Secondary solar concentrator

Abstract

An external concentrator is provided for use with heat collection elements (HCE's of a solar parabolic trough power plant. In one arrangement, the concentrator includes a plurality of ribs that are adapted to extend radially outward from the outside surface of an HCE and along the linear length of the HCE to help redirect stray/spilled light into the absorber tube of the HCE. In another arrangement, the concentrator includes a shield placed on or near a surface of the HCE opposite of the parabolic reflective trough. The reflective shield includes ribs or brims that are disposed adjacent to one or both lateral edges of a reflective shield applied to the outside surface of a HCE tube to increase the collection of stray light reflected by the reflective trough.

What is claimed is: 
     
         1 . A solar concentrator configured for attachment to a generally cylindrical outside surface of a heat collection element (HCE) positioned along a focal line of a parabolic reflector, comprising:
 at least first and second elongated ribs each having, in cross-section, an edge surface adapted for disposition along a length of the HCE and at least one reflective side surface extending outward from the outside surface of the HCE, wherein said elongated ribs are radially spaced about the outside surface of the HCE.   
     
     
         2 . The solar concentrator of  claim 1 , wherein said first and second elongated ribs comprise a first set of elongated ribs and a second set of elongated ribs, respectively. 
     
     
         3 . The solar concentrator of  claim 1 , wherein each rib of each set of ribs is spaced from at least one adjacent rib when attached to the outside surface of the HCE. 
     
     
         4 . The solar concentrator of  claim 3 , further comprising:
 a reflective shield having a reflective surface disposed toward the outside surface of the HCE.   
     
     
         5 . The solar concentrator of  claim 4 , wherein said reflective shield covers between about 15° (i.e., ˜0.25 rad) and about 120° (i.e., ˜2.1 rad) of the outside surface of the HCE. 
     
     
         6 . The solar concentrator of  claim 5 , wherein said reflective shield is disposed on the outside surface of the HCE between said first and second elongated ribs. 
     
     
         7 . The solar concentrator of  claim 4 , wherein said reflective shield is corrugated. 
     
     
         8 . The solar concentrator of  claim 4 , further comprising:
 first and second brims attached to lateral edges of said reflective shield at first and second attachment points.   
     
     
         9 . The solar concentrator of  claim 8 , wherein said brims are, in cross-section, disposes at an angle +/−90° (β) on either side of a radial line extending through a centerline axis of the HCE. 
     
     
         10 . The solar concentrator of  claim 9 , wherein said brims, in cross-section, are:
 rectangular,   parabolic; or   curved.   
     
     
         11 . The solar concentrator of  claim 2 , wherein said first and second sets of elongated ribs are disposed on opposite sides of a reference line extending between a vertex of the parabolic reflector and a centerline of the HCE. 
     
     
         12 . The solar concentrator of  claim 11 , wherein each set of elongated ribs are radially spaced over about 15° (i.e., ˜0.25 rad) and about 120° (i.e., ˜2.1 rad) of the outside surface of the HCE. 
     
     
         13 . The solar concentrator of  claim 1 , wherein a height of said ribs, in cross section, is between about 1% and about 40% of a diameter of said generally cylindrical heat collection element (HCE). 
     
     
         14 . A solar concentrator configured for attachment to a generally cylindrical outside surface of a heat collection element (HCE) positioned along a focal line of a parabolic reflector, comprising:
 a reflective shield extending over an outside surface of the HCE, having a reflective surface disposed toward the outside surface of the HCE;   at least first and second elongated brims extending from lateral edges of the reflective shield each having at least one reflective side surface extending outward from the outside surface of the HCE, wherein the elongated brims are connected to the reflective shield at first and second attachment points.   
     
     
         15 . The solar concentrator of  claim 14 , wherein the first and second elongated brims, in cross-section, extend from the HCE a length between 1-40% of the HCE diameter. 
     
     
         16 . The solar concentrator of claim of  claim 15 , wherein the brims, in cross-section, are:
 rectangular;   parabolic; or   curved.   
     
     
         17 . The solar concentrator of  claim 16 , wherein the first and second elongated brims are oriented at an angle relative to first and second cross-sectional radial lines, respectively, wherein the first and second cross-sectional radial lines extend from a central axis of the HCE through the first and second attachment points, respectively. 
     
     
         18 . The solar concentrator of  claim 17 , wherein the first and second elongated brims are oriented at an angle between 0-90° in either direction of the first and second cross-sectional radial lines, respectively. 
     
     
         19 . The solar concentrator of  claim 14 , wherein the reflective shield forms a corrugated surface comprising a plurality of alternating ridges and grooves. 
     
     
         20 . The solar concentrator of  claim 19 , wherein the corrugated surface, in cross-section, is formed from one of alternating:
 rectangular sections;   parabolic sections; or   curved sections.