Abstract
Worldwide research efforts are aiming to push the operating temperature limit of CSP systems to improve efficiency and, as a result, the levelized cost of electricity. Furthermore, with higher operating temperatures, a number of new concepts become feasible, the most important of which are supercritical CO2 cycles and air Brayton cycles. Hybrid CSP-fossil fuel systems fall within the air Brayton family of concepts, where the solar field is used to preheat air, while a fossil fuel is burned to bring the air temperature to the firing temperature of a gas-fired Brayton turbine. To make this approach more attractive and environmentally friendly, it is desirable to maximize the solar "contribution" and minimize fuel assistance. This can be done by using novel receivers that increase the air temperature significantly and/or employing a recuperator, where the operating pressure and temperature are lower than conventional Brayton cycles. This paper presents information about an experimental integrated gas turbine-solar particle heating system that uses the hybrid approach. The system is located on the campus of King Saud University in Riyadh, Saudi Arabia and has a peak thermal power of 300 kW. In addition to providing details about the individual components and how they are integrated, the paper explains the start-up procedure, which consists of preheating the system with the heliostat field, followed by additional heating from the turbine itself until the nominal heat exchanger operating temperature is reached, at which point on-sun operation can commence. The study shows that solar preheating requires one to two days to complete, followed by a few hours of heating by the turbine to bring the temperature to about 560 degrees C. Furthermore, with a temperature rise of up to 180 degrees C in the particle heating receiver (and a drop of 10 degrees C in the particle conveyor), the maximum particle temperature will approach 730 degrees C, making the solar contribution significant. As larger scale systems will naturally allow for larger particle drop heights and higher temperature rises in the receiver, it is envisaged that maximum particle tempertures in those systems will approach the firing temperatures of recuperated turbines, making this solution technically, economically, and environmentally worth considering.