Reduction of energy requirements without affecting productivity of P. tricornutum and T. suecica by integrating shading devices in GWP® photobioreactors

One of the most important cost of microalgae biomass production in closed photobioreactors is the purchase of electrical energy necessary to run electromechanical components. In our work, two microalgae, Phaeodactylum tricornutum UTEX640 and Tetraselmis suecica F&M-M33 were grown outdoors in 40-L, 50°-tilted, facing south GWP® -III photobioreactors in which the direct illuminated surface was shaded (from 20 to 80% of PAR) with four different materials, mimicking photovoltaic devices or reducing/modifying the light reaching the cultures, with the aim of evaluating the potential production of electrical energy and/or the reduction of cooling needs. For each species one reactor, without shading devices, acted as control. Cultivation was conducted in fed-batch and in semicontinuous in summer and autumn, during which growth and biomass composition were evaluated. Interestingly, in most of the cases productivity of cultures in the shaded photobioreactors were similar to that of the control (24.8 g m -2 d -1 for T. suecica and 18.4 g m -2 d -1 for P. tricornutum batch cultures). According to our measurements, the use of shading devices allows to reduce energy need for cooling of 20-55%. The calculated electrical energy produced by the hypothetical photovoltaic devices was enough to cover all the energy needs for microalgae cultivation and harvesting.