The overall goal of this investigation was to develop an innovative high-temperature chloride molten salt flow control valve capable of operation up to 750 °C. The team developed an integrated active and passive thermal management system to ensure robust design for freeze-thaw cycles, with either a bellows-sealed configuration, a high-temperature stuffing box, or combination of the two. The STM system is unique in the industry.
A third-generation chloride salt tank system was designed for a 1 MWth pilot-scale system to be investigated at the National Solar Thermal Test Facility (NSTTF) in Albuquerque, NM, USA. This prototype Gen 3, concentrating solar power (CSP) system was designed to facilitate a minimum of 6 hrs. of thermal energy storage (TES) with operational nominal temperatures of 500°C and 720°C for a cold and hot tank respectively. For this investigation, the researchers developed steady and transient computational fluid mechanics (CFD) circulation models to assess thermal-fluid behavior within the tanks, and their respective interactions with environmental heat transfer. The models developed for this novel CSP system design included unique chloride molten salt thermodynamic properties and correlations. The results of this investigation suggest thermal gradients for the steady flow model less 1oC with overall circulation velocities as high as approximately 2.1 m/s. Higher steady flow rates of salt passing into and out of the tanks resulted in smaller thermal gradients than the slower flow rates as the molten salt mixes better (an increase of around 120% in the heat transfer coefficient) at the higher velocities associated with the higher flow rate. The port spacing of 3.85 m was found to have a highly uniform temperature distribution. For the unsteady model, nitrogen flow was found to become appreciably steady after approximately 10 minutes, and resultant molten salt flow was found to increase slowly as the overall salt level rose.
The United Sates Department of Energy (DOE) Generation 3 Concentrated Solar Power (CSP) program is interested in higher efficiency power systems at lower costs, potentially with systems utilizing chloride molten salts. Ternary chloride molten salts are corrosive and need to be held at high temperatures to achieve higher power system efficiencies. However, materials and cost of manufacturing of such a facility can be very expensive, particularly using exotic materials that are not always readily available. Materials that can withstand the harsh corrosive and thermal-mechanical environments of high-temperature molten salt systems (>700 ℃) are needed. High temperature systems offer greater thermodynamic efficiency but must also make cost efficient use of corrosion-resistant alloys. To ensure reliable high-performance operation for molten salt power plant designs confidence in materials compatibility with CSP Gen 3 halide salts must be established. This paper will present an analysis of Inconel 625 as an alternative to the costly Haynes 230 at 760℃ for 500 hours. Both metals were tested in an unaltered state as well as a homogenous weld. Each sample was weighed pre- and post-test, with a final composition analysis using Scanning Electron Microscopy (SEM) and Energy Dispersive X-Ray Spectroscopy (EDS). Preliminary findings suggest that Haynes 230 outperformed Inconel 625, but more research at longer durations, 1,000 hours will be required for full reliable assessment.
The Sandia National Laboratories (SNL) National Solar Thermal Test Facility (NSTTF) conducted efficacy testing on a shut-off isolation valve for use with molten ternary chloride salt. A ball valve was tested under controlled N2 ullage gas pressure and connected with flanged fittings that featured a spiral-wound gasket. The valve assembly consisted of boronized nickel coated SS316 components, with design features that greatly reduce the cost of overall valve assembly. Testing results showed that the valve did not leak, and post-test analysis demonstrated that the ball, seat, packing, and body all survived both the heat loads and the relative corrosive environment. Spiral-wound gaskets for flanged connections used in the system also functioned nominally, with no leaks or signs of failures during post-test analysis. However, testing was ultimately forced to rapidly stop after testing between 500-530°C as the actuator used on the valve failed in the heat, preventing the valve from sealing in the closed position. In addition, salt plugs and salt vapor plating also prevented the test from continuing.
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.
Research is presented for carbon emissions abatement utilizing concentrating solar power (CSP) heating for culinary industrial process heat applications of roasting peppers. For this investigation the Sandia National Laboratories (SNL) performed high-intensity flux profile heating, as high as approximately 12.2 W/cm2 roasting peppers near 615oC. This work also explores the suitability of culinary roasting as applied to different forms of CSP heating as well as techno-economic costs. Traditionally, chile pepper roasting has used propane gas source heating to achieve similar temperatures and food roasting profiles in batch style processing. Here, the investigators roasted peppers on the top level of the National Solar Thermal Test Facility (NSTTF) solar tower for multiple roasting trials, with and without water. For comparison, the team also performed roasting from a traditional propane gas heating source, monitoring the volume of propane being consumed over time to assess carbon emissions that were abated using CSP. Results found that roasting peppers with CSP facilitated approximately 26 MJ of energy that abated approximately 0.122 kg CO2/kg chile for a 10 kg bag. The team also determined that pre-wetting the peppers before roasting both under propane and CSP heat sources increased the roast time by approximately 3 minutes to achieve the same qualitative optimal roast state compared to dry peppers.
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.
Photovoltaic (PV) system certifications and codes have been modified to allow 1,500 V products onto the market which facilitate the plant engineering, procurement, and construction; however, the codes inadequately address the increased hazards to people and equipment in a high-voltage, photovoltaic plant that emanate from the rapid release of thermal energy, pressure waves, and electromagnetic interference of an arc-fault event. Existing calculations can contradict one another and are rooted in theory, not in physical testing. For this investigation, a localized arc-plasma model for a cylindrical geometry arc was developed from coupled electrodynamic, thermodynamic, and fluid mechanics equations, that were convolved together based on previous arc-discharge models [1]. The model was developed to assess incident energy, used for determining appropriate personal protective equipment (PPE), as a function of spark-gap current. To validate the model, preliminary experiments were performed at Sandia National Laboratories (SNL) with voltage levels as high as 1,500 V. Further utility-scale PV experiments were also conducted with current levels as high as 1,607 A to provide further data. Arc-stability, plasma column spectral features and radiative temperature rise were all evaluated during each respective test to provide radiated power values for validation. Overall preliminary results suggest a logarithmic increase in radiative power between 250 and 2800 W/cm for a current increase from 100 to 300 A.
Field tests of air-copper arcs were completed at a high-voltage, photovoltaic power plant using a simplified, 'arc-in-a-box' geometry to study dc arc-faults. Copper electrodes, 12.7 mm in diameter, were arranged in three configurations and an arc was initiated using < 700 VDCwith applied energy varying from 40-3900 kJ. Constitutive modeling of the arc-discharge predicts arc temperatures much greater than 1000 K. Two diagnostic techniques were fielded to characterize the spectral and thermal emission. Optical emission spectroscopy determined the time-resolved and mean arc temperatures were approximately T_{mean}= 7500 with standard deviations of ± 600 K, and infrared (IR) imaging mapped the mean temperature field, T_{mean}=1500\ \mathrm{K}, of the arc-heated environment.
Field tests of air-copper arcs were completed at a high-voltage, photovoltaic power plant using a simplified, 'arc-in-a-box' geometry to study dc arc-faults. Copper electrodes, 12.7 mm in diameter, were arranged in three configurations and an arc was initiated using < 700 VDCwith applied energy varying from 40-3900 kJ. Constitutive modeling of the arc-discharge predicts arc temperatures much greater than 1000 K. Two diagnostic techniques were fielded to characterize the spectral and thermal emission. Optical emission spectroscopy determined the time-resolved and mean arc temperatures were approximately T_{mean}= 7500 with standard deviations of ± 600 K, and infrared (IR) imaging mapped the mean temperature field, T_{mean}=1500\ \mathrm{K}, of the arc-heated environment.
Photovoltaic (PV) system certifications and codes have been modified to allow 1,500 V products onto the market which facilitate the plant engineering, procurement, and construction; however, the codes inadequately address the increased hazards to people and equipment in a high-voltage, photovoltaic plant that emanate from the rapid release of thermal energy, pressure waves, and electromagnetic interference of an arc-fault event. Existing calculations can contradict one another and are rooted in theory, not in physical testing. For this investigation, a localized arc-plasma model for a cylindrical geometry arc was developed from coupled electrodynamic, thermodynamic, and fluid mechanics equations, that were convolved together based on previous arc-discharge models [1]. The model was developed to assess incident energy, used for determining appropriate personal protective equipment (PPE), as a function of spark-gap current. To validate the model, preliminary experiments were performed at Sandia National Laboratories (SNL) with voltage levels as high as 1,500 V. Further utility-scale PV experiments were also conducted with current levels as high as 1,607 A to provide further data. Arc-stability, plasma column spectral features and radiative temperature rise were all evaluated during each respective test to provide radiated power values for validation. Overall preliminary results suggest a logarithmic increase in radiative power between 250 and 2800 W/cm for a current increase from 100 to 300 A.
Sandia National Laboratories (SNL) National Solar Thermal Test Facility (NSTTF) and Tech Library have been collaborating over the course of the FY19 period to establish and maintain the first and only digital collection in the world of Concentrating Solar Power (CSP) related historical documents, dating back to the CSP program inception here at Sandia in the 1970's thru to the present. The unclassified, unrestricted (UUR) collection, comprised of internally generated Sandia documents as well as a significant number of external reports will be searchable via both the Sandia website and OSTI, DOE's document repository. DOE is currently championing efforts to get the collection launched, where international partners, which include Australia and Germany, plan to forward related documents to be included in the CSP archive. Advancing this transformative project will make the CSP collection accessible to the Sandia and global communities.
In this investigation a series of small-scale tests were conducted, which were sponsored by the Nuclear Regulatory Commission (NRC) Office of Nuclear Regulatory Research (RES) and performed at Sandia National Laboratories (SNL). These tests were designed to better understand localized particle dispersion phenomena resulting from electrical arcing faults. The purpose of these tests was to better characterize aluminum particle size distribution, rates of production, and morphology (agglomeration) of electrical arc faults. More specifically, this effort characterized ejected particles and high-energy dispersion, where this work characterized HEAF electrical characteristics, particle movement/distributions, and morphology near the arc. The results and measurements techniques from this investigation will be used to inform an energy balance model to predict additional energy from aluminum involvement in the arc fault. The experimental setup was developed based on prior work by KEMA and SNL for phase-to-ground and phase-to-phase electrical circuit faults. The small-scale tests results should not be expected to be scale-able to the hazards associated with full-scale HEAF events. Here, the test voltages will consist of four different levels: 480V, 4160V, 6900V and 10kV, based on those realized in nuclear power plant (NPP) HEAF events.
Further development of the Gen3 Liquid-Pathway project is necessary to address technical engineering challenges with respect to incorporation of a flow control valve and sodium system for the 2.0 MWth Pilot-Scale system. For the Thermal Transport development task 1.3, Sandia National Laboratories (SNL) originally set aside $\$$388,425 for the development of a heat trace test bed, however while the team felt that this work is necessary to de-risk a number critical design-related issues the team also has identified items that require more near-term attention. These items largely pertain to the Chloride molten salt values development, with operation up to 720°C, as well as operational mode/system design development as it pertains to the sodium system design, which is currently not included as part of the system design work. The Gen 3 project team requests the ~$\$$388k of funds be used to address these issues, where the previous work requested may be addressed with the 300kWth chloride molten salt loop. These funds would only be spent during the remainder of the Phase 1 budget period, in preparation of final design work for the Phase 2 portion of the project. For the Budget Summary below, please note that the values are burdened values and not raw values, so the actual values going to the entities will be less due to National Laboratory tax costs.
The primary objective of this report is to determine a viable pipe preheating system for a chloridesalt blend (40%MgCl2/20%NaCl/40%KCI) that can preheat the pipe to 450 °C and withstand a maximum exposure temperature of 740 °C. Preheating involves heating the pipe to a specific desired temperature, called preheat temperature, of the pipe. The temperature is maintained by heated molten salt flowing through the piping system. This report reviews 5-types of pipe preheating systems, of which three pipe preheating systems- MI cable, heat tape, and ceramic fiber heaters, were found to be viable for the Gen 3 Liquid Pathway application. The report reviews the pipe preheating efficiency of conduction verses radiant heat transfer. For each of the 5 types of pipe preheating systems, the report describes the system and addresses installation requirements, temperature control, reliability survey, and pre-construction verification testing for the most applicable preheating system. Under Appendix A, images from design drawings demonstrate pipe routing with the preheating system and insulation attached to the pipe along with pipe guides and pipe supports, as designed using Caesar II finite element analysis within the SNL NSTTF Solar Power Tower.
This specification provides to the supplier with requirements for design, manufacturing, inspection and testing in works and cleaning, painting, packing and protection for transport to site for the hot molten salt pumps, receiver circulation pumps and the attemperation molten salt pumps to be used at Sandia National Laboratories, Albuquerque, NM, NSTTF Solar Power Tower.
The primary objective of this report is to determine a viable pipe preheating system for a chloride-salt blend that can preheat the pipe to 450°C and withstand a maximum exposure temperature of 750°C. Preheating involves heating the pipe to a specific desired temperature, called preheat temperature, of the pipe. The temperature is maintained by heated molten salt flowing through the piping system. This report reviews 5-types of pipe preheating systems, of which three pipe preheating systems- MI cable, heat tape, and ceramic fiber heaters, were found to be viable for the Gen 3 Liquid Pathway application. The report reviews the pipe preheating efficiency of conduction verses radiant heat transfer. For each of the 5 types of pipe preheating systems, the report describes the system and addresses installation requirements, temperature control, reliability survey, and pre-construction verification testing for the most applicable preheating system. Under Appendix A, images from design drawings demonstrate pipe routing with the preheating system and insulation attached to the pipe along with pipe guides and pipe supports, as designed using Caesar II finite element analysis within the SNL NSTTF Solar Power Tower.
This paper evaluates the on-sun performance of a 1 MW falling particle receiver. Two particle receiver designs were investigated: obstructed flow particle receiver versus free-falling particle receiver. The intent of the tests was to investigate the impact of particle mass flow rate, irradiance, and particle temperature on the particle temperature rise and thermal efficiency of the receiver for each design. Results indicate that the obstructed flow design increased the residence time of the particles in the concentrated flux, thereby increasing the particle temperature and thermal efficiency for a given mass flow rate. The obstructions, a staggered array of chevron-shaped mesh structures, also provided more stability to the falling particles, which were prone to instabilities caused by convective currents in the free-fall design. Challenges encountered during the tests included nonuniform mass flow rates, wind impacts, and oxidation/deterioration of the mesh structures. Alternative materials, designs, and methods are presented to overcome these challenges.
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.
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 750°C 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 800°C it was found that CTP's SiC composite tubes were able to survive thermal shock, while the SiC monolithic tubes did not.
The photovoltaics industry is in dire need of a cheap, robust, reliable arc fault detector that is sensitive enough to detect arc faults before they can develop into a fire while robust enough to noise to limit unwanted tripping. Management Sciences has developed an arc fault detector that is housed in a standard PV connector, which will disconnect the PV array when it detects the surge current from an arc fault. Sandia National Labs, an industry leader in the detection, characterization, and mitigation of arc faults in PV arrays, will work with Management Sciences to characterize, demonstrate, and develop their arc fault detection/connector technology.
Multiphase computational models and tests of falling water droplets on inclined glass surfaces were developed to investigate the physics of impingement and potential of these droplets to self-clean glass surfaces for photovoltaic modules and heliostats. A multiphase volume-of-fluid model was developed in ANSYS Fluent to simulate the impinging droplets. The simulations considered different droplet sizes (1 mm and 3 mm), tilt angles (0°, 10°, and 45°), droplet velocities (1 m/s and 3 m/s), and wetting characteristics (wetting=47° contact angle and non-wetting = 93° contact angle). Results showed that the spread factor (maximum droplet diameter during impact divided by the initial droplet diameter) decreased with increasing inclination angle due to the reduced normal force on the surface. The hydrophilic surface yielded greater spread factors than the hydrophobic surface in all cases. With regard to impact forces, the greater surface tilt angles yielded lower normal forces, but higher shear forces. Experiments showed that the experimentally observed spread factor (maximum droplet diameter during impact divided by the initial droplet diameter) was significantly larger than the simulated spread factor. Observed spread factors were on the order of 5 - 6 for droplet velocities of ~3 m/s, whereas the simulated spread factors were on the order of 2. Droplets were observed to be mobile following impact only for the cases with 45° tilt angle, which matched the simulations. An interesting phenomenon that was observed was that shortly after being released from the nozzle, the water droplet oscillated (like a trampoline) due to the "snapback" caused by the surface tension of the water droplet being released from the nozzle. This oscillation impacted the velocity immediately after the release. Future work should evaluate the impact of parameters such as tilt angle and surface wettability on the impact of particle/soiling uptake and removal to investigate ways that photovoltaic modules and heliostats can be designed to maximize self-cleaning.
While arc-faults are rare in electrical installations, many documented events have led to fires that resulted in significant damage to energy-generation, commercial and residential systems, as well as surrounding structures, in both the United States and abroad. Arc-plasma discharges arise over time due to a variety of reliability issues related to cable material degradation, electrical and mechanical stresses or acute conductive wiring dislocations. These may lead to discontinuity between energized conductors, facilitating arcing events and fires. Arc-flash events rapidly release significant energy in a localized volume, where the electric arc experiences a reduction in resistance. This facilitates a reduction in electrical resistance as the arc temperature and pressure can increase rapidly. Strong pressure waves, electromagnetic interference (EMI), and intense light from an arc pose a threat to electrical worker safety and system equipment. This arc-fault primer provides basic fundamental insight into arc-fault plasma discharges, and an overview of direct current (DC) and alternating current (AC) arc-fault phenomena. This primer also covers pressure waves and EMI arc-fault hazard analyses related to incident energy prediction and potential damage analysis. Mitigation strategies are also discussed related to engineering design and employment of protective devices including arc-fault circuit interrupters (AFCIs). Best practices related to worker safety are also covered, especially as they pertain to electrical codes and standards, particularly Institute of Electrical and Electronics Engineers (IEEE) 1584 and National Fire Protection Agency (NFPA) 70E. Throughout the primer various modelling and test capabilities at Sandia National Laboratories are also covered, especially as they relate to novel methods of arc-fault/arc-flash characterization and mitigation approaches. Herein, this work describes methods for producing and characterizing controlled, sustained arcs at atmospheric pressures as well as methods for mitigation with novel materials.
Concentrating solar power (CSP) utilizes solar thermal energy to drive a thermal power cycle for the generation of electricity. CSP systems are facilitated as large, centralized power plants , such as power towers and trough systems, to take advantage of ec onomies of scale through dispatchable thermal energy storage, which is a principle advantage over other energy generation systems . Additionally, the combination of large solar concentration ratios with high solar conversion efficiencies provides a strong o pportunity of employment of specific power cycles such as the Brayton gas cycle that utilizes super critical fluids such as supercritical carbon dioxide (s CO 2 ) , compared to other sola r - fossil hybrid power plants. A comprehensive thermal - fluids examination is provided by this work of various heat transfer phenomena evident in CSP technologies. These include sub - systems and heat transfer fundamental phenomena evident within CSP systems , which include s receivers, heat transfer fluids (HTFs), thermal storage me dia and system designs , thermodynamic power block systems/components, as well as high - temperature materials. This work provides literature reviews, trade studies, and phenomenological comparisons of heat transfer media (HTM) and components and systems, all for promotion of high performance and efficient CSP systems. In addition, f urther investigations are also conducted that provide advanced heat transfer modeling approaches for gas - particle receiver systems , as well as performance/efficiency enhancement re commendations, particularly for solarized supercritical power systems .
Sodium Heat transfer fluids (HTF) such as sodium, can achieve temperatures above 700°C to obtain power cycle performance improvements for reducing large infrastructure costs of high-temperature systems. Current concentrating solar power (CSP) sensible HTF's (e.g. air, salts) have poor thermal conductivity, and thus low heat transfer capabilities, requiring a large receiver. The high thermal conductivity of sodium has demonstrated high heat transfer rates on dish and towers systems, which allow a reduction in receiver area by a factor of two to four, reducing re-radiation and convection losses and cost by a similar factor. Sodium produces saturated vapor at pressures suitable for transport starting at 600°C and reaches one atmosphere at 870°C, providing a wide range of suitable operating conditions that match proposed high temperature, isothermal power cycles. This advantage could increase the efficiency while lowering the cost of CSP tower systems. Although there are a number of desirable thermal performance advantages associated with sensible sodium, its propensity to rapidly oxidize presents safety challenges. This investigation presents a literature review that captures historical operations/handling lessons for advanced sodium receiver designs, and the current state-of-knowledge related to sodium combustion behavior. Technical and operational solutions addressing sodium safety and applications in CSP will be discussed, including unique safety hazards and advantages using latent sodium. Lessons obtained from the nuclear industry with sensible and latent systems will also be discussed in the context of safety challenges and risk mitigation solutions.
Sodium Heat transfer fluids (HTF) such as sodium, can achieve temperatures above 700°C to obtain power cycle performance improvements for reducing large infrastructure costs of high-temperature systems. Current concentrating solar power (CSP) sensible HTF's (e.g. air, salts) have poor thermal conductivity, and thus low heat transfer capabilities, requiring a large receiver. The high thermal conductivity of sodium has demonstrated high heat transfer rates on dish and towers systems, which allow a reduction in receiver area by a factor of two to four, reducing re-radiation and convection losses and cost by a similar factor. Sodium produces saturated vapor at pressures suitable for transport starting at 600°C and reaches one atmosphere at 870°C, providing a wide range of suitable operating conditions that match proposed high temperature, isothermal power cycles. This advantage could increase the efficiency while lowering the cost of CSP tower systems. Although there are a number of desirable thermal performance advantages associated with sensible sodium, its propensity to rapidly oxidize presents safety challenges. This investigation presents a literature review that captures historical operations/handling lessons for advanced sodium receiver designs, and the current state-of-knowledge related to sodium combustion behavior. Technical and operational solutions addressing sodium safety and applications in CSP will be discussed, including unique safety hazards and advantages using latent sodium. Lessons obtained from the nuclear industry with sensible and latent systems will also be discussed in the context of safety challenges and risk mitigation solutions.
Since the SunShot Vision Study (DOE 2012) was published, global deployment of concentrating solar power (CSP) has increased threefold to nearly 4,500 MW, with a similar threefold increase in operational capacity to 1,650 MW within the United States. Growth in U.S. CSP capacity has primarily been driven by policy support at the state and federal levels. State-driven renewable portfolio standards (RPSs), combined with a 30% federal investment tax credit (ITC) and federal loan guarantees, provided the opportunity for CSP developers to kick-start construction of CSP plants throughout the Southwest. Figure ES-1 demonstrates that deployment and private- and public-sector research and development have led to dramatic cost reductions that have placed CSP well on the path to reaching the U.S. Department of Energy’s SunShot Initiative goal of 6 cents/kWh by 2020. In comparing the estimated capital costs from the SunShot Vision Study and the current analysis, we find that parabolic trough solar-field costs have fallen more rapidly than predicted, although the drop in solar-field costs was offset by the additional costs of moving from a wet-cooled power block in 2010 to a more expensive dry-cooled power block in 2015. The predicted 2015 decline in tower costs was in line with expectations, primarily driven by reduced heliostat costs. Figure ES-1 shows the reduction in levelized cost of electricity (LCOE) for both parabolic trough and tower systems, in addition to the projected 2020 SunShot target.
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
This paper evaluates the on-sun performance of a 1 MW falling particle receiver. Two particle receiver designs were investigated: obstructed flow particle receiver vs.free-falling particle receiver. The intent of the tests was to investigate the impact of particle mass flow rate, irradiance, and particle temperature on the particle temperature rise and thermal efficiency of the receiver for each design. Results indicate that the obstructed flow design increased the residence time of the particles in the concentrated flux, thereby increasing the particle temperature and thermal efficiency for a given mass flow rate. The obstructions, a staggered array of chevronshaped mesh structures, also provided more stability to the falling particles, which were prone to instabilities caused by convective currents in the free-fall design. Challenges encountered during the tests included non-uniform mass flow rates, wind impacts, and oxidation/deterioration of the mesh structures. Alternative materials, designs, and methods are presented to overcome these challenges.
Three balance of systems (BOS) connector designs common to industry were investigated as a means of assessing reliability from the perspective of arc fault risk. These connectors were aged in field and laboratory environments and performance data captured for future development of a reliability model. Comparison of connector resistance measured during damp heat, mixed flowing gas and field exposure in a light industrial environment indicated disparities in performance across the three designs. Performance was, in part, linked to materials of construction. A procedure was developed to evaluate new and aged connectors for arc fault risk and tested for one of the designs. Those connectors exposed to mixed flowing gas corrosion exhibited considerable Joule heating that may enhance arcing behavior, suggesting temperature monitoring as a potential method for arc fault prognostics. These findings, together with further characterization of connector aging, can provide operators of photovoltaic installations the information necessary to develop a data-driven approach to BOS connector maintenance as well as opportunities for arc fault prognostics.
The continued exponential growth of photovoltaic technologies paves a path to a solar-powered world, but requires continued progress toward low-cost, high-reliability, high-performance photovoltaic (PV) systems. High reliability is an essential element in achieving low-cost solar electricity by reducing operation and maintenance (O&M) costs and extending system lifetime and availability, but these attributes are difficult to verify at the time of installation. Utilities, financiers, homeowners, and planners are demanding this information in order to evaluate their financial risk as a prerequisite to large investments. Reliability research and development (R&D) is needed to build market confidence by improving product reliability and by improving predictions of system availability, O&M cost, and lifetime. This project is focused on understanding, predicting, and improving the reliability of PV systems. The two areas being pursued include PV arc-fault and ground fault issues, and inverter reliability.
Solar spectral data for all parts of the US is limited due in part to the high cost of commercial spectrometers. Solar spectral information is necessary for accurate photovoltaic (PV) performance forecasting, especially for large utility-scale PV installations. A low-cost solar spectral sensor would address the obstacles and needs. In this report, a novel low-cost, discrete- band sensor device, comprised of five narrow-band sensors, is described. The hardware is comprised of commercial-off-the-shelf components to keep the cost low. Data processing algorithms were developed and are being refined for robustness. PV module short-circuit current ( I sc ) prediction methods were developed based on interaction-terms regression methodology and spectrum reconstruction methodology for computing I sc . The results suggest the computed spectrum using the reconstruction method agreed well with the measured spectrum from the wide-band spectrometer (RMS error of 38.2 W/m 2 -nm). Further analysis of computed I sc found a close correspondence of 0.05 A RMS error. The goal is for ubiquitous adoption of the low-cost spectral sensor in solar PV and other applications such as weather forecasting.
This work investigates balance of systems (BOS) connector reliability from the perspective of arc fault risk. Accelerated tests were performed on connectors for future development of a reliability model. Thousands of hours of damp heat and atmospheric corrosion tests found BOS connectors to be resilient to corrosion-related degradation. A procedure was also developed to evaluate new and aged connectors for arc fault risk. The measurements show that arc fault risk is dependent on a combination of materials composition as well as design geometry. Thermal measurements as well as optical emission spectroscopy were also performed to further characterize the arc plasma. Together, the degradation model, arc fault risk assessment technique, and characterization methods can provide operators of photovoltaic installations information necessary to develop a data-driven plan for BOS connector maintenance as well as identify opportunities for arc fault prognostics.
The solar spectrum varies with atmospheric conditions and composition, and can have significant impacts on the output power performance of each junction in a concentrating solar photovoltaic (CPV) system, with direct implications on the junction that is current-limiting. The effect of changing solar spectrum on CPV module power production has previously been characterized by various spectral performance parameters such as air mass (AM) for both single and multi-junction module technologies. However, examinations of outdoor test results have shown substantial uncertainty contributions by many of these parameters, including air mass, for the determination of projected power and energy production. Using spectral data obtained from outdoor spectrometers, with a spectral range of 336nm-1715nm, this investigation examines precipitable water (PW), aerosol and dust variability effects on incident spectral irradiance. This work then assesses air mass and other spectral performance parameters, including a new atmospheric component spectral factor (ACSF), to investigate iso-cell, stacked multijunction and single-junction c-Si module performance data directly with measured spectrum. This will then be used with MODTRAN5® to determine if spectral composition can account for daily and seasonal variability of the short-circuit current density Jsc and the maximum output power Pmp values. For precipitable water, current results show good correspondence between the modeled atmospheric component spectral factor and measured data with an average rms error of 0.013, for all three iso-cells tested during clear days over a one week time period. Results also suggest average variations in ACSF factors with respect to increasing precipitable water of 8.2%/cmH2O, 1.3%/cmH2O, 0.2%/cmH2O and 1.8%/cmH2O for GaInP, GaAs, Ge and c-Si cells, respectively at solar noon and an AM value of 1.0. For ozone, the GaInP cell had the greatest sensitivity to increasing ozone levels with an ACSF variation of 0.07%/cmO3. For the desert dust wind study, consistent ACSF behavior between all iso-cells and c-Si was found, with only significant reductions beyond 40mph.