Design of solar-biogas hybrid energy system for a mining process in Chile considering technical, economic and environmental aspects

Abstract

One of the main challenges of the mining industry from an environmental prospect is the growing increase in energy consumption. Over the next ten years, energy demand is expected to increase by 41% since mines are getting older and deeper, a change in the copper production structure and the increase in seawater consumption. Within the energy demand of a mining process, final energy consumption and electricity generation are the primary sources of greenhouse gas (GHG) emissions. Thus, decreasing energy consumption and studying new energy sources with a lower environmental impact becomes necessary. In this context, the use of hybrid renewable energy systems has proven to be an attractive option regarding costs, operability, and environmental impact. Besides, they are more resilient than single energy systems. The interest of this research is to design a hybrid renewable energy system to supply the electrical demand of a mining process and evaluate the possible trade-offs that may exist. For this purpose, a multi-objective optimization problem has been formulated considering two objectives: minimizing annual costs and minimizing GHG emissions. The calculation of GHG emissions includes direct emissions associated with fuel combustion and indirect emissions associated with electricity purchase. The proposed energy system considers solar energy and biogas generated from organic waste as primary energy sources, two energy storage systems (lithium-ion batteries and hydrogen storage), and a connection to the electrical grid. The approach is applied to a case study that considers a typical mine located in the North of Chile. The model has been implemented in the computational program Julia and solved using Gurobi. In the first instance, the problem has been solved considering each objective function separately, and then the multi-objective problem has been solved using the -constraint method. Finally, a sensitivity analysis has been performed, considering the variation in energy demand, biogas availability, costs, and grid emissions factor. The results show that biogas and solar energy are attractive options to reduce costs and emissions in the mining industry. However, the biogas does not have the potential to cover the demand as it is limited by the biomass available. Regarding the system configuration, all the proposed technologies were selected in the simulations. The energy was primarily stored in batteries; nonetheless, there is no preference between storage systems considering GHG emissions. The use of energy storage systems showed to increase the costs. However, these systems are needed to use more renewable energy and reduce emissions. A trade-off between costs and emissions was observed. Therefore, the prioritization of one criterion will significantly impact the other. Lastly, a second environmental criterion is suggested to evaluate the impact of renewable energy and energy storage systems such as abiotic depletion or the use of land.