The power of the sun, better known as solar energy, can be collected and harnessed with solar cells, and used to power 3D printers, modes of transportation, load-bearing carts, long-running motors, and patient monitoring alarms; it can even keep your drink cold. But engineers at multimission Sandia National Laboratories, based in New Mexico, have developed something that’s even better at absorbing sunlight than current solar cells.

As part of a Laboratory Directed Research and Development project, Sandia designed, created, and studied 3D printed, fractal-like, concentrating solar power receivers, which will also be applied to its work for the Solar Energy Research Institute for India and the United States (SERIIUS). The 3D printed receivers, for small to medium-scale use, are up to 20% more effective at absorbing sunlight than the technology currently used.

The five-year SERIIUS project is sponsored by the US Department of Energy and the government of India, and co-led by the National Renewable Energy Laboratory (NREL) and the Indian Institute of Science. The goal is to address market challenges in the US and Indian markets, and work to develop and improve cost-effective solar technology for both countries.

Sandia has been focused on scalable solar power systems, and according to Clifford Ho, Acting Manager, R&D S&E, Mechanical Engineering for Sandia, India wants to develop facilities that are 1 megawatt or smaller that could power small villages; if the efficiency of smaller receiver designs can be improved, this could become a reality.

Clifford Ho [Image: Sandia]

Typical receiver designs have tubes arranged in a cylinder, or just a flat panel of tubes, and they can absorb up to 80% to 90% of concentrated sunlight, taking heat loss and reflections into account. But Ho said in order to improve scalability and lower costs, design improvements to make the receivers more efficient are necessary.

“When light is reflected off of a flat surface, it’s gone. On a flat receiver design, 5 percent or more of the concentrated sunlight reflects away,” explained Ho. “So we configured the panels of tubes in a radial or louvered pattern that traps the light at different scales. 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.”

Other efficiency research has revolved around applying special coatings to the receiver, but many of these can break down over time, which results in increased costs and reduced ability to absorb sunlight. The fractal-like receiver designs by the Sandia engineers can increase the efficiency of solar absorption without having to resort to coatings.

The team created several prototype receivers at its National Solar Thermal Testing Facility, and tested their ability to absorb sunlight that can be used to generate electricity while withstanding high pressures and temperatures. The facility aims rows of mirror-like heliostats, which reflect and concentrate sunlight, at a central receiver on top of a tall building; the receiver absorbs the heat from the sun and transfers it to gas that flows through its paneling, which can either be stored or used immediately to produce electricity.

Year-round Sandia intern Jesus Ortega inspects one of the new bladed receivers at Sandia’s National Solar Thermal Testing Facility. [Image: Randy Montoya]

Various 3D printed prototype receiver designs were scaled in size, to see which one would work best for small and medium-scale concentrating solar facilities. The designs can be paired with other media for heat transfer and storage, and work well with conventional heat-transfer fluids for concentrating solar power.

Ho said, “Additive manufacturing enabled us to generate complex geometries for the receiver tubes in a small-scale prototype. Fabricating these complex geometries using traditional methods such as extrusion, casting or welding would have been difficult.”

The Sandia team utilized high-temperature nickel alloy Iconel 718 and a powder bed fusion technique to print the small-scale receiver designs. The novel 3D printing method was a cost-effective way to test various designs at a smaller scale, and Ho said they may even use it again to print whole sections of scaled-up solar receivers.

Sandia National Laboratories principal investigator Darryn Fleming surrounded by the workings of the lab’s 1 megawatt thermal supercritical carbon dioxide recompression closed Brayton cycle test loop. [Image: Randy Montoya]

In an effort to ultimately pair the new receivers with supercritical carbon dioxide Brayton cycles, engineers are flowing air, helium, and carbon dioxide through the receiver tubes, and evaluating the performance. Ho said that both India and the US are interested in potentially using supercritical carbon dioxide to develop next-gen concentrating solar power technology.

“The goal of concentrating solar power and SERIIUS is to develop efficient, cost-effective solar-driven electricity production with energy storage. The use of a solarized supercritical carbon-dioxide Brayton cycle would increase efficiencies, reduce space requirements and reduce costs associated with current large-scale concentrating solar power systems,” Ho explained.

Supercritical describes carbon dioxide’s semi-liquid state when it’s heated past its normal critical temperature and pressure, while a Brayton cycle uses the pressurized, hot supercritical carbon dioxide to spin a turbine, which then spins a generator to produce electricity.

By lowering both the cost, and the footprint, of solar power systems, it could eventually be possible to make small-scale solar plants based off of supercritical carbon dioxide Brayton cycles, which would make “concentrating solar power more competitive with other types of renewable energy.”

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[Source: Sandia National Laboratories]



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