Solar payback depends heavily on how much of what you generate you actually use versus export, which is where most simple estimates go wrong. This calculator models both self-consumption savings and Smart Export Guarantee income separately, and lets you see whether adding a battery genuinely shortens your payback or just adds cost.
How this calculation works
Annual generation is estimated at roughly 850 kWh per kW of installed capacity, the standard UK average. Without a battery, self-consumption is assumed at around 40-50% of generation, with the rest exported; with a battery, self-consumption rises to roughly 70-80%, since stored energy can be used in the evening instead of exported at the lower SEG rate. Bill savings apply your import rate to self-consumed electricity, and export income applies your SEG rate to whatever's left. Payback simply divides the total install cost by your combined annual saving.
A battery meaningfully increases how much of your own generation you use rather than export, but it also adds several thousand pounds to the install cost. Whether that trade-off is worth it depends heavily on the gap between your import and export rates, a bigger gap makes self-consumption more valuable, and a smaller gap makes exporting at the SEG rate more competitive. See our Solar Panel ROI guide for the fuller reasoning behind when a battery does and doesn't pay for itself.
Frequently asked questions
Why does self-consumption matter so much for payback?
Because your import rate is almost always higher than your export rate, so electricity you use yourself is worth more than electricity you export. A household that's home during the day, and uses more electricity while the sun is out, gets a shorter payback than one that's out at work and exports most of its generation.
Does this account for the 0% VAT on solar installations?
The install cost figures used here already reflect 0% VAT pricing, current UK policy for residential solar and battery installations. Enter your own quoted price if you have one, since actual costs vary by installer, roof complexity, and location.
What happens to my savings after the payback period?
Once the system has paid for itself, the same annual saving continues for the rest of its working life, commonly 25 years or more with panels retaining the large majority of their original output. That's a genuinely long tail of essentially free electricity once the initial cost is recovered.
Continue your research
About the author
✓ Editorially reviewed — all Poqet guides are checked for factual accuracy before publication and updated when UK rates or legislation change. Editorial Policy