Do you know how partial shadows affect split-cell modules?

In the design of photovoltaic systems, it is common to assume a module as a unitary component that supplies voltage and current. However, if you want to evaluate the impact of shadows on a module, you must remember that internally a module consists of an association of solar cells along with so-called bypass diodes.

In standard panels, the cells are all connected in series with bypass diodes in parallel. When the modules are of split-cell type, they are "split in two," with each half having an association of cells in series that are connected in parallel with the other half and with the bypass diodes.

In both types of modules, when there is no shading, the bypass diodes remain inactive and do not produce any effect on the module. However, when shadows are projected, the affected cells generate a voltage drop that activates these diodes, "bypassing" this part of the module and thus preventing the appearance of hotspots.

In the image, you can observe the behavior of a 360 W split-cell module affected by partial shading and under 2 operating points:

• In the first situation, 2 bypass diodes are activated, bypassing 4 substrings of cells. The current is maintained, reducing the operating voltage, resulting in a production of 108 W (slightly less than ⅓ of the production due to the voltage drop across the diodes).
• In the second situation, the operating point is modified by decreasing the current to 5 A, preventing the bypass diodes from being activated. In this case, the operating voltage is maintained, reducing the power by half, i.e., 180 W.

The second operating point represents an advantage compared to standard modules since it allows us to obtain higher power under the same shading condition.

However, when working with modules in series, the operating point must be the same for all.

The consequence of this is that a partially shaded split-cell module at its bottom part would behave the same way as a standard module since the bypass diodes would bypass the 4 associated substrings.

However, if shading affected all the modules at their bottom part, we could obtain an advantage by changing the operating point (reducing the current).