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When are your solar panels most profitable?

It is often believed that solar panels reach their maximum efficiency in summer and produce almost no energy in winter.

But that's not true! Hours of sunshine are not the only condition that causes performance to fluctuate with the seasons.

What kind of weather conditions influence photovoltaic performance?

Number of hours of sunshinental uren zonneschijn

This makes sense: with longer days, starting in spring, there is greater potential for capturing solar energy.

However, this should be put into perspective, since the influence of weather conditions is often more decisive than the number of daylight hours.


Your solar panels don't appreciate heat! Ambient heat causes the electrical components of your installation to overheat, which then become less efficient. This explains why performance is lower in summer than in spring.

As soon as the temperature rises above 25°C, the performance of the panels decreases by about 0.4% per additional degree. Do the math: during heat waves, performance loss is easily as high as 15%!

The moral of the story is that a freezing but sunny winter day can be as productive as a hot summer day!


This is a serious constraint for solar energy in Belgium. Especially from mid-October to mid-March, when there is a thick cloud cover, your solar panels will find it difficult to capture much.


Although falling rain often means clouds, it is an excellent ally to naturally clear your solar panels of the dust and dirt that prevent them from capturing light properly.

Rain is particularly useful in late spring, when pollen covers every surface. So watch out for droughts, which are becoming more frequent in Belgium. A study from the University of California has shown that after 145 days without rain, performance loss can exceed 7%!


Fortunately rare in Brussels, snow remains the worst enemy of photovoltaic panels. A thin layer of powder will not totally prevent the sun's rays being captured and will melt quickly.

But if it covers them with a thick layer, production can be zero!

Best performance: May and June

It is often thought that the climate in Belgium is not the most favourable for solar energy. However, the efficiency of our panels (up to 950 kWh produced per year per installed kilowatt-peak) is relatively high. This is not only because technologies are evolving and have adapted to our cloudy climate, but also because the “ideal” weather for the panels is not always what we think it is.

In Belgium, your solar panels produce the most in late spring. In May and June, the days get longer, clouds become scarcer, rainfall is generally sufficient and temperatures are not yet too high.In 2020 and 2019, production peaks were reached on May 2 and May 13, respectively.
  • The months of April and August generally offer good performance as well. 
  • On the other hand, the worst months for photovoltaic production are December and January.

To find out the daily and monthly solar power generation in Belgium, see the Elia website.

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