A Detailed Review of Organic Rankine Cycles Driven by Combined Heat Sources

The Organic Rankine Cycle (ORC) is an effective method for transforming low- and medium-grade heat into electricity that has recently gained significant attention. Several review studies in the literature are focused on working fluids, system architecture, and the individual utilization of renewable and alternative heat sources in ORCs, like solar irradiation, geothermal, biomass, and waste heat energy. However, no studies have yet investigated ORC systems driven by two of the aforementioned sources combined. This work aims to review and explore multiple aspects of hybrid ORC systems. Such systems are categorized based on source combinations and configurations, and the results regarding their thermodynamic, thermo-economic, and environmental performance are discussed. The source arrangements follow the following three main configurations: series, parallel, and heat upgrade. Most of the examined systems include solar energy as one of the sources and only four cases involve combinations of the other three sources. The reported results show that hybrid ORCs generally perform better thermodynamically compared to their respective single-source systems, exhibiting an enhancement in power production that reaches 44%. An average levelized cost of energy (LCOE) of 0.165 USD/kWh was reported for solar–geothermal plants, 0.153 USD/kWh for solar–biomass plants, and 0.100 USD/kWh for solar–waste plants. Solar–biomass plants also reported the lowest reported LCOE value of 0.098 USD/kWh. The payback periods ranged from 2.88 to 10.5 years. Further research is proposed on multiple source combinations, the in-depth analysis of the three main configurations, the integration of polygeneration systems, the incorporation of zeotropic mixture working media and experimental research on ORCs with combined sources.