Abstract: Hydrogen permeations through a ferritic pipe from a heat conducting aqueous fluid to a heated surface, such as, in a solar collector, is prevented by the utilization of a composite pipe structure which includes means to intercept and convey radially flowing hydrogen.

Abstract: A solar collector of the CPC-type is described. The collector is provided in modular form with a plurality of elongate forming reflectors housed within an outer metal tray and a glass cover. An absorber tube passes sequentially through the reflectors and is normally located at the focus of the reflectors to permit fluid passing therethrough to be located. To provide on-going heat regulation and shut-down capability, the absorber tubes are movable out of the reflector focus by an automatic device which senses excessive temperatures and effects the defocussing movement in response thereto.

Abstract: An efficient solar collector includes an outer evacuated envelope having an upper transparent surface to admit light rays to the envelope and a tube extending in the envelope from one end towards the other for conveying fluid to be heated into the collector and for removing heated fluid from the collector. A selectively absorbing surface is provided on the tube for selectively absorbing energy having predetermined wavelengths and rejecting other wavelengths. An elongate reflector having a particular locus is located internally of the light and arranged to reflect light received through the transparent surface onto the tube at a concentration ratio which is the ratio of the transverse width of the upper transparent surface to the outer circumference of the tube. The locus of the reflector surface is the shape required to ensure that all incident rays received through the upper transparent surface within the acceptance angle .theta. determined by the equation C=1/sin .theta.