Tethered-Balloon Tests Ensure Safety of Particle-Based Solar Tech

A team from Sandia National Laboratories received $25 million from the U.S. Department of Energy to build a pilot plant that will incorporate an emerging solar power technology. The Sandia researchers recently used 22-foot-wide tethered balloons (equipped with sensors) to collect samples of airborne dust particles to ensure the safety of the technology. The study determined that the dust created by the technology falls below hazardous levels, said Cliff Ho, the lead researcher on the project.

The technology is called a high-temperature, falling-particle receiver for concentrating solar power. Though less common than solar panels or wind turbines, this renewable energy source carries certain advantages, including the ability to store energy in the form of heat before converting it into electricity for the power grid.

Helium-filled tethered balloons carry sensors to measure concentration of fine ceramic dust. Courtesy of Randy Montoya/Sandia National Laboratories.

For example, one concentrating solar power plant in Arizona uses molten salt to store this heat for six hours. Other plants can, in theory, store heat for days or weeks, Ho said.

Ho’s team tested a design that drops dark, sand-like ceramic particles through a beam of concentrated sunlight, then stores the heated particles. These round particles cost around $1 for 1 kg and are able to get much hotter than conventional molten sand-based systems, which increases efficiency and lowers cost. The team also looked at other particles, such as sand itself. While sand costs only a few cents per pound, the team favored the ceramic particles, which absorbed more energy and provided a smoother flow.

The DOE’s goal is to get the cost of electricity from concentrating solar power down to 5 cents per kilowatt hour, comparable to conventional fossil fuel-based power.

However, the re-used particles can eventually break down into fine dust, which poses a risk for lung damage.

“We did some computer modeling using the EPA’s particle dispersion model,” Ho said. “Basically it would take an emission of particles 400 times greater than what we found in previous tests to start to get close to the EPA standards. Based on our measurements and model, I don’t foresee any conditions where we’re really hitting those thresholds.”

With information from the tests and simulations, the team developed methods to reduce the emission of fine dust particles. Members optimized the shape and geometry of the falling-particle receiver to reduce particle loss, Ho said. They also developed a stair-like system that slows the particles in the receiver as they fall and a “snout” that helps mitigate the impacts of wind on the falling particles.

The balloon tests were funded by the DOE’s Solar Energy Technologies Office as one of three teams testing different high-temperature concentrating solar power systems with built-in heat storage.