Energy yield modelling for High Efficiency Heterojunction Silicon Solar Cells

Description of field of research:

The purpose of this project is to improve modelling of ultra-high efficiency bifacial silicon heterojunction PV modules in energy yield simulations. This will i) allow a proper evaluation of the economic and technical targets for these modules to reach in production and ii) Provide confidence for end users considering these products.

As heterojunction solar cells approach theoretical limits of silicon performance, they are testing common assumptions used in yield modelling calculations. For simulation packages such as PVSyst, SAM and pvlib module I-V characteristics are usually described using a single diode model or equivalent, with no consideration of injection level dependence. Recent results on heterojunction cells have demonstrated that under high-injection conditions the cell fill factor can be greatly enhanced, due to a shift in dominant recombination mechanisms from n=1 processes (SRH recombination) to n=2/3 (Auger). If this is not considered, the performance of ultra-high efficiency modules will be underestimated in simulation programs. Furthermore, this effect has significant implications for the temperature coefficient of the open-circuit voltage, which is heavily dependent on recombination.

This project will implement a more complete model within the pvlib-python modelling package for ultra-high efficiency silicon modules. This will include injection level dependence and improved accuracy for module temperature and bifacial irradiance. These will be adapted from first principles calculations. This model will be verified against injection- and temperature- dependent I-V data provided by SunDrive.