What determines a professional quote
Panel count, roof height and pitch, safe access, soil type, bird debris, water treatment, travel and whether inspection is included all affect price. Ask whether the quote is flat-rate or per-panel, whether deionized water is used and what happens if the crew identifies cracked glass, loose wiring or roof damage.
Compare the cleaning price with the estimated annual value of lost production. A small percentage loss on a modest system may be worth less than the service call.
Use monitoring to decide
Compare production with a weather-adjusted expectation or with similar clear days from an earlier clean period. A one-day drop can come from clouds, temperature or grid curtailment. A persistent unexplained gap plus visible soiling is stronger evidence.
Recovered energy value equals restored kWh multiplied by the rate that energy actually offsets. Exported energy may be worth less than retail consumption, so do not automatically value every recovered kWh at the full bill rate.
DIY safety and warranty checks
Do not walk on modules, use abrasive tools or direct high-pressure water at seals and electrical equipment. Follow the module manufacturer and installer maintenance instructions. Working on a wet or steep roof creates serious fall risk; ground-accessible rinsing is not equivalent to roof work.
If safe access is uncertain, hire an insured professional and confirm the cleaning method in writing.
When rain may be enough
Regular rain can remove loose dust but may not clear sticky pollen, bird droppings, ash, mineral deposits or debris trapped at a low frame edge. Low-slope arrays, nearby agriculture, wildfire smoke, unpaved roads and long dry seasons increase the chance that manual cleaning helps.
Inspect after unusual events and use production evidence. A universal twice-a-year schedule can waste money in one location and under-maintain another.