Optimal design of a renewable energy-driven polygeneration system: An application in the dairy industry

The world is experiencing an unprecedented transition towards a low-carbon and renewable-based energy system, driven by the imperatives of mitigating climate changes, building climate resilience and ensuring sus-tainable development. Recently, polygeneration systems based on renewable energies have emerged as a viable solution to support the energy transition since they can improve resource utilization and energy efficiency, thus reducing the dependency on fossil fuels and the environmental impacts on ecosystems.Renewable polygeneration systems can play a significant role in the decarbonization of the food processing industry due to its high thermal energy demand at low and medium temperature levels.This paper presents a detailed analysis of a renewable polygeneration system integrating solar, geothermal and biomass energies and able to produce electricity, heat and cold water. The novelty of this study is the analysis of polygeneration system configurations relying solely on renewable energies and the optimization of the strategy to control the energy exchange between power systems, storage facilities and utilities. Two system configurations based on different power technologies and control strategies are investigated and compared, considering as end-user a milk production process with hot and cold water requirements at different temperature levels and load profiles.To this end, a dynamic model in Matlab/Simulink has been developed to simulate the behaviour of the pol-ygeneration system over time and evaluate its overall energy performance parameters. For each system configuration, the optimal operating strategy has been identified by maximizing the energy conversion efficiency and minimizing the unmet thermal and cooling loads. Simulation results highlighted that, compared to poly-generation systems relying only on fluctuating renewable energies, those including a backup heat source (i.e., a biomass boiler) were able to meet the thermal energy needs of larger and more complex milk production processes.