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Solar calculators

Five free calculators for UK homes. They run in the Be Solar Wise app, in your browser, and give rough estimates to help you check quotes and ask better questions.

• Battery size and payback calculatorEnter your yearly electricity use, your tariff and a battery price. It suggests a battery size and works out the yearly saving and simple payback, and compares that with a battery's typical life.
• Solar generation estimatorChoose where you are in the UK, the size of system, which way the panels face, their angle and any shade. It estimates the yearly and monthly generation and what it could be worth.
• Inverter size checker (rooftop solar)Enter your panels and your supply. It compares inverter sizes, shows the DC to AC ratio, estimates the energy lost to clipping and says whether each option fits the G98 limit.
• Plug-in solar savings calculatorEnter your kit, where it will go and how much you are at home in the day. It estimates what the kit makes, how much you will use, the saving and the payback.

• Portable power station plannerChoose a portable power station or enter your own figures, list what you want to run, and where you are. It works out how long it runs your appliances, how much a solar panel adds each month and how long it takes to fill, what that free solar energy saves you over a year, and what charging on a cheap night rate could save.

How the estimates are made

• Generation: a typical yearly output per kWp for your latitude, adjusted for direction, angle and shade, with a typical monthly pattern. Well-sited UK systems usually make around 750 to 1,100 kWh a year per kWp.
• Value: Ofgem's average price cap rate for October to December 2026 (26.32p per kWh, with no VAT until 31 March 2027) and a typical export rate of 12p, which you can change.
• Batteries: the four-step sizing method in our batteries guide, with a 10% reserve and 90% round-trip efficiency. It starts with a 10 kWh battery at £5,250, a typical 2026 installed price (see battery prices); change both to match your quote.
• Portable power stations: about 85% of the capacity is usable after inverter losses, about 92% of mains charging is stored, and solar uses PVGIS monthly averages for London and Edinburgh (interpolated by latitude) with a 10% charging loss and an adjustment for the panel’s angle, which matters most in winter.
• Inverters: the G98 limit of 16 amps per phase (about 3.68 kW single-phase) and a typical UK clipping curve.

Updated 2026-10-05.