Proposed photovoltaic module form factor to reduce levelized cost of energy
This paper discusses a proposed photovoltaic (PV) module form factor designed for utility-scale, one-axis tracking projects. The purpose of the form factor is to: 1) reduce total installed costs for utility-scale projects; 2) improve module reliability; 3) reduce operating and maintenance (O&M) costs, and 4) improve the project return on investment. The proposed module uses a double-glass construction to improve reliability and service lifetime in a form factor that is longer and narrower than existing 60-cell modules. This form factor places more module area per linear meter of torque tube when used with single-axis trackers. These changes are expected to lower the levelized cost of energy.
The effect of cell thickness on module reliability
This paper addresses the issue of the reliability of modules using ultra-thin crystalline silicon cells. Do thin cells have a greater likelihood of cracking during production, transport, installation or use and if so does this result in long term degradation of the power? The present qualification test sequence, IEC 61215 does not adequately address this issue, The only mechanical test in IEC 61215 is a static mechanical load test consisting of three load cycles that are performed after the accelerated stress tests. So even if this mechanical load test does break cells, it is unlikely to result in significant power loss. BP Solar has developed a test sequence for evaluation of cracked cells in PV modules. The test sequence incorporates a dynamic mechanical load test performed before the 50 thermal cycles/10 humidity freeze cycles of IEC 61215. Usually there is no significant power loss after the dynamic load testing. However, the subsequent thermal cycling opens up the cracks that propagated during the dynamic load test resulting in significant power loss. Having a test sequence that identifies damaged cells allows us to develop processes and handling procedures to minimize or eliminate damage to the ultra-thin cells, resulting in reliable modules.
Characterization of ethylene vinyl acetate (EVA) encapsulant: Effects of thermal processing and weathering degradation on its discoloration
Ethylene vinyl acetate (EVA) copolymer used as an encapsulant in photovoltaic (PV) modules turns from clear to yellow-brown after four or more years of weathering. EVA films on PV modules stored in the dark at ambient temperature for six years have not degraded. Various analytical methods were used to analyze and characterize the degraded EVA and to determine the cause of discoloration. As a result of degradation, the gel content increased greatly while the UV absorber, Cyasorb UV 531, decreased concomitantly. The increase in the gel content indicates that a cross-linking reaction was dominant in EVA's structural change. Degradation of the polymer near the cover glass surface took place more rapidly and to a greater extent than that next to the solar cells. While EVA remaines clear when it retains more than 70% of the initial Cyasorb UV 531 concentration, a moderate increase in the gel content indicates that some degradation occurred without producing the yellow color. Further depletion of Cyasorb during the weathering process resulted in the yellow to brown color in the EVA due to formation of polyconjugated (C=C)n double bonds of various lengths (n>3). The discoloration deepens as the extent of degradation increases. Acetic acid and other volatile organic components are also produced from the photothermal decomposition of EVA. The EVA discoloration significantly reduces the electrical performance of solar cells.