Solar panel cost calculator

Start with the installed price

A solar panel cost calculator should start with the installed price you will actually pay. That means panels, inverter, mounting, scaffolding, electrical work, monitoring, handover paperwork and the VAT treatment shown on the quote.

Energy Saving Trust currently describes an average home solar panel system as around £6,100, with domestic systems generally around 3.5kWp. Your quote can be higher or lower because roof access, equipment and design matter.

Calculate cost per kW

Cost per kW is a useful comparison check: divide the solar-only installed price by the system size. If a 4kW solar-only system costs £7,000, the rough cost is £1,750 per kW.

This number is useful, but it isn't the whole story. A cheaper quote can still be poor value if the generation estimate is padded, the inverter is undersized in a way that hurts output, or the aftercare is weak.

Separate the battery

If the quote includes a battery, split it out before judging payback. The solar-only system might pay back reasonably, while the battery add-on takes much longer.

Energy Saving Trust says battery storage costs depend on type and size, with a 5kWh system around £4,600 and wider costs ranging from £1,500 to £10,000. Use your installed battery quote, not a generic battery price from a shop.

VAT and quote checks

GOV.UK VAT Notice 708/6 says a temporary zero rate applies to the installation of specified energy-saving materials from 1 May 2023 to 31 March 2027. The notice includes photovoltaic panels, and from 1 February 2024 it also includes batteries for storing energy converted from electricity when the conditions are met.

Ask the installer to show the VAT rate clearly. If the quote includes roof repairs, an EV charger or unrelated electrical work, ask whether those items are treated separately.

• Check the solar-only price.
• Check the battery add-on price.
• Check cost per kW and annual kWh estimate.
• Check whether non-solar extras are separated.