Utilization of solar energy for continuous bioethanol production for energy applications

The focus of the present research is to develop energy-efficient, sustainable, and continuous-flow bioethanol production based on solar energy. Solid-state fermentation of glucose was performed in a specially designed solar-energy-driven continuous flow reactor. Aqueous glucose solutions of 10 and 20 wt% were fed into the reactor bed containing baker's yeast (Saccharomyces cerevisiae), resulting in 4.7 and 8.7 wt% ethanol yields, respectively. The bioethanol produced was separated from the yeast bed soon after its formation by an evaporation-condensation process. High ethanol yields (91.2 and 85.5% of the theoretical yield, respectively) indicate the atom-efficiency of the process. No loss in the activity of yeast was observed even after two months of continuous operation of the reactor. The current study demonstrates an energy-efficient methodology for bioethanol production utilizing solar energy. The bioethanol obtained (8.7 wt%, ca. 2 M) was further tested in alkaline-acid direct ethanol fuel cells operated at 303 K, resulting in a power density value of 330 mW cm^-2 at a modest open circuit voltage value of 1.65 V (65.5% voltage efficiency).