Engineering and economic considerations are given for nontracking solar energy collectors where the absorbing surface is insulated by an evacuated space. Each collector is a long glass tube, about two in. in dia, silvered in the lower portion. The selectively blackened conduit through which liquid flows is suspended within the evacuated tube, passing through the tube wall at only one end. Prototype tubular collectors were built, and tested when evacuated and when air-filled. The measured efficiencies at different temperatures are given, and the data fitted by empirical equations. Costs per tube and per Btu are given together with an indication of applicability to solar air conditioning. Mass production of these collectors will depend on the indicated demand.