Integrating photovoltaic devices to photobioreactors: a tool to couple biomass with electricity production

According to literature, microalgae cultivation plants require from 4.5 to 48 kWh per kg of harvested biomass (Ruìz et al., 2016; Norsker et al., 2011) depending on the reactor type and process adopted. An amount of 6 kWh kg-1 of electrical energy is required when Green Wall Panel (GWP®) are used, where the main energy inputs are represented by mixing and biomass harvesting followed by culture cooling, which accounts for up to 11% of the total (Tredici et al., 2015). A promising strategy to exploit solar radiation more efficiently is the development of a photovoltaic-photobioreactor integrated system that combines the generation of electricity with biomass production without altering productivity and occupying extra space (Sampietro, 2014). The partial shading of the photovoltaic devices may reduce energy requirements for cooling and potentially prevent photoinhibition phenomena affecting cells in the sunniest days, improving culture growth performance and light use efficiency (Tredici, 2010; Sampietro 2014, Detweiler et al., 2015). In this work, cultures of the marine green alga Tetraselmis suecica F&M-M33 were set up outdoors in raceway-ponds and GWP®-III photobioreactors integrated with different photovoltaic devices. In the preliminary trial, 20% of the direct illuminated surface of a GWP®-III was covered by opaque photovoltaic strips. In a second trial, besides the opaque strips, the adoption of photovoltaic modules was evaluated by applying a photoselective film covering the whole or part of the illuminated surface both in GWP® and Raceway Pond (RWP). An optimization trial was carried out in GWP® covered by 20 or 35% with opaque strips and different culture management, and in RWP covered with a commercially vailable module made of interspaced photovoltaic tubes. In each trial one culture without shading acted as control.