Performance analysis of a novel energy storage system based on the combination of positive and reverse organic Rankine cycles

Abstract

Energy storage systems (ESSs) play a vital role in the efficient utilization of intermittent renewable energy and off-peak electricity. However, the traditional ESSs with air and CO2 have the limitations of geographic dependence and high operating pressure. In this paper, a novel ESS based on reverse and positive organic Rankine cycles with refrigerants, integrating the concept of combined cooling, heating, and power, is proposed to effectively reduce the operating pressure and to improve the energy efficiency and system flexibility. Thermodynamic optimization of this efficient system is performed by connecting the genetic algorithm (GA) toolbox of MATLAB and Aspen HYSYS, and R134a, R1234yf, R1234ze(E), and R152a are considered as working fluids. Three objective functions: maximization of round trip efficiency (RTE), energy density, and total exergy efficiency (TEE), are selected. Parametric analysis and performance comparison are used to evaluate the effects of key parameters on the RTE, energy density, and TEE of the system. An optimal RTE of 0.70 and energy density of 8.61 kW/m3 are achieved by using R1234yf and R152a, respectively. The maximum TEE of 0.77 is obtained by using R152a and R1234ze(E). The comparison results revealed that the proposed system exhibits distinct advantages of low operating pressure below 3000 kPa and stable operating conditions. Therefore, commercial off-the-shelf items utilized in the fields of refrigeration and heat pump can be applied in most of the components of the system. Further, this system is particularly useful for unit distributed system.