Increasing Predictability and investor confidence in PV power plants through latent defect screening

Solar power plant investors expect photovoltaic (PV) modules to safely and efficiently produce electricity for 25 years. International certification standards such as IEC are designed to evaluate modules for defects and design flaws that contribute to product safety or early lifetime performance issues. This certification testing is performed on a small number of preproduction panels. The majority of solar panel issues observed in the field, however, are driven by deviations in the manufacturing process, not by fundamental design flaws. These off-specification manufacturing defects are typically latent. This means that the panels initially meet performance expectations, but suffer accelerated performance degradation. Accurate data on the percentage of panels that exhibit significant latent defects is hard to come-by, but several studies suggest that the industry rate is around 4%. The appearance of latent defects significantly increases operating costs for the installation. The ability to gain knowledge of the exact quality of the PV panels installed at a power plant provides opportunity for improved output predictability and investor confidence. This knowledge will be increasingly important as the market penetration of PV increases, especially considering the more than 600 module suppliers. There is currently no certification to insure against PV panel underperformance caused by latent defects. In this article we introduce the concept of latent defect screening for PV modules. Latent defect screening involves the random sampling and accelerated-life testing of the PV panels to be installed at the construction site. We find that for an additional system cost of 1 penny per watt, we can be 95% sure that there are fewer than 3% defects in a 20MW installation.