Conceptual design of energy storage systems for continuous operations in renewable-powered chemical processes

This work aims to develop an energy storage system that allows fluctuating energy inputs (i.e. from process sections driven by renewable sources) to power two process units that are operated continuously at different temperatures. The system consists of two vessels storing diathermal mediums: one for the hotter- and the other for the colder-energy fluxes. The investigated solutions include sensible-heat-, latent-heat-, and thermochemical-TES (thermal energy storage). Organic Rankine cycles (ORCs) with lithium-ion batteries and thermoelectric generators were also assessed. Indeed, all these technologies allow the exploitation of low-temperature thermal energy to supply the high-temperature unit during periods of energy scarcity. Both vessels aim for total self-sufficiency; however, the option to rely on external utilities has been included to meet the energy demand of both units when sufficient process-side power is unavailable. Two energy profiles were investigated to assess the proposed storage systems� performance: one showing only solar energy inputs and the other showing only wind energy inputs. Finally, an optimization problem was formulated to estimate the optimal size of both storage vessels. Indeed, increasing their capacities would lead to higher capital expenses (CAPEX) and lower operating expenses (OPEX). As a result, the assessed process-integrated configurations (i.e. those featuring any energy storage system) proved competitive with the non-integrated solution (i.e. the one fully relying on external sourcing of electricity) only if referring to high electric energy prices (300�USD/MWh). Conversely, when considering an electricity price of 100�USD/MWh, all the assessed process-integrated configurations proved more expensive than the non-integrated solution.