Abstract
Operating photovoltaic (PV) modules are frequently shaded by nearby structures, vegetation, droppings, etc., and this reduces the effective incident solar radiation received by the modules. Shading also reduces the power output of PV modules and, under certain conditions, causes the formation of hotspots. In this study, a wide variety of partial shading scenarios were investigated to evaluate their effects on the output current, voltage and efficiencies, and hotspot formation in mono-crystalline and poly-crystalline PV modules operating under the ambient conditions experienced in Nsukka, Nigeria. Sixteen shading cases were considered, including 20%, 40%, 60% and 80% of the modules’ surface areas shaded parallel to the long sides, parallel to the short sides, diagonally and randomly. Test ambient conditions, module outputs and surface thermal patterns were simultaneously monitored using a digital solarimeter, multimeter and infrared thermal imager, respectively. The outputs of the modules decreased to almost zero when as little as 40% of the module surfaces were shaded, with the reductions in performance being more severe in the mono-crystalline modules than in the poly-crystalline modules. The infrared thermography revealed the thermal patterns under the different shading conditions and showed that the random shading of the modules was the most likely to result in hotspots.
Highlights
Shading impacts negatively on the performance of solar PV systems by reducing power output and causing permanent damage of photovoltaic (PV) modules by the formation of hotspots
The effects of partial shading conditions on the performances of monocrystalline and polycrystalline PV modules were compared for modules subjected to similar shading patterns and ambient conditions
Subjective shading is further divided into dynamic shading, caused by objects that create shadows based on the sun’s angle, and static shading, caused by obstructing objects such as bird droppings, accumulated dirt, leave droppings, etc, that have come to rest on the solar module surface
Summary
Shading impacts negatively on the performance of solar PV systems by reducing power output and causing permanent damage of photovoltaic (PV) modules by the formation of hotspots. It is natural to expect the decrease in power production to be proportional to the shaded module area, and this may be true for a shaded single cell. It is hardly so at array or module levels. Subjective shading is further divided into dynamic shading, caused by objects that create shadows based on the sun’s angle, and static shading, caused by obstructing objects such as bird droppings, accumulated dirt, leave droppings, etc, that have come to rest on the solar module surface. Subjective shadings are preventable by proper installation, improved PV system design and periodic cleaning
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