A sizeable solar plant will consist of a large number of strings, and monitoring each one individually can be cumbersome. However, as the performance of each string within an array impacts the maximum power point of the entire array, it is important to identify disconnected or underperforming strings as early as possible to avoid significant energy loss.

String underperformance can be due to:

• Underperformance of one or more modules in the string;
• Electrical connection fault in the string;
• Shading.

Identifying underperforming strings is a step in the process of identifying and rectifying underperforming solar modules.

Soiling loss refers to lost production caused by reduced irradiance on the PV modules resulting from accumulation of dirt (“soiling”) on the face of the modules. Dirt on the face of the modules will reflect or absorb radiation, reducing the irradiance available to the modules for conversion to electrical power.

Soiling can significantly reduce solar plant production, and can be reduced by cleaning the modules at suitable intervals. The ideal cleaning timing and frequency will depend on a few factors:

• How quickly soiling gathers on the modules at the site (may vary seasonally);
• How frequently it typically rains at the PV plant;
• Cost of cleaning.

An analysis should be carried out to establish the optimal cleaning frequency to maximize net revenue considering these factors.