1 - Overview: Power Degradation and Failure of PV Systems

Abstract

Solar power based on photovoltaics has introduced a revolution in sustainable energy in the modern world, since the initial development under US Department of Energy funding of the Flat-Plate Solar Array Block Program in the late 1970s. This research led to the successful development of crystalline silicon photovoltaic modules and their demonstration in PV power plants such as the 1MW Lugo power plant in Hesperia California, and the 5.4MW Carrisa Plains power plant in San Luis Obispo County California constructed by the Atlantic Richfield Oil Company (ARCO) in the early 1980s. The Carrisa Plains power plant suffered severe reliability problems as demonstrated by its annual power degradation rate (Rd), or performance loss rate (PLR), of approximately 10%/year, far beyond the designed Rd of 1%/year. The Carrisa Plains power plant was a “large scale” technology demonstration project that dramatically showed how a technology that performs well in the lab may still suffer catastrophic reliability failures when implemented at commercial scale outdoors under real-world environmental conditions. This led to a long period of research into the multiple root causes and contributors to the plant's failure, that to this day underpin the reliability of crystalline silicon PV modules with their aluminum-back surface field cells with front side-silver metalization and ethylene vinyl acetate encapsulants with fluoropolymer based backsheets. The evolution of PV technology and industry, as it has incorporated new technologies such as thin film absorbers, alternative concentrating optical designs, or lower cost materials, has always existed under the threat that the fundamental reliability of the PV module will not hold up for the 20 to nowadays 35year lifetimes that are assured in the module's product warranties. This reliability challenge arises because PV modules are used with essentially little maintenance, under harsh real-world conditions in hostile climate zones, for long expected lifetimes. This serves as a continuing reminder of the critical importance of understanding the degradation science of materials and modules under actual real-world conditions, and how these correspond to the more idealized conditions of rapid lab-based qualification or acceptance tests that are used during technology development.