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Solar panels only generate electricity when it is light, so they produce the least during short winter days when the sun is low in the sky. To give you an idea, the shortest day of the year (around December 21) lasts 8 hours, while the longest (around June 20) lasts more than 16 hours.

The amount of energy produced is also reduced by cloudy skies and snowfall in winter. Solar radiation does not fall directly on the panels, but is refracted by clouds or snowflakes. This means that diffused light hits the power plant, from which the panels produce less energy than from direct radiation. In addition, production is not helped if the panels are covered with a thin layer of snow or frost.

Exactly how much the panels produce in winter depends on the weather and location, but as a rough guide, in the winter months you can expect to get about 20-25% of the summer output from a PV system.

It may seem paradoxical, but low temperatures are good for photovoltaic panels. Silicon atoms have lower initial energy in winter, so the sunlight that hits them causes a more significant increase in their energy than in summer, when their initial energy is higher. This more significant increase in energy is responsible for the higher efficiency of the panels, but it is far from compensating for the shorter days, so production is still significantly lower in winter.

You can store summer surpluses for winter
During the summer, when your photovoltaic system produces more than you consume, you can store part of the surplus in physical batteries for a short time or use it to heat water. Any excess can be fed into the grid and stored in a virtual battery.

This is not real energy storage as in the case of a physical battery; the electricity is immediately consumed elsewhere after flowing into the grid. However, your supplier will credit you for this overflow, and you can then withdraw it from the grid later – usually in winter. You only pay distribution fees for this electricity.

In addition to the virtual battery, you can also share or sell summer surpluses from your photovoltaic power plant to your supplier. In all cases, you physically overflow into the distribution grid; the only difference is how you deal with these overflows.

Overdimensioned photovoltaics are not worthwhile
Lower winter production may also lead some people interested in PV systems to consider oversizing their photovoltaic systems so that they cover as much of their consumption as possible, even in winter. However, we do not recommend this. You will pay more for a large photovoltaic system, you will only slightly increase winter production, but in summer you will generate such huge surpluses that your distributor may limit or completely prohibit overflow into the grid.

It is therefore best to design a system that best matches your annual consumption rather than oversizing it just for the winter months.