Transparent insulation - materials

Three fields of material development can be identified. If one uses granulated aerogel with different mean sphere diameters, the conductivity scales approximately linearly with this diameter, whereas transmittance measurements show a markedly reduced value below 3 mm, but minor variation of transmittance above 3 mm diameter. Capillary structures produced from different plastics, which may whithstand higher temperatures than the usual ones, have been investigated. Some materials, in particular a special PMMA capillary, showed very good performance, whereas others have difficulties in reaching sufficiently high solar transmittances. From preliminary results of an optimisation of rectangular polycarbonate honeycombs, a new material has been produced which, in spite of some limitations due to the production process, shows a 10 % decrease in thermal conductance when compared to the previous design. The solar characteristics of the materials are identical.