Solar panels are obviously affected by the amount of sunlight that they are exposed to, both by the number of hours' sunlight and the intensity of the sun. In the UK, our temperate climate means that solar panels will not produce a constant amount of power all year round.
If you have purchased a 100W solar panel, you can expect to generate this amount on a clear sunny day from late spring to early autumn. On overcast days and in winter, the weather is likely to reduce this amount, as the sunlight is less intense and there are less sunlight hours during each day. When we are calculating what size panel or solar array necessary for a specific application, we base our figures on a panel operating at 70% efficiency for 5-hours a day; this ensures we can produce the energy needed all year round.
Luckily, solar panels do conitinue producing energy, even when the sky is overcast, the panel is slightly shaded or covered by up to an inch of light snow. Some panels perform better in such conditions than others and our monocrystalline solar panels undoubtedly perform best in less than perfect conditions.
There is no 'exact science' involved in predicting the exact amount of energy a solar panel will produce in given conditions, but the diagram below is a useful guide:
(example: a 100W panel operating at 25% will produce 25W)
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