Researchers at the Department of Energy have 3D-printed solar-power receivers that are up to 20 percent better at absorbing sunlight than current technology, as well as less expensive to fabricate.
Engineers at Sandia National Laboratories developed the fractal-like receivers for small- to medium-scale use as part of the Laboratory Directed Research and Development project. The receivers are aimed at regions that are economically challenged but rich in solar energy, such as India, that aim to develop smaller-scale, concentrated solar-power facilities for specific purposes.
Concentrating solar-power systems generate solar power by using mirrors or lenses to concentrate a large area of sunlight onto a small area. Most concentrating solar-power facilities throughout the world are large, said Sandia engineer Cliff Ho, who worked on the project. However, India has interest in developing 1 megawatt or smaller facilities that could provide power for a small village or community, he said.
Improving the efficiency of smaller receiver designs—like the ones the team recently developed—is an important step toward allowing for these facilities, Ho said.
“India has different market drivers than the U.S.,” he explained. “The competition for renewable energy there is diesel generators, which create a lot of pollution and are extremely expensive. It gives us a little more flexibility to create a smaller concentrating solar power system that will work for their needs.”
Ho and the team are applying the work to the Solar Energy Research Institute for India and the United States (SERIIUS), a five-year project sponsored by the U.S. Department of Energy and the government of India and co-led by the Indian Institute of Science and the National Renewable Energy Laboratory. The project aims to develop and improve cost-effective solar technology for both countries.
Sandia National Laboratories intern Jesus Ortega inspects one of the new bladed receivers at Sandia’s National Solar Thermal Testing Facility. Researchers at the Department of Energy lab have 3D-printed solar-power receivers that are up to 20 percent better at absorbing sunlight than current technology, as well as less expensive to fabricate. (Source: Randy Montoya, Sandia National Labs)
Researchers developed and tested multiple prototype fractal-like receiver designs scaled specifically for small- and medium-scale concentrating solar facilities. To do this, they used a new additive manufacturing technique called powder-bed fusion to print their receiver designs from Iconel 718--a high-temperature nickel alloy.
Using this technique allowed the team to test cost-effectively develop multiple fractal designs at a small scale, Ho said. In the future, it also could be used to print entire sections of larger solar receivers, he said.
“Additive manufacturing enabled us to generate complex geometries for the receiver tubes in a small-scale prototype,” Ho said. “Fabricating these complex geometries using traditional methods such as extrusion, casting, or welding would have been difficult.”
The new designs work with conventional heat-transfer fluids for concentrating solar power--including molten salts and steam—as well as other media for heat transfer and storage, he added.
Sandia researchers developed and tested the new receivers at the National Solar Thermal Testing Facility with rows of mirror-like heliostats aimed at a tall building that has a central receiver installed at the top.
The heliostats reflect and concentrate the sunlight on the receiver, which absorbs the sunlight’s heat and transfers it to gas flowing through the receiver’s paneling, according to researchers. The gas can then be used in a conventional power plant cycle to produce electricity, or with a storage system to be saved for on-demand electricity production when the sun is not shining.
Ho’s team designed the receivers differently than typical designs, which usually have a flat panel of tubes or tubes arranged in a cylinder. However, these designs can only absorb about 80 to 90 percent of the concentrated sunlight directed at them when considering reflections and heat loss, he said.
“When light is reflected off of a flat surface, it’s gone,” Ho explained. “On a flat receiver design, 5 percent or more of the concentrated sunlight reflects away.”
To remedy this, the team configured the panels of tubes in a radial or louvered pattern that traps the light at different scales, he said. “We wanted the light to reflect, and then reflect again toward the interior of the receiver and get absorbed, sort of like the walls of a sound-proof room,” Ho said.
Sandia is currently evaluating the receivers’ performance with different gases by flowing air, carbon dioxide, and helium through the receiver tubes. The ultimate goal is to pair them with what are called supercritical carbon dioxide Brayton cycles, he said.
A Brayton cycle uses hot, pressurized supercritical carbon dioxide to spin a turbine, which in turn spins a generator for electricity production. “Supercritical” describes the semi-liquid state of carbon dioxide when it is heated above its normal critical temperature and pressure.
Researchers hope that the smaller footprint and cost of the receivers will be used in concentrating solar power plants in the 1-10 megawatt range, making this type of solar power more competitive with other types of renewable energy, Ho said.
Elizabeth Montalbano is a freelance writer who has written about technology and culture for more than 15 years.