India is interested in developing 1 megawatt or smaller concentrating solar energy facilities to provide power for a small village or community. Improving the efficiency of smaller receiver designs is a key step toward making that goal a reality. As part of a cooperative project, U.S. Sandia National Laboratory engineers designed fractal-like concentrating receivers for small- to medium-scale use which are up to 20 percent more effective in absorbing solar radiation than current equipment.

Sandia National Lab’s intern Jesus Ortega inspects one of the new bladed receivers at Sandia’s National Solar Thermal Testing Facility. (Photo by Randy Montoya) Sandia National Lab’s intern Jesus Ortega inspects one of the new bladed receivers at Sandia’s National Solar Thermal Testing Facility. (Photo by Randy Montoya) The receivers were designed and studied as part of a Laboratory Directed Research and Development project and are also being applied to Sandia’s work for the Solar Energy Research Institute for India and the U.S., or SERIIUS.

SERIIUS is a five-year project co-led by the Indian Institute of Science and the National Renewable Energy Laboratory, sponsored by the U.S. Department of Energy and the government of India. The initiative was launched to develop and improve cost-effective solar technology for both countries by addressing barriers and challenges of each market. Sandia has led the group’s research in concentrating solar power, focusing on scalable systems.

The researchers tested the new receivers at Sandia’s National Solar Thermal Testing Facility to assess their ability to withstand high temperatures and pressures while absorbing sunlight as heat that can be stored or transferred to a power cycle to generate electricity. Rows of mirror-like heliostats are aimed at a tall building with 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. The gas can be consumed in a conventional power plant cycle to produce electricity or stored for on-demand electricity production when the sun is not shining.

Conventional receiver designs with a flat panel of tubes or tubes absorb about 80 to 90 percent of concentrated sunlight. By contrast, the fractal-like designs feature panels of tubes in a radial or louvered pattern. Reflected light is reflected again and directed toward the receiver’s interior. Solar absorption efficiency is enhanced without the need for coatings typically applied to receivers.

The compact solar receiver designs were 3D-printed from Iconel 718, a high-temperature nickel alloy, using a powder-bed fusion process. The approach supports testing of multiple fractal designs at a small scale and could lead to printing whole sections of larger receivers.

The new devices operate with conventional heat-transfer fluids for concentrating solar power, including molten salts and steam. Performance with different gases is being evaluated by flowing air, carbon dioxide and helium through the receiver tubes with the ultimate goal of pairing the new receiver designs with supercritical carbon dioxide Brayton cycles.

Both the U.S. and India are interested in pursuing supercritical carbon dioxide for the next generation of concentrating solar power technology because it can reach greater efficiencies with smaller footprints.

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