Particle heating receivers are a promising technology that can allow operation of CSP systems at temperatures higher than what today’s commercial molten salt systems can achieve, making them suitable for use in a variety of applications, including supercritical CO₂ cycles, air Brayton cycles, and high-temperature process heat. One of the ways to improve cost-competitiveness of particle heating receivers is to use low-cost particulate materials, such as sand, as the working medium. Red sand is particularly attractive due to its abundance and acceptable absorptance. This paper presents the results of on-sun testing of a particle heating receiver that uses red sand as the working medium. Tests were conducted at the experimental central receiver facility at King Saud University in Riyadh, Saudi Arabia. Performance of the receiver was assessed in two ways. First, the rate of thermal energy absorption was calculated using the measured temperature rise across the receiver, particle flow rate, and red sand’s specific heat. Second, receiver efficiency was calculated using the rate of thermal energy absorption and the thermal power incident on the receiver, which was estimated using a raytracing software. Results show that a temperature rise of 130°C was achieved with an incident heat flux of 230-280 kW/m². Receiver efficiency was found to range from 60% to 70%. These results are encouraging and show that red sand is a promising particulate material, especially when it is used with a proper cavity receiver design where the effect of absorptance of the particulate material becomes less significant.

Utilizing solid particles as a heat-transfer medium in concentrated solar power applications has gained growing attention lately. Unlike molten salts, solid particles offer many benefits, which include: high operating temperatures (greater than 1000 °C), a lack of freezing issues and corrosivity, abundant availability, high thermal energy storage capacity, a low cost, and applicability in direct irradiation. Comprehensive knowledge of thermophysical and optical properties of solid particles is essential to ensure an effective harnessing of solar energy. The most important considerations when selecting solid particles include: thermophysical and optical properties, thermal resistance, crack resistance, satisfactory health and safety risks, availability, and low cost. It is also imperative to consider optical and thermophysical characteristics that might change from what they were “as received” after cyclic heating for a long period. Therefore, the knowledge of thermal performance of particulate materials becomes significant before using them as a heat-transfer medium. In this study, some particulate materials were chosen to study their feasibilities as heat-transfer and storage media for a particle-based central receiver tower system. These particulate materials included white sand, red sand, ilmenite, and Carbobead CP. The candidate particulate materials were heated at high temperatures for 6 h and then cooled to room temperature. After that, cyclic heating was performed on the particulate materials for 500 h at 1200 °C. The optical properties were represented by weighted solar absorptance, and the thermophysical properties of the particulates were measured “as received” and after cyclic heating (aging). EDX and XRD were conducted to quantify the chemical composition and interpret the changes in appearance associated with the particulate materials after cyclic heating. The results showed a considerable agglomeration in all particulates except for white sand in the 6 h heating test, and high agglomeration in the ilmenite. A slight decrease in the optical properties in the white sand and Carbobead CP was found after the aging test. The specific heat was decreased for red and white sand. The EDX and XRD results for white sand and Carbobead CP showed chemical stability, indicating high durability and reliability.

Improvement in the performance of a solar still is investigated with the integration of a geothermal cooling system and a vacuum pump. Geothermal cooling is simulated to provide a cold, effective underground water temperature, which could reach 15–25 °C below ambient. Cooling is achieved by circulating water underground. As a result of this circulation, the cold fluid from the ground flows into a counter flow shell and tube heat exchanger. A vacuum pump is used to keep the solar still at a certain vacuum pressure. The sizes of the geothermal system and solar still are designed in such a way that the water outlet temperature from the ground and its flow rate are capable of condensing the entire vapor produced by the still. An analytical model was developed and then solved using the Newton–Raphson method for solving non-linear equations. A prototype was built to validate the analytical model. The results were in close agreement. A 305% increase in daily water productivity resulted from the proposed enhancements. After experimental validation, the effects of various parameters such as vacuum pressure, ambient temperature, and wind speed on the yield of geothermal solar still were examined. It was found that the increase in vacuum pressure enhanced performance, whereas the increase in wind speed had a detrimental effect on the yield of the solar still. A higher ambient temperature increased the yield of the solar still. Finally, the design of the heat exchanger for condensing the distilled water using geothermal cooling water was also investigated in terms of the increase in UA (the product of overall heat transfer coefficient and the area of heat exchanger) with inlet cooling geothermal water temperature.

This paper presents a thermal performance evaluation of a novel particle-to-air heat exchanger. The heat exchanger has a patented design with a shell-and-tube configuration. Solid particles move as a dense packed-bed inside the vertical tubes of the heat exchanger whereas air flows on the shell-side. This design avoids a number of limitations associated with the state-of-the-art heat exchangers in the same category, such as the stagnant/void zones and the prolonged residence time. The heat exchanger has a 50-kW thermal duty; it has been integrated into the particle-based concentrating solar power facility located at the campus of King Saud University in Riyadh, Saudi Arabia. The detailed description of the heat exchanger and the integration process is introduced. The recuperated air of the facility’s power cycle is used to heat the solid particles being circulated inside the facility. The solid particles used in this study are engineered particles called Carbobead CP with 0.3 mm mean diameter. The effect of particle flow rate on the thermal performance of the heat exchanger is investigated. The results show that as the particle flow rate increases, the overall heat transfer coefficient (U) increases; a maximum value was measured to be 150 W/m²-°C based on LMTD calculations. The measurement accuracy was verified by repeating several tests; a slight variation was observed in the measured U. The results also show that only a small air pressure drop (~5 kPa) was measured across the heat exchanger. Furthermore, it was found that a significant part of the heat exchange occurred at the bottom section of the heat exchanger.

This paper presents the results of an extensive study of two thermal energy storage (TES) systems. The goal of the research is to make solar energy cost-competitive with other forms of electricity. A small-scale TES system was first built. The inner to outer layers were made of firebrick (FB), autoclaved aerated concrete (AAC) and reinforced concrete brick (CB). The experiments were conducted at temperatures of up to 1000 °C for sustained periods of time. AAC was found to be prone to cracking at temperatures exceeding 900 °C; as a result, AAC was eliminated from the second TES system. The second, larger-scale TES system was subsequently built of multiple layers of readily available materials, namely, insulating firebrick (IFB), perlite concrete (PC), expansion joint (EJ), and CB. All of the surfaces were instrumented with thermocouples to estimate the heat loss from the system. The temperature was maintained at approximately 800 °C to approximate steady state conditions closely. The steady state heat loss was determined to be approximately 4.4% for a day. The results indicate that high-temperature TES systems can be constructed of readily available materials while meeting the heat loss requirements for a falling particle receiver system, thereby contributing to reducing the overall cost of concentrating solar power systems.

In this paper, energy and exergy analysis of typical gas turbines is performed using average hourly temperature and relative humidity for selected Gulf cities located in Saudi Arabia, Kuwait, United Arab Emirates, Oman, Bahrain and Qatar. A typical gas turbine unit of 42 MW is considered in this study. The electricity production, thermal efficiency, fuel consumption differences between the ISO conditions and actual conditions are determined for each city. The exergy efficiency and exergy destruction rates for the gas turbine unit and its components are also evaluated taking ISO conditions as reference conditions. The results indicate that the electricity production losses occur in all cities during the year, except in Dammam and Kuwait for the period between November and March. During a typical day, the variation of the power production can reach 4 MW. The rate of exergy destruction under the combined effect of temperature and humidity is significant in hot months reaching a maximum of 12 MW in July. The presented results show also that adding inlet cooling systems to the existing gas turbine units could be justified in hot periods. Other aspects, such as the economic and environmental ones, should also be investigated.