Falling particle receivers are a promising receiver design to couple with particle-based concentrating solar power to help meet future levelized cost of electricity targets in next generation systems. The thermal performance of receivers is critical to the economics of the overall system, and accurate models of particle receivers are necessary to predict the performance in all conditions. A model validation study was performed using falling particle receiver data recently collected at the National Solar Thermal Test Facility at Sandia National Laboratories. The particle outlet temperature, the thermal efficiency of the receiver, and the wind speed and direction around the receiver were measured in 26 steady-state experiments and compared to a corresponding receiver model. The results of this study showed improved agreement with the experimental data over past validation efforts but did not fully meet all predefined validation metrics. Future model improvements were identified to continue to strengthen the modeling capabilities.
This report documents the results and conclusions of a recent project to understand the technoeconomics of utility-scale, particle-based concentrating solar power (CSP) facilities leveraging unique operational strategies. This project included two primary objectives. The first project objective was to build confidence in the modeling approaches applied to falling particle receivers (FPRs) including the effect s of wind. The second project objective was to create the necessary modeling capability to adequately predict and maximize the annual performance of utility-scale, particle-based CSP plants under anticipated conditions with and without active heliostat control. Results of an extensive model validation study provided the strongest evidence to date for the modeling strategies typically applied to FPRs, albeit at smaller receiver scales. This modeling strategy was then applied in a parametric study of candidate utility-scale FPRs, including both free-falling and multistage FPR concepts, to develop reduced order models for predicting the receiver thermal efficiency under anticipated environmental and operating conditions. Multistage FPRs were found to significantly improve receiver performance at utility-scales. These reduced order models were then leveraged in a sophisticated technoeconomic analysis to optimize utility-scale , particle-based CSP plants considering the potential of active heliostat control. In summary, active heliostat control did not show significant performance benefits to future utility-scale CSP systems though some benefit may still be realized in FPR designs with wide acceptance angles and/or with lower concentration ratios. Using the latest FPR technologies available, the levelized-cost of electricity was quantified for particle-based CSP facilities with nominal powers ranging from 5 MWe up to 100 MWe with many viable designs having costs < 0.06 $/kWh and local minimums occurring between ~25–35 MWe.
Falling particle receivers are an emerging technology for use in concentrating solar power systems. In this study, quartz half-shells are investigated for use as full or partial aperture covers to reduce receiver thermal losses. Quartz half-shell aperture covers offer the ability to minimally interfere with incoming solar radiation from the heliostat field while obstructing thermal radiation and advection from leaving the receiver cavity. The fluid dynamics and heat transfer of a receiver subdomain and surrounding air are modeled using ANSYS® FLUENT. We compare the percentage of total incident solar power lost due to conduction through the receiver walls, advective losses through the aperture, and radiation exiting the aperture. Contrary to expected outcomes, results show that quartz aperture covers can increase radiative losses and result in modest to nonexistent reductions in advective losses. The increased radiative losses are driven by elevated quartz half-shell temperatures and have the potential to be mitigated by active cooling and/or material selection. Quartz half-shell total transmissivity was measured experimentally using a radiometer and the National Solar Thermal Test Facility heliostat field with values up to 0.97 ± 0.01. Quartz half-shell aperture covers did not yield expected efficiency gains in numerical results due to increased radiative losses, but efficiency improvement in some numerical results and the performance of quartz half-shells subject to concentrated solar radiation suggest that quartz half-shell aperture covers should be investigated further.
This paper summarizes the evolution of the Gen 3 Particle Pilot Plant (G3P3) receiver design with the goal of reducing heat losses and increasing thermal efficiencies. New features that were investigated included aperture covers and shrouds, active airflow, multistage catch-and-release devices (stairs), and optimization of receiver cavity geometry. Simulations and ground-based testing showed that a reduced receiver volume and aperture shroud could reduce advective heat losses by ∼40 - 50%, and stairs could increase opacity and reduce backwall temperatures. The reduced volume receiver and stairs were selected for on-sun testing, and receiver efficiencies up to 80 - 90% were achieved in the current test campaign. The receiver thermal efficiency generally increased as a function of incident power and particle mass flow rates. In addition, particle outlet temperatures were maintained to within ±10 °C of a prescribed setpoint temperature up to ∼700 °C using a PID controller that adjusted the particle mass flow rate into the receiver in response to the measured particle outlet temperatures.
This paper summarizes the evolution of the Gen 3 Particle Pilot Plant (G3P3) receiver design with the goal of reducing heat losses and increasing thermal efficiencies. New features that were investigated included aperture covers and shrouds, active airflow, multistage catch-and-release devices (stairs), and optimization of receiver cavity geometry. Simulations and ground-based testing showed that a reduced receiver volume and aperture shroud could reduce advective heat losses by ∼40 - 50%, and stairs could increase opacity and reduce backwall temperatures. The reduced volume receiver and stairs were selected for on-sun testing, and receiver efficiencies up to 80 - 90% were achieved in the current test campaign. The receiver thermal efficiency generally increased as a function of incident power and particle mass flow rates. In addition, particle outlet temperatures were maintained to within ±10 °C of a prescribed setpoint temperature up to ∼700 °C using a PID controller that adjusted the particle mass flow rate into the receiver in response to the measured particle outlet temperatures.
The U.S. Department of Energy Solar Energy Technologies Office initiated the Generation 3 Concentrating Solar Power (CSP) program to achieve higher operating temperatures (>700 °C) to enable next-generation CSP high-temperature power cycles such as the supercritical CO2 (sCO2) Brayton Cycle. Three teams were selected to pursue high-temperature gas, liquid, and solid pathways for the heat-transfer media. Phases 1 and 2, which lasted from 2018 – 2020, consisted of design, modeling, and testing activities to further de-risk each of the technologies and develop a design for construction, commissioning, and operation of a pilot-scale facility in Phase 3 (2021 – 2024). This report summarizes the activities in Phases 1 and 2 for the solid-particle pathway led by Sandia National Laboratories. In Phases 1 and 2, Sandia successfully de-risked key elements of the proposed Gen 3 Particle Pilot Plant (G3P3) by improving the design, operation, and performance of key particle component technologies including the receiver, storage bins, particle-to-sCO2 heat exchanger, particle lift, and data acquisition and controls. Modeling and testing of critical components have led to optimized designs that meet desired performance metrics. Detailed drawings, piping and instrumentation diagrams, and process flow diagrams were generated for the integrated system, and structural analyses of the assembled tower structure were performed to demonstrate compliance with relevant codes and standards. Instrumentation and control systems of key subsystems were also demonstrated. Together with Bridgers & Paxton, Bohannan Huston, and Sandia Facilities, we have completed a 100% G3P3 tower design package with stamped engineering drawings suitable for construction bid in Phase 3.
There is a dearth in the literature on how to capture the uncertainty generated by material surface evolution in thermal modeling. This leads to inadequate or highly variable uncertainty representations for material properties, specifically emissivity when minimal information is available. Inaccurate understandings of prediction uncertainties may lead decision makers to incorrect conclusions, so best engineering practices should be developed for this domain. In order to mitigate the aforementioned issues, this study explores different strategies to better capture the thermal uncertainty response of engineered systems exposed to fire environments via defensible emissivity uncertainty characterizations that can be easily adapted to a variety of use cases. Two unique formulations (one physics-informed and one mathematically based) are presented. The formulations and methodologies presented herein are not exhaustive but more so are a starting point and give the reader a basis for how to customize their uncertainty definitions for differing fire scenarios and materials. Finally, the impact of using this approach versus other commonly used strategies and the usefulness of adding rigor to material surface evolution uncertainty is demonstrated.
Two active airflow control methods are investigated to mitigate advective and particle losses from the open aperture of a falling particle receiver. Advective losses can be reduced via active airflow methods. However, in the case of once-through suction, energy lost as enthalpy of hot air due to active airflow needs to be minimized so that thermal efficiency can be maximized. In the case of forced air injection, a properly configured aerowindow can reduce advective losses substantially for calm conditions. Although some improvement is offered in windy conditions, an aerowindow in the presence of winds does not show an ability to mitigate advective losses to values achievable by an aerowindow in the absence of wind. The two active airflow methods considered in this paper both show potential for efficiency improvement, but the improvement many not be justified given the added complexity and cost of implementing an active airflow system. While active airflow methods are tractable for a 1 MWth cavity receiver with a 1 m square aperture, the scalability of these active airflow methods is questionable when considering commercial scale receivers with 10–20 m square apertures or larger.
A strategy to optimize the thermal efficiency of falling particle receivers (FPRs) in concentrating solar power applications is described in this paper. FPRs are a critical component of a falling particle system, and receiver designs with high thermal efficiencies (~90%) for particle outlet temperatures > 700°C have been targeted for next generation systems. Advective losses are one of the most significant loss mechanisms for FPRs. Hence, this optimization aims to find receiver geometries that passively minimize these losses. The optimization strategy consists of a series of simulations varying different geometric parameters on a conceptual receiver design for the Generation 3 Particle Pilot Plant (G3P3) project using simplified CFD models to model the flow. A linear polynomial surrogate model was fit to the resulting data set, and a global optimization routine was then executed on the surrogate to reveal an optimized receiver geometry that minimized advective losses. This optimized receiver geometry was then evaluated with more rigorous CFD models, revealing a thermal efficiency of 86.9% for an average particle temperature increase of 193.6°C and advective losses less than 3.5% of the total incident thermal power in quiescent conditions.
A set of on-sun experiments was performed on a 1 MWth cavity-type falling particle receiver at Sandia National Laboratories. A computational model of the receiver was developed to evaluate its ability to predict the receiver performance during these experiments and to quantify the thermal losses from different mechanisms. Mean particle outlet temperatures and the experimental receiver thermal efficiencies were compared against values computed in the computational model. External winds during the experiments were found to significantly affect the receiver thermal efficiency, and advective losses from hot air escaping the receiver domain were found to be the most significant contribution to losses from the receiver. Losses from all other mechanisms including radiative losses amounted to less than 10% of the total incident thermal power.
A set of on-sun experiments was performed on a 1 MWth cavity-type falling particle receiver at Sandia National Laboratories. A computational model of the receiver was developed to evaluate its ability to predict the receiver performance during these experiments and to quantify the thermal losses from different mechanisms. Mean particle outlet temperatures and the experimental receiver thermal efficiencies were compared against values computed in the computational model. External winds during the experiments were found to significantly affect the receiver thermal efficiency, and advective losses from hot air escaping the receiver domain were found to be the most significant contribution to losses from the receiver. Losses from all other mechanisms including radiative losses amounted to less than 10% of the total incident thermal power.
Falling particle receivers are an emerging technology for use in concentrating solar power systems. In this work, quartz tubes cut in half to form tube shells (referred to as quartz half-shells) are investigated for use as a full or partial aperture cover to reduce radiative and advective losses from the receiver. A receiver subdomain and surrounding air volume are modeled using ANSYS® Fluent®. The model is used to simulate fluid dynamics and heat transfer for the following cases: (1) open aperture, (2) aperture fully covered by quartz half-shells, and (3) aperture partially covered by quartz half-shells. We compare the percentage of total incident solar power lost due to conduction through the receiver walls, advective losses through the aperture, and radiation exiting out of the aperture. Contrary to expected outcomes, simulation results using the simplified receiver subdomain show that quartz aperture covers can increase radiative losses and, in the partially covered case, also increase advective losses. These increased heat losses are driven by elevated quartz half-shell temperatures and have the potential to be mitigated by active cooling and/or material selection.
A computational fluid dynamics model of a 50 MWe falling particle receiver has been developed to evaluate the ability of the receiver concept to scale to intermediate sized systems while maintaining high thermal efficiencies. A compatible heliostat field for the receiver was generated using NREL's SolarPILOT, and this field was used to calculate the irradiance on the receiver at seventeen different dates and times throughout the year. The thermal efficiency of the receiver was evaluated at these seventeen different samples using the CFD model and found to vary from 83.0 - 86.8%. An annualized thermal efficiency was calculated from the samples to be 85.7%. A table was also generated that summarized this study along with other similar CFD studies on falling particle receivers over a wide ranges of scales.
A thorough code verification effort has been performed on a reduced order, finite element model for 1D fluid flow convectively coupled with a 3D solid, referred to as the 'advective bar' model. The purpose of this effort was to provide confidence in the proper implementation of this model within the SIERRA/Aria thermal response code at Sandia National Laboratories. The method of manufactured solutions is applied so that the order of convergence in error norms for successively refined meshes and timesteps is investigated. Potential pitfalls that can lead to a premature evaluation of the model's implementation are described for this verification approach when applied to this unique model. As a result, through observation of the expected order of convergence, these verification tests provide evidence of proper implementation of the model within the codebase.
This report summarizes the results of a two-year project funded by the U.S. Department of Energy's Solar Energy Technologies Office (SuNLaMP 1506) to evaluate the performance of high-temperature (>700 °C) particle receivers for concentrating solar power (see Appendix A for project information). In the first year, novel particle release patterns were designed and tested to increase the effective solar absorptance of the particle curtain. Modeling results showed that increasing the magnitude and frequency of different wave-like patterns increased the effective absorptance and thermal efficiency by several percentage points, depending on the mass flow rate. Tests showed that triangular-wave, square-wave, and parallel-curtain particle release patterns could be implemented and maintained at flow rates of ~10 kg/s/m. The second year of the project focused on the development and testing of particle mass-flow control and measurement methods. An automated slide gate controlled by the outlet temperature of the particles was designed and tested. Testing demonstrated that the resolution accuracy of the slide-gate positioning was less than ~1 mm, and the speed of the slide gate enabled rapid adjustments to accommodate changes in the irradiance to maintain a desired outlet temperature range. Different in-situ particle mass-flow measurement techniques were investigated, and two were tested. The in-situ microwave sensor was found to be unreliable and sensitive to variations in particle flow patterns. However, the in-situ weigh hopper using load cells was found to provide reliable and repeatable measurements of real-time in-situ particle mass flow. On-sun tests were performed to determine the thermal efficiency of the receiver as a function of mass flow rate, particle temperature, and irradiance. Models of the tests were also developed and compared to the tests.
ASME 2017 11th International Conference on Energy Sustainability, ES 2017, collocated with the ASME 2017 Power Conference Joint with ICOPE 2017, the ASME 2017 15th International Conference on Fuel Cell Science, Engineering and Technology, and the ASME 2017 Nuclear Forum
Novel particle release patterns have been proposed as a means to increase the thermal efficiency of high-temperature falling particle receivers. Innovative release patterns offer the ability to utilize light-trapping and volumetric heating effects as a means to increase particle temperatures over a conventional straight-line particle release pattern. The particle release patterns explored in this work include wave-like patterns and a series of parallel curtains normal to the incident irradiation that have shown favorable results in previous numerical studies at lower particle temperatures. A numerical model has recently been developed of an existing falling particle receiver at the National Solar Thermal Test Facility at Sandia National Laboratories to evaluate these patterns at elevated temperatures necessary to evaluate radiative and convective losses. This model has demonstrated that thermal efficiency gains of 2.5-4.6% could be realized using these patterns compared to the conventional planar release depending on the particle mass flow rate. Increasing the number of parallel curtains, increasing the spacing between curtains, and shifting the particle mass flow rate deeper in the receiver cavity was also found to increase the thermal efficiency. These effects became less significant as the particle mass flow rate increased.
A 10 MWe north-facing falling particle receiver (FPR) is proposed in this document to support performance comparisons of this design when compared with a direct s-CO2 solar receiver concept. This document describes the modeling and simulation effort for the proposed FPR to evaluate its thermal performance. A description of the modeling strategy is provided in the following section including details on the receiver and heliostat field. Then, this model is used to evaluate the performance of the receiver at various times of throughout the year. Finally, the results of this analysis are summarized. Direct comparisons with a similarly sized s-CO2 solar receiver concept are not discussed here.
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 novel particle release patterns for high-temperature falling particle receivers. Spatial release patterns resembling triangular and square waves are investigated and compared to the conventional straight-line particle release. A design of experiments was developed, and a simulation matrix was developed that investigated three twolevel factors: amplitude, wavelength, and wave type. Results show that the wave-like patterns increased both the particle temperature rise and thermal efficiency of the receiver relative to the straight-line particle release. Larger amplitudes and smaller wavelengths increased the performance by creating a volumetric heating effect that increased light absorption and reduced heat loss. Experiments are also being designed to investigate the hydraulic and thermal performance of these new particle release configurations.
A verification effort was undertaken to evaluate the implementation of the new advective bar capability in the Aria thermal response code. Several approaches to the verification process were taken : a mesh refinement study to demonstrate solution convergence in the fluid and the solid, visually examining the mapping of the advective bar element nodes to the surrounding surfaces, and a comparison of solutions produced using the advective bars for simple geometries with solutions from commercial CFD software . The mesh refinement study has shown solution convergence for simple pipe flow in both temperature and velocity . Guidelines were provided to achieve appropriate meshes between the advective bar elements and the surrounding volume. Simulations of pipe flow using advective bars elements in Aria have been compared to simulations using the commercial CFD software ANSYS Fluent (r) and provided comparable solutions in temperature and velocity supporting proper implementation of the new capability. Verification of Advective Bar Elements iv Acknowledgements A special thanks goes to Dean Dobranich for his guidance and expertise through all stages of this effort . His advice and feedback was instrumental to its completion. Thanks also goes to Sam Subia and Tolu Okusanya for helping to plan many of the verification activities performed in this document. Thank you to Sam, Justin Lamb and Victor Brunini for their assistance in resolving issues encountered with running the advective bar element model. Finally, thanks goes to Dean, Sam, and Adam Hetzler for reviewing the document and providing very valuable comments.
