New Aerogel Generates More Solar Heat

While the sun may serve as a free energy source, harnessing its power often comes at a significant expense. Although the U.S. Department of Energy has already surpassed its goal to reduce residential- and commercial-scale solar costs, meeting the next goal will come down to innovative researchers like the MIT team that recently unveiled a new solar energy material.

The team’s research focused on developing a material that could harness solar heat at intermediate chambers, 120–220°C, which has seen a rise in demand. Capturing heat at those temperatures is accompanied by costly components and is often difficult to maintain with intermittent sunlight. The team has created a solar receiver that can surpass 265°C using only sunlight and a newly developed aerogel.

Although aerogels—lightweight insulating materials composed of silica—have been around for years, the team set out to develop one that was transparent enough to collect solar heat. After four years, their efforts produced a new monolithic silica aerogel that maintains its insulating properties and lets in 95 percent of sunlight.

A new transparent aerogel insulating material, made visible in the photo using parallel laser beams, transmits 95 percent of sunlight. Researchers spent four years developing the silica-based material. (Image courtesy of MIT.)

Mostly made of air, the material is a precise mix of a catalyst with grains of a silica-containing compound formed from common and inexpensive materials. It begins as a gel-like substance that must be dried out using a specialized tool, the most costly part of the process. Called a critical point dryer, the tool extracts the solvents from the gel while preserving its nanoscale structure. The next step is actually harnessing the material’s power.

The team tested the material on a roof at MIT during winter, with temperatures at 0°C, using a passive device with a heat-absorbing dark material that had a layer of the aerogel. The material was able maintain a temperature of 220°C.

“Like a greenhouse effect, the material we use to increase the temperature acts like the Earth’s atmosphere does to provide insulation, but this is an extreme example of it,” said Lin Zhao, MIT graduate student.

A test device installed on a rooftop at MIT proved the effectiveness of the new insulating material. When placed in sunlight, the device heated up to 220°C while the outdoor temperature was 0°C. (Image courtesy of MIT.)

Current systems to heat water, which require concentrating systems, typically only reach 80°C. The team’s passive system, which does not require concentration, has the potential to eliminate the need for vacuum-based connectors while still being connected to heat pipes. This could potentially have far-reaching benefits to power home heating systems and, on a larger scale, manufacturing and other industrial processes. For a more in-depth look at how solar energy works, check out Infographic: Solar Power by the Numbers.