Solar Energy (photovoltaics)

Technical Symposium

The Heat is on PV Modules

Author(s)

• 

  Kent Whitfield, MS, PE

  Principal Engineer, Renewable Energy
  UL LLC

Background, Description and Delivery : PV modules are evaluated to several domestic and international safety and performance standards, however, the majority of these presume an operational climate that does not exceed 40°C ambient air temperature coincident with full sun irradiance (i.e., 1000W/m2). Many new and emerging markets, on the other hand, have climates that routinely exceed this temperature as do some domestic locations with good solar resource. The consequence of temperatures above 40°C, coincident with high irradiance, is that products may exceed their material temperature ratings with an impact to both safety and performance as a result. This presentation will describe both modeling and actual system operating temperatures to understand how hot modules really get in the field as a function of their installation method (for example, open-rack versus building integrated) and their operating climate. A module’s maximum operating temperature, however, is rarely significant by itself since the clear majority of failure modes require time at temperature to develop with a major distinction made between short-term, or catastrophic, and long-term, or cumulative damage, failure modes. Both types of failure modes will be discussed as well as a strategy for risk reduction of each. A means to characterize a climate based upon knowledge of a failure mode’s Arrhenius behavior, specifically, its activation energy, will be presented for long-term failure modes and how this can drive not only better standards, but better testing as well. Finally, this presentation will discuss the status and approach being taken in the international standards writing body, IEC TC82 WG2, to address the challenge of high-temperature module operation.