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The main objective of this work is to investigate the efficiency of three different power cycles coupled with parabolic through collectors in Athens/Greece. The power cycles analyzed where: subcritical ORC with n-Pentane and R245fa as working fluids, trans-critical ORC with R245fa as working fluid and super-critical Brayton cycle with CO 2 and R245fa as working fluid. Mathematical models were developed for both the solar farm and the power cycles in order to optimize the necessary parameters for the optimal operation of the plant. The inlet temperature and pressure of the turbine are the optimization parameters. The overall efficiency of the system (power to solar) for the sub-critical ORC with n-Pentane and R245fa is 14.12% and 10.31% respectively. For the trans-critical ORC with R245fa the efficiency is 15.14% and for the super-critical Brayton cycle for CO 2 and R245fa, 13.23% and 8.87% respectively.

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This study presents a combined thermal and optical, three-dimensional analysis of an asymmetric compound parabolic collector (ACPC) with an integrated hybrid photovoltaic/thermal (PV/T) receiver with the aim of establishing a sustainable approach in two ways: firstly, by determining the optimal tilt angle for operations, and secondly, by introducing an innovative simulation method which reduces computational cost while calculating thermal performance. Initially the Incident Angle Modifier ( ) was calculated for a wide range of incident angles, and the ray-tracing results were verified using three different simulation tools (Tonatiuh, COMSOL, and SolidWorks) with mean deviations being lower than 4%. The optimal tilt angle of the collector was determined for seven months of the year by conducting a detailed ray-tracing analysis for the mean day of each month considering whole day operation. In the thermal analysis part, the authors introduced novel numerical modeling for numerical simulations. This modeling method, designed with sustainability in mind, enables lighter computational domains for the air gap while achieving accurate numerical results. The approach was established using two distinct simulation tools: COMSOL and SolidWorks. From the optical analysis, it was found that in all months examined there is a four-hour time range around solar noon in which the optimum tilt angle remains constant at a value of 30°. The numerical models constructed for the thermal analysis were verified with each other (6.15% mean deviation) and validated through experimental results taken from the literature regarding the examined collector (<6% mean deviation). In addition, the two simulation tools exhibited a deviation of around 6% between each other. Finally, the thermal performance of the collector was investigated for the mean day of September at solar noon by adopting the optimal tilt angle for that month according to the optical analysis, considering inlet temperatures from 20 °C up to 80 °C.