How does shading affect photovoltaic production?

The Invisible Impact of Shading: How Small Shadows Can Drastically Reduce Photovoltaic Output.

🤔 Shading is one of the primary factors affecting the efficiency of photovoltaic installations. Even small shadows that cover only a minimal portion of a panel can have a large impact on energy production. The reason lies in the internal structure of the modules and how the cells are interconnected in series to generate electricity. For example, if a small percentage of shading completely covers a single cell at the start of a series of cells in a photovoltaic panel, it can significantly reduce the current flowing through the entire panel. This happens because all the cells in a series must operate at the same current; if one cell is affected, it acts as a bottleneck, limiting the production of all the others, even if the rest of the panel is fully exposed to sunlight.

To illustrate this, let’s consider a module with 72 cells (6x12) arranged horizontally, as shown in Figure A). The module is divided into three submodules, each one protected by a bypass diode.

In Figure B), we see that the bottom-right cell is completely shaded, representing 1/72 = 1.39% shading of the entire module. On the other hand, in Figure C), we observe that all the cells in the first row are partially shaded at 10 % each, resulting in 0.1/6 = 1.67% shading of the module. Despite the higher total shading percentage in Figure C), the module's energy production is lower in the first case. This is because, in the first case, the bottom submodule does not produce energy due to having one cell fully shaded. Consequently, the bypass diode is activated, and the total module production is limited to the output of the other two submodules. In contrast, in the second case, the first submodule does contribute to the total module output since the shading of each cell is minimal, and the reduction in the submodule’s output is smaller, without triggering the bypass diode.

In Figure D), all the cells in the right column are fully shaded (1/12 = 8.33% total shading of the module), while in Figure E), all the cells in the bottom row are shaded (1/6 = 16.67% module shading, double that of the previous case). In this scenario, in Figure D), the module does not produce any energy since each submodule has at least one fully shaded cell. However, in Figure E), the bypass diode for the bottom submodule is triggered, causing it to produce nothing, while the other two submodules continue to generate energy, so the module’s output is not zero. In fact, the production in this case is equivalent to that observed in Figure B), where only one cell was shaded.

👉 In conclusion, the presence of shadows on photovoltaic modules can significantly affect energy production, even if the shading percentage seems small. The series configuration of cells and the activation of bypass diodes can influence the overall system efficiency. Therefore, it is crucial to consider and minimize the impact of shading on photovoltaic installations to optimize performance and ensure more efficient energy production.