Reduced Module Operating Temperature and Increased Yield of Modules With PERC Instead of Al-BSF Solar Cells

Abstract

We demonstrate a reduced operating temperature of modules made from passivated emitter rear cells (PERCs) compared with modules made from cells featuring an unpassivated full-area screen-printed aluminum rear side metallization aluminum back surface field (Al-BSF). Measurements on specific test modules fabricated from p-type silicon PERC and Al-BSF solar cells reveal a 4 $^{\circ }$ C lower operating temperature for the PERC module under 1400 W/m $^2$ halogen illumination, if no temperature control is applied. For detailed analysis of the temperature effect, we perform a 3-D ray tracing analysis in the spectral range from 300 to 2500 nm to determine the radiative heat sources in a photovoltaic (PV) module. We combine these heat sources with a 1-D finite element method model solving the coupled system of semiconductor, thermal conduction, convection, and radiation equations for module temperature and power output. The simulations reveal that the origin of the reduced temperature of the PERC modules is a higher efficiency, as well as a higher reflectivity, of the cells rear side mirror. This reduces the parasitic absorptions in the rear metallization and increases the reflection for wavelengths above 1000 nm. This operating temperature difference is simulated to be linear in intensity. The slope depends on the spectral distribution of the incoming light. Under 1000 W/m $^2$ in AM1.5G, our simulations reveal that the operating temperature difference is about 1.7 $^{\circ}$ C. The operating temperature can be lowered another 3.2 $^{\circ}$ C, if all parasitic absorption for wavelengths longer than 1200 nm can be prevented. Standard testing conditions applying a temperature control to the module do not show this effect of enhanced performance of the PERC modules. Yield calculations for systems in the field will thus systematically underestimate their electrical power output unless the inherently lower operating temperature of PERC modules is taken into account.