Researchers covered part of a rooftop solar power plant with different numbers of layers of shade cloth to measure their power, current and voltage. They were able to identify a point after which the value of the system current and maximum power is no longer sensitive to the severity of the shadow.
A group of scientists from India’s Aligarh Muslim University conducted a field experiment to analyze the impact of shade heaviness on voltage, current and power on PV modules and strings.
To measure the shade’s heaviness, the group used several layers of shade cloth to identify a critical point, at which point the value of the system current and maximum power became insensitive to the heaviness of the shade.
“The energy yield of a PV installation can decrease during partial shade, because the maximum power of the PV installation can drop sharply. This article addresses another aspect of shading, namely the severity of shading and its impact on performance parameters,” the group said. “The purpose of this study is to investigate the sensitivity of shading strength for a partially shaded photovoltaic system and to investigate the critical point that reduces the sensitivity of shading.”
The experiment was conducted on a 119 kW solar power plant located on the roof of Aligarh Muslim University. This installation consists of 19 strings, each with 20 PV modules connected in series. The modules have a tilt angle of 27 degrees and a nominal power of 315 W. Sun protection measurements were taken on the modules of one string.
“The data logger recording showed that partial shading or changing shade strength has a negligible effect on the system voltage, while the current shows a significant impact and therefore power,” the academics said. For example, on a string shaded by two layers of fabric the power was measured at 28.4 W, the current at 38 A and the voltages at 245 V, while a string shaded by four layers measured 22.5 W, 23.5 A and 23.5 A. 243 V, respectively. An unshaded string produced 30.7 W of power, 418 A of current, and 244 V of voltage.
“From the observed measurements we see that the standard deviation up to the first four layers is significant for current and power, but is insignificant for the fifth to eighth layers of shading, but for voltage it remains insignificant for both intervals,” the paper notes. . “The critical point for gravity shading is the point at which the value of the system current and maximum power becomes insensitive to gravity.”
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 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 on the ‘critical point’, the relationship between shade severity and voltage, current and power, will be helpful in the planning and forecasting of any solar power plant,” the research team concluded. “If the critical point is known, some unnecessary reconfiguration work can be reduced because the photovoltaic system becomes insensitive to heavy shading when the critical point is reached.”
Their findings were presented in “Impact of the heaviness of the sun protection on the voltage, current and power of the solar photovoltaic string”, published in Next Sustainability.
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