Novel soiling loss measurement system for PV installations

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An international research group led by Spain’s DLR Institute of Solar Research has developed Radguard, a novel system that measures soiling losses in PV systems.

Radguard uses a lamp to illuminate a pyranometer or PV reference cell for about 45 minutes at night. The lamp is protected from soiling by a 25-cm collimator. The scientists said this is crucial for the correct functioning of the device, as well as the fixed position of the lamp.

“By comparing the irradiance measured at night with that of another night when the sensor was clean, the soiling loss can be derived,” the scientists said. “Several 45-minute long measurements are combined to detect erroneous soiling measurements caused by dew, rain droplets on the radiometer, or other effects that might only be present in some of the various measurements.”

They placed the RS2600 pocket lamp on one end of a 90-degree angle structure. On the other side of the structure, they used a corresponding sensor, a CM11 pyranometer, and an NES SOZ-03 reference cell with textured cover glass. They also used a Campbell CR1000 data-logger to collect data on the reference cell’s short-circuit current and the pyranometer’s voltage.

“The batteries of the lamp are replaced by a power supply that is controlled with a common time controller that switches on the lamp during one or more 45-minute intervals at night,” said the academics.

The group validated the new technique in four-month testing held in outdoor conditions, which it claims showed an accuracy that is close to that of the reference method, which however includes the daily cleaning of the reference devices.

“The measured soiling losses were compared to soiling losses derived by comparing the test radiometer to a clean device of the same model,” the scientists said. “The deviations between the data sets were found to be below the expected uncertainty of the reference data with low biases of <0.3%.”

They described the new technique in “Autonomous measurement system for photovoltaic and radiometer soiling losses,” which was recently published in Progress in Photovoltaics. The research team includes academics from Sweden’s DLR Remote Sensing Data Center, Spain’s CIEMAT Plataforma Solar de Almería, and Germany’s DLR Institute of Remote Sensing Technology.

“In the future, the method will be tested at further sites and in longer measurement campaigns that are now under preparation,” they concluded.

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