Heliostat-based concentrating solar-thermal power (CSP) systems can offer immense potential to provide low-cost, dispatchable renewable thermal and electrical energy to help achieve 100% decarbonized energy infrastructure in the United States. Heliostats are a major determinant of both capital cost and performance of state-of-the-art commercial molten salt towers and Generation 3 CSP systems. 1 In 2021, the U.S. Department of Energy (DOE) Solar Energy Technologies Office (SETO) launched the Heliostat Consortium (HelioCon), a five-year initiative to advance heliostat technologies. The HelioCon mission is threefold: (1) establish strategic core testing and modeling capabilities and infrastructure at national labs; (2) support heliostat technology development in relevant industries; and (3) serve as a central repository to integrate industry, academia, and other stakeholders for heliostat technology research, development, validation, and deployment. In this report, HelioCon presents a roadmapping study on advancing heliostat technologies, intended as a central reference for the entire CSP community.1 More information on Gen3 technologies can be found at https://www.energy.gov/eere/solar/generation-3concentrating-solar-power-systems-gen3-csp. vii This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications. Metrology and StandardsAppropriate measurement techniques and industry standards are fundamental for product design, prototyping, engineering, and improvement. Gaps in metrology:Opto-mechanical metrology (mirror slope error, mirror facet canting error, and heliostat tracking error) is complex, error-prone, and requires high optical precision, necessitating rigorous validation of different technologies using the same measurement parameter(s). Current metrology gaps include:• Lack of at least two viable metrology techniques for a given measurement parameter (such as heliostat tracking error, available for the global CSP industry)• Insufficient or missing validation of any viable metrology technique against a different, trusted metrology technique or ground-truth article. Gaps in standards:Gaps in community-wide standards for site characterization and heliostat design, testing, field design, and field acceptance test protocols result in significant barriers for new developers, extended design cycles, lower investor confidence, and more complicated arbitration between project parties. Gaps include:• Heliostat terminology • Heliostat design guidelines • Heliostat solar field design/simulation guidelines • Heliostat test guidelines • Heliostat solar field acceptance test guidelines • Site characterization guidelines (e.g., wind, topography, soiling characteristics). Recommended pathway forward: Addressing these gaps requires continuing development of new metrology tools and round-robin tests of existing/to-be-developed tools. More importantly, ix This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications.o...
Solid particle receivers provide an opportunity to run concentrating solar tower receivers at higher temperatures and increased overall system efficiencies. The design of the bins used for storing and managing the flow of particles creates engineering challenges in minimizing thermomechanical stress and heat loss. An optimization study of mechanical stress and heat loss was performed at the National Solar Thermal Test Facility at Sandia National Laboratories to determine the geometry of the hot particle storage hopper for a 1 MWt pilot plant facility. Modeling of heat loss was performed on hopper designs with a range of geometric parameters with the goal of providing uniform mass flow of bulk solids with no clogging, minimizing heat loss, and reducing thermomechanical stresses. The heat loss calculation included an analysis of the particle temperatures using a thermal resistance network that included the insulation and hopper. A plot of the total heat loss as a function of geometry and required thicknesses to accommodate thermomechanical stresses revealed suitable designs. In addition to the geometries related to flow type and mechanical stress, this study characterized flow related properties of CARBO HSP 40/70 and Accucast ID50-K in contact with refractory insulation. This insulation internally lines the hopper to prevent heat loss and allow for low cost structural materials to be used for bin construction. The wall friction angle, effective angle of friction, and cohesive strength of the bulk solid were variables that were determined from empirical analysis of the particles at temperatures up to 600°C.
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