Performance enhancement of a power generation unit–organic Rankine cycle system through the addition of electric energy storage

Abstract

Combined heat and power (CHP) systems generate onsite power using a power generation unit (PGU) while recovering waste heat from the PGU to provide heating or hot water to a facility. One variation of the typical CHP configuration uses recovered waste heat from the PGU on an organic Rankine cycle (ORC) to generate additional power. This paper proposes the use of an electric energy storage (EES) device in conjunction with a PGU-ORC. The idea is to use the energy stored by EES at different times of the day so that continuous operation of the PGU is not required. The potential of the proposed PGU-ORC-EES system is assessed by evaluating the performance in terms of operational cost, primary energy consumption (PEC), and carbon dioxide emissions (CDE) of simulations of a restaurant facility at different geographical locations in the U.S. reflecting a variety of climate conditions and thus a variety of electric loads required by the building. This paper compares the performance of a PGU-ORC-EES system with that of a conventional system where electric power and fuel for heating are obtained from the utility grids. This comparison is completed by analyzing the building’s electric demand only since the thermal demand will be the same between the PGU-ORC-EES and conventional system. Results indicate that the addition of EES is beneficial to the PGU-ORC system for most U.S. locations in terms of the three evaluated parameters. Ratios between the cost of electricity and fuel (Rcost), between the electricity and fuel CDE conversion factors (RCDE), and between the electricity and fuel PEC conversion factors (RPEC), are obtained for each location and used to estimate the potential of the system to provide benefits with respect to a conventional system in terms of cost, CDE, and PEC. In addition, the effect of the EES size on the system performance is also analyzed in this paper as well as the capital cost available for different payback periods.