Effect of Electric Energy Storage on the Performance of a Power Generation Unit-Organic Rankine Cycle System

Combined heat and power (CHP) systems simultaneously generate on-site electricity and provide useful heat by utilizing waste heat from a power generation unit (PGU). CHP systems can enhance energy production efficiency and energy sustainability by reducing grid dependency, often yielding cost savings in the process. Furthermore, CHP systems can provide savings over conventional systems in terms of operational cost, primary energy consumption (PEC), and carbon dioxide emissions (CDE). Typical CHP systems generate onsite power using a PGU, and the waste heat from the PGU is used to provide heating or hot water to the facility. Another variation for this system is to incorporate an organic Rankine cycle (ORC) to allow for increased potential reductions in operational cost, PEC, and CDE when compared to separate heat and power. This paper evaluates the effect of using electric energy storage on the performance of a PGU-ORC system. In the proposed system, the waste heat from a PGU is used to generate and to store electricity using an ORC coupled with electric energy storage (ES) (battery). Then, the electricity that is stored in the batteries could be used during the system operation at different times of the day so the PGU does not have to operate all the time. The PGU-ORC-ES system (with battery storage) is compared with a conventional system in terms of operational cost, PEC, and CDE. A restaurant building located in Chicago, IL is used to evaluate the potential of the proposed PGU-ORC-ES system. Results indicate that the addition of electric energy storage is beneficial to the proposed PGU-ORC system in terms of operational cost, PEC, and CDE. Furthermore, the effect of the size of the electric energy storage on the system performance is analyzed in this paper.