Solar energy collector having an absorber element of coated foil

DETAILED DESCRIPTION An object of the invention is to provide an improved solar energy collector.
Another object is to provide an absorber element for a collector comprising coated foil.
A related object is to provide a solar energy absorbent element comprising a coated foil that is insensitive to the presence of surface contaminants on other parts of the collector.
A further object is to provide a solar energy absorber element having increased long-term stability.
These and other objects are realized by a solar energy collector which, in one form, comprises spaced-apart wall members of which one wall member is adapted to face solar radiation and the other wall member is spaced on the remote side of the first wall member and adapted to contact a heat-absorbing medium.
The wall members are preferably fabricated from glass.
A coated foil, such as a precoated metallic foil, is disposed between the wall members and has coatings on its opposite sides.
The side of the foil facing the wall member exposed to solar radiation has a solar selective coating comprising a semi-conductor material, and the side of the coated foil facing the other wall member has an emissive coating providing relatively high emissivity in the infrared spectrum.
The solar energy collector may be either of the flat plate or tubular type and the space between the wall members preferably is maintained at a subatmospheric pressure.
The coated foil acts as a photothermal energy converter and may be easily and readily placed in position without undue regard for the presence of contaminants on the wall members.
In preparing the present solar energy collector, the foil may be precoated on both sides and then assembled between the wall members.
Or just the emissive coating may be precoated, and the solar selective coating deposited on the foil after it has been placed in position.