Thermal insulation for energy storage

Efficient thermal-energy storage requires effective thermal insulation. From a consideration of the possible heat-transfer modes, the requirements for a thermal barrier can be deduced. In a good conventional thermal insulation, most of the heat transfer takes place by conduction through the gas (air) in the insulation voids, the conductivity of the `still¿ gas representing the limiting performance of such a material. It follows that a better performance can be obtained only by reducing this gas-conducted heat by having voids smaller than the molecular mean-free path (`microporous¿), by replacing the air by a low-conductivity gas or by partially evacuating the insulation.