Energy Saving Trust solar calculator guide

What this guide is for

People often search for an Energy Saving Trust solar calculator because they want a trusted starting point. That makes sense. Energy Saving Trust is a useful UK consumer source for solar panel costs, savings and suitability.

This site is not connected with Energy Saving Trust. The useful approach is to use their public figures as a benchmark, then run your own quote and tariff assumptions through a transparent calculator.

Start with the benchmark

Energy Saving Trust says an average home solar panel system costs around £6,100 to install and that domestic systems are generally around 3.5kWp. That gives a sensible first check against quotes that look unusually high or suspiciously cheap.

The catch is that an average is not your roof. Access, roof condition, scaffolding, shade, panel layout, inverter choice and battery storage can all move the price.

Then replace the generic assumptions

A proper savings estimate needs your own electricity unit rate, export tariff, annual generation and self-consumption. Ofgem's current price cap data gives useful market context, but your actual tariff can be different.

Export also needs its own figure. Ofgem says SEG suppliers set their own export tariff rates and terms. If you can access a strong export rate, exported solar can be a meaningful part of the annual benefit.

Check the annual generation number

Generation is where estimates often drift. A quick UK planning range is 800 to 1,000kWh per kWp installed each year, but a roof-specific figure is better.

Use PVGIS or an installer design to sense-check annual kWh. If a quote assumes much higher output than a roof-specific estimate, ask what is driving the difference.

A practical workflow

Use Energy Saving Trust figures to sense-check the broad cost and suitability. Then use this calculator to test your actual quote, tariff and household routine.

Run the numbers more than once. Start with solar-only, then test a battery case separately. Try a lower-generation case too, because a decision that only works in perfect conditions is a fragile one.

• Compare your quote with the average-cost benchmark.
• Replace the default import rate with your actual tariff.
• Use the export tariff you can actually access.
• Use a roof-specific annual kWh estimate where possible.
• Test no battery before adding storage.