Energy generation from the renewable sources are becoming a more popular option, especially harvesting the sun using a solar photovoltaic (PV) technology. The use of fossil fuels are slowly reducing and the world is transiting into the solar era. The expansion of PV technology is occurring rapidly, leading to increased demand for investigations into factors that affect its efficiency. Shading plays a crucial role in impacting the efficiency of PV systems. Even the small area of shade on a PV module can result in significant reductions in power output, efficiency, and overall system performance.
Shading losses refer to the reduction in electricity generation caused by an obstruction that prevents the direct sunlight reaching solar panels. The shading on a single PV module effectively mitigates the overall electricity generation output of a modules string. When installing a Solar PV System, it’s important to take into account various types of shading. There are two main types of shading: dynamic and static. Dynamic shading, such as the shadows created by drifting clouds and falling leaves, adds a dynamic element to the scene. Shading can also occur due to various factors such as snow, bird droppings, and the accumulation of dust on the surface. Static shading involves considering factors such as shade from nearby trees, buildings, chimneys etc.
In fact, the shading of 10% of the area of a system could cause a loss of 50% in the performance of PV system. Soiling, which is a prominent factor contributing to energy loss in certain areas. In regions with frequent dust deposits, the losses may lead up to 5-7%. According to an NREL study, implementing an annual cleaning on a system with a soiling loss of 1.9% would result in a reduction of the loss to approximately 1.5%. Performing two cleanings annually has the potential to decrease the average loss to 1.3%. Additionally, implementing three cleanings per year would further limit the average annual loss to 1.2%.
Bird droppings can cause significant blockage in one or two cells, and they may not be easily washed away by rain. If a module does not have bypass diodes, the loss of operation can occur if one or two cells are completely blocked. Hence, reduction in the power generation. Snow loads also are also a limiting factor. A NREL study found that fixed-tilt systems can experience losses ranging from 10-30% due to snow loads.
Installing Bypass diodes allows for the isolation of shaded cells. These intelligent devices redirect the electrical current, effectively bypassing the underperforming cells. So that their influence is minimized on the entire system. However, by implementing this approach, the output of the bypassed components will be loss. Another way to enhance the performance when dealing with shading is by implementing Module-level power electronics (MLPE) device. These include DC optimisers and microinverters that can be easily attached to individual PV modules. DC optimisers have the ability to adjust both the output voltage and current under the influence of shading on the PV panel. When microinverters are installed, the panels are connected in parallel. This ensures that when one panel is under the shadow, every panel will function at its highest capacity without any negative effects on the rest of the panels.
In a nutshell, the performance and efficiency of PV systems can be greatly affected by shading. By understanding the mechanisms of shading losses, and implementing smart mitigation strategies, it becomes possible to greatly reduce these losses and improve the overall performance and reliability of solar PV systems. Efficient system design, cutting-edge technologies at the module level, consistent maintenance, and state-of-the-art monitoring play a crucial role in effectively managing and minimizing shading losses in PV systems.
