One of the advantages of thin-film PV is the superior high-temperature performance, which results in higher efficiency compared to standard crystalline wafer-based silicon PV. For all solar cells, the efficiency begins to drop once the panel temperature exceeds 25oC (77 oF), and this drop is quantified using a metric known as the “temperature coefficient.” The temperature coefficient relates the the loss in efficiency observed for each one degree increase in the temperature (ie. % / oC).
As an example, a traditional crystalline silicon solar panel has a temperature coefficient of approximately -0.50 % / oC, and therefore when the panel temperature increases by 20oC, the efficiency drops by 10%. In this e xample, the temperature increase refers to the temperature of the panel itself, and not the air temperature. During the summer months, the temperature of the panel can reach 60-70oC, and even as high as 80-90oC in extreme climates such as the Middle East. Even at 65oC, the efficiency drop for a typical crystalline silicon panel is about 20%. Beyond efficiency loss, the lifetime of the solar panels themselves are also degraded when operated at higher temperatures.
The primary underlying issue with crystalline silicon PV is that the use of thick wafers makes it difficult to remove the heat produced within the solar cell itself, producing higher temperatures than desired. Typical silicon panels use wafers with thickness of approximately 125-150 microns, though the market has been moving towards thinner wafers to help improve the thermal management. To address this challenge, Panasonic has developed a high-performance line of crystalline silicon solar panels that reduces the wafer thickness down to 90 microns, resulting in substantial reduction of the temperature coefficient to -0.26, nearly half of the typical value. While reducing the power output loss by nearly 50%, the panels also operate at a lower temperature and therefore should help to minimize degradation over the lifetime of the panel.
Furthermore, thin-film PV technologies such as that from PI Energy are expected to have additional improvements of the temperature coefficient, as a result of the solar cell device having a thickness of less than 5-10 microns. At this thickness, heat removal is significantly improved, and results in temperature coefficients of -0.21 for Cadmium Telluride and -0.13 for amorphous-silicon based PV.