Most pitched roof systems in Switzerland largely clean themselves through rain – routine cleaning is generally not necessary. Cleaning only makes sense in the case of a flat pitch, heavy soiling from dust or bird droppings, or if the monitoring shows a clearly measurable reduced yield.
Key points in brief
- In most cases, rain takes care of the cleaning of pitched roofs by itself.
- Exceptions are flat pitch, proximity to agriculture, bird droppings or stubborn edges on module margins.
- The trigger for cleaning should be monitoring data, not the visual impression.
- No high-pressure cleaner, no aggressive agents – and roof work belongs in professional hands.
Do I have to clean my solar system regularly?
In most cases, no. On pitched roofs, the rain largely washes down dust, pollen and loose dirt by itself. Furthermore, solar systems are designed as external components and laid out for wind and weather – a regular cleaning subscription «on suspicion» generally brings no measurable additional yield and is thus mostly unnecessary money.
That might surprise some homeowners, because people like to visually compare solar modules with windows, which you also clean. The difference: For the yield, it is not a flawless glossy image that counts, but whether enough light gets through. A light, even layer of dust makes hardly a noticeable difference here.
In which cases is cleaning nevertheless sensible?
Cleaning becomes sensible where the natural self-cleaning by rain is not sufficient. This primarily concerns the following situations:
- very flat roof pitch where water does not run off quickly enough
- locations near agriculture with increased occurrence of dust or pollen
- visible, stubborn bird droppings that cast a local shadow
- encrusted edges on module margins that can accumulate over years
In all these cases, soiling can actually permanently shade individual cells and noticeably depress the yield. Exactly then – and not routinely – a closer look is worthwhile.
How do I recognise whether a cleaning is necessary?
The most reliable trigger is data from the monitoring, not the visual impression from the ground. Looked at from below, a module can appear slightly dusty and still deliver completely inconspicuous yields – conversely, an inconspicuous soiling in an unfavourable place can impair an entire module string.
We therefore advise keeping an eye on the annual yield in the monitoring and specifically investigating in the event of a striking decline that cannot be explained by weather. Anyone who is unsure whether a reduced yield is actually due to soiling or has another cause will find a structured classification in the guide System delivers too little? The most frequent causes.
How is a solar system cleaned professionally?
If cleaning is actually indicated, the rule is: soft water, a soft brush and calm, even movements. A high-pressure cleaner does not belong on solar modules – it can damage seals, frames and the sensitive surface. We likewise advise against aggressive cleaning agents that can attack coatings.
A safety notice absolutely belongs here: Work on the roof belongs in the hands of professionals with appropriate fall protection. Unsecured stepping onto a pitched roof is a considerable risk that is in no proportion to the possible yield gain.
| Situation | Cleaning requirement | Note |
|---|---|---|
| normal pitched roof, no special influences | hardly | rain largely takes care of the cleaning |
| flat pitch or proximity to agriculture | occasionally | observation in the monitoring recommended |
| visible bird droppings or encrusted edges | occasionally to regularly | selective cleaning mostly sufficient |
| proven reduced yield in the monitoring | depending on the findings | clarify cause first, then act specifically |
Classification from practice, As of: July 2026 — the cleaning requirement always depends on the concrete location and roof.
During our service assignments in the Zurich region, we regularly notice that systems on normally pitched roofs deliver stable yields over years without any cleaning. We therefore mostly decline requests for a cleaning subscription until a concrete reduced yield is proven in the monitoring – that is lost money for the clientele, even if it would be easy business for us.
Frequently asked questions
How often do I have to clean my solar system?
On most pitched roofs in Switzerland, no routine cleaning is necessary at all, because rain washes away the dirt by itself. A cleaning is only worthwhile specifically when special circumstances or a proven reduced yield in the monitoring speak for it.
May I hose down my modules with the garden hose?
Carefully from below with soft water is fundamentally unproblematic. Do without high pressure, however, and without cold water if the modules are strongly heated up by solar radiation, as the temperature shock can stress the modules.
How much does a professional cleaning cost?
That strongly depends on roof shape, accessibility and actual effort on site, which is why a blanket figure cannot be named seriously. For a reliable assessment, a site visit or at least a quote based on your system is needed.
Does cleaning actually bring more yield?
Only when a soiling demonstrably depresses the yield – for example with bird droppings or stubborn dust in an unfavourable place. With a slightly dusty, otherwise inconspicuous system, the effect of a cleaning is mostly hardly measurable.
Free initial consultation
Are you unsure whether your system needs a cleaning?
We look into your yield data first – and recommend a cleaning only if it is actually worthwhile. Free of charge and without obligation.
Prefer to talk? +41 78 830 83 35
Photovoltaics Switzerland – installation by a specialist company →
Swissolar-certified specialist company · ESTI installation authorisation (Art. 14 NIV) · in Zurich since 2017 · over 150 systems completed · a personal answer from the specialist company, no call centre
Sources: EnergieSchweiz, Swissolar, manufacturer documentation.
Last updated: 9 July 2026 · Author: ecoEn editorial team
