Fabrication and characterisation of slim flat vacuum panels suitable for solar applications

The concept of providing an evacuated space between two planar surfaces and exploiting its thermal properties was initially proposed in 1913 for window applications in buildings (Zoller, 1913). Since then a number of designs for the fabrication of evacuated windows have been proposed investigating sealing methods for the periphery of the glass panes and methods of maintaining the separation of the glass panes under the influence of atmospheric pressure (Collins et al., 1995). Evacuated windows have also been used in solar applications by creating a vacuum (less than 0.01mbar) around a solar absorber to reduce the convective heat losses resulting in higher efficiencies. Maintaining the vacuum pressure over the life time of the panel is challenging. This is largely dependent on the materials used in the fabrication process. Forming a durable hermetic seal around the periphery of the vacuum enclosure is particularly crucial. In this work prototypes of flat vacuum panels with solar applications are fabricated and tested. Indium is used as a sealing material to create a hermetic seal around the periphery the panel. A heat transmission of 0.86 Wm-2 K-1 in the centre of the vacuum panel has been achieved for a 0.4m by 0.4m panel.