DETAILED DESCRIPTION What is claimed is: 1.
A solar collector which comprises an evacuated transparent envelope; an absorber arranged within said envelope; a duct arranged at least partially within said envelope and containing a heat-transport medium, said absorber being associated with said duct so as to transfer heat derived from incident solar radiation to the heat-transport medium in said duct during operation; a reversible heatable hydrogen getter positioned in said envelope and consisting of a partial hydride of one or more of titanium, zirconium, hafnium, scandium, yttrium, lanthanum, the rare earths, strontium, barium, vanadium, niobium, tantalum, thorium, and alloys of said metals; and a fully hydrogenized metal hydride also positioned in said envelope and being thermally more stable and having a higher affinity for oxygen than said partial hydride.
2.
A solar collector according to claim 1, in which the reversible heatable hydrogen getter is a partial hydride of an alloy of niobium and titanium, and the fully hydrogenized metal hydride is zirconium hydride.
Description:
This invention relates to a solar collector comprising an absorber for transferring heat derived from solar radiation incident on the absorber during operation to a heat-transport medium in a duct which exchanges heat with the absorber, and a cover which thermally insulates the absorber from the surroundings and which consists of at least one sealed and evacuated transparent tube or envelope containing a heatable, reversible hydrogen getter consisting of one or more of the metals titanium, zirconium, hafnium, scandium, yttrium, lanthanum, the rare earths, strontium, barium, vanadium, niobium, tantalum, thorium and alloys thereof in a partly hydrogenized condition.
A solor collector of the kind set forth is described in U.
S.
Pat.
No.
4,142,509.
The reversible heatable hydrogen getter serves to control one of the loss factors of the solar collector, namely, the thermal conduction losses thereof, by controlling the hydrogen pressure in the evacuated envelope
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Heat Accumulators 
