Solar-panel report : April

Shortly after the end of every month throughout 2012, I am reporting on how an array of PV solar panels, owned by friends of ours, has performed in rural Aberdeenshire. This will be of limited interest to most of you, I know, but it fills a huge gap in the information available to prospective solar-panel buyers.

Everyone I know who has installed solar-panel arrays has said how scarce was real-life information on how much electricity a solar-panel array could actually generate in Scotland. The Energy Saving Trust has a helpful website, but even that is wary of giving a definitive answer on likely returns from the investment.

That is no surprise; there are so many variables (hours of sunshine, roof pitch, geographic latitude, panel efficiency, compass direction, tree cover) that it is impossible to say exactly what power savings and tariff earnings will be.

This leaves the way open for installers to provide the guidelines and some, in the obvious interests of a sale, are a little more ambitious in their projections than others.

This is why we’ll track the performance of this array through the year. It will offer a real-life example of what a PV solar-panel array can do beneath the chill, grey skies of North-east Scotland. We’re now four months in.

Size of array: 16 panels

Array capacity: 3.95kW

Type of panel: Samsung 247

Co-ordinates of installation: 57N, 03W

Compass direction: 165S (180S is the ideal)

Roof pitch: 30 degrees (30 degrees is the ideal)

Shade: 10-metre birch trees at 30 metres. Leaf budding.

April average noon temperature:  7.0C

April average number of daylight generating hours: 12hr 07min

April weather: seven days’ sunshine, 22 days overcast, one day of snow.

April units generated: 205.0

Jan-Apr total units generated: 639.7

Manufacturer’s rated annual output for this array: 3,600 units

The array needs to generate 200 units a month to break even on installation cost (£12,600), plus the loss of investment returns had the money not been spent. Woefully bad weather in April (a day of blizzards in the first week and constant driving rain and dark skies in the final two weeks) depressed the generation figures. Longer daylight hours compensated slightly, but the array barely broke even, at 205.0 units.

It is becoming clearer that solar panels would be impossible to justify without feed-in tariffs. Home-owners need the Government paybacks per unit generated to make panels financially viable. Solar arrays don’t generate enough usable electricity in the UK for power savings alone to cover the cost of buying and installing them.

• With thanks to Anne and George for allowing us to share their figures.