Solar panels perform at their best on a clear sunny day with no cloud cover. This does not mean that the conditions are going to be favorable all the time. Most often panel performance is reduced due to weather conditions like cloud cover or rain. In such conditions, solar panels produce their power from diffused solar radiation (radiation scattered by molecules in the atmosphere) as there is hardly any direct sunlight.
To understand this better, let us look at the following.
How does cloud and rain contribute to solar panel performance?
As a general rule, there is a considerable decrease in solar panel performance due to cloud cover or rain. If the cloud cover is very heavy, solar panels may produce only 5-10% of the energy they normally produce.
But it may be noted that some solar panels are designed to work well with diffused solar radiation on a typical overcast day. Countries like Germany and UK are prime examples of cloudy countries that have successfully installed solar panels. Thin-film cells are especially suited for these overcast conditions.
Rains can also be helpful in some ways. For example, rain cleans the solar panels by removing dust and dirt which otherwise affects solar panel performance. And this decreases maintenance which is normally a problem in the case of rooftops.
What are the load requirements on a cloudy or rainy day?
When you look at the usability of a solar panel on a cloudy or rainy day, the more important factor is to know if the solar panels will produce sufficient power to run you house. On a rainy or cloudy day, many of the appliances like fans or air-conditioning may not be needed. This means that modest power requirements which can easily be met by the solar system.
What happens when solar panels don’t perform?
In case the power requirements can’t be met, you have to rely on grid power. If your house is connected to the grid, there is no problem. But in an off-grid location, you will have to depend on battery backup. As long as you have enough energy stored in the battery bank, there won’t be any power shortage.
Conclusion
So, the answer to the question is yes. Solar panels work but they are not as productive as they are on a sunny day. On an average, it can be said that a cloud cover can reduce solar panel performance by 50%. But depending on how heavy and dark the rain and clouds are, your solar panels may perform at around 20-60% of their rated capacity.
Please understand that the more important factor when sizing your solar system is to consider the number of sunny days available over the entire year instead of a couple of rainy or cloudy days that could hardly affect the overall performance.
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