How much shade is enough?

Researchers have covered part of a rooftop solar plant with a different numbers of shading cloth layers to measure their power, current, and voltage. They have been able to identify a point after which the value of system current and maximum power is no longer sensitive to shading heaviness.

August 26, 2024 Lior Kahana

Image: Andreas Weiland, Unsplash

A group of scientists from Aligarh Muslim University conducted a field experiment to analyze the impact of shading heaviness on voltage, current, and power on PV modules and strings.

To measure shading heaviness, the group used varying layers of shading cloth to identify a critical point, following which the value of system current and maximum power becomes insensitive to shading heaviness.

“The energy yield of a PV system can decrease during partial shading because the maximum power of the PV system can drop harshly. This paper covers a different aspect of shading, that is, shading heaviness and its impact on performance parameters,” the group said. “The aim of this research is to investigate the susceptibility of the shading heaviness to a partially shaded photovoltaic system and the critical point that decreases the susceptibility of shading.”

The experiment was carried out on a 119 KW solar plant situated on the roof of the Aligarh Muslim University. This plant consists of 19 strings, each with 20 PV modules connected in series. The modules have a tilt angle of 27 degrees and a rated power of 315 W. Shading measurements were done on the modules of one string.

“It was observed from the datalogger recording that partial shading or changing shading heaviness has a negligible effect on the system voltage whereas current shows significant impact and hence power,” the academics said. For example, on a string shaded by two layers of the cloth, the power was measured at 28.4 W, the current at 38 A, and the voltages at 245 V, while a string shaded with four layers showed 22.5 W, 23.5 A, and 243 V, respectively. An unshaded string produced 30.7 W of power, 418 A of current, and 244 V of voltage.

“From the observed readings, we see that standard deviation up to the first four layers is significant for current and power but is insignificant for the 5th to 8th layer of shading, but for voltage, it remains insignificant for both intervals,” the paper notes. “Shading heaviness critical point is that point where the value of system current and maximum power becomes insensitive to heaviness.”

According to the results, while five layers of shading cloth resulted in 17.8 W, 22 A, and 241 V, in the case of eight layers of shade, it changed to 14.7 W, 19.8 A, and 241 V. In the case of six layers, the measurements showed 16.3 W, 20.6 A, and 241 V, while in the case of seven layers, the results measured 14.9 W, 20.5 A, and 242 V.

“More experimental and simulation studies of ‘critical point’, the relation between shading heaviness and voltage, current and power, will be helpful in the planning and forecasting of any solar power plant,” concluded the research team. “If the critical point is known, some unnecessary reconfiguration work can be reduced as the photovoltaic system becomes insusceptible to shading heaviness when the critical point is met.”

Their findings were presented in “Impact of shading heaviness on voltage, current and power of the solar photovoltaic string,” published in Next Sustainability.

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