Let’s assume that you pay 34p per kWh for grid electricity and use 30% of what your panels produce, i.e. about 1,020kWh. Then you will save about £350 pa and your £6,000 will take 17 years to pay off.  If you use 45% the payback period comes down to 12 years and for 60% it’s 9 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 continue to rise in the coming years. For every increase in the cost of electricity that happens, the payback period for your panels comes down.