Chapter 33 - Solar intervention in bioenergy

Abstract

Research interest in the integration of solar energy-harvesting technology with bioenergy production is growing at a remarkable pace. The time of fruition of a completely off-grid solar-powered refinery facility is not too far, at least in the specific instance of bioenergy sources, namely, biodiesel and bioethanol. Electricity generated from solar panels is used for the cultivation of microalgae in outdoor open ponds. The solar thermal energy is converted into electricity by solar panels, and the electricity is stored in lead-acid batteries that are used to power the motors to rotate the agitator blades for stirring the contents of the algal culture. The biomass productivity of outdoor open ponds completely powered by solar energy (5.8gm2/d of Nannochloropsis oceanica SCS-1981) is on par with the traditional raceway ponds. Such innovation in harvesting microalgae has led to energy savings and cost reduction. A solar energy-driven biodiesel production process using waste cooking oil as feedstock catalyzed by SrO solid base catalyst supported on activated carbon was found to yield 98.5wt.% fatty acid methyl ester (FAME, biodiesel) in 60min at 46°C upon direct exposure of the reaction vessel to sunlight. The integration of solar energy with biodiesel production resulted in economically viable production strategies ($0.73, 0.54, and 1.27/L of biodiesel from palm oil, rapeseed oil, and Chlorella vulgaris, respectively). Solar energy is used for the downstream biodiesel purification process, that is, distillation facilitating recovery of alcohol used in the transesterification of lipids used for biodiesel production. Alcohol recovery of as high as 41kg/m2/24h was achieved in the membrane-assisted solar-driven distillation process. A completely off-grid solar thermal energy-powered bioethanol production process from coastal hay and cane sugar was found to yield 0.474 and 0.05 mole fractions of bioethanol, respectively. In the first-ever report, bioethanol concentration of up to 18wt. % was produced from the aqueous glucose (40wt. %) feedstock in a completely solar-powered fermentation reactor operated on a unique evaporation–condensation process powered by solar energy. Bioethanol (8.7wt.%) produced in a solar fermenter was successfully used as fuel for operating an alkaline-acid direct ethanol fuel cell at 303K with current and power density values of 700mA/cm and 330mW/cm, respectively, and an open-circuit voltage of 1.65V. Nanotechnology is effectively used for harnessing solar thermal energy, which is subsequently used for driving vital processes involved in biodiesel (harvesting of microalgae, lipid extraction, esterification of free fatty acids, transesterification of triglycerides, purification of biodiesel) and bioethanol (pretreatment, cellulose hydrolysis, fermentation and distillation of aqueous ethanol) production processes. Nanoparticles such as multiwalled carbon nanotubes (with high thermal conductivity) and MgO (high specific heat capacity) and Au-nanoshells (photothermal conversion) were exploited for the effective harnessing of solar energy. A unique fusion of advanced technologies, namely nanotechnology, solar technology, and biochemical technology, is on the verge of a breakthrough leading to energy sustainability with reduced emission of pollutants. Many such path-breaking innovations are awaited in the realm of biomass conversion to bioenergy by integrating bioenergy production processes with solar technology. Specific examples of many such smart technologies are summarized in this chapter by scanning 40 years’ worth of literature (1980–2020) in the realm of solar energy and bioenergy.