Soiling, or dust/sand and pollutants on PV modules, can reduce power output by as much as 25% in certain cases. If panels are not clean, the yields can decrease by approximately 40% within months in a desert or industrial climate. Research has indicated that automated robotic cleaning can regain most of this loss. In one case, the daily output of dry-robot cleaning was recovered by up to ~31% in a Saudi trial, while a U.S. pilot showed an 18% yield increase on robot-cleaned arrays as compared to uncleaned controls.

Robots also require substantially less water and labor. Candi Solar’s report estimates that robots use only 0.3-0.5 L/panel, manual washing requires 1-2 L, and a 1 MW park requires only 2 cleaning robot washes rather than 4-8 people operators. There are already several effective cleaning methods that are commercialized, such as brushes, water- or air-driven, or electrostatic. In Pakistan’s arid environment (with high dust loads and seasonal rains), locally adapted robotic solutions can significantly enhance solar PV production, save valuable water, and significantly reduce operation & maintenance (O&M). We summarize findings and make policy recommendations. Encourage the mass deployment of solar farms with a view to running the facilities at peak efficiency in Pakistan. Soiling losses are a problem in Pakistan’s climate.

Soiling Losses in Pakistan’s Climate

Irradiance is the most important factor affecting PV yield, after dust. Pakistan has a dry climate. The weather in Pakistan is dry. The amount of soiling is extremely high in dry and windy air. A study on the roofs of Lahore detected a build-up of 0.8% on panels during the months of October to January. Internationally, tests have demonstrated that 40–50% of the power is lost in a few weeks in desert environments. For instance, desert sand can reduce the productivity of a farm by ~40%, as reported by the National Renewable Energy Lab (NREL), if not cleaned. Even in moist and coastal regions, pollutants such as Soot, pollen, and salt crusts stick very well to glass. This is far below nameplate outputs. Pakistan’s long, dry summers are followed by monsoon rainfall, and thus panels need to be cleaned more frequently than is required in temperate climates. 

Globally, NREL’s soiling analysis puts annualized losses as low as 0.5%/year in temperate, rainy climates but as high as 30%/year in deserts such as the Middle East, with revenue losses that can reach millions of dollars per year on large utility-scale systems. The IEA-PVPS global soiling task-force report similarly documents wide regional variation, with the highest losses concentrated in arid, low-rainfall zones. Even in humid........

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