Enhancing Algae Biomass Production by Using Dye-Sensitized Solar Cells as Filters

One of the most promising options for decreasing the costs of microalgae production is enhancing the production and reducing the energy demand of the culturing systems and the high surface area requirements. Because microalgae growth requires only specific wavelengths of the solar spectrum, the remaining part of the solar spectrum may be simultaneously used by a translucent photovoltaic (PV) layer to produce electricity, which leads to a reduction of space and energy requirements. This work presents the results of a new concept of a positive energy culturing system for microalgae, where the light source is selectively shared between the needs of the algal biomass through photosynthesis and the production of PV energy through dye-sensitized solar cells (DSCs). To ascertain the DSC (DSC-Red, DSC-Green) light-filtering effects on microalgal biomass, (1) the variation of growth kinetics, (2) microalgae pigments [chlorophylls-(a + b) and carotenoids], and (3) macromolecule content (carbohydrates, proteins, and lipids) were investigated and compared to control cultures under two different solar-simulated light intensities (200 and 600 W/m2). The results showed a net improvement of the growth rate and dry weight at the higher irradiance using both colored DSC filters compared to control cultures. The highest growth rates (μ) and doubling time (td) of Chlorella vulgaris cells were obtained using the DSC-Red (DSC-R) and DSC-Green (DSC-G) solar cells as filters with μ = 0.86 ± 0.01 day–1; td = 0.80 day and μ = 0.85 ± 0.03 day–1; td = 0.81 day, respectively, compared to normal glass control μ = 0.51 ± 0.03 day–1; td = 1.35 day. A significant increase in the chlorophyll-a content was obtained under low light intensity for both DSC-colored compared to control culture, and there was no significant variation in the macromolecule content measured under the tested light intensities. Finally, a life cycle assessment based on a functional unit of 1 kg of the produced algal biomass using the DSC–photobioreactor (DSC–PBR) was performed and compared to a normal glass PBR. The results were expressed in terms of CO2 emission equivalents produced and electricity generated. A fraction of electricity generated by DSC–PBR is used for bubbling, and the extra electricity is injected into the electricity grid. This resulted in net negative GHG emissions.