Why cleaning frequency should follow soiling loss.
Start with the loss, not the calendar
A fixed schedule is easy to administer, but it can clean too early, too late or at the wrong frequency. Rainfall, local dust, site activity, array geometry and seasonal conditions change the accumulation and natural recovery pattern.
Use a simple decision equation
Expected net benefit of cleaning = value of recoverable energy − total cleaning cost.
The calculation period should be explicit. Recoverable energy depends on the estimated soiling loss, expected irradiance, system response and how long the benefit is likely to persist. Total cost should include labour, water, equipment, access, safety controls and any operational disruption.
Practical assessment framework
- Estimate the current soiling-related performance loss and its uncertainty.
- Review rainfall history, forecast conditions and the likely re-soiling rate.
- Estimate the energy that cleaning could recover over the decision period.
- Apply the relevant energy value and compare it with the complete cleaning cost.
- Consider whether partial, staged, manual or robotic cleaning better fits the site.
- Measure or review performance after cleaning and update the next decision.
Assumptions and limitations
A change after cleaning does not always represent soiling recovery alone; irradiance, temperature, availability and data quality may also change. A defensible assessment records the comparison conditions and avoids claiming precision beyond the available measurements.
References
- IEA PVPS Task 13: Soiling Losses—Impact on the Performance of Photovoltaic Power Plants.
- IEC 61724-1:2021 — PV performance monitoring terminology and methods.