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Question : How bad is it if a solar panel is not ideally orientated?

Read first: "How can you orientate a solar panel?
and: "How is a solar panel orientated ideally?"

The ideal orientation of a solar panel can be found here. But what if your roof is not orientated to the South, but to the West or the East. Is it worth the effort to install solar cells? And what is the slope of the roof is not 35°?

Examine the following figure, which gives data for Belgium.

The maximum (=100% on the figure ) is 123 W/m² for an ideally orientated solar panel in Belgium. We notice that an ideal panel is orientated to the South (S), and has a slope of about 35°. You notice that the red-orange spot is quite large; this means that the orientation is not critical. A deviation of 30° in whatever direction results in a loss of maximum 8 W/m², i.e. about 7% less than the maximum.

So it is worth the effort op installing photovoltaic solar cells, even if the roof is not aimed perfectly to the South, of the slope is more or less than 35°!

Answer: The orientation is not critical. A deviation of 30° in whatever direction results in only a small loss.