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Your Roof

. Making sense of solar

Your roof


Below is a PV calculator that you can use to estimate how much power and income your solar PV panel will generate. This calculator is based on the same input assumptions that the Solar Trade Association uses in its internal modelling.  These assumptions are conservative. For example, the calculator assumes electricity prices will rise 2.6% per annum (in reality they have increased 6.6% on average over the past 10 years). The calculator will give you a breakdown of your expected cash flows that you will receive as part of your Feed-in-Tariff, as well as the savings you will make from using your own electricity.  You can ask the calculator to produce a 2 page document detailing income year by year, by selecting “Export this report as a PDF”.

A generous domestic 4kWp solar PV system will cost around £6,500 and will yield about 3,400kWh of electricity per year if your home is south(ish) facing and you are based in the middle of the country.  Expect a higher yield if you live further south, and slightly less if you live further north. It is a assumed that your panels will not be shaded in the summer months. Income will also depend on your behaviour in the home. The more your home is occupied during daylight hours, the better your returns will be, as you will avoid importing more electricity from the grid.

Try entering the details you get from your installer below and see what return on your investment you get. The example above should give you over 12% per year for 25 years, tax free and linked with inflation. Alternatively you can look up here how much solar radiation there is in your area of the country in this solar radiation map.

Our members have a more detailed version of the calculator which takes account of important variable factors (like roof orientation) to give more accurate results. Please use the calculator below as a rough guide only.

in kWh/year

in kWp

The total initial cost of the system in pounds

Percentage real rate of electricity price increase (DECC = 2.6%)

The relevant FIT tariff for selected system in pence

Tariff rate for any electricity exported back to the grid in pence

Percentage inflation rate percentage - set to zero to allow real ROI

Starting price of electricity in pence

Tariff life in years

Export life in years

Usage life in years

Percentage of electricity that the government assumes you export to the grid

Percentage of electricity used (rest is exported back to grid)

Panel efficiency loss per year in percentage

Maintenance costs as a percentage of capital cost

Hide advanced inputs

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