Abstract: A solar radiation collector comprises a receiver (2-5) through which passes a medium to be heated by solar radiation, and a concentrator (2-1, 2-4) for concentrating solar radiation onto the receiver (2-5). The receiver (2-5) is an elongate structure of polygonal or approximately polygonal section, and the concentrator may be a Fresnel lens system (2-1) and cycloidal mirrors (214). Between the concentrator (2-1, 2-4) and the receiver (2-5) is an intermediate device (2-6) surrounding the receiver (2-5) for reducing energy losses due to radiation emitted by the receiver (2-5). The intermediate device (2-6) has a reflective, internal surface (1-3, 1-5, 1-6) for reflecting back onto the receiver (2-5) radiation emitted therefrom, and at least one window (1-4, 1-7) in its perimeter through which radiation is focussed onto the receiver (2 -5) by the concentrator (2-1, 2-4).

Abstract: A solar radiation collector comprises a receiver (2-5) through which passes a medium to be heated by solar radiation, and a concentrator (2-1, 2-4) for concentrating solar radiation onto the receiver (2-5). The receiver (2-5) is an elongate structure of polygonal or approximately polygonal section, and the concentrator may be a Fresnel lens system (2-1) and cycloidal mirrors (2-4). Between the concentrator (2-1, 2-4) and the receiver (2-5) is an intermediate device (2-6) surrounding the receiver (2-5) for reducing energy losses due to radiation emitted by the receiver (2-5). The intermediate device (2-6) has a reflective, internal surface (1-3, 1-5, 1-6) for reflecting back onto the receiver (2-5) radiation emitted therefrom, and at least one window (1-4, 1-7) in its perimeter through which radiation is focussed onto the receiver (2-5) by the concentrator (2-1, 2-4).