Abstract: A plural stage solar radiation fluid heater comprises a housing having a top in which there is an array of lenses. Near the inside bottom of the housing, there is a first fluid conduit located at the foci of the lenses for absorbing primary solar radiation focused thereon. One or more additional conduits are interposed between the first conduit means and the lenses and are arranged to permit passage of the ray bundles from the lenses to the first conduit means. The arrangement is such that the intervening circuit means intercept secondary terminal radiation which is re-radiated from the next adjacent hotter conduit means.