Techno-economic study and environmental analysis of a solar-aided lignocellulosic biorefinery: a South African case study

A techno-economic study and environmental analysis of various configurations of solar-aided corn stover to ethanol biorefineries were conducted using South Africa as a case study. The study was performed with the help of Chemcad simulation software along with the system advisory model (SAM). Five design scenarios were considered: one standalone scenario where lignin was combusted alongside biogas from the adjacent wastewater treatment plant to supply energy to the biorefinery (scenario 1). Two solar-aided scenarios where lignin-rich residues were sold as a co-product, and combinations of concentrated solar thermal, concentrated solar power, and solar photovoltaic were used to supply energy to the biorefinery (scenarios 2 and 3). Two additional solar-aided scenarios where 60% of lignin residues were combusted for process heat and solar photovoltaic/concentrated solar power were used for process electricity (scenarios 4 and 5). Results obtained showed that scenarios 2 and 3 have the highest overall energy conversion efficiency, followed by scenarios 4 and 5. A similar trend was observed for the biorefinery net energy. The minimum ethanol selling price (MESP) for the standalone scenario was found to be 25.88 $/GJ, which was comparable to the 2020’s South African gasoline price of 25 $/GJ. The incorporation of solar energy inflated the MESP to $58.05/GJ for scenario 2, $68.84/GJ for scenario 3, $43.17/GJ for scenario 4 and 53.97/GJ for scenario 5. Although the non-combustion of lignin-rich residues resulted in the biorefinery’s potential environmental impact being reduced by up to 50%, the commercialisation of these lignin-rich residues as a co-product was found not to be economically viable without a 50% reduction in capital investment or substantial government subsidies.