Linearly concentrating solar collector and method for reflector tracking in such a solar collector

Abstract

The basis for the function of a linearly concentrating solar collector lies, in simple terms, in the fact that reflectors reflect incident sunlight onto a receiver tube through which a heat-absorbing medium flows. Owing to the rotation of the Earth, the reflectors need to be adjusted regularly, however, in order to ensure that the sunlight hits the receiver tube. Known tracking methods use calculated positions of the sun for this purpose, which, in the case of structural deviations, for example as a result of expansion and material stress, results in inaccuracies and losses in efficiency. The invention is intended to improve the tracking of the reflectors in such a linearly concentrating solar collector. This is achieved by virtue of the fact that the radiation intensity in the region on both sides next to the receiver tube is measured and, by means of regulation, in the case of uneven emission on both sides of the receiver tube, the reflectors are tracked to such an extent that the radiation intensity on both sides of the receiver is the same and thus the maximum of the radiation intensity is on the receiver tube.

1 . Linearly concentrating solar collector comprising a receiver tube ( 21 ) mounted in an elevated manner for the absorption of thermal energy, and a plurality of reflectors ( 30 ), arranged on both sides of the receiver tube ( 21 ) and pivoted around their longitudinal axis, for the reflection of incident sunlight onto the receiver tube ( 21 ), wherein at least one sensor arrangement ( 10 ) for the recording of intensities of radiation is assigned to the receiver tube ( 21 ) on both sides, in each instance,
 wherein first sensors ( 11 ) of each sensor arrangement ( 10 ) are oriented in the same direction toward the reflectors ( 30 ) on a first side ( 43 ) of the receiver tube ( 21 ) and second sensors ( 12 ) of each sensor arrangement ( 10 ) are oriented in the same direction toward the reflectors ( 30 ) on a second side ( 44 ) of the receiver tube ( 21 ), wherein reflectors ( 30 ) of the first side ( 43 ) of the receiver ( 20 ) and reflectors ( 30 ) on the second side ( 44 ) of the receiver ( 20 ) are connected with one another, and orientation of the first and second sensors ( 11 ,  12 ) takes place exclusively, in each instance, with regard to a group of reflectors ( 30 ) coupled with one another in the transverse direction.   
     
     
         2 . Linearly concentrating solar collector according to  claim 1 , wherein at least one first sensor ( 11 ) and one second sensor ( 12 ) are arranged in a common housing, whereby the two sensors ( 11 ,  12 ) receive light falling through openings in opposite surfaces ( 14 ) of the housing, or project outward through these openings. 
     
     
         3 . Linearly concentrating solar collector according to  claim 2 , wherein the opposite surfaces ( 14 ) form an acute angle with one another. 
     
     
         4 . Linearly concentrating solar collector according to  claim 2 , wherein at least one light-repellent shield ( 13 ) to repel dispersed radiation is arranged around each opening. 
     
     
         5 . Linearly concentrating solar collector according to  claim 1 , wherein the receiver tube ( 21 ) is surrounded by a receiver cover ( 22 ) at whose longitudinal edges at least one sensor arrangement ( 10 ) is disposed on each of both sides. 
     
     
         6 . Linearly concentrating solar collector according to  claim 1 , wherein on both sides of the receiver tube ( 21 ), several reflectors ( 30 ) mounted parallel to it on a support frame ( 40 ) are coupled by at least one connecting rod ( 32 ), which can be displaced relative to a fixed bearing ( 34 ) by means of a servomotor ( 35 ). 
     
     
         7 . Linearly concentrating solar collector according to  claim 6 , wherein the pivoted reflectors ( 30 ) each have at least one swiveling lever ( 31 ), and the free ends of these swiveling levers ( 31 ) are connected to the at least one connecting rod ( 32 ). 
     
     
         8 . Linearly concentrating solar collector according to  claim 7 , wherein the fixed bearing ( 34 ) is connected to or identical to a receiver mast ( 41 ) bearing the receiver tube ( 21 ), and the servomotor ( 35 ) operates a preferably telescoping adjusting element ( 33 ) mounted between the connecting rod ( 32 ) and the fixed bearing ( 34 ). 
     
     
         9 . Linearly concentrating solar collector according to  claim 7 , wherein a connecting rod ( 32 ) moves only reflectors ( 30 ) on one side of the receiver tube ( 21 ), in each instance, or reflectors ( 30 ) on both sides of the receiver tube ( 21 ). 
     
     
         10 . Linearly concentrating solar collector according to  claim 1 , wherein the reflectors ( 30 ) have clinometers assigned to them, for recording the angle of inclination of the reflectors ( 30 ). 
     
     
         11 . Linearly concentrating solar collector according to  claim 1 , wherein the sensors ( 11 ,  12 ) are photovoltaic cells, temperature sensors or photo-detectors. 
     
     
         12 . Method for reflector tracking in a linearly concentrating solar collector, in which method a receiver tube ( 21 ) mounted in an elevated manner for the absorption of thermal energy and a plurality of reflectors ( 30 ), arranged on both sides of the receiver tube ( 21 ) and pivoted around their longitudinal axis, for the reflection of incident sunlight onto the receiver tube ( 21 ), are provided, wherein intensities of radiation are recorded by means of at least two sensor arrangements ( 10 ) disposed on both sides of the receiver tube ( 21 ), wherein first sensors ( 11 ) of each sensor arrangement ( 10 ) are oriented in the same direction toward the reflectors ( 30 ) on a first side ( 43 ) of the receiver tube ( 21 ) and second sensors ( 12 ) of each sensor arrangement ( 10 ) are oriented in the same direction toward the reflectors ( 30 ) on a second side ( 44 ) of the receiver tube ( 21 ), and wherein in the case of a difference from a predetermined relationship between the intensities of radiation of the first sensors ( 11 ) or between the intensities of radiation of the second sensors ( 12 ), the reflector groups ( 30 ) are automatically panned, together or separately, in such a way that the relationship of the intensities of radiation recorded on both sides of the receiver tube ( 21 ) by the first sensors ( 11 ) or the second sensors ( 12 ) approaches the predetermined relationship, wherein because of mechanical coupling, reflectors ( 30 ) of the first side ( 43 ) of the receiver ( 20 ), in each instance, and reflectors ( 30 ) on the second side ( 44 ) of the receiver ( 20 ) are connected with one another, and orientation of the first and second sensors ( 11 ,  12 ) takes place exclusively, in each instance, with regard to a group of reflectors ( 30 ) coupled with one another in the transverse direction. 
     
     
         13 . Method according to  claim 12 , wherein panning of the reflectors ( 30 ) is effected on the basis of the output signal of a regulator whose input signal is the difference between the measured intensities of radiation of the first sensors ( 11 ) or between the measured intensities of radiation of the second sensors ( 12 ), and which regulates this difference from the predetermined relationship to zero.