National Labs Gain Headway on Concentrating Solar Power
Headed by the Department of Energy, two national laboratories are advancing their research in concentrating solar-thermal power systems.
Through its network of national labs, the U.S. Department of Energy (DOE) recently unveiled two significant announcements in concentrating solar power (CSP). The agency broke ground on a new CSP pilot plant in New Mexico and started testing its high-temperature molten chloride salt system in Tennessee.
New Mexico-based National Solar Thermal Test Facility, the only research site of its kind in the U.S. Image used courtesy of Sandia National Laboratories
CSP systems use mirrors to pull energy from the sun, convert it to heat, and generate electricity via a steam turbine or engine. They’re typically used in utility-scale power generation projects and industrial steam applications.
According to the Solar Energy Industries Association, the U.S. currently operates around 1.8 gigawatts (GW) of CSP plants, and the National Renewable Energy Laboratory lists more than two dozen projects nationwide.
Concentrating Solar Power Pilot Plant
Earlier this month, the DOE broke ground on a new CSP facility at Sandia National Laboratories in Albuquerque, New Mexico. The pilot plant is the final step in a $100 million research program called Generation 3, which launched in 2017 to develop superior storage solutions capable of supplying 1 GW of storage for one hour.
Alejandro Moreno, the DOE’s acting assistant secretary for energy efficiency and renewable energy, said in a news release that the facility would demonstrate how CSP systems can meet the demands of long-duration energy storage while reducing costs and other barriers.
The pilot plant is situated at Sandia’s National Solar Thermal Test Facility, home to a 200-foot power tower and a field of more than 200 heliostats (mirrors).
Existing technologies on the market use heliostats to harvest sunlight and work by heating molten salt atop a tower, but they can only reach 1,049 degrees Fahrenheit. The DOE wanted to create a more efficient and affordable solution to raise the temperature of heat delivered to the power cycle above 1,292 F. In 2021, the agency awarded $25 million to Sandia to build, test, and operate a facility that meets those targets. The laboratory added another $5 million in cost-sharing for the project.
The result is a CSP system that replaces molten salt with sand-like ceramic particles that transfer/store heat or power a supercritical carbon dioxide turbine. Capable of withstanding 1,472 F temperatures, the plant can provide about 100 megawatts of low-cost and continuous power if successful.
Video used courtesy of Sandia National Laboratories
The practical appeal of such a system is compelling. When the pilot plant is complete in 2024, it will confirm that a particle-based system can help meet the DOE’s goal of reducing the CSP costs to 5 cents per kilowatt-hour for facilities with at least 12 hours of storage via thermal energy. CSP costs have declined by more than 50% over the last decade as systems became more efficient and the adoption of thermal energy storage increased.
Sandia National Labs is working with particle researchers in Australia and Saudi Arabia to test different system components.
Molten Chloride Salt Test Loop
Meanwhile, the DOE’s Oak Ridge National Laboratory in Tennessee recently started operating its Facility to Alleviate Salt Technology Risks (FASTR), a high-temperature molten chloride salt test system that will spearhead new CSP technologies in the department’s Generation 3 program.
The 23-foot-tall system features a salt preparation function that feeds clean salt into a forced convection loop. It can test in 1,337-degree F temperatures and flow rates of 3 to 7 kilograms per second.
A visualization of FASTR’s layout and flow processes. Image used courtesy of Oak Ridge National Laboratory
FASTR is designed to use molten chloride salts as high-temperature energy storage and heat-transfer fluid. Conventional CSP plants use steam or nitrate salts to transfer energy and power cycles, but FASTR uses a lower-cost combination of chloride salts incorporating sodium, potassium, and magnesium chloride.
The researchers behind FASTR recently detailed the system’s design in a 66-page report.
Oak Ridge National Laboratory’s FASTR testing system. Image used courtesy of Oak Ridge National Lab