Trough collector for a solar power plant

Abstract

A trough collector ( 1 ) for solar power plants comprises a pressure cell ( 25 ) containing an absorber pipe ( 42 ) for a heat-carrying fluid and also a secondary concentrator which is likewise arranged in the pressure cell ( 25 ). The pressure cell ( 25 ) thus can be reduced in height, which eliminates the need for reinforcements in the form of a framework structure for the pressure cell ( 25 ), which are otherwise required.

1 . A trough collector for a solar power plant comprising:
 a concentrator arranged in a pressure cell such that it can be loaded with pressure and constructed as a flexible membrane;   wherein the concentrator concentrates solar radiation incident into the pressure cell under operating pressure towards a focal line region running outside of the pressure cell, and with an absorber element for absorption of a concentrated solar radiation;   wherein the absorber element is arranged in the pressure cell; and   wherein further within the pressure cell a secondary concentrator is provided which lies in a path of a concentrating radiation and is constructed in such a manner that the concentrated radiation is further concentrated toward a secondary focal line region or a secondary focal line at a location of the absorber element.   
     
     
         2 . The trough collector as claimed in  claim 1 , wherein:
 the pressure cell at least partially formed from a flexible membrane has a transparent region for solar radiation to be reflected;   the concentrator comprises:   a side which faces the transparent region and reflects the solar radiation; and   a side which faces away from the radiation;   wherein the concentrator subdivides the pressure cell into a first pressure chamber and a second pressure chamber; and   wherein means constructed as fans are provided to operationally generate and maintain pressure at a predefined level in the first and second pressure chambers if a volume of one or both pressure chambers is changed in operation by means of external influences.   
     
     
         3 . The trough collector as claimed in  claim 1 , wherein a predefined pressure difference is less than 0.5 mbar, preferably in a range from 0.05 to 0.2 mbar, and particularly preferably in the range from 0.05 to 0.1 mbar. 
     
     
         4 . The trough collector as claimed in  claim 1 , wherein:
 the secondary concentrator is arranged opposite the concentrator in a vicinity of a membrane with a region which is transparent for solar radiation; and   wherein the absorber element runs between the concentrator and the secondary concentrator.   
     
     
         5 . The trough collector as claimed in  claim 1 , wherein:
 the absorber element comprises a jacket for reducing heat emission to the outside;   wherein the absorber element further comprises a thermal opening running longitudinally in the jacket;   wherein the thermal opening allows passage of solar radiation further concentrated by the secondary concentrator through the jacket into an interior of the absorber element; and   wherein the absorber element is further constructed in such a manner that a heat-transporting fluid can circulate between the jacket and the interior for transporting radiant heat incident through the thermal opening away.   
     
     
         6 . The trough collector as claimed in  claim 1 , wherein the concentrator and the secondary concentrator are each divided into two longitudinally running mutually symmetrical regions. 
     
     
         7 - 9 . (canceled) 
     
     
         10 . A method for producing a secondary concentrator for a solar collector, which comprises the following steps for defining a shape of a reflective surface of the secondary concentrator:
 taking at least one cross-sectional plane of the secondary concentrator, wherein the following is carried out therein:   defining a unit vector  s (φ) of an incident solar ray;   defining the unit vector  s ′(φ) of the solar ray reflected on the concentrator;   taking the unit vector  s ″(φ) of the solar ray reflected on the secondary concentrator;   defining a number of points  SM (φ) on the secondary concentrator by means of a vector  PM (φ), wherein the vector  PM (φ) lies on the concentrator, and where  SM (φ)= PM (φ)+k· s ′(φ);   defining a factor k in such a manner that  s ″(φ) goes through a predefined focal point or a focal line  F  of the arrangement consisting of the concentrator and the secondary concentrator;   defining a curve, and thus the sought shape of the reflective surface which goes through the obtained number of points  SM (φ); and   transferring the curve obtained using the above steps onto the secondary concentrator to form its reflective surface.   
     
     
         11 . The method as claimed in  claim 10 , wherein the factor k is defined by an equalization of scalar products
       s ′· t   (φ)=   s ″· t   (φ)
   wherein t(φ) is a tangent which is placed on the secondary concentrator at the point  SM (φ).   
     
     
         12 . The method as claimed in  claim 11 , wherein the equation
       s ′· t   (φ)=   s ″· t   (φ)
   
       is resolved according to dk/dφ, wherein the values of k are defined numerically from a resulting elliptical integral. 
     
     
         13 . The method as claimed in  claim 10 , wherein the incident solar rays are assumed to be parallel for simplification. 
     
     
         14 . The method as claimed in  claim 10 , wherein the concentrator is assumed to have an arcuate cross section. 
     
     
         15 . The method as claimed in  claim 10 , wherein an origin of the co-ordinate system is assumed to lie in a center point of curvature of the concentrator. 
     
     
         16 . The method as claimed in  claim 10 , wherein the curve is defined by means of the method of least squares by means of the points  SM (φ) obtained. 
     
     
         17 . The method as claimed in  claim 10 , wherein the curve is transferred to a foam block and the produced curved surface is covered with a reflective foil. 
     
     
         18 . (canceled) 
     
     
         19 . A trough collector for a solar power plant comprising the following steps for defining a shape of a reflective surface of a secondary concentrator:
 taking at least one cross-sectional plane of the secondary concentrator, wherein the following is carried out therein:   defining a unit vector s(φ) of an incident solar ray;   defining the unit vector s′(φ) of the solar ray reflected on the concentrator;   taking the unit vector s″(φ) of the solar ray reflected on the secondary concentrator;   defining a number of points SM(φ) on the secondary concentrator by means of a vector PM(φ), wherein the vector PM(φ) lies on the concentrator, and where SM(φ)=PM(φ)+k·s′(φ);   defining a factor k in such a manner that s″(φ) goes through a predefined focal point or a focal line F of the arrangement consisting of the concentrator and the secondary concentrator;   defining a curve, and thus the sought shape of the reflective surface which goes through the obtained number of points SM(φ); and   transferring the curve obtained using the above steps onto the secondary concentrator to form its reflective surface.   
     
     
         20 . (canceled)