Solar CSP R&D Activities at Sandia

The first step in a concentrating solar power system is to “collect” and focus the sunlight using a large array of mirrors, or collectors. Different configurations of mirrors can be used depending on the type of CSP technology being employed. CSP system technologies include dish, parabolic trough, linear Fresnel, and central receiver (power tower) systems. Because the direct cost of the collectors can comprise up to ~40% of the total direct costs of the entire CSP system, finding ways to increase the performance and/or reduce the costs of the collectors is an important challenge. Sandia is engaged in several R&D efforts to increase performance and reduce costs of collector materials and systems:

• Test and evaluation of novel reflective materials (reflective polymer films) for specular reflectance, durability, and long-distance applications
• Development and testing of anti-soiling coatings and devices (nano-particle based liquid coatings and electrodynamic screens) to increase reflectance and reduce water use
• Development of advanced characterization and facet-alignment tools to improve optical accuracy and collector performance
• Development of automated tracking-error correction methods to improve heliostat beam tracking for large numbers of heliostats
• Modal testing and analyses to evaluate impacts of dynamic wind loads on optical performance and structural fatigue
• Coupled structural/fluid/optical modeling for performance evaluation and design optimization
• Development of novel concepts for low-cost manufacturing/assembly and smart, wireless, autonomous operation of collectors
• Evaluation of glint and glare from solar collectors to quantify potential hazards and interference to pilots, motorists, and workers
  

Collectors Publications

• U.S. Patent Application 13/238431, Ghanbari, C., Ho, C.K., and Kolb, G., “Long Range Heliostat Target Using Array of Normal Incidence Pyranometers,” SD-11781, Filed September 21, 2011.
• U.S. Patent Application 13/085118, Yellowhair, J.E., Ho, C.K., Diver, R.B., and Moss, T.A., “Alignment and Focus of Mirrored Facets of a Heliostat,” SD-11629, Filed April 12, 2011.
• Ho, C.K., D.T. Griffith, J. Sment, A.C. Moya, J.M. Christian, J.K. Yuan, and P.S. Hunter, 2012, Dynamic Testing and Analysis of Heliostats to Evaluate Impacts of Wind on Optical performance and Structural Fatigue, in proceedings of SolarPACES 2012, Marrakech, Morocco, September 11-14, 2012.
• Ho, C.K., J. Sment, J. Yuan, and C.A. Sims, 2012, Characterization of Metallized Polymer Films for Long-Distance Heliostat Applications, in proceedings of SolarPACES 2012, Marrakech, Morocco, September 11-14, 2012.
• Sment, J.N, C.K. Ho, A.C. Moya, and C.M. Ghanbari, Flux Characterization System for Long-Distance Heliostats, in proceedings of SolarPACES 2012, Marrakech, Morocco, September 11-14, 2012.
• Sment, J. and C.K. Ho, 2012, Characterization of Wind Velocity Distributions within a Full-Scale Heliostat Field, in proceedings of the World Renewable Energy Forum, Denver, CO, May 13 – 17, 2012.
• Menicucci, A.R., C.K. Ho, and D.T. Griffith, 2012, High Performance Computing for Static and Dynamic Analyses of Heliostats for Concentrating Solar Power, in proceedings of the World Renewable Energy Forum, Denver, CO, May 13 – 17, 2012.
• Ho, C.K., C.M. Ghanbari, M.B. O’Neill, and J. Yuan, 2011, On-Sun Testing of a Heliostat Using Facets with Metallized Polymer Films, in proceedings of SolarPACES 2011, Granada, Spain, September 20-23, 2011.
• Ho, C.K., 2011, Observations and Assessments of Glare from Heliostats and Trough Collectors: Helicopter Flyover and Drive-By Sightings, in proceedings of SolarPACES 2011, Granada, Spain, September 20-23, 2011.
• Khalsa, S.S., C.K. Ho, and C.E. Andraka, 2011, An Automated Method to Correct Heliostat Tracking Errors, in proceedings of SolarPACES 2011, Granada, Spain, September 20-23, 2011.
• Ho, C.K., S.S. Khalsa, and D.D. Gill, 2011, Evaluation of a New Tool for Heliostat Field Flux Mapping, in proceedings of SolarPACES 2011, Granada, Spain, September 20-23, 2011.
• Ho, C.K., C.M. Ghanbari, and R.B. Diver, 2011, Methodology to Assess Potential Glint and Glare Hazards from Concentrating Solar Power Plants: Analytical Models and Experimental Validation, J. Solar Energy Engineering, August 2011, Vol. 133, 031021-1 – 031021-9.
• Christian, J.M., and C.K. Ho, 2011, Finite Element Modeling and Ray Tracing of Parabolic Trough Collectors for Evaluation of Optical Intercept Factors with Gravity Loading, ESFuelCell2011-54238, in proceedings of the ASME 2011 Energy Sustainability and Fuel Cell Conference, Washington D.C., August 7-10, 2011.
• Moya, A.C., and C.K. Ho, 2011, Modeling and Validation of Heliostat Deformation Due to Static Loading, ESFuelCell2011-54216, in proceedings of the ASME 2011 Energy Sustainability and Fuel Cell Conference, Washington D.C., August 7-10, 2011.
• Griffith, D.T., A.C. Moya, C.K. Ho, and P.S. Hunter, 2011, Structural Dynamics Testing and Analysis for Design Evaluation and Monitoring of Heliostats, ESFuelCell2011-54222, in proceedings of the ASME 2011 Energy Sustainability and Fuel Cell Conference, Washington D.C., August 7-10, 2011.
• Iverson, B.D. C.E. Andraka, J. Yellowhair, and C.K. Ho, Optical Error Impacts on Flux Distribution for a Dish Concentrator Using Probabilistic Modeling, in proceedings of SolarPACES 2010, Perpignan, France, Sep. 21-24, 2010.
• Ho, C.K. and S.S. Khalsa, Hazard Analysis and Web-Based Tool for Evaluating Glint and Glare from Solar Collector Systems, in proceedings of SolarPACES 2010, Perpignan, France, Sep. 21-24, 2010.
• Christian, J.M., and C.K. Ho, 2010, Finite Element Modeling of Concentrating Solar Collectors for Evaluation of Gravity Loads, Bending, and Optical Characterization, ES2010-90050, in proceedings of the ASME 2010 4^th International Conference on Energy Sustainability, Phoenix, AZ, May 17-22, 2010.
• Ho, C.K., S.S. Khalsa, and N.P. Siegel 2010, Analytical Methods to Evaluate Flux Distributions from Point-Focus Collectors for Solar Furnace and Dish Engine Applications, ES2010-90054, in proceedings of the ASME 2010 4^th International Conference on Energy Sustainability, Phoenix, AZ, May 17-22, 2010.
• Yellowhair, J., and C.K. Ho, 2010, Heliostat Alignment Methods: An Overview and Comparison, ES2010-90356, in proceedings of the ASME 2010 4^th International Conference on Energy Sustainability, Phoenix, AZ, May 17-22, 2010.
• Ho, C.K., C.M. Ghanbari, and R.B. Diver, 2009, Hazard Analyses of Glint and Glare from Concentrating Solar Power Plants, SAND2009-4131C, in proceedings of SolarPACES 2009, Berlin, Germany, September 15-18, 2009.

The sunlight that is reflected by the mirrors (collectors) in a concentrating solar power system is directed and concentrated onto a receiver, which contains flowing fluid or media that absorbs the energy. The fluid or media can be a gas (e.g., air, CO₂), liquid (water, molten salt), or solid (ceramic particles). Fluid can pass through tubes or a porous media that is irradiated by the concentrated sunlight, while solid particles can be dropped through a cavity receiver and irradiated directly. The hot working fluid or media is then used as a source of thermal energy in a heat engine/power cycle (e.g., steam Rankine, Stirling, or Brayton cycles) to generate electricity. The direct cost of the receiver system and tower for a central receiver CSP plant can comprise ~20% of the total direct costs of the entire plant. Therefore, finding ways to increase the efficiency and/or reduce the costs of the receiver system is an important challenge. Sandia is engaged in several R&D efforts to increase the efficiency and reduce costs of receiver systems:

• Development of solar selective absorber coatings and materials to achieve greater efficiencies at higher temperatures (>650 °C) for more efficient power cycles
• Development, testing, and analysis of falling particle receiver systems and components for high-temperature storage and power cycles
• Evaluation of novel receiver designs, configurations, and processes (e.g., internal air recirculation) to increase solar irradiance and absorptance while minimizing thermal emittance and convective losses
• Testing and evaluation of quartz window covers for cavity receiver apertures to reduce convective and radiative heat loss
• Development of novel flux mapping tools to characterize and improve receiver irradiance distributions
• Development of advanced modeling techniques to simulate coupled heat transfer processes (e.g., multiband radiation, convection, conduction, discrete phase particles) for improved understanding of complex thermal processes in receivers for design improvement
• Evaluation of glint, glare, and infrared emissions from solar thermal receivers to quantify potential hazards and interference to pilots, motorists, workers, and aircraft instrumentation

Receivers Publications

• Ho, C.K., and S.S. Khalsa, 2012, A Photographic Flux Mapping Method for Concentrating Solar Collectors and Receivers, J. Solar Energy Engineering, Transactions of the ASME, 134(4), 041004-1 – 041004-8.
• Ho, C.K. and B.D. Iverson, 2012, Review of Central Receiver Designs for High-Temperature Power Cycles, in proceedings of SolarPACES 2012, Marrakech, Morocco, September 11-14, 2012.
• Yuan, J.K., C.K. Ho, and J.M. Christian, 2012, Numerical Simulation of Natural Convection in Solar Cavity Receivers, ESFuelCell2012-91064, in proceedings of the ASME 2012 Energy Sustainability and Fuel Cell Conference, San Diego, CA, July 23-26, 2012.
• Christian, J.M. and C.K. Ho, 2012, CFD Simulation and Heat Loss Analysis of the Solar Two Power Tower Receiver, ESFuelCell2012-91030, in proceedings of the ASME 2012 Energy Sustainability and Fuel Cell Conference, San Diego, CA, July 23-26, 2012.
• Ho, C.K., A.R. Mahoney, A. Ambrosini, M. Bencomo, A. Hall, and T.N. Lambert, 2012, Characterization of Pyromark 2500 for High-Temperature Solar Receivers, ESFuelCell2012-91374, in proceedings of the ASME 2012 Energy Sustainability and Fuel Cell Conference, San Diego, CA, July 23-26, 2012.
• Hall, A., A. Ambrosini, and C. Ho, 2012, Solar Selective Coatings for Concentrating Solar Power Central Receivers, Advanced Materials & Processes, article featured on cover, 170(1), 28 – 32.
• Khalsa, S.S. and C.K. Ho, 2011, Radiation Boundary Conditions for Computational Fluid Dynamics Models of High-Temperature Cavity Receivers, J. Solar Energy Engineering, Vol. 133, 031020-1 – 031010-6.
• Ho, C.K. and S.S. Khalsa, 2011, A Flux Mapping Method for Central Receiver Systems, ESFuelCell2011-54216, in proceedings of the ASME 2011 Energy Sustainability and Fuel Cell Conference, Washington D.C., August 7-10, 2011.
• Khalsa, S.S., J.M. Christian, G.J. Kolb, M. Roger, L. Amsbeck, C.K. Ho, N.P. Siegel, A.C. Moya, 2011, CFD Simulation and Performance Analysis of Alternative Designs for High-Temperature Solid Particle Receivers, ESFuelCell2011-54430, in proceedings of the ASME 2011 Energy Sustainability and Fuel Cell Conference, Washington D.C., August 7-10, 2011.
• Ambrosini, A., T.N. Lambert, M. Bencomo, A. Hall, K. vanEvery, N.P. Siegel, and C.K. Ho, 2011, Improved High Temperature Solar Absorbers for Use in Concentrating Solar Power Central Receiver Applications, ESFuelCell2011-54241, in proceedings of the ASME 2011 Energy Sustainability and Fuel Cell Conference, Washington D.C., August 7-10, 2011.
• Khalsa, S.S., and C.K. Ho, Development of Rigorous Boundary Conditions to Simulate Receiver Irradiance from Heliostat-Fields and Dish Concentrators, in proceedings of SolarPACES 2010, Perpignan, France, Sep. 21-24, 2010.
• Siegel, N.P., C.K. Ho, S.S. Khalsa, and G.J. Kolb, 2010, Development and Evaluation of a Prototype Solid Particle Receiver: On-Sun Testing and Model Validation, J. Solar Energy Engr., 132(2), 021008-1 – 021008-8.
• Khalsa, S.S., and C.K. Ho, 2010, Development of a “Solar Patch” Calculator to Evaluate Heliostat-Field Irradiance as a Boundary Condition in CFD Models, ES2010-90051, in proceedings of the ASME 2010 4^th International Conference on Energy Sustainability, Phoenix, AZ, May 17-22, 2010.
• Ho, C.K., M. Roeger, S.S. Khalsa, L. Amsbeck, R. Buck, N. Siegel, and G. Kolb, 2009, Experimental Validation of Different Modeling Approaches for Solid Particle Receivers, SAND2009-4140C, in proceedings of SolarPACES 2009, Berlin, Germany, September 15-18, 2009.
• Ho, C.K., S.S. Khalsa, and N.P. Siegel, 2009, Modeling On-Sun Tests of a Prototype Solid Particle Receiver for Concentrating Solar Power Processes and Storage, ES2009-90035, 2009 ASME 3rd International Conference on Energy Sustainability, SAND2009-2740C, San Francisco, CA, July 19-23, 2009.

Thermal energy storage (TES) is the key differentiating factor of Concentrating Solar Power. CSP has the significant advantage of being able to collect the sun’s energy as heat and then to efficiently store that heat until it is needed for electricity production. Current TES technology, molten nitrate salts, have demonstrated the ability to store and provide energy with efficiency exceeding 98%. Thermal energy storage also allows better utilization of the powerblock leading to reduced Levelized Cost of Electricity. Sandia’s work in Thermal Energy Storage for CSP is in 3 primary areas:

1. Integrated Material Studies – including the development of heat transfer/storage materials with optimized properties and the characterization of corrosion and thermal breakdown.
2. Cost Reduction Opportunities – including the conception, development, testing, and validation of hardware solutions for TES that will help reduce cost including capital and maintenance costs.
3. TES System Modeling – including evaluations of potential TES systems to predict performance and cost.

Integrated Material Studies

Sandia studies heat transfer/storage materials and their effects on containing materials. Potential storage materials include salts, liquid metals and metal alloys, particles and larger solids. These materials are evaluated for materials compatibility, material properties, and cost. Sandia’s materials compatibility capability includes high temperature salt pots and tests that have utilized these salt pots for long-term corrosion analysis at temperatures up to 680C. These studies have included corrosion rates, effects of chloride and other impurities. Additionally, Sandia has mechanical testing capability in many environments including nitrate salts which has been used to provide customers with information on Stress Corrosion Cracking, Low Cycle Fatigue, and other important lifetime considerations for containing materials.

• Gill, D.D., et al., Design, Fabrication and Testing of an Apparatus for Material Compatibility Testing in Nitrate Salts at Temperatures Up to 700°C, in 5thInternational Conference on Energy Sustainability. 2011, ASME: Washington, DC, USA. p. 6.
• Kruizenga, A.M., Corrosion Mechanisms in Chloride and Carbonate Salts.”, Sandia Report SAND2012-7594
• Kruizenga, A.M. and Gill, D.D. Material Performance of Alloys in NaNO3/KNO3 at 600C ECS 2012, Oct. 8-12, 2012, Honolulu, HI SAND2012-8621P
• Bradshaw, R.W. and W.M. Clift, Effect of Chloride Content of Molten Nitrate Salt on Corrosion of A516 Carbon Steel. 2010, SNL: Livermore, CA. SAND2010-7594
• Iverson, B.D., et al., Thermal and mechanical properties of nitrate thermal storage salts in the solid-phase. Solar Energy, 2012.
• Iverson, B.D., J.G. Cordaro, and A.M. Kruizenga, Thermal Property Testing of Nitrate Thermal Storage Salts in the Solid-Phase. ASME Conference Proceedings, 2011. 2011(54686): p. 495-502.
• Kruizenga, A. and J.G. Cordaro, Preliminary development of thermal stability criterion for alkali nitrates, in SolarPACES 2011. 2011, SolarPACES: Grenada, Spain.

Cost Reduction Opportunities

This effort includes studies and development of technologies that can be used to reduce the overall cost of thermal energy storage. Studies include thermocline analyses and testing which are used to reduce tank and heat transfer material costs, valve packing analyses to reduce maintenance and operations cost on valves. Additionally, Sandia performs extensive testing and validation on components individually and in flowing molten nitrate salt to help customers reduce implementation risk and reduce costs while verifying lifetime predictions in plant-like service. Sandia has a one-of-a-kind Molten Salt Test Loop (MSTL) system that provides flowing nitrate salt at plant-like conditions. This newly completed facility is being used to test and evaluate customer components and systems in on-sun testing as well as research evaluations of new technology.

• Kolb, G.J., et al., Freeze-thaw tests of trough receivers employing a molten salt working fluid, in ASME Energy Sustainability. 2010: Phoenix, AZ, USA.
• Gill, D.D. et al., Customer Interface Document for the Molten Salt Test Loop (MSTL) System, Sandia Report SAND2012-1905

TES System Modeling

Sandia researchers perform analyses of Thermal Energy Storage systems to evaluate the performance of the system as well as potential costs and benefits. These evaluations include both current technology (nitrate salts) as well as novel concepts in fluid, solid, and latent (phase-change) storage.

• Kolb, G.J., Evaluation of Annual Performance of 2-Tank and Thermocline Thermal Storage Systems for Trough Plants. Journal of Solar Energy Engineering, 2011. 133(3): p. 031023-5.
• Kolb, G.J., An Evaluation of Possible Next-Generation High-Temperature Molten-Salt Power Towers. 2011: Albuquerque, NM
• Moore, R.C., et al., Design considerations for concentrating solar power tower systems employing molten salt. 2010, Sandia National Laboratories: Albuquerque, NM.

Accurate development, manufacturing, quality assurance, and deployment of CSP collectors requires fast tools providing detailed optical performance data. Sandia is developing computer-driven tools to provide this data in both production and development environments.

• SOFAST (Sandia Optical Fringe Analysis Slope Tool) provides rapid full-facet surface shape and error information at millimeter scales by using fringe reflection (deflectometry). Development and production-integrated systems have been demonstrated and are available for licensing.
• AIMFAST (Alignment Implementation for Manufacturing using Fringe Analysis Slope Technique) provides near-real-time (5-second) updates of facet relative rotations during alignment and canting processes. Using a full-facet data gathered with fringe reflection (deflectometry), AIMFAST can provide alignment accuracies in the range of 0.1 mrad. A dish version exists, with heliostat versions in development.
• Flux Mapping provides an end-product incident flux map of concentrated sunlight on a flat target, for comparison to system optical models. This provides assurance of optical system performance.
• PHLUX (Photographic fLUX mapping) is a web-based tool that provides a rapid, low cost estimate of concentrated flux distribution on a non-flat target or receiver.
• Glint and Glare characterization tools analytically and empirically evaluate glint and glare form solar surfaces such as collectors and PV panels, to quantify potential hazards and sight interference for pilots, motorists, and workers.

Includes R&D on dish structures, mirrors, optics, and Stirling engines

Includes R&D to improve system and component performance of parabolic trough technologies.

Includes R&D relevant to heliostats, receivers, and overall system issues for central-receiver solar plants. Also includes work-for-others testing.

       Power Tower

• Strachan J.W. and R.M. Houser, 1993, Testing and Evaluation of Large-Area Heliostats for Solar Thermal Applications, SAND92-1381, Sandia National Laboratories, Albuquerque, NM.
• 2009 Power Tower Project Summary

Heliostat Analysis and Flux Mapping

Cavity Heat-Loss Analysis

• Siebers, D. and J. Kraabel, New Experiments on Convective Heat Loss, Sandia National Laboratories, Livermore, CA.

• Ma, R.Y., 1993, Wind Effects on Convective Heat Loss from a Cavity Receiver for a Parabolic Concentrating Solar Collector, Sandia National Laboratories, Livermore, CA.

Work for Others (e.g., NASA)

Includes cross-cutting characterization and testing of CSP materials, components, and systems, modeling and analysis, and other CSP technology development.