Partial Shade Endurance Testing for Monolithic Photovoltaic Modules

In monolithically integrated photovoltaic (PV) modules, including CdTe, CIGS, and a-Si modules, some shadows can cause permanent damage under some operating conditions. This damage reduces efficiency and causes shunts that are visible to the eye and in luminescence imaging. Although these shadows are sometimes forbidden by product documentation, we have observed this type of damage in utility-scale PV systems. Existing standards ensure that qualified modules are safe to use after they are damaged by shadows. But no standard test exists to quantify the loss of efficiency that can result from this damage. In this work we describe new, accelerated tests to quantify the power loss that occurs due to shadows from human bodies and narrow objects, such as tools, placed nearby or directly touching modules. The tests are designed to be easy to conduct uniformly across products and laboratories. The tests can be performed outdoors and last only a few minutes. In our trials on commercial products, these tests resulted in 2%-27% permanent loss in power at standard test conditions (STC). The relative loss was several times larger when measured at lower irradiance. The tests we describe can be used to differentiate products, to direct the development of technological solutions to shadow sensitivity at the cell and module levels, and to establish the need for system-level and administrative solutions to the occurrence of shadows. Similar tests will be the basis of a new International Electrotechnical Commission (IEC) technical specification (TS) 63140.