ASME 2016 10th International Conference on Energy Sustainability, ES 2016, collocated with the ASME 2016 Power Conference and the ASME 2016 14th International Conference on Fuel Cell Science, Engineering and Technology
The high-temperature particle - supercritical carbon dioxide (sCO2) Brayton power system is a promising option for concentrating solar power (CSP) plants to achieve SunShot metrics for high-temperature operation, efficiency, and cost. This system includes a falling particle receiver to collect solar thermal radiation, a dry-cooled sCO2 Brayton power block to produce electricity, and a particle to sCO2 heat exchanger to couple the previous two. While both falling particle receivers and sCO2 Brayton cycles have been demonstrated previously, a high temperature, high pressure particle/sCO2 heat exchanger has never before been demonstrated. Industry experience with similar heat exchangers is limited to lower pressures, lower temperatures, or alternative fluids such as steam. Sandia is partnering with three experienced heat exchanger manufacturers to develop and down-select several designs for the unit that achieves both high performance and low specific cost to retire risks associated with a solar thermal particle/sCO2 power system. This paper describes plans for the construction of a particle sCO2 heat exchanger testbed at Sandia operating above 700 °C and 20 MPa, with the ability to couple directly with a previously-developed falling particle receiver for on-sun testing at the National Solar Thermal Test Facility (NSTTF).
ASME 2016 10th International Conference on Energy Sustainability, ES 2016, collocated with the ASME 2016 Power Conference and the ASME 2016 14th International Conference on Fuel Cell Science, Engineering and Technology
Multiple receiver designs have been evaluated for improved optics and efficiency gains including flat panel, vertical-finned flat panel, horizontal-finned flat panel, and radially finned. Ray tracing using SolTrace was performed to understand the light-trapping effects of the finned receivers. Re-reflections of the fins to other fins on the receiver were captured to give an overall effective solar absorptance. The ray tracing, finite element analysis, and previous computational fluid dynamics showed that the horizontalfinned flat panel produced the most efficient receiver with increased light-trapping and lower overall heat loss. The effective solar absorptance was shown to increase from an intrinsic absorptance of 0.86 to 0.96 with ray trace models. The predicted thermal efficiency was shown in CFD models to be over 95%. The horizontal panels produce a re-circulating hot zone between the panel fins reducing convective loss resulting in a more efficient receiver. The analysis and design of these panels are described with additional engineering details on testing a flat panel receiver and the horizontal-finned receiver at the National Solar Thermal Test Facility. Design considerations include the structure for receiver testing, tube sizing, surrounding heat shielding, and machinery for cooling the receiver tubes.
The contribution of each component of a power generation plant to the levelized cost of energy (LCOE) can be estimated and used to increase the power output while reducing system operation and maintenance costs. The LCOE is used in order to quantify solar receiver coating influence on the LCOE of solar power towers. Two new parameters are introduced: the absolute levelized cost of coating (LCOC) and the LCOC efficiency. Depending on the material properties, aging, costs, and temperature, the absolute LCOC enables quantifying the cost-effectiveness of absorber coatings, as well as finding optimal operating conditions. The absolute LCOC is investigated for different hypothetic coatings and is demonstrated on Pyromark 2500 paint. Results show that absorber coatings yield lower LCOE values in most cases, even at significant costs. Optimal reapplication intervals range from one to five years. At receiver temperatures greater than 700 °C, non-selective coatings are not always worthwhile while durable selective coatings consistently reduce the LCOE-up to 12% of the value obtained for an uncoated receiver. The absolute LCOC is a powerful tool to characterize and compare different coatings, not only considering their initial efficiencies but also including their durability.