1. Potential induced degradation is a potential induced performance degradation in crystalline photovoltaic modules, caused by so-called stray currents. This effect may cause power loss of up to 30 percent.
2. Potential Induced Degradation is a phenomenon that negatively affects the cells of PV modules. It is a process which occurs only a few years after installation. PID causes an accelerated degradation in performance which expands exponentially.
https://en.wikipedia.org/wiki/Potential_induced_degradation (1.); http://pidbull.com/what-is-pid/ (2.)