Cylindrical solar energy collector

Abstract

A system is disclosed to employ optical collectors 10 including cylindrical troughs 14 below ground level for solar-thermal generation of electricity. In one preferred embodiment, the interior wall 24 of the cylindrical trough 14 is coated with reflective material to act as primary cylindrical collector mirror 20 . Since the trough 14 is situated in the ground, this mirror 20 can be very large and large concentrated power densities can be obtained. A set of corrector mirrors 28 in a relative small boxlike structure 22 focus all rays on a receiver tube 16 situated at the center of curvature of the trough 14 . The tracking of the sun is achieved by rotating this collector box 22 in the trough 14 about the center of curvature. No movement of large mirrors is required since the large primary mirror 20 is fixed and the corrector mirrors 28 in the corrector box 22 are relatively small. The collector 10 can also be used as concentrator for photovoltaic cells or it can be used for water heating.

1 . Apparatus for collection of solar energy, said apparatus comprising a part cylindrical trough, an elongate receiver extending in a generally axial direction relative to the cylindrical trough and at least one reflective surface disposed within the trough and configured to reflect incoming solar radiation towards the receiver.  
     
     
         2 . Apparatus as claimed in  claim 1 , wherein said reflective surface is part cylindrical in shape and extends along the inside of the cylindrical trough, said apparatus further including at least one corrector mirror disposed within the trough and support means configured to support the corrector mirror in a position where it can reflect radiation reflected from the cylindrical reflective surface of the trough, to the receiver.  
     
     
         3 . Apparatus as claimed in  claim 2 , wherein the receiver extends generally along the cylinder axis of the trough.  
     
     
         4 . Apparatus as claimed in  claim 3 , wherein the support means is configured to rotate the corrector mirror relative to the cylinder axis.  
     
     
         5 . Apparatus as claimed in  claim 2 , wherein the corrector mirror is part cylindrical.  
     
     
         6 . Apparatus as claimed in  claim 2 , wherein the corrector mirror is disposed between the focal curve of the cylindrical trough and the reflective surface of the cylindrical trough.  
     
     
         7 . Apparatus as claimed in  claim 2 , which includes a system of corrector mirrors, supported by the support means.  
     
     
         8 . Apparatus as claimed in  claim 1 , which includes a parabolic mirror, said reflective surface being defined on the inside of the parabolic mirror, said apparatus further including support means configured to support the parabolic mirror in a position where the principal axis of its parabolic shape generally intersects the receiver.  
     
     
         9 . Apparatus as claimed in  claim 8 , wherein the receiver extends generally along the cylinder axis of the trough.  
     
     
         10 . Apparatus as claimed in  claim 9 , wherein the support means is configured to rotate the parabolic mirror relative to the cylinder axis.  
     
     
         11 . Apparatus as claimed in  claim 1 , in which the cylindrical trough extends below the ambient ground surface, at least in part.  
     
     
         12 . A method for collection of solar energy, said method comprising receiving solar radiation in a part cylindrical trough, reflecting the radiation from a reflective surface to an axially orientated, elongate receiver and collecting the energy from the radiation at the receiver.  
     
     
         13 . A method as claimed in  claim 12 , wherein the reflective surface is part cylindrical and is defined on the inside of the cylindrical trough, said method further comprising receiving the solar radiation on the cylindrical reflective surface, reflecting the radiation from the cylindrical reflective surface and correcting the radiation reflected from the cylindrical reflective surface by reflecting it to the receiver.  
     
     
         14 . A method as claimed in  claim 13 , wherein the radiation reflected from the cylindrical reflective surface is corrected by reflecting it from at least one corrector mirror.  
     
     
         15 . A method as claimed in  claim 14 , wherein the radiation reflected from the cylindrical reflective surface is corrected by reflecting it from a system of corrector mirrors, towards the receiver.  
     
     
         16 . A method as claimed in  claim 14 , wherein the receiver extends generally along the cylinder axis of the cylindrical surface, said method including rotating each corrector mirror relative to the cylinder axis to track angular changes in the incoming solar radiation.  
     
     
         17 . A method as claimed in  claim 12 , wherein the reflective surface is defined on the inside of a parabolic mirror that is supported within the cylindrical trough, the principal axis of the parabolic shape of the reflective surface generally intersecting the receiver, said method further comprising receiving the radiation on the parabolic reflective surface and reflecting it from the reflective surface to the receiver.  
     
     
         18 . A method as claimed in  claim 17 , wherein the receiver extends generally along the cylinder axis, said method including rotating the reflective surface relative to the cylinder axis to track angular changes in the incoming solar radiation.