Concentrating solar power (CSP) plants can be a key part of a comprehensive renewable energy strategy, but progress is often focused on making the facilities bigger and bigger. Now, engineers from Sandia National Laboratories are improving the efficiency of smaller plants, by designing a new receiver that can absorb greater amounts of sunlight.

Where regular photovoltaic solar panels work by absorbing sunlight and directly converting it into electricity, CSP facilities use huge arrays of mirrors called heliostats to reflect sunlight onto receivers. That focused light heats up fluids piped through the receiver panels, producing steam that then drives a turbine to create energy.

Normally, those receiver panels are made up of tubes arranged in flat panels or cylinders, but those designs don't capture 100 percent of the light, meaning there is room for improvement. To that end, the Sandia team tweaked the receiver design so that instead of flat panels, the new design uses a fractal shape to capture more of the incoming sunlight.

"When light is reflected off of a flat surface, it's gone," says Cliff Ho, a mechanical engineer at Sandia. "On a flat receiver design, five percent or more of the concentrated sunlight reflects away. 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."

The researchers say the new design makes the receivers up to 20 percent more effective at absorbing sunlight than current systems. Better yet, the new receivers can be 3D-printed from a nickel alloy called Inconel 718, meaning they can be produced relatively quickly and inexpensively.

The team is testing the receivers with air, carbon dioxide and helium flowing through the tubes and powering a turbine, but the long-term goal is to use supercritical carbon dioxide – a hot, highly-pressurized, semi-liquid version of the gas.

Combining supercritical carbon dioxide with the new receiver design in this way could mean that small scale CSP plants – those with capacities of 1 to 10 MW – could be more affordable and efficient. These smaller scale facilities could then be used to power individual communities.

The new receivers were developed as part of a project for the Solar Energy Research Institute for India and the United States (SERIIUS).