A simple ray tracer to compute the optical concentration of photovoltaic module

In a conventional photovoltaic module, some light that falls between the solar cells is internally reflected onto the cells via the backsheet and the glass-air interface of the module; thus, a module can be considered a static concentrator. We present a simple ray tracer that computes a module's optical concentration as a function of cell separation, cell geometry, and the optical properties of the encapsulants. The ray tracer's primary simplification is to divide the module's backsheet into small pixels and, since the reflection from the backsheet is approximately Lambertian and independent of the incident angle, to sum the intensity of all rays that enter a pixel and treat them as one. The advantage of this pixel approximation is that it makes it simple to simulate curved surfaces - such as the corners of a pseudo-square solar cell- within short computation times. The results of the simple ray tracer are shown to be consistent with those of a conventional ray tracer and an LBIC experiment. We also apply the ray tracer to a present-day SunPower module and find that 25% of the photons that fall between the cells are internally reflected onto the cells, which results in an optical concentration of 1.024.