Investigation of a Novel CO2 Transcritical Organic Rankine Cycle Driven by Parabolic Trough Solar Collectors  
[PERSON] and in the Rankine cycle. In the Brayton cycle, the main devices are a compressor, a burning chamber, a turbine and a gas cooler. In the Rankine cycle, there is a liquid pump, a boiler (or a heat recovery system), a turbine and a condenser. The main difference between these cycles is the existence of a gas compressor in the Brayton cycle, while the Rankine cycle includes a liquid pump. The compressor consumes high amounts of work for the compression, while the pump consumes small amounts of work. The use of a transcritical Rankine cycle is a very common configuration in the literature, while there are also studies about Brayton systems. [PERSON] et al. [17] studied a simple transcritical ORC with CO\({}_{2}\) as the working fluid. They performed parametric work and they used genetic algorithms and artificial neural networks. According to their results, the thermodynamic efficiency of the cycle is about 29.5% with turbine pressure at 107 bar and temperature in the turbine inlet at 75 \({}^{\circ}\)C. [PERSON] et al. [18] studied a waste heat recovery system that includes a transcritical CO\({}_{2}\) ORC system that is fed by the exhaust gases of an internal combustion engine. They compared a simple cycle and an advanced cycle with a regenerator and preheater. They found a 150% electricity production increase with the advanced systems, the fact that proves the need for recovering as much as heat is possible in a transcritical cycle. [PERSON] et al. [19] examined different CO\({}_{2}\) power cycles and they found that the low-temperature transcritical Rankine cycle leads to 12% efficiency while the high temperature to 40%, so they found the great importance of the heat source temperature level on the results. In another work about a complex configuration, [PERSON] et al. [20] studied a unit with an air-based gas turbine as the prime mover with a supercritical CO\({}_{2}\) Brayton cycle as the intermediate cycle and a transcritical CO\({}_{2}\) Rankine cycle as the last bottoming cycle. The overall system electricity efficiency is found to be 52.33% which is a relatively high value. The next part of the literature regards investigations about the use of solar-fed CO\({}_{2}\) systems. [PERSON] and [PERSON] [21] examined a solar-driven supercritical CO\({}_{2}\) Brayton thermodynamic cycle with a bottoming ORC with parabolic trough collectors (PTC) as the solar technology. They used an indirect system with thermal oil in the solar field as it is done in the usual system. They found that the use of R407c in the ORC is the best choice which leads to 3740 kW electricity production and total system efficiency (electricity to solar) at 21.8%. [PERSON] and [PERSON] [22] studied a system with oil-based PTC that drives a supercritical CO\({}_{2}\) Brayton system in an indirect way and also the Brayton cycle drives a bottoming ORC. It is found that the best organic fluid is the R1233 zd(E) and in the optimum design the solar collector efficiency is 62.93%, the thermodynamic efficiency is 48.61% and consequently, the system efficiency is 30.59%. In another work, [PERSON] et al. [23] studied the use of a thermal oil-based nanofluid as the working fluid in a solar field that feeds a transcritical CO\({}_{2}\) Rankine cycle and there is an extra auxiliary system in order to aid the solar energy. Moreover, the Rankine cycle rejects heat to a liquefied natural gas system which includes a turbine for extra electricity production. They calculated the system exergy efficiency at 8.53% and they also indicated that the nanofluid-based system has higher performance than the operation with pure thermal oil in the PTC field. In another interesting work, [PERSON] and [PERSON] [24] studied an oil-based PTC field that feeds a transcritical CO\({}_{2}\) power system coupled to an absorption chiller. They conducted a parametric analysis and they concluded that the thermodynamic efficiency is 34% and the system efficiency is 20%.