What to expect from your PV panels throughout the year
Posted by Cathy Debenham on 4 February 2011 at 9:20 am
We're often asked how much electricity you should expect to generate from a solar PV system, and how much it will vary through the year. I'm going to use my 2.1kWp system as an example to give you an idea of what you might expect.
Our system is mounted on the garage roof. It's a steep (45 degree), south east facing roof, and it is shaded for most of the morning in winter when the sun is low.
My installer (Abacus Renewable Energy) did a prediction of the amount the system would generate based on the Standard Assessment Procedure (SAP) for energy rating. This is the system that all MCS accredited installers are expected to use. He also used a gadget called a SolarPathfinder which gave a range of data, for monthly generation with and without shading, and if the roof were ideal (ie a slope of 38 degrees).
These were the predictions:
SAP 1672 kWh per year
Actual with shade 1,589
Actual without shade 1,852
We're currently six days short of a year's generation and the system has produced 1,765 kWhs, so we're very happy to have generated more than predicted.
Not surprisingly, given the differing length of day and strength of sun, we do much better in summer than in winter. The best month for us is May with a predicted generation between 215 and 240 kWhs per month (figures with and without shade). This contrasts sharply with the December figure of estimate of between 36 and 45 kWhs.
We're based in the warm, sunny (wet) south west, so, as you go north, you'll get less sun, and correspondingly less generation.
If you have a question about anything in the above blog, please ask it in the comments section below.
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