A hybrid facade that combines an algal bioreactor with photovoltaics

For an algal facade that is operated as a flat plate bioreactor, the biomass in the facade is capable of producing energy as oil, or through methane digestion of the cells, while absorbing radiation that would heat the building. However, an algal facade could also produce electricity if coupled to a photovoltaic (PV) module. Experiments were conducted with a PV module situated behind a flat plate, algal bioreactor to determine the relative power output for such a hybrid facade compared to a PV module without the algal layer. Two container materials were tested (polypropylene and ac rylic), for two algal species (a green algae and a coccolithophore), at 4 biomass concentrations. The containers were two rectangular boxes with a volume of 0.4 liters and 1 liter, corresponding to path lengths (i.e. thicknesses) of 0.9 cm and 2.8 cm, respectively. Experimental re sults were presented as attenuation coefficients versus algal biomass, photovoltaic power output versus scalar irradiance, and modeled power output based on biomass concentration and container thicknesses. The acr ylic container transmitted more light than the polypropylene and had statistically lower attenuation coefficients. Water in both container types had a minor contribution to attenua tion while algal concentrations gave high attenuation. The highest attenuation occurred for the green algae and was a result of increased pigments. The highest coccolithophore concentration, in combination with the shorter path length, produced 95% of the maximum PV power output. Generally, power output increased with decreasing algal concentration since more light was transmitted to the PV module. The amount of light transmitted through the container to the PV module was modeled based on light attenuation by algal biomass and container thickness. Using the model for full sunlight, we determined that with high algal concentrations and realistic facade thicknesses, high power output can be achieved from PV modules in parallel with algal growth. The next step is to build a prototype facade to assess the effect of full sunlight under these design criteria, as well as the effect of heat dissipation by the facade.