Should you wash your solar panels? Insights from a small solar farm experiment and community discussion

Overview

Cleaning the panels produced a modest power gain. The author observed that after washing one bank of eight panels the power ratio between the two banks rose by roughly 2% to 5% compared to the baseline.

Methodology

The author compared power ratios between two banks before and after cleaning one bank. Sixteen panels are wired as two independent banks of eight panels each, with the inverter reporting output per bank. By measuring the ratio of bank‑A output to bank‑B output, variations in cloud cover and sun angle are largely cancelled out. Readings were taken before washing, after washing half a panel (initial ineffective attempt), and after each additional panel was cleaned, ending with all eight panels washed.

Results

The cleaned bank showed a 2‑5% rise in power ratio, with some noise. The ratio was stable before washing, dipped slightly when the first panel was wetted, then climbed as more panels were cleaned, and finally fell again after all panels were dry. The author interprets the peak as a 2‑5% improvement in output attributable to cleaning.

Economic assessment

The gain translates to £60‑£150 annually, diminishing over a few years. Based on the farm’s size and local electricity rates, a 2‑5% increase corresponds to about £60‑£150 per year. The benefit is expected to decay as dust re‑accumulates, making the intervention worthwhile only if repeated infrequently.

Safety and electrical notes

Tingles felt during cleaning suggest possible capacitive leakage; proper grounding is advised. The author felt a tingling sensation while wiping wet panels, which a commenter attributed to missing grounding lugs and recommended bonding all panels to a grounding rod with a 12 AWG copper conductor.

Environmental and operational factors

Rain often removes dust, but local conditions (pollen, desert dust) can increase soiling; temperature changes from water can affect readings. Several commenters noted that in regions with frequent rain, panels may stay clean enough that washing is unnecessary. Conversely, in dusty deserts or during heavy pollen seasons, soiling can cut output by 25%‑40%. One commenter suggested that the early dip in the power ratio could be due to water cooling the panels, as photovoltaic efficiency drops with temperature.

Feed‑in tariff and upgrade considerations

Upgrading panels would lose valuable feed‑in tariff benefits, making cleaning more attractive than expansion. The author notes that the existing system benefits from a high UK feed‑in tariff that pays for generated electricity, not just exported. Adding new panels would forfeit that tariff on the extra capacity, reducing the effective rate to about one‑quarter of the current one. A commenter echoed this, describing the situation as a market‑distorting incentive that discourages upgrades.

Community perspectives

Opinions vary from seeing cleaning as worthwhile to viewing it as unnecessary or a potential scam. Some users reported 35%‑40% gains after years of neglect, while others argued that rain suffices and that cleaning can be a lucrative but overhyped service. A few warned against attempting to clean roof‑mounted panels due to fall risk, and others emphasized the importance of checking installer advice.

Conclusion

For modestly dusty panels, cleaning offers a small, short‑term economic benefit; safety and local soiling conditions should guide frequency. If panels are only lightly soiled, the 2‑5% gain may barely cover effort and risk. In environments with heavy dust, pollen, or lack of rain, cleaning can yield larger returns, but proper electrical grounding and personal safety must be observed.