Solar thermal concentrator apparatus, system, and method

Abstract

An apparatus is disclosed including: a trough shaped reflector extending along a longitudinal axis and including at least one reflective surface having a shape which substantially corresponds to an edge ray involute of the absorber.

1 . An apparatus for concentrating light to an elongated absorber comprising:
 a trough shaped reflector extending along a longitudinal axis having at least one reflective surface having a shape which substantially corresponds to an edge ray involute of the absorber.   
     
     
         2 . The apparatus of  claim 1 , wherein:
 the reflector has a first side and a second side disposed symmetrically on opposing sides of an optic plane transverse the longitudinal axis, and   wherein each side of the reflector comprises a reflective surface having a shape which substantially corresponds to an edge ray involute of the absorber.   
     
     
         3 . The apparatus of  claim 2 , wherein the absorber comprises a cylindrical absorber extending in the direction of the longitudinal axis and disposed at the bottom of the trough shaped reflector. 
     
     
         4 . The apparatus of  claim 3 , wherein the reflector comprises an entrance aperture located at a top of the trough, and wherein substantially all light incident on the entrance aperture at angles less than an acceptance angle are concentrated to the absorber. 
     
     
         5 . The apparatus of  claim 4 , wherein the reflector concentrates light at the thermodynamic limit. 
     
     
         6 . The apparatus of  claim 1 , wherein:
 the absorber is spaced apart from the reflector by a gap distance; and   a portion of the reflector at the bottom of the trough comprises a reflective cavity having a reflective surface with a shape that deviates substantially from the edge ray involute of the absorber.   
     
     
         7 . The apparatus of  claim 6 , wherein the cavity comprises a V-shaped trough extending along the bottom of the reflector in the direction of the longitudinal axis. 
     
     
         8 . The apparatus of  claim 7 , wherein the V-shaped trough comprises an aperture positioned such that the image of the absorber reflected in a wall of the V-shaped trough has a top which is positioned proximal or above the aperture of the V-shaped top in the direction extending from the top of the trough to the bottom of the trough. 
     
     
         9 . The apparatus of any of  claim 6 , further comprising: an efficiency loss averaged over the acceptance angle relative to an equivalent gapless concentrator of 0.02 or less. 
     
     
         10 . The apparatus of any of  claim 6 , further comprising:
 concentration ratio equal to at least 90% of that of an equivalent gapless concentrator.   
     
     
         11 . The apparatus of any of  claim 6 , wherein the gap distance is less than a radius of the absorber. 
     
     
         12 . The apparatus of  claim 1 , wherein the reflector concentrates light to the absorber with a concentration ratio C of 1.0 or greater. 
     
     
         13 . The apparatus of  claim 1 , wherein the reflector concentrates light to the absorber with a concentration ratio C of 1.25 or greater. 
     
     
         14 . The apparatus of  claim 1 , wherein the reflector concentrates light to the absorber with a concentration ratio C of 1.5 or greater. 
     
     
         15 . The apparatus of  claim 1 , wherein the reflector concentrates light to the absorber with a concentration ratio C of 1.75 or greater. 
     
     
         16 . The apparatus of  claim 1 , wherein the reflector concentrates light to the absorber with a concentration ratio C of 2.0 or greater. 
     
     
         17 . The apparatus of  claim 1 , wherein a reflective surface of the reflector has a reflectivity of 90% or more for solar light. 
     
     
         18 . The apparatus of  claim 1 , wherein a reflective surface of the reflector has a reflectivity of 94% or more for solar light. 
     
     
         19 . The apparatus of  claim 1 , wherein the reflector has an acceptance angle of at least 25 degrees. 
     
     
         20 . The apparatus of  claim 1 , wherein the reflector has an acceptance angle of at least 35 degrees. 
     
     
         21 . The apparatus of  claim 1 , wherein the reflector has an acceptance angle of at least 45 degrees. 
     
     
         22 . The apparatus of  claim 1 , wherein the reflector has an acceptance angle of at least 60 degrees. 
     
     
         23 . An apparatus for concentrating light to an absorber comprising:
 at least one reflective surface configured to receive light incident at angles less than an acceptance angle and concentrate the received light to the absorber; and   wherein the concentrator includes a configuration in that substantially any light ray emitted from the absorber would exit the concentrator without returning to the absorber.   
     
     
         24 . The apparatus of  claim 23 , wherein the at least one reflective surface comprises a surface which corresponds to an edge ray involute of the absorber. 
     
     
         25 . An apparatus for converting incident solar light to heat, comprising:
 an evacuated tubular enclosure extending along a longitudinal axis from a proximal end to a distal end;   a tubular absorber element located within the evacuated enclosure, and comprising a selective surface configured to absorb solar light incident through the evacuated enclosure and convert the solar light to heat; and   a U-shaped tube in thermal contact with the absorber element and comprising:
 a fluid input and a fluid output located at the proximal end of the tubular enclosure, 
 an input portion extending from the fluid input along an interior surface of the tubular absorber element; 
 an output portion extending from the fluid output along an interior surface of the tubular absorber element; 
 a curved portion located proximal the distal end of the enclosure and providing fluid communication between the input and output portions; and 
 wherein the input portion and the output portion are spaced apart. 
   
     
     
         26 . The apparatus of  claim 25 , wherein fluid input into the fluid input at a first temperature travels though the U-shaped tube, absorbs heat from the selective absorber, and is output from the output at a second temperature higher than the first. 
     
     
         27 . The apparatus of  claim 25 , wherein the selective surface has an absorptivity of at least 0.75 and an emissivity of 0.25 or less at temperatures greater than 100 C. 
     
     
         28 . The apparatus of  claim 25 , wherein the selective surface has an absorptivity of at least 0.9 and an emissivity of 0.1 or less at temperatures greater than 100 C. 
     
     
         29 . The apparatus of  claim 25 , wherein the selective surface has an absorptivity of at least 0.9 and an emissivity of 0.1 or less at temperatures greater than about 200 C. 
     
     
         30 . An apparatus for concentrating light to an elongated absorber comprising:
 a trough shaped reflector extending along a longitudinal axis, the reflector spaced apart from the absorber;   wherein the reflector has a portion of at least one reflective surface having a shape which substantially corresponds to an edge ray involute of a virtual absorber surrounding the absorber and contacting the reflector.   
     
     
         31 . The apparatus of  claim 30 , wherein the ratio of the area of the virtual absorber to the area of the absorber is 0.9 or greater. 
     
     
         32 . The apparatus of any of  claim 30 , wherein:
 a portion of the reflector at the bottom of the trough comprises a reflective cavity having a reflective surface with a shape that deviates substantially from the edge ray involute of the virtual absorber.   
     
     
         33 . The apparatus of  claim 32 , wherein the cavity comprises a V-shaped trough extending along the bottom of the reflector in the direction of the longitudinal axis. 
     
     
         34 . The apparatus of  claim 33 , wherein the V-shaped trough comprises an aperture positioned such that the image of the absorber reflected in a wall of the V-shaped trough has a top which is positioned proximal or above the aperture of the V-shaped top in the direction extending from the top of the trough to the bottom of the trough. 
     
     
         35 . The apparatus of  claim 31 , wherein the apparatus has an efficiency loss averaged over the acceptance angle relative to an equivalent gapless concentrator of 0.02 or less. 
     
     
         36 . A method of manufacturing a trough shaped reflector extending along a longitudinal axis having at least one reflective surface having a shape which substantially corresponds to an edge ray involute of the absorber, the method comprising:
 manufacturing a reflective surface; and   manipulating the reflective surface so the reflective surface comprises an involute shape.   
     
     
         37 . The method of  claim 36 , further comprising: coating the reflective surface. 
     
     
         38 . A collector system for converting solar light to heat comprising:
 a working fluid;   at least one absorber element; and   at least one concentrator;   wherein the at least one concentrator concentrates solar light onto the absorber element to generate heat; and the working fluid flows through the absorber element to extract heat from the absorber element; and   wherein the at least one concentrator comprises a trough shaped reflector extending along a longitudinal axis having at least one reflective surface having a shape which substantially corresponds to an edge ray involute of the absorber.   
     
     
         39 . An optimal solar concentrator comprising:
 a window for receiving a radiation source; and   an absorber, wherein the absorber includes a convex or flat shaped geometry where a distance from a top to the bottom of the convex or flat approaches an amount that includes a predetermined maximum probability to receive and concentrate a maximum amount of solar radiation.   
     
     
         40 . The solar concentrator of  claim 39 , further comprising a first lateral side and a second lateral side of the convex or flat absorber shape, wherein the first and second lateral side have the same length. 
     
     
         41 . The solar concentrator of  claim 40 , further comprising a base. 
     
     
         42 . The solar concentrator of  claim 39 , wherein the convex or flat shape absorber includes a concentration that is maximum if and only if F 31 =1.