This work details the development of a concentrating solar power (CSP) and thermal (CST) library archive. This work included digitization of one-of-a-kind documents that could be degraded or destroyed over time. Sandia National Laboratories (SNL) National Solar Thermal Test Facility (NSTTF) and Sandia?s Technical Library departments collaborated to establish and maintain the first and only digital collection in the world of Concentrating Solar Power (CSP) related historical documents. These date back to the CSP program inception here at Sandia in the early 1970?s thru to the present.
This investigation explores thermal-fluid flow phenomena in a proportional flow control valve (FCV) within a 2 in. ID high-temperature piping transport system. The FCVs are critical components to ensure flexible nominal operation of a 2 MWth concentrating solar power (CSP) pilot-scale system in present development at Sandia National Laboratories (SNL). A computational fluid dynamics (CFD) / finite element analysis (FEA) model was developed in ANSYS that investigates multifluid phase-change transport within various sections of an FCV to explore plating and subsequent thermal-mechanical stress challenges that can exist with operations as high as 730°C. Results from the thermal-fluid model in development suggest salt vapor phase change in the N2 gas purge lines as low as approximately 476°C, which can have a negative impact on valve reliability.
In this investigation, heat transfer analysis of cold and hot pump-tank interfaces for a 2 MWth pilot-scale system is assessed using a developed computational fluid dynamics (CFD) model using ANSYS Fluent. A DOE Generation 3 concentrating solar power (CSP) ternary chloride molten salt mixture is used as the working fluid of each system and evaluated at different temperatures and pressures. In this CFD model work an analysis was performed for a pump assembly at the interface between the test loop and a storage tank. The model was developed for three scenarios with molten salt inlet temperatures set at 500 °C, 720 °C, and 730 °C. The real-world complex geometry was simplified and evaluated as a two- dimensional model with the purpose of estimating overall heat transfer and velocity profiles for the respective system configurations. Preliminary results indicate that pump field insulation absorbs most of the heat from radiating from the molten salt region at a max temperature of 39.48 °C and that heat transfer within the N2 ullage gas region is primarily due to natural convection and radiation.
The development of a Generation 3 Liquid-Pathway, Pilot-scale sodium and molten chloride salt concentrating solar power system at Sandia National Laboratories requires extensive permitting to ensure code and environmental safety & health compliance for nominal, safe operation. This includes permitting for National Environmental Policy Act, U.S. Airforce approvals, and abiding by the National Fire Protection Association Life Safety Code. This work also details the failure modes effects analysis procedures to address design engineering and administration controls for technical risks. To facilitate permitting and safety procedures, staged sodium spray and pool fire variants were demonstrated. Soda ash extinguishing agents were utilized to demonstrate fire mitigation by Fire Department personnel. For this work, temperature data was measured for characterizing sodium fire temperatures and the zone of influence to provide PPE level information to emergency response personnel.
The following report contains data and data summaries collected for the SkySun LLC elevated Ganged PV arrays. These arrays were fabricated as a series of PV panels in various orientations, suspended by cables, at the National Solar Thermal Test Facility (NSTTF) at Sandia National Laboratories (SNL). Starting in February of 2021, Sandia personnel have collected power and accelerometer data for these arrays to assess design and operational efficacy of varying ganged- PV configurations. The purpose of this power data collection was to see how the various array orientations compare in power collection capability depending on the time of day, year, and the specific daily solar direct normal irradiance (DNI). The power data was collected as a measurement of the power output from the various series strings. The project team measured direct current (DC) voltage and current from the respective arrays. The accelerometer data was collected with the purpose of demonstrating potential destructive mode shapes that could take place with each of the arrays when exposed to high winds. This allowed the team to evaluate whether impacts with respect to specific array orientations using suspended cables is a safe design. All data collection was performed during calendar year 2021.
The limit of traditional solar-salt thermal stability is around 600 °C with ambient air as the cover gas. Nitrate molten salt concentrating solar power (CSP) systems are currently deployed globally and are considered to be state-of the art heat transfer fluids (HTFs) for present day high-temperature operation. However, decomposition challenges occur with these salts for operation beyond 600. Although slightly higher limits may be possible with solar salt, to fully realize SunShot efficiency goals of $15/kWhth HTFs and an LCOE of 6¢/kWh, molten-salt technologies working at higher temperatures (e.g., 650 °C to 750 °C) will require an alternative salt chemistry composition, such as chlorides. In this investigation a 2.0MWth Pilot-scale CSP plant design is developed to assess thermodynamic performance potential for operation up to 720 . Here, an Engineering Equation Solver (EES) model is developed with respect to 14 state-points from the base of a solar tower at the Sandia National Laboratories, National Solar Thermal Test Facility (NSTTF), to solar receiver mounted 120 ft. above the ground. The system design considers a ternary chloride ternary chloride (20%NaCl/40%MgCl/40%KCl by mol%) salt as the HTF, with 6 hrs. of storage and a 1 MWth primary salt to sCO2 heat exchanger. Preliminary system modelling results indicate a minimum non-dimensional Cv of 60 required for both cold and hot-side throttle recirculation valves for the operational pump operating between speeds of 1800 and 2400 RPM. Further receiver comparison study results suggest that the ternary salt requires an average 15.2% higher receiver flux with a slightly lower calculated receiver efficiency when compared to a binary carnelite salt to achieve a 2.0 MWth desired input power design.
CSP power tower receiver systems during rapid transient weather periods can be vulnerable to thermal shock conditions from rain that which can facilitate the onset of leaks and failures that can have catastrophic consequences. Silicon carbide (SiC) materials have attractive receiver application characteristics for being light weight, having high-strength and excellent thermal shock resistance performance which make them a particularly good fit for receiver absorber materials in CSP. In this investigation, the performance characteristics of Ceramic Tubular Products (CTP) SiC ceramic matrix composite (CMC), multilayered tubes were explored with respect to thermal shock performance for solar receiver applications in next generation CSP plants. Here, thermal shock testing was performed at the Sandia National Laboratories (SNL) Solar Furnace facility using a dynamic stage and thermal shock tube test setup. The tubes tested under incident solar heat flux of 100 W/cm2 were heated with inner tube temperatures reaching approximately 800 °C, with outer temperatures exceeding or just reaching 1000 ℃ for the multilayer and monolithic SiC tubes respectively. The tubes were then quenched with simulated rain. The tubes were then cooled and subjected to hoop stress analysis using an Instron device to assess their subsequent mechanical strength. The on-sun study experimental results indicate an average of 24.2% and 97% higher hoop strength for the CMC tubes than those composed of monolithic SiC and aluminum oxide (Al2O3) respectively.
In order for Concentrating Solar Power plants (CSP) to achieve the desired cost breakpoint, significant improvement in performance is required resulting in the need to increase temperatures of fluid systems. A US DOE Small Business Voucher project was established at Sandia to explore the performance characteristics of Ceramic Tubular Products (CTP) silicon carbide TRIPLEX tubes in key categories relating to its performance as a solar receiver in next generation CSP plants. Along these lines, the following research tasks were completed : (1) Solar Spectrum Testing, (2) Corrosion Testing in Molten Chloride Salt, (3) Mechanical Shock Testing, and (4) Thermal Shock Testing. Through the completion of these four tasks, it has been found that the performance of CTP's material across all of these categories is promising, and merits further investigation beyond this initial investigation. Through 50 solar aging cycles, the CTP material exhibited excellent stability to high temperatures in air, exhibited at or above 0.95 absorptance, and had measured emittances within the range of 0.88-0.90. Through molten salt corrosion testing at 750degC it was found that SiC exhibits significantly lower mass change (-- 90 times lower) than Haynes 230 during 108 hours of salt exposure. The CTP TRIPLEX material performed significantly better than the SiC monolithic tube material in mechanical shock testing, breaking at an average height of 3 times that for the monolithic tubes. Through simulated rain thermal shock testing of CTP composite tubes at 800degC it was found that CTP's SiC composite tubes were able to survive thermal shock, while the SiC monolithic tubes did not. ACKNOWLEDGEMENTS * US Department of Energy Office of EERE for sponsorship of this project * Andrew Dawson of the DOE Office of EERE for Project Management, including the excellent technical insights that he provided throughout the project * Ken Armijo lead the Thermal Shock Testing activities * Cliff Ho and Julius Yellowhair led the Solar Spectrum Testing activities * Jeff Halfinger prepared the CTP specimens for each of the research tasks * Herb Feinroth provided guidance and input into the preparation for the test specimens and the associated research tasks * Alan Kruizenga collaborated with CTP to apply for and be awarded this project from DOE EERE. The scope for the project was developed by Alan together with CTP. * Rio Hatton and Jesus Ortega (student interns) helped with portions of the solar simulator testing, reflectance/emittance data collection, and image (including microscope) collection. * Kent Smith helped design and fabricate the high temperature molten salt corrosion setup * Jeff Chames and Javier Cebrian completed the microscopy for the molten salt corrosion test specimens * Amy Bohinsky (student intern) and Kevin Nelson helped complete the mechanical shock testing for the monolithic and composite tubes, including organizing the results for the final report. * Josh Christian and Daniel Ray helped with portions of the Thermal Shock Testing * Mark Stavig completed the polyethylene plug testing associated with the Thermal Shock Testing
Designs of conventional heliostats have been varied to reduce cost, improve optical performance or both. In one case, reflective mirror area on heliostats has been increased with the goal of reducing the number of pedestals and drives and consequently reducing the cost on those components. The larger reflective areas, however, increase torques due to larger mirror weights and wind loads. Higher cost heavy-duty motors and drives must be used, which negatively impact any economic gains. To improve on optical performance, the opposite may be true where the mirror reflective areas are reduced for better control of the heliostat pointing and tracking. For smaller heliostats, gravity and wind loads are reduced, but many more heliostats must be added to provide sufficient solar flux to the receiver. For conventional heliostats, there seems to be no clear cost advantage of one heliostat design over other designs. The advantage of ganged heliostats is the pedestal and tracking motors are shared between multiple heliostats, thus can significantly reduce the cost on those components. In this paper, a new concept of cable-suspended tensile ganged heliostats is introduced, preliminary analysis is performed for optical performance and incorporated into a 10 MW conceptual power tower plant where it was compared to the performance of a baseline plant with a conventional radially staggered heliostat field. The baseline plant uses conventional heliostats and the layout optimized in System Advisor Model (SAM) tool. The ganged heliostats are suspended on two guide cables. The cables are attached to rotations arms which are anchored to end posts. The layout was optimized offline and then transferred to SAM for performance evaluation. In the initial modeling of the tensile ganged heliostats for a 10 MW power tower plant, equal heliostat spacing along the guide cables was assumed, which as suspected leads to high shading and blocking losses. The goal was then to optimize the heliostat spacing such that annual shading and blocking losses are minimized. After adjusting the spacing on tensile ganged heliostats for minimal blocking losses, the annual block/shading efficiency was greater than 90% and annual optical efficiency of the field became comparable to the conventional field at slightly above 60%.
Various ganged heliostat concepts have been proposed in the past. The attractive aspect of ganged heliostat concepts is multiple heliostats are grouped so that pedestals, tracking drives, and other components can be shared, thus reducing the number of components. The reduction in the number of components is thought to significantly reduce cost. However, since the drives and tracking mechanisms are shared, accurate on-sun tracking of grouped heliostats becomes challenging because the angular degrees-of-freedom are now limited for the multiple number of combined heliostats. In this paper, the preliminary evaluation of the on-sun tracking of a novel tensile-based cable suspended ganged heliostat concept is provided. In this concept, multiple heliostats are attached to two guide cables. The cables are attached to rotation spreader arms which are anchored to end posts on two ends. The guide cables form a catenary which makes tracking on-sun interesting and challenging. Tracking is performed by rotating the end plates that the two cables are attached to and rotating the individual heliostats in one axis. An additional degree-of-freedom can be added by differentially tensioning the two cables, but this may be challenging to do in practice. Manual on-sun tracking was demonstrated on small-scale prototypes. The rotation arms were coarsely controlled with linear actuators, and the individual heliostats were hand-adjusted in local pitch angle and locked in place with set screws. The coarse angle adjustments showed the tracking accuracy was 3-4 milli-radians. However, with better angle control mechanisms the tracking accuracy can be drastically improved. In this paper, we provide tracking data that was collected for a day, which showed feasibility for automated on-sun tracking. The next steps are to implement better angle control mechanisms and develop tracking algorithms so that the ganged heliostats can automatically track.