Over-irradiance events affect utility scale PV components

Sudden spikes in irradiance can affect the components of large scale PV power plants, especially if they last longer than a minute and occur in temperatures above 30 degrees Celsius.

That is the main conclusion of a preliminary study into the effects of such ‘over-irradiance’ events on PV power generation. Researchers from the U.S.-based Sandia National Laboratories; Brazil’s Universidade Federal de Santa Catarina; the Solar Energy Research Institute of Singapore; Loughborough University, in the U.K.; and Germany’s Anhalt University of Applied Sciences have studied the phenomenon, which is usually triggered by the ‘cloud-edge effect’ which occurs when sunlight reflected off passing clouds temporarily raises irradiance on panels.

Measurements were taken for a year at test sites in Florianópolis and Brotas de Macaúbas, in Brazil; Bernburg in Germany; Albuquerque, in the USA; and Loughborough. The figures showed over-irradiance events were evenly distributed throughout the year.

Most occurrences last less than five seconds, according to the researchers, rendering them harmless for PV power generation, but around 7% of over-irradiance events lasted more than a minute. Such duration is enough to affect PV systems, said the scientists.

When such long-duration events occur in high temperatures, the combination could be enough to cause even slow-blow fuses to fail, especially in arid regions such as Brazil, according to the study.

The scientists added: “In addition to the issue of long duration over-irradiance events, the analysis also reveals that multiple over-irradiance events frequently occur within a short period of time of each other. These findings are especially concerning as over-irradiance combined with high operating temperatures may lead to widespread fuse failures in utility scale PV plants, and inverter clipping.”

The research is being conducted under the international PhotoVoltaic Collaborative to Advance Multi-climate Performance and Energy Research project, which aims to better understand PV performance in varied climates, share field instrumentation and validation best-practice, support emerging technologies with field studies and further PV deployment.

Dutch researchers recently observed solar power generation peaks may be stronger in partially cloudy conditions than from clear skies. They stated, the light reflected from clouds, together with intermittent shadows on arrays which reduced module temperatures, could boost generation.