Tower-based power systems

Sandia is investigating a major solar energy deployment capable of providing 100% of the combined energy needs of Kirtland Air Force Base, including the Sandia National Laboratories and National Nuclear Security Agency tenants. In 2024, a computational model was developed on Sandia’s High-Performance Computing infrastructure to run advanced energy balance calculations to determine how much solar energy could be harvested on available KAFB land. The outcome of this analysis determined that the lowest cost and highest yield system would be hybrid, with daytime photovoltaic energy generation that delivers AC power directly to the Sandia grid and converts all excess DC power above the current load to Lithium-ion batteries. Once the batteries are fully charged, any remaining PV energy is converted to heat that is stored in a particle-based thermal energy storage system. Additionally, a concentrating solar power plant will be used to provide low-cost heat to the TES system during the day.

A FEED study was commissioned by the Solar Energy Technology Office at the U.S. Department of Energy to reduce cost and deployment uncertainty associated with the first-of-kind particle-based CSP system at this scale. The scope of the study will involve down selection of the key technology options for the CSP portion of the project such as the type of turbine and heat exchanger, and work with an Engineering, Procurement, and Construction firm to better estimate the cost of tower construction, field deployment, storage bin construction and system integration. The study will also establish a supply chain by submitting drawings and specifications to vendors, and where no vendor currently exists for first-of-kind components, such as falling particle receivers, we will provide fabrication drawings to custom vendors.

Supercritical CO2 Brayton power cycles used in Generation 3 concentrating solar power require a heat exchanger that can deliver heat to the sCO2 from the particle thermal energy storage and heat transfer fluid. This heat exchanger is typically made from exotic and expensive alloys due to the high temperature and pressure operating conditions. The goal of the Compact Counter Flow Fluidized Bed Heat Exchanger project is to increase the particle-to-sCO2 heat transfer coefficient relative to the current state-of-the-art heat exchange design to decrease the cost and improve the performance of the component. The project features Babcock & Wilcox and TU Wien as project partners.

The Heliostat Consortium for Concentrating Solar-Thermal Power, or HelioCon, was established by the U.S. Department of Energy’s Solar Energy Technologies Office to improve CSP components for the concentrated solar-thermal power industry. Member organizations include the National Renewable Energy Laboratory, (lead), Sandia National Laboratories, and the Australian Solar Thermal Research Institute (ASTRI). Together, these organizations perform research and development activities to validate, commercialize, and deploy low-cost and high-performance heliostats. The goal of these activities is to optimize operations and maintenance for concentrating solar power and concentrating solar-thermal applications.

HelioCon objectives include:

• Developing strategic core capabilities and infrastructure to support high-performance heliostat manufacturing, validation, and optimization and facilitate industry’s ability to design, manufacture, install, and operate central receiver heliostat fields with higher technical and economic performance
• Ensuring that these capabilities are readily available to industry, and meeting their needs
• Funding research on new technologies with significant potential to improve heliostat field economic performance
• Forming U.S. centers of excellence focused on heliostat technology to restore U.S. leadership in heliostat research, development, and validation
• Promoting workforce development by encouraging student internships and postdoctoral positions, the formation of a HelioCon early career scientist group to promote networking, and highlighting existing training and educational programs in heliostat design, production, and operation.

In order to remove commercial risks, improve economic competitiveness, and attract additional investors, HelioCon’s first step was to conduct a roadmapping study to identify and address technical and nontechnical gaps that limit the development of low-cost, high-performance heliostat technologies with minimized annual operation and maintenance expenses.

In September 2022, HelioCon released the Roadmap to Advance Heliostat Technologies for Concentrating Solar-Thermal Power, to guide heliostat research and deployment.

Contact: Margaret Gordon

Generation 3 concentrating solar power systems can use solid particles as the heat transfer and thermal energy storage medium. While these particles have a number of benefits as a heat transfer fluid, including high durability, low potential for environmental harm, low cost, and high energy density, they can be highly abrasive to the materials containing them. Valves, ducting, lifts, heat exchangers, and storage bins are exposed to high-temperature flowing particles for decades, leading to concerns about the lifetime of these components. The goal of the High Temperature Particle Recirculation Test Loop (HoTPROP) project is to develop a system that can continuously flow 800 °C particles at 25 kg/s over hundreds of hours to assist with the characterization of particle handling component lifetime.

The Long Term Particle Wear project investigates surface wear in packed bed and fluidized bed particle systems at high temperatures for concentrating solar power relevant materials, and use that data to validate numerical models that can predict material lifetimes for given temperature and particle flow regimes. Using solid particles as energy storage and transfer media is seen as one of the most practical ways to achieve the temperature targets needed to drive advanced high efficiency power cycles and generate alternative fuels via solar thermochemistry, while simultaneously driving down the cost of thermal energy storage. However, one of the biggest engineering challenges of next generation concentrated solar power plants is the handling of bulk materials at elevated temperatures. The current particle of choice for Sandia National Lab’s Generation 3 Particle Pilot Plant is primarily made of sintered bauxite. These particles have excellent optical and thermophysical properties for CSP applications. These particles also have the potential to cause severe wear in chutes, valves, heat exchangers, and other high temperature CSP components. These models can be used for CSP plant design where expected material lifetimes are measured in 10⁵-10⁶ hours. Furthermore, this project will develop two lab-scale particle wear test rigs which will be capable of simulating accelerated particle wear and will add to the capability of Sandia’s National Solar Thermal Test Facility as a particle-based CSP research and development facility.

Contact: Matthew Sandlin

When falling particle receivers are used to directly heat particles using concentrated solar power, they generate a particle curtain that cascades through an open cavity. This curtain can be approximately 10 meters wide and 6 cm thick. The goal of the Particle Curtain Generating Valve (PCGV) project is to develop a modular valve that can be strung together to create a continuous particle curtain that can span over 10 meters and operate at 900 °C.

The U.S. Department of Energy’s Solar Energy Technology Office recently awarded funding for a collaborative effort between General Electric (GE) and Sandia National Laboratories to design and demonstrate a techno-economically viable multi-component Silicon carbide (SiC) air receiver technology to achieve 1100 °C gas temperature for concentrating solar thermal applications using adaptations of GE’s additively manufactured SiC and scalable SiC-based ceramic matrix composite technologies. Increasing operating temperatures of solar receivers is paramount to the efficiency of concentrating solar thermal and concentrating solar power systems. Owing to its high temperature stability, combined with excellent thermal and optical properties, SiC – a hard, synthetic ceramic material made of silicon and carbon – has been the material of choice for application in high-temperature solar receivers. The state-of-the-art SiC volumetric concentrating solar air receivers like the honeycomb design have been demonstrated in field tests to achieve exit air temperatures approaching 800 ^oC. However, successful application of CST systems to decarbonize the industrial sectors’ use of hydrocarbon fuels to generate heat requires a significant increase in both temperature capability and Sic technology’s potential impact, competitiveness and feasibility.

Contact: Ken Armijo