Most people know that if you leave a car in the driveway for long enough is will naturally accumulate dirt. In the PV industry this causes a significant and avoidable loss of power known as ‘soiling’. Studies have found that the soiling effects on various PV systems have exhibited over 25% energy loss during dry periods.
Soiling is the greatest avoidable performance loss in photo-voltaic (PV) systems. Soiling comes from many anthropogenic and natural sources, which make it difficult to develop a standard model for accumulation across all PV systems operating today. The issue of soiling is compounded when PV system owners clean arrays at set-time intervals. This method is potentially cash flow detrimental to the lifetime performance of the PV system. Due to these factors, a system should consider local measurement analysis with an automated device like ARES.
The cost of washing a photovoltaic system can be quite a large portion of the operating and maintenance expenses. The normalized cost for cleaning an array can be anywhere from $2-$4 per kW. This means that a 1,000kW system could cost $2000 – $4000 to clean. We must factor in the cleaning equipment required, location, and access to the panels. Washing too often, or not enough, can drastically reduce both the levelized cost of energy (LCOE) and return of investment (ROI) over the life of the system. Therefore, determining the best day to wash is critical to increasing the overall efficiency of the array. A non-cost safety risk to washing PV systems is also important. Cleaning a PV array only when absolutely necessary avoids risk to personnel by avoiding work-at-height and arc flash dangers, which account for a vast majority of serious injuries when dealing with PV array maintenance.
At present, system owners are forced to undergo field experimentation in a very manual fashion if they wish to determine the soiling rate of their arrays. These experiments fail for a number of reasons and three are the most glaring.
As financing institutions more often become the owner of systems across the country (over 72% of Residential Solar in 2014 according to GTM Research of solar installations in the US), the direct effect of soiling to system ROI has become an avoidable loss on everyone’s mind.