Shading has more impact on solar PV than orientation or pitch
Posted by Paul Hutchens on 9 March 2011 at 9:15 am
Many of our clients ask about the orientation and pitch of solar panels - it appears that this has been well publicised. However, the effects of orientation and pitch are less than most people think. Moving the orientation from south to south-west, for example, reduces efficiency by less than 5% as does reducing the pitch from 30 degrees to less than 20 degrees.
What does make a more significant difference is shading to the solar panel; particularly hard shading from a tree, chimney, flue or another building to a solar PV array. In the worst case scenario, this can prevent the system from working at all - a bit like putting a resistor in a circuit!
As a result hard shading should be avoided at all if possible or, at least, limited to early morning/late evening and preferably in the winter only.
Recent evidence from one of our installations has demonstrated that hard shading can create the bizarre situation where solar energy yield is higher in cloudy conditions than in full sunlight. This appears to be because the hard shading "shadow" is limiting the flow of electricity through the array - even though more energy has been created!
On one occasion a 15% level of shading on an array reduced the output to less than 5% of what would otherwise be expected.
There are solutions to this - apart from avoiding shading in the first place. The main one is to split the array into two or more "strings"; each of which carries an independent parallel flow of electricity. That way, even if one panel or string is shaded, the other will continue to produce useful energy.
We continue to monitor our installations and research the market in order to find better solutions where they exist.
If you have a question about anything in the above blog, please ask it in the comments section below.
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