Engineers at the US Department of Energy’s Sandia National Laboratories have developed 3D-printed, fractal-like concentrating solar-power receivers that absorb sunlight up to 20% more efficiently than current technology and are less expensive to fabricate.
These new types of solar-power receivers are conceptualized for small to medium-scale concentrated solar-power (CSP) facilities in economically poorer but sunshine-rich regions, such as India, etc. India, according to the experts, namely has interest in developing 1-megawatt or smaller CSP facilities to power small villages. And smaller, fractal-like receiver designs like those by the Sandia Lab could pave the way.
Innovative receiver designs
“Our receiver designs include novel shapes and arrangements to capture more incident light for concentrating solar power,” says Cliff Ho, PhD, from the Concentrating Solar Technologies division at Sandia National Laboratories. The team experimented with shapes and features at multiple length scales in an effort to promote light trapping and reduce the amount of radiative heat loss from the hot receiver. “We implemented 3D-printing methods — powder bed fusion — to create some of these novel features and patterns at a small centimeter-scale that could be tested rapidly in our solar furnace,” the engineer reports. “I believe our work was the first use of additive manufacturing to create prototype receivers with novel shapes and features for high-flux, high-temperature testing of solar thermal receivers for concentrating solar power.”
What is powder-bed fusion?
The team used a new additive manufacturing technique called powder-bed fusion to print their solar-power receivers. “Powder-bed fusion allowed us to create these unique, monolithic shapes and structures using a high-strength, high-temperature nickel-based alloy, Inconel 718, which can withstand the high temperatures and pressures that we are seeking for gas-based receivers,” Ho says.
The new solar-power receivers absorb sunlight up to 20% better than existing technologies. How? “The crux of the new solar receivers is the novel shapes and geometric arrangement of the tube panels, which allows light to be reflected toward the interior of the receiver,” Ho explains. In a conventional solar thermal receiver, the panels of tubes are arranged in a cylindrical or cubical fashion, and any light that is reflected off of the panels is lost to the environment. “In our designs, light that is reflected from one tube panel can be absorbed by another panel,” the expert says, likening the concept to the design of a sound-proof room, where the walls are bumpy or textured to allow sound to be reflected and reflected again until it is absorbed.
Enabling new applications
The new kind of solar-power receiver could enable applications that were not feasible before. “Higher efficiency solar receivers are critical for enabling higher-temperature operations, which are being pursued for advanced high-temperature supercritical CO2 Brayton cycles that can yield higher power conversion efficiencies,” Ho says. “In addition, high-temperature thermochemistry that produce fuels from sunlight (e.g., H2 or CO) can be enabled by these more efficient receivers.”
The Sandia team’s goal is to pair their receivers with supercritical carbon dioxide Brayton cycles: “These high-efficiency receivers can be used to generate high-temperature (>700 °C) heat for supercritical CO2 Brayton power cycles,” Ho explains. “The heat is stored in high-temperature molten salt or solid media and discharged when needed to the sCO2 power cycle.”
Ho and his colleagues are working closely with the U.S. Department of Energy to develop these solarized sCO2 power cycles and are currently proposing new research work to enable this technology. “We are working on developing necessary components, like the primary heat exchanger, to make this technology a reality.”
The research work is part of the Solar Energy Research Institute for India and the United States (SERIIUS), a five-year project sponsored by the US Department of Energy and the government of India and co-led by the Indian Institute of Science and the National Renewable Energy Laboratory.
Written by Sandra Henderson, Research Editor, Solar Novus Today