Capturing sunlight into a photobioreactor: Ray tracing simulations of the propagation of light from capture to distribution into the reactor

The Green Solar Collector (GSC), a photobioreactor designed for area efficient outdoor cultivation of microalgae uses Fresnel lenses and light guides to focus, transport and distribute direct light into the algae suspension. Calculating the path of rays of light, so-called ray tracing, is used to determine local light intensities inside the photobioreactor based on the focused rays of sunlight. Reflection and refraction of the propagating rays of sunlight from point of focus to refraction into the photobioreactor is calculated. Refraction out of smooth and sandblasted distributor surfaces is simulated. For the sandblasted surface a specific structure is assumed and corresponding reflection and refraction patterns are described by a 2-dimensional modeling approach. Results of the simulations are validated by measurements on real light guide surfaces. The validated model is used to determine the influence of the solar angle on the uniformity and efficiency of light distribution over the light distributor surface.The simulations show that efficient capturing of sunlight and redistribution inside the algal biomass can be achieved in the Green Solar Collector at higher elevation angles of the sun, making the Green Solar Collector suitable for operation at low latitudes with a high level of direct irradiance.