If you’ve had solar panels for a few years and you’re on the Feed-in Tariff, you’re already getting paid to generate electricity. But there’s a good chance a significant chunk of what your panels produce goes back to the grid during the day — while you pay full rate to import from the grid in the evening. A battery changes that by storing the surplus and making it available when you actually need it.
The question is whether the numbers add up. Use the calculator below to run the figures for your setup, and read on for what you need to understand before adding a battery to a FIT system.
How your FIT payments work
The Feed-in Tariff pays you in two ways. The generation tariff pays a rate per kilowatt-hour for everything your panels produce, regardless of whether you use it yourself or send it to the grid. The export tariff pays for the portion you export.
Most FIT households are on deemed export, which means the export payment is calculated at a fixed 50% of your generation — no meter required. If your panels produce 3,000kWh in a year, you’re paid the export rate on 1,500kWh regardless of how much you actually export.
A smaller number of FIT customers have metered export, where a meter records actual exports and you’re paid on that figure. If you’re not sure which arrangement you’re on, your FIT licensee (usually your energy supplier) can tell you.
Why deemed export makes adding a battery straightforward
If you’re on deemed export, adding a battery doesn’t reduce your FIT income at all. Your export payments are based on 50% of generation, not on what actually leaves your property — so whether that solar goes into a battery or onto the grid makes no difference to what you’re paid. You get the same generation and export income either way.
What the battery changes is your grid import in the evening. Instead of buying electricity at the current rate (typically 24p–28p per kWh) to cover the hours after the panels stop producing, you draw from what you stored during the day. That saved spend is effectively your battery’s return on investment.
If you’re on metered export, the calculation is different. The battery will reduce what you actually export, which reduces your export payments. That doesn’t necessarily make it a bad investment — you’re trading export income for higher self-consumption — but you need to account for it in your payback figure. The calculator below handles this for you.
What a battery actually saves a FIT household
The saving comes from the difference between what your exported solar earns and what you’d otherwise pay to import. FIT export rates are typically a few pence per kilowatt-hour. Grid import rates are many times higher. Every unit of solar you capture in a battery and use in the evening — rather than exporting it for a few pence and buying it back at 25p — is that difference in your pocket.
How much that adds up to depends on the size of your system, how much you’re generating versus using during the day, your tariff rates, and the size of battery. For a typical 3–4kWp FIT system on a household that’s out during the day, a battery of 5–10kWh can shift a meaningful proportion of that daytime surplus into the evening — often enough to substantially reduce evening imports.
Payback calculator
Enter your details below to see a payback estimate for your system. The calculator factors in your FIT generation and export rates, current import tariff, annual generation, and battery cost.
Solar Battery Payback Calculator
Adjust the figures to match your setup and see your estimated payback period.
Based on self-consumption uplift, overnight cheap-rate battery charging, and EV savings. Figures are estimates — actual results will vary.
Want to know exactly what a battery could save you? Get a free, no-obligation quote from our MCS-certified team.
A few things to check before going ahead
Your export type. As above, deemed export and metered export affect the payback differently. If you don’t know which you’re on, call your FIT licensee before committing to a battery size.
DNO notification. Adding a battery to an existing solar installation usually requires notifying your Distribution Network Operator under G98 (for systems with an inverter output of 3.68kW or less) or G99 (for larger systems). Your installer will handle this, but it’s worth knowing it’s part of the process.
MCS certification. Ofgem requires that any addition to an FIT-registered installation is carried out by an MCS-certified installer to maintain your FIT eligibility. Make sure any battery quote you get is from a certified installer — if you’re not sure, you can check at mcscertified.com.
Smart tariff compatibility. If you’re considering switching to a time-of-use tariff like Octopus Go to charge the battery cheaply overnight as well, bear in mind that FIT and Octopus Intelligent aren’t straightforwardly compatible (Intelligent requires a smart meter and is designed around EV charging). Octopus Go and similar off-peak tariffs can work alongside FIT with a battery, but it’s worth discussing with us before switching.
Is it worth it?
For most FIT households on deemed export with a working solar system and reasonable evening demand, a battery is a sound investment at current electricity prices. Payback periods have shortened considerably as import rates have risen, and the case is now often clearer than it was even three or four years ago.
If you’d like to talk through the numbers for your specific setup, get in touch. We install battery storage across Bristol and South Gloucestershire and can advise on the right size and system for what you already have.
