Vacuum solar collectors

A solar collector, comprising:

• a tubular housing of radiation-transparent material hermetically closed at one end;
• a smaller-diameter tubular absorber having a radiation-absorber surface, the absorber being coaxially disposed within the tubular housing and hermetically closed at one end;
• the opposite ends of the tubular housing and absorber being sealed together by a fused seal, and the space between the two being evacuated;
• a plug inserted into said opposite end of the tubular absorber where sealed by the fused seal to the tubular housing;
• an inlet tube passing through an opening in said plug for introducing a heat-exchange medium into the interior of the tubular absorber;
• an outlet tube passing through an opening in said plug for removing the heat-exchange medium from the interior of the tubular absorber;
• means for mounting the collector at a tilt to the horizontal plane, with said opposite end of the tubular absorber carrying the plug being at a higher level than said one end;
• said inlet tube extending through the plug into the interior of the tubular absorber for substantially the complete length of the absorber;
• said outlet tube extending through the plug only into the upper end of the tubular absorber;
• and a boiler mounted at a higher elevation than the solar collector;
• the boiler including a vapour-phase zone connected to said outlet tube of the absorber, and a liquid-phase zone connected to the inlet tube of the absorber, the heated solar collector and boiler constituting a vapour pump whereby heat is transferred from the solar collector to the boiler without the need for a mechanical pump.