Selection of working fluids for solar organic Rankine cycle—A review

The performance of renewable energy systems can be significantly improved if power is produced from low-temperature heat sources. The organic Rankine cycle (ORC) is suitable for producing power from low-temperature heat sources. ORC finds applications alongside solar power, geothermal power, waste heat and biomass. ORC-enabled systems can contribute significantly to raising the effectiveness of renewable power sources. Solar power, for example, can deliver affordable electricity to remote locations and small industries. By employing ORC, power generation is possible at lower temperatures on cloudy days. Its main difference from the steam Rankine cycle is its working fluid. The ORC makes use of an organic, high molecular mass fluid as the working fluid. Compared to steam Rankine cycles, ORC works at a lower temperature (<250°C) and pressure. The only working fluid in the steam Rankine cycle is water, but the ORC can operate on hundreds of different working fluids. The design and performance of ORC systems are entirely dependent upon the suitable working fluid and, hence identification of the working fluid for ORCs is of utmost importance for diverse applications. Properties of working fluid have a considerable impact on the efficiency of the system. The main objective of this study is to identify the most suitable organic fluids having characteristics necessary for use in solar ORCs. In addition, a detailed review of the various types of heat transfer fluids now available in the market that are often used in ORC systems was conducted. This research assists in selecting the most appropriate organic fluids for various solar ORC applications in terms of operating circumstances.