In the context of solar tower power, the significance of the receiver has to do with its capacity to convert sun rays into heat. This heat is then conveyed to a heat transfer fluid. The extremely high velocity of the heat transfer fluid, motivates for the use of smart geometry to simultaneously enhance the heat transfer process and strengthen the structure of the tubes. In this study, a new molten salt receiver design was numerically investigated, following the addition of square, rectangular, circular and triangular longitudinal fins, that come at various heights (w=1,2,4 and 6 mm). Molten salt was used as the heat transfer fluid that flown through the receiver tubes with the Reynolds number ranging between 14,000 and 38,000. In comparison to a smooth tube, it was observed that while the inclusion of fins led to a dip in pressure, the overall efficiency level was improved. An increase in the number of fins, led to an improvement in the heat transfer process. The use of four square fins delivered the highest heat transfer enhancement. In the use of a singular fin, a triangular fin with a height of 1 mm delivered the best heat transfer performance. For a similar flow rate and hydraulic area, the triangular fins exhibited a better heat transfer performance than the square, circular and rectangular fins. In terms of the receiver's efficiency, the triangular fins produced the heights efficiency.

This study was performed in outdoor conditions to quantify the level of influence on the electrical performance of the Multi-junction (MJ) solar cells. It was discovered that non-uniform illumination on the solar cell could reduce the MJ electrical output by more than 40%. Also, the irradiation uniformity was improved by applying several methods; increasing the distance between the concentrator and the receiver (l) and introducing a secondary optical element (SOE) on the receiver. The outdoor measurement also revealed that the electrical efficiency of the solar cell increased from around 22% to 37% with an increment of 68%, due to improvement of irradiation uniformity. However, the optical efficiency substantially fell when increasing the distance (l). To address this issue, a 0.06 m high SOE having a surface reflectivity of 90% above the PV assembly was implemented to enhance the irradiation uniformity and to minimise the dramatic decline in optical efficiency. The hot spot initiated by non-uniform illumination was also examined in outdoor conditions by measuring the temperature at the centre and both sides of the PV cell. Accordingly, a variance of about 13 K was observed between the centre and both sides (0.005 m distance) of the PV cell's surface area, which was further reduced to 1 K after improving the illumination uniformity.

The solar receiver is considered the cornerstone of the solar tower power system. In particular, it receives hightemperature heat flux rays, and extracts the maximum heat energy to be transferred to the heat transfer fluid, while minimising any thermal and mechanical stresses. Reducing the solar receiver size helps to reduce the loss of spillage; consequently, the thermal stress increases. Using a solar receiver with inserted triangular longitudinal fins enhances the heat transfer as well as strengthens the receiver tube. This study aims to optimise the number of fins, heat flux aiming point, heat transfer fluid, nanoparticle effect with molten salt as the base fluid, and type of receiver material. Non-uniform heat flux with the cosine and Gaussian effects have been considered. When the number of fins (N) increases, the maximum temperature (T max ) decreases and the heat transfer is enhanced. When N ¼ 20, T max ¼ 656.4 K and when N ¼ 1, T max ¼ 683.55, while the efficiency for N ¼ 1 is greater by 3% compared to when N ¼ 20. The cosine distribution of heat flux has a higher maximum temperature than the Gaussian distribution by 29% and is 102% higher in receiver efficiency. The thermal efficiency when the heat flux is aimed at the middle point of the receiver is higher by 10% compared with a lower or upper aiming point. Using Al 2 O 3 nanoparticles with a concentration of 0.5 wt.% increases the thermal efficiency by 14% more than when using pure molten salt when Re ¼ 38000. Using liquid sodium is not required to monitor the peak heat flux, and by adding triangular fins the displacement and thermal stress are 6.5 % lower compared to a smooth receiver.

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