Linear receivers for solar collectors

Abstract

Described herein are linear receivers for use in concentrating solar collection applications. For example, linear receivers incorporating a volume displacement element within an internal volume of a linear solar radiation absorbing element are provided. The volume displacement element provides, for example, enhanced heat transfer characteristics between the absorber element and the heat transfer fluid, efficiency improvements associated with maintaining a position of the linear receiver at an optimal location for absorbing concentrated solar radiation and/or the ability to recover the linear receiver from a freeze event. Also provided are methods for making a linear receiver, methods for collecting concentrated solar radiation, methods for recovering a linear receiver from a freeze event, methods for improving overall receiver efficiency, such as by reducing bowing/sagging of the receiver element, and methods for reducing a circumferential temperature distribution of the absorber element.

We claim: 
     
         1 . A linear receiver for a concentrating solar collector, said receiver comprising:
 a linear solar radiation absorbing element extending along a first length, wherein said linear solar radiation absorbing element comprises a hollow structure having a first internal volume and an external surface for absorbing incident or reflected solar radiation;   a linear volume displacement element positioned within said linear solar radiation absorbing element and extending along at least a portion of said first length of said linear solar radiation absorbing element, wherein said first internal volume includes a second volume occupied by said linear volume displacement element and a third volume not occupied by said linear volume displacement element and wherein said second volume occupies a percentage of said first internal volume greater than 15%; and   a first heat transfer fluid provided within said third volume of said linear solar radiation absorbing element, wherein said first heat transfer fluid flows at a first flow rate within said linear solar radiation absorbing element and does not flow within said second volume.   
     
     
         2 . The linear receiver of  claim 1 , wherein said second volume occupies a percentage of said first internal volume selected from the range of 15% to 90%. 
     
     
         3 . The linear receiver of  claim 1 , wherein said linear volume displacement element extends along a percentage of said first length selected from the range of 50% to 100%. 
     
     
         4 . The linear receiver of  claim 1 , wherein said linear volume displacement element comprises a solid structure or a hollow structure. 
     
     
         5 . The linear receiver of  claim 1 , wherein said linear volume displacement element comprises an electrically conductive material. 
     
     
         6 . The linear receiver of  claim 1 , wherein said linear volume displacement element has a cross-sectional shape selected from the group consisting of a circle, an oval, an ellipse, a rectangle and a square. 
     
     
         7 . The linear receiver of  claim 1 , wherein said linear volume displacement element is positioned concentrically within said linear solar radiation absorbing element. 
     
     
         8 . The linear receiver of  claim 1 , wherein said linear volume displacement element comprises two or more linear volume displacement elements. 
     
     
         9 . The linear receiver of  claim 1 , wherein said linear volume displacement element has an overall density less than a density of said first heat transfer fluid. 
     
     
         10 . The linear receiver of  claim 1 , wherein said linear volume displacement element comprises a cylindrical tube or a solid structure. 
     
     
         11 . The linear receiver of  claim 1 , wherein said linear volume displacement element comprises a second hollow structure. 
     
     
         12 . The linear receiver of  claim 11 , wherein said second hollow structure has a wall thickness that is a percentage of a diameter of said second hollow structure selected from the range of 1% to 40%. 
     
     
         13 . The linear receiver of  claim 11 , further comprising a second heat transfer fluid provided within said second hollow structure. 
     
     
         14 . The linear receiver of  claim 1 , wherein said linear volume displacement element comprises a collapsible geometry. 
     
     
         15 . The linear receiver of  claim 1 , wherein said linear solar radiation absorbing element comprises a cylindrical tube. 
     
     
         16 . The linear receiver of  claim 1 , wherein said linear solar radiation absorbing element has a cross-sectional shape selected from the group consisting of a circle, an oval, an ellipse, a rectangle and a square. 
     
     
         17 . The linear receiver of  claim 1 , further comprising one or more turbulators positioned within said third volume. 
     
     
         18 . The linear receiver of  claim 1 , further comprising a hollow glass structure, wherein said linear solar radiation absorbing element is positioned within said hollow glass structure. 
     
     
         19 . A solar collector comprising the linear receiver of  claim 1 . 
     
     
         20 . The solar collector of  claim 19 , wherein said solar collector comprises a linear concentrating solar collector, a reflective parabolic trough solar collector or a reflective linear Fresnel solar collector positioned to reflect incident solar radiation onto said linear receiver. 
     
     
         21 . A method of collecting concentrated solar radiation, the method comprising steps of:
 providing a linear solar radiation absorbing element extending along a first length, wherein said linear solar radiation absorbing element comprises a hollow structure having a first internal volume and an external surface for absorbing incident or reflected solar radiation;   providing a linear volume displacement element within said linear solar radiation absorbing element and extending along at least a portion of the first length of said linear solar radiation absorbing element, wherein said first internal volume includes a second volume occupied by said linear volume displacement element and a third volume not occupied by said linear volume displacement element and wherein said second volume occupies a percentage of said first internal volume greater than 15%; and   flowing a first heat transfer fluid within said third volume of said linear solar radiation absorbing element, wherein said first heat transfer fluid flows at a first flow rate within said linear solar radiation absorbing element and does not flow within said second volume; and   exposing said linear solar radiation absorbing element to concentrated solar radiation, wherein said first flow rate is sufficient to maintain a maximum circumferential temperature difference of the linear solar radiation absorbing element to achieve a target amount of bowing, stress and/or strain in the linear solar radiation absorbing element.   
     
     
         22 . A method of making a concentrating solar collector, the method comprising steps of:
 providing a linear solar radiation absorbing element extending along a first length, wherein said linear solar radiation absorbing element comprises a hollow structure having a first internal volume and an external surface for absorbing incident or reflected solar radiation;   providing a linear volume displacement element within said linear solar radiation absorbing element and extending along at least a portion of said first length of said linear solar radiation absorbing element, wherein said first internal volume includes a second volume occupied by said linear volume displacement element and a third volume not occupied by said linear volume displacement element and wherein said second volume occupies a percentage of said first internal volume greater than 15%;   flowing a first heat transfer fluid at a first flow rate within said third volume and between an internal surface of said linear solar radiation absorbing element and said linear volume displacement element, wherein said first heat transfer fluid does not flow within said second volume; and   positioning said linear receiver at a location to receive concentrated solar radiation from one or more reflective surfaces.   
     
     
         23 . The method of  claim 22 , wherein said one or more reflective surfaces comprise one or more parabolic trough mirrors or one or more mirrors of a linear Fresnel solar collector.