“The transparent aerogel can transform a widely deployed solar hot water heater into a high-performance solar collector that can output heat at higher temperatures with improved efficiency and hence generate greater economic value”Lin Zhao
Researchers at MIT have developed a new type of aerogel material that is very transparent to sunlight and can passively and effectively capture solar heat. The material, which achieves greater temperatures than standard solar collectors, gets enough heat out of sunlight to heat a house and for industrial processes and power generation that need high temperatures, and also has potential applications in chemical, food production and manufacturing processes.
With much research going into identifying cheaper systems for collecting solar heat at higher temperature levels, aerogels – a foam-like material consisting mostly of air with a structure of silica particles – are seen as pivotal as they allow sunlight to pass through easily but stop solar heat from escaping, acting as an efficient and lightweight thermal insulating material. Although producing aerogels with sufficient transparency to be effective for solar heat collection is difficult, as reported in ACS Nano [Zhao et al. ACS Nano (2019) DOI: 10.1021/acsnano.9b02976], this material lets in more than 95% of incoming sunlight while maintaining highly insulating properties.
Many existing solar heat collectors have a vacuum positioned between a layer of glass and a dark, solar-absorbing material, but are quite expensive to install and maintain. However, the materials used to make this new aerogel are abundant and cheap, with the only big expense being the drying, which requires a specialized device for an accurate drying process that extracts the solvents from the gel while preserving its nanoscale structure.
The aerogel was produced by mixing a catalyst with a silicon-containing compound in a liquid solution. This wet gel is then dried to remove all liquid, with the resulting matrix being mostly air but with some of the original mixture's structure. Finding a mix that chemically reacts much faster than those in standard aerogels offered a gel with smaller pore spaces between its grains, and therefore scattered the light much less.
Tests demonstrated a temperature of 220C was reached with an external air temperature below 0C. The heat collection system can also be connected to pipes containing a liquid that circulates to transfer the heat to where it might be needed, or connected to heat pipes to transfer heat without the need for pumps. As first author Lin Zhao told Materials Today, “The transparent aerogel can transform a widely deployed solar hot water heater into a high-performance solar collector that can output heat at higher temperatures with improved efficiency and hence generate greater economic value”.
As existing aerogel fabrication is a batch process at the lab scale, this could limit the rate of production if scaled up to industrial production levels, so developing a mass production process that maintains the aerogel’s useful properties while reducing costis key to taking the technology to the next level.
Multiple light beams from a solar simulator transport through an aerogel sample, fabricated by MIT researchers. While a small portion of the light is scattered and renders the light path visible, 95% of the incident beams are transmitted through the aerogel layer.