Supporters of solar thermal power have weathered a storm of criticism over the years, but the dream just won’t die. They talk about a 100-megawatt facility that can deliver electricity 24/7, just like a nuclear power plant but without the risk factor and outlandish price tag, too. That’s a tall order, but the US Department of Energy has latched on to a new ceramic-based technology that could deliver electricity at a suitable price.
New Mexico will be home to a new concentrating solar power plant aimed at ending coal, gas, and nuclear power at the same time (photo courtesy of the US Department of Energy)
The ups and downs of solar thermal power in the United States
For those of you who are new to the subject, solar thermal power plants do not use conventional photovoltaic panels to collect solar energy. Instead, they deploy a field of specialized mirrors that bounce sunlight off a central point. Solar energy heats a reservoir of oil or molten salt, which is then piped to a generating station where it can run a turbine.
If that sounds expensive, inefficient, and complicated, it can be. Even so, concentrated solar power has caught on in other parts of the world. The advantage is that the energy-absorbing medium, whether oil or salt, also acts as a built-in energy storage reservoir, allowing the turbines to keep turning long after the sun goes down.
Getting a foothold here in the US is a different task. The Obama administration showcased a cluster of five CSP plants in the Southwest, but the program did not spur much follow-up interest among private investors.
The Department of Energy came back to the table in 2015 and introduced a program called CSP:APOLLO. The program aims to identify new technologies and systems that can provide high-temperature operation, defined as greater than 720°C, with the idea that higher temperatures can result in efficiency improvements and lower costs. The official goal is a minimum of 50% thermal-to-electric conversion efficiency, which the Department of Energy describes as “dramatically more efficient than current technology.”
A strange trick could make solar thermal power succeed: ceramics
Oddly enough, the Trump administration continued to support the Department of Energy’s R&D work on high-temperature concentrated solar power, despite the former president’s repeated promise to save coal jobs and also create more jobs in nuclear power.
During Trump’s first year in office, an Energy Department article extolled the benefits of CSP installations. The article mentioned about $62 million in funding for a new program called Generation 3 CSP Systems, and that’s where things get interesting.
Gen 3 CSP focuses on identifying new high-temperature technologies that have passed the test on a laboratory scale and assembling them into systems that can be tested in the field under various conditions.
“This includes the development of a test facility that enables diverse teams of researchers, labs, developers, and manufacturers to eliminate key technology risks for next-generation CSP technology and enable the reduction of the Levelized Cost of Energy (LCOE) for generated electricity. by CSP. at 6¢/kWh or less, without subsidies, at the end of the decade”, explains the Department of Energy.
In 2018, some new CSP Gen 3 projects began crossing the radar, including an innovative ceramic-based gravity “falling particle” system developed by Sandia National Laboratories. We also had the opportunity to speak with experts about another project related to new alloys for high-temperature solar thermal installations.
A new dawn for the solar thermal
Another focus of the Department of Energy’s attention is Heliogen, Bill Gates’ CSP company, which came out of stealth mode in 2019 with the goal of operating at 1,000 degrees Celsius.
When we last looked at Heliogen, they were in the process of installing their CSP system to help reduce emissions at a boron mine in California.
That was in 2021. In the meantime, it looks like Sandia National Laboratory is ready for racing. Last week, the Department of Energy announced that it has selected Sandia for a $25 million award to build, test and operate a new solar thermal system at the agency’s National Solar Thermal Test Facility in Albuquerque, New Mexico.
The new concentrating solar thermal power system culminates in a total of $100 million in financing for the high-temperature solar thermal. It will showcase Sandia’s particle fall technology, which can operate at temperatures in excess of 800°C.
“These particles can be used to transfer and store heat or power a supercritical carbon dioxide (sCO2) turbine. If successful, this type of solar thermal plant could provide 100 megawatts of power continuously, 24 hours a day, at low cost,” enthused the Department of Energy, adding that its electricity plus storage goal is 5 cents. per kilowatt hour.
Wait, what particles?
DOE stacked the particle approach compared to other systems and identified several key advantages.
“After this review, the DOE determined that particulate-based systems require fewer components and are less complex to operate compared to liquid and gas-based systems,” they explained. “In addition, particle-based systems need relatively few high-cost materials to collect and transport thermal energy. These factors could increase plant availability and reliability and allow for easier plant construction and commissioning.”
The DOE also noted that particle-based technology could help decarbonize industries that rely on high process heat of more than 800° Celsius, in addition to generating electricity.
As for the particles themselves, they are based on aluminum oxide and register a diameter of only 300 micrometers each.
“The heated particles are then stored in an insulated container before passing through a particle-to-working fluid heat exchanger. The heat exchanger working fluid will simulate a high-efficiency Brayton cycle using supercritical carbon dioxide (sCO2) with an outlet temperature of 720°C,” the DOE explains, “The cooled particles are then collected and moved from return to the top of the receiver via a lift or forklift.”
That still sounds complicated and expensive, but apparently it isn’t. If you got that supercritical carbon dioxide thing, that’s part of the reason. Supercritical carbon dioxide (sCO2) is the liquid form of CO2. When deployed to run a turbine, sCO2 can deliver efficiency gains and a much more compact footprint, leading to reduced costs.
The Department of Energy anticipates that the falling particle concentration solar thermal power setup could produce 100 megawatts of low-cost power throughout the day.
If private investors were worried about concentrating solar power in the US before, they may change their minds after 2024, when the Sandia system is expected to come online.
Meanwhile, Heliogen seems to be going through a rough patch, but earlier this month the company announced a new CEO, Christie Obaya, who has a plan to turn things around. In addition to her experience developing energy-related projects, Ms. Obaya is an engineer with a B.S. in Chemical Engineering from MIT.