Evaluation of high-temperature exposure of rack-mounted photovoltaic modules

Photovoltaic (PV) modules operate in an extreme environment and are exposed to radiation, humidity, and hot and cold thermal extremes. This paper focuses on polymeric-material degradation during PV-module operation at high ambient temperatures, high solar irradiance and low wind speed. The 2004 version of the IEC 61730 specification requires all polymeric materials used in a photovoltaic module to have a Relative Thermal Index (RTI) or Relative Thermal Endurance Index (RTE) at least 20°C greater than the maximum material temperature measured during the temperature test conducted at 40°C ambient. There is currently an international debate regarding this requirement. This paper explores the thermal exposure of photovoltaic modules in the field as a technical basis for this debate. For the hottest cities, the thermal exposure is found to be equivalent to aging at a constant temperature of 42-53°C, with maximum temperatures of 75°C.