Balancing the cost of a cleaning cycle against the revenue lost from dust and dirt soiling a PV panel is often a difficult equation for PV plant operators, one that’s as unpredictable as the weather. Getting it wrong either way can lead to a significant loss of revenue, so there is plenty of interest in the topic and the development of models to predict the effects of soiling and calculate an optimal schedule for module cleaning.
While the soiling profile can vary greatly even between two sites in the same region, there is value in looking at regional data. Scientists led by East West University in Bangladesh analyzed soiling trends in different regions, aiming to provide a global overview of the effects of soiling in different parts of the world, and to develop a model to calculate the best cleaning cycle to optimize project revenue.
The model is described in the paper Global analysis of optimal cleaning cycle and profit of soiling affected solar panels, published in Applied Energy. In their analysis the scientists assumed a project size (yield under 1-sun) of 100 MW, a cost per cleaning operation of US$2670, which it notes is at the lower end of cost estimates for cleaning, and an electricity tariff for the project of US$0.069/kWh – though they note that cleaning costs can be much higher in certain regions, which will affect optimal cycle calculation.
The group was able to show that based on studies of two solar plants located in Saudi Arabia and Chile, calculations from their model fell within 0.1% of the actual numbers, demonstrating the model’s validity to PV project investors.
The study also concluded that there is little value in seasonal variations to cleaning schedules, with only negligible increases in revenue resulting from such optimization. For regions prone to sandstorms, the modeling becomes much more complicated, and the researchers warn that investors should carefully consider the viability of projects in such regions.
And a global level, the model finds the worst soiling conditions in Asia and the Middle East, where even with optimal cleaning schedules implemented – usually every 5-6 days – soiling losses still amount to around 2.5%. In Europe and North America, a cleaning schedule every 10-12 days is enough to limit soiling losses to below 1.5%.
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