You only use part of your own solar power

Solar panels feel like a closed system: what the roof generates goes into the house. That is not how it works, and it changes how you should look at maintenance.

Dutch consumer authority Milieu Centraal gives the share: of the solar power your panels generate, you use on average around 30 percent yourself. The rest goes to the grid. On the generation side there is a second figure — Milieu Centraal writes that the best-selling panels convert 19% to 25% of sunlight into electricity.

Those two figures together explain why a few percent of lost yield weighs more than it sounds. You start from an efficiency that is already limited, and of what remains, the part you use yourself is the most valuable — that is power you do not have to buy. Anything that structurally depresses yield hits precisely that part hardest, because your consumption does not shift along with a dirty roof.

The practical conclusion is unsentimental: maintenance is arithmetic, not cosmetics. Dirt that builds up gradually costs a little every sunny day, and it adds up unnoticed — you see no fault, just a curve sitting lower than last year. A single cleaning visit costs € 75-175; at two visits a year a subscription (€ 65-140 per visit) is cheaper. Every rate is in the price index.