Performance improvement of two-stage serial organic Rankine cycle (TSORC) driven by dual-level heat sources of geothermal energy coupled with solar energy

Solar energy is used as the supplementary heat source of geothermal energy. Based on two-stage serial organic Rankine cycle (TSORC) system driven by a single heat source (SHS), the TSORC driven by dual-level heat sources(DHS), geothermal energy as the low temperature heat source coupled with solar energy as the high temperature heat source, was proposed. A numerical model for performance optimization of combined system was constructed. A compound objective function was used to optimize the cycle parameters, such as the thermal efficiency, exergy efficiency, net output power, irreversible loss, thermal conductance, size parameter of turbine and the system performances. The TSORC driven by DHS were also compared with those driven by DHS, with the heat source ranging from 110 to 150℃. The results show that the TSORC driven by DHS can output more net power but the thermal efficiency is lower compared with the TSORC driven by SHS for heat source temperature below 140℃. Generally, the TSORC driven by DHS can improve the system performance, and it can be adopted in engineering application if there are dual-level heat sources.