AEROGELS – A VALUE ADDITION TO HARVEST SOLAR ENERGY

Rathindra Nath Biswas

Abstract

Aerogels are a class of synthetic porous ultralight material that was created in 1930 and derived from a gel, in which the liquid component has been replaced with a gas without collapsing the gel structure by freeze-drying. It is made of silica, but carbon, iron oxide, gold, copper, polymer etc. can also be used. During freeze drying the liquid in the gel is slowly dried off without collapsing the solid matrix retaining the original geometrical structure. The final product is extremely porous with very little solid material, with up to 99.8% of the aerogel consisting of nothing but air. It has a typical density of about 0.001 gm cm -3 and has been produced at a density of only three times heavier than air with extremely low thermal conductivity. The aerogel blankets have a very low thermal conductivity in combination with acoustic property of noise abatement that makes the material very suitable for insulating the walls of a building to improve the energy performance and to minimize sound pollution. Transparent monolithic silica aerogel is the holy grail of future glazing technology, with potential to achieve U-values as low as 0.1W/m2.k. It effectively transmits solar light, but blocks thermal infrared radiation. It provides energy and cost savings due to reduced loss of conditioned indoor air envisaging healthier indoor environment. In all solar thermal plants , it is necessary to install solar receivers which would convert incident sunlight into heat. It should be so designed that it would strongly absorb sunlight with minimum heat loss. Aerogels are low density materials and can be made transparent across the solar spectrum, but opaque in the IR and also it has extremely low thermal conductivity, thus making it most suitable for using as a volumetric radiation shield for solar receivers. By reducing heat losses and at the same time being transparent, aerogels allow a solar plant to operate at higher temperature and at higher efficiency without using any vacuum device. These advantages make an aerogel assisted solar thermal plant very economical and eliminates lot of maintenance problems. Aerogel receivers, due to these reasons are being used increasingly for harvesting solar energy .

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