Transparent aerogel for more efficient solar collectors

Researchers at MIT developed a new type of aerogel so transparent you can barely see it, for the use of in solar collector.

When thinking about solar energy, most people will think about solar panels. However, while these panels turn sunlight into energy, solar collectors collect and focus the energy from the sun and use it to heat water.

The key to efficient heat collection lies in being able to keep something hot internally while remaining cold on the outside. Many solar collectors use a vacuum between a layer of glass and a dark, heat absorbing material, but this is relatively expensive to install and maintain.

Aerogels are foam-like material made of silica particles, consisting mostly of air. The material is incredibly insulating, and would therefore be great to use in solar collectors. The problem is, however, that common aerogels have limited transparency to visible light, with around a 70 per cent transmission level, which would mean 30 per cent of the energy is lost in the use in solar collectors.

The new aerogel material, on the other hand, lets through over 95 per cent of incoming sunlight with maintaining its highly insulating properties. The key to making it world was in the precise ratios of the different materials used to create the aerogel, which are made by mixing a catalyst with grains of a silica-containing compound in a liquid solution. This creates a kind of gel, which is then dried to leave a matrix that is mostly air but retains the original mixture’s strength. Drying out the gel faster than conventional aerogel produces a gel with smaller pore spaces between the grains, which scatters the light much less.

In tests on a rooftop on the MIT campus, a flat solar collector covered with a layer of the new aerogel was able to reach and maintain a temperature of 220 degrees Celsius, in the middle of winter when the outside air was below 0 degrees Celsius. Normal flat solar collectors only get to about 80 degrees Celsius.

The higher temperatures enabled by the aerogel system could make such simple systems usable for home heating as well, and even for powering an air conditioning system. Large-scale versions could be used to provide heat for a wide variety of applications in chemical, food production, and manufacturing processes.

Photos: MIT