Mr Smith spends £600 per year on electricity and pays 14p per unit. (Based on average cost of electricity per kWh from ukpower)
He has had a 4kW PV system installed, as follows:
Feed In Tariff
3969 kWh at 3.93 pence = £156
3936kW is how many units his system should produce in a year, and the Feed In Tariff rate is currently 3.93 pence for every kW of renewable electricity produced.
Energy Exported
1984 kWh at 5.24 pence = £104
The exported energy is a deemed figure- it is not metered. This is worked out at 50% of the energy he has have produced, and the export tariff is paid at 5.24 pence per unit.
Energy Used
992.25 kWh at 14 pence = £138.92
In this instance, our customer is not at home all day and is therefore only able to use 25% of the energy his system produces.
He will, therefore, save £139 per year by not having to buy these 992 units from his electricity provider.
The Energy Saving Trust gives some examples of savings here – although we would also advise customers to set washing machines etc on a timer, to utilise the solar electricity, even if you are not at home.
The total amount of saving & earnings made annually is £398.92, and the system cost him £6,119.40. This means he will get an annual return on investment of 6.52%.