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.

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.

Tests were performed at the particle-based CSP test facility at King Saud University to demonstrate a viable solution to overcome the limitations of using molten salt as a working medium in power plants. The KSU facility is composed of a heliostat field, particle heating receiver (PHR) at the top of a tower, thermal energy storage (TES) bin, a particle-to-working fluid heat exchanger (PWFHX), power cycle (microturbine), and a particle lift. During pre-commissioning, a substantial portion of the collected solar energy was lost during particle flow through the TES bin. The entrained air is shown to be the primary cause of such heat loss. The results show that the particle temperature at the PHR outlet can reach 720 °C after mitigating the entrained air issue. Additionally, during on-sun testing, a higher temperature of the air exiting the PWFHX than that of the air entering is observed, which indicates the effective solar contribution. Half-hour plant operation through stored energy was demonstrated after heliostat defocusing. Lastly, a sealable TES bin configuration for 1.3 MWe pre-commercial demonstration unit to be built in Saudi Arabia by Saudi Electric Company (SEC) is presented. This design modification has addressed the heat loss, pressure build-up, and contamination issues during TES charging.

Particle-based power tower systems are a promising technology that can allow operation of concentrating solar power (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. In this concept, particles, instead of molten salt, are heated by the concentrated sunlight. In 2015, this concept was successfully tested at Sandia National Laboratories. In the mean time, an integrated system incorporating a particle heating receiver, a particle-to-air heat exchanger and a 100-kWe microturbine was designed, built, and tested at King Saud University in Riyadh, Saudi Arabia. The integrated system was run in 2018, and results from that test campaign were very promising, with temperatures of the particles leaving the receiver exceeding 600°C despite a number of challenges. The utility sponsoring the project is now planning to move forward with building a 1-MWe plant using the same concept, thereby moving closer to large-scale deployment, and making this facility the world’s first commercial concentrating solar power plant that uses the particle heating receiver concept. Moving from a 100-kWe scale to a 1-MWe scale requires modifications to the design of some components. The most likely plant location is the city of Duba in northwestern Saudi Arabia where the average daily total DNI is 7,170 Wh/m² and an integrated solar combined cycle power plant exists on the premises. This paper discusses the design features of the main components of the new plant. Those features include a north field design, a 7.22-m² single-sheet heliostat design, a cavity receiver to improve receiver efficiency by reducing radiative and convective losses, temperature-based particle flow regulation within the receiver, six hours of full-load thermal energy storage, with the tanks integrated into the tower structure and made of cost-effective masonry material, a shell-and-tube particle-to-air heat exchanger, a 45% efficiency recuperated intercooled gas turbine, and a high-temperature bucket elevator. The heliostat field was optimized using SolarPILOT. Results show that 1,302 heliostats are needed. The aperture area was found to be approximately 5.7 m², while the total illuminated receiver surface area is about 16.8 m². This design was found to be capable of achieving the particle temperature rise of 416°C, which is necessary to allow the turbine to rely entirely on the solar field to bring the temperature of air to the firing temperature of the turbine, thereby eliminating the need for fuel consumption except for back-up and for assistance at off-design conditions.