Free tools

Home energy calculators

Eight free calculators, with no login required. Your inputs are saved in this browser so you can return to them later. See how many panels fit on your roof, then explore solar generation, battery payback, a combined solar-and-battery setup, EV running and charging costs, a heat-pump comparison, or the arithmetic behind a simple energy bill. Check the numbers before buying equipment or changing tariffs.

Roof Solar Panel Calculator

Enter your address and see how many panels fit on your roof, with the system size in kWp.

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Annual Solar Generation Calculator

Your postcode and up to three arrays in, monthly and yearly kWh for your exact location out.

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Battery-Only Payback Calculator

See how long a battery on its own takes to pay for itself on your tariff, worked out for every 30 minutes of a year.

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Solar & Battery System Calculator

Panels, an optional battery, and your real tariff together - one simulation for self-sufficiency, savings and payback.

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EV vs Petrol/Diesel Running Cost Calculator

Compare a year of electric charging against petrol/diesel for your real mileage and rates, plus an optional purchase-price break-even.

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EV Charging Time Calculator

Enter your EV battery size and the charge you need. See how long it could take and whether a cheap overnight window covers it.

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Energy Bill Checker

Check the arithmetic behind a simple electricity bill using its usage, unit rate, standing charge and billing period.

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Heat Pump Running Cost Calculator

Compare a heat pump with your current heating system using your own heat demand, efficiency, SCOP and electricity tariff.

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