Reference block comparison

Reference block comparison checks the production trend of a suspect area against nearby reference blocks, when such blocks exist on site. It is one step in diagnosing granular dust soiling losses, alongside soiling station data, rainfall records and cleaning logs. Start with normalized production trends and find dry periods where output falls even though availability, clipping, curtailment and irradiance sensor issues do not explain the drop. Dust on the module glass lowers transmittance and array current, and the loss can build up between rain or cleaning events. Next, check whether the assumed soiling model explains the recovery seen after rain or cleaning. If it does not, update the local accumulation and wash-off assumptions. Do not judge soiling from a single dirty irradiance sensor. Sensor drift, poor cleaning practice or a local obstruction can make it look like soiling when the array is not affected.