Technical and economic viability of using solar thermal energy for microalgae drying

Abstract

The solar thermal energy is evaluated to microalgae drying active processes as an alternative more economical and sustainable than conventional methods such as spray-dryer. A case study of microalgae production in a 10,000 m2 raceway reactor was considered where the biomass production capacity per year was calculated based on previously existing models, thus as the heat required. Different designs, configurations and operation modes of solar collectors were studied. Due to the parallel variation of biomass production and solar radiation availability throughout the year, the optimal solution was to design the solar collector for the summer season, the operation mode was optimized, thus the utilization of auxiliary energy systems and air recirculation being analysed. The final design considers the utilization of solar air collectors operating in a recirculation mode. At these conditions, it is possible to completely supply the required heat by using a 200 m2 surface collector, the operation in recirculation mode allowing to save up to 30% of the collectors’s surface required. The techno-economic analysis demonstrates that the utilization of the proposed system avoid the utilization of fossil energy, moreover the cost of the drying step reduces to 1.16 €/kg versus a cost of 2.37 €/kg for conventional spray dryers. Thus, it is demonstrated that the utilization of thermal solar energy is an opportunity to improve sustainability and economy of microalgae drying process.