Electricity costs 8p per kWh from national grid House wants to install a solar panel The house uses 4000kWh of electric per year Solar cell installation is 6400 Pounds per kW What is the payback time?

Answer 1

Your electricity from the grid will cost £320 per annum. What you have not given is the max wattage you need at any time. There are 8760 hours per year, so your average usage is 4000/8760 =0.46 KW. But this would not be adequate. If you want to use it for cooking you would need 6KW at least. But assuming you don't use electricity for cooking or heating, only for lighting, computer, TV, then perhaps 2 KW would be enough, though you would be struggling to use a washing machine and have lighting on. This would cost you £12,800 to instal, so your payback time would be 40 years.

Of course this neglects the fact that you would be using your electricity mostly after dark so there would be no solar output then. What you would need to do to make any sort of economic sense would be to export the electricity during the day when you are not using it, and get paid or have an off-set to your electricity bill, but it is hardly worthwhile especially in the UK where sunshine is limited. To use it at all in your normal house system you would also need an inverter to produce 230V ac from the panel's low dc voltage, is that included in the £6400/KW? You could also invest in a large storage battery to provide electricity at night, at some extra cost.