend the best approach. Most retrofits use AC coupling because it's simpler and works with virtually any existing system.
Why add a battery
What are the benefits of adding a battery to existing solar?
A battery lets you use 60-85% of your solar generation instead of 30-50%, and unlocks cheaper off-peak grid charging. See our solar vs battery comparison for the full breakdown.
Use more of your own solar
Without a battery, you export 50-70% of your daytime generation. A battery lets you store it for evening use, boosting self-consumption from 30-50% to 60-85%.
Grid arbitrage savings
Charge your battery at off-peak rates (around 7p/kWh) and use that electricity during peak times instead of paying 28p/kWh — a significant saving on every kWh shifted.
Backup power
Some battery systems provide limited backup power during grid outages, keeping essential circuits running when the grid goes down.
Future-proofs your investment
Adding a battery extends the value of your existing solar panels by making the generation more useful and flexible as electricity prices and tariffs evolve.
Retrofit costs
How much does it cost to add a battery to existing solar?
A typical 9-10kWh battery retrofit costs from £5,500 including 0% VAT and installation. Finance is available subject to status.
| Battery size | Typical cost | Best for |
|---|---|---|
| 5-6kWh | £3,500-£4,500 | Small households |
| 9-10kWh | from £5,500 | Typical 3-4 bed homes |
| 13-15kWh | £6,500-£8,000 | Large homes / heat pumps |
Prices include 0% VAT and installation. Actual quotes vary based on your existing system, wiring, and chosen battery brand.
Installation process
How does the battery retrofit process work?
Adding a battery to existing solar is straightforward: survey, compatibility check, installation in 1-2 days, and MCS handover. See our full process guide.
Survey & compatibility
An installer visits to check your existing inverter, panel array and wiring. They recommend AC or DC coupling and the right battery capacity.
Written quote
You receive an itemised quote with battery brand, capacity, total cost and finance options. No obligation.
Installation
The battery and any additional inverter are installed in 1-2 days. Your existing solar panels keep working throughout.
Commissioning & handover
The system is commissioned, tested and registered. You get a handover pack with warranty documents and user guide.
Common questions
Frequently asked questions about adding a battery
Can I add a battery to my existing solar panels?
Yes. Batteries can be retrofitted to most existing solar PV systems. Your installer checks inverter compatibility during the survey and recommends a suitable capacity.
How much does adding a battery cost?
A 9-10kWh battery typically costs from £5,500 including 0% VAT. Smaller 5-6kWh batteries cost less. Finance is available, subject to status.
What size battery do I need for my solar panels?
For a 4kW solar system, a 9-10kWh battery is typical. This stores roughly one full day of summer generation. Your surveyor recommends the right size based on your usage.
Will a battery work with my existing inverter?
Most modern inverters are compatible with AC-coupled batteries. Some installations may need an additional battery inverter. DC-coupled systems may require an inverter upgrade.
Can I charge my battery from the grid overnight?
Yes. On a time-of-use tariff like Octopus Go, you can charge your battery at cheap off-peak rates (around 7p/kWh) and use that electricity during peak times — saving significantly on bills.
Does adding a battery qualify for 0% VAT?
Yes. Batteries installed alongside or after solar panels qualify for 0% VAT until 31 March 2027, the same as solar panel installations.
More answers at Scottish Energy Efficiency questions.
Last updated: 1 November 2026
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