Standalone photovoltaic water-pumping systems provide critical water access in remote and off-grid communities, yet their performance under real-world soiling conditions remains poorly characterized. A new simulation-based study conducted for semi-arid Fez, Morocco quantifies how dust accumulation cascades through energy generation to final water delivery and system reliability—revealing a far sharper response than energy analysis alone would suggest.
The researchers modeled a 2.01 kilowatt-peak PV array with centrifugal pump, storage tank, and realistic daily demand cycles using hourly irradiance data from PVGIS-SARAH3. Dust soiling was represented as a progressive transmittance loss, with rates ranging from 0.5% to 1.5% per day—typical for semi-arid regions with infrequent rainfall. Under no cleaning, a 1.5% daily soiling rate reduced both energy output and water delivery by approximately 20% during a 30-day dry season. This near-linear relationship between energy loss and water deficit initially appears manageable.
However, the reliability analysis revealed a critical inflection point. A 50-cubic-meter storage tank serving a 25-cubic-meter daily demand achieved annual reliability of 0.997 when clean. At just 0.5% daily soiling, reliability plummeted to 0.219, and at 1.0% daily soiling fell further to 0.150. This sharp cliff reflects how storage buffers gradually deplete when daily generation falls below demand, eventually triggering complete supply loss on windless, dusty days.
Using Loss of Water Supply Probability (LWSP)—the water industry analogue of energy-focused loss-of-load probability—the study demonstrates that maintenance intervals must be far more aggressive than energy performance targets would justify. At 1.0% daily soiling, a 41-day annual cleaning interval maintains reliability under annual rainfall averaging, whereas energy-deficit rules alone suggest 13-day intervals. The findings underscore that water reliability, not energy yield, should drive maintenance planning for critical off-grid water systems in arid climates.
