Let’s assume that you pay 30p per kWh for grid electricity (typical domestic electricity unit price from April 2022) and use 30% of what your panels produce, i.e. about 1,020kWh. Then you will save just over £300 pa and your £6,000 will take 20 years to pay off.

If you use 45% the payback period comes down to 15 years and for 60% it’s 10 years. Quotes from some installers will make assumptions about inflation rates and will get smaller payback periods. You have to make your own judgement on how much weight to give to this but there seems to be general agreement that electricity prices will rise rapidly in the coming years. For every increase in the cost of electricity that happens, the payback period for your panels comes down.