DE102006058995A1 - Fresnel solar collector arrangement has primary mirror, where adjustment of primary mirror is done automatically on basis of normal and actual value comparison and inclination of primary mirror is determined by inclination sensor - Google Patents

Abstract

The Fresnel solar collector arrangement has a primary mirror (6,6'). The adjustment of the primary mirror is done automatically on the basis of a normal and actual value comparison. The inclination of the primary mirror is determined by an inclination sensor and the calculated value of a control circuit is applied as actual value. Multiple inclination sensors and multiple linear drives are connected by a bus with an automatic controller.

Description

The invention relates to a Fresnel solar collector arrangement according to the European patent EP 06002605 ,

this includes One understands a line-focusing system in which several, parallel arranged to a receiver mirror strips of the sun position tracked be and the solar radiation on a fixed absorber tube is steered, in which a heat storing medium flows. Additionally distracts a secondary reflector, which is associated with the absorber tube, the radiation to the substantially from the absorber tube formed focal line. The absorber tube and the secondary reflector make the raised above the Mirror strips arranged receiver. Such a Fresnel solar collector is currently in field trials in Australia, for example. The heat generated can be used as process heat be or z. B. converted by means of a Stirling engine into electricity become.

The advantage of the Fresnel solar collectors over the usual parabolic trough collectors lies in their clearly simplified design. Parabolic trough collectors consist of a reflector, which has the shape of a parabolic cylinder. The light is also focused here on a line, the focal line. In this line is the absorber tube of the parabolic trough collector, which absorbs the concentrated radiation and releases it to the medium flowing through. The medium is typically heated to values of about 400 ° C. To improve the efficiency of the absorber may be surrounded with a glass tube. In the space between the absorber and glass tube there is a vacuum for insulation. The _" solar steam" produced in this way can also be used directly for process heat applications or for conventional steam and combined cycle power plants.

alternative are flat collectors and CPC collectors as additional collector types known.

Of the The efficiency of the Fresnel solar collector depends essentially on this how good the reflected solar radiation on the absorber tube is focused. For this purpose, it is useful to the absorber tube assigned primary mirror track the sun. Only so can acceptable efficiencies of the system can be achieved. This usually happens by means of an associated with each primary mirror The electric motor. The electric motors are usually in turn with a Timing provided, so the tracking so rather a control as a rule.

One The main problem of Fresnel solar collectors is that that such arrangements have the best efficiencies in areas of maximum solar radiation, So in desert areas, achieve in which extreme temperature fluctuations of minus degrees to plus degrees from far above 40 ° C at least not uncommon are. The materials and support structures used are considerable Exposed to stress, with thermal deformations of the material almost are inevitable and therefore to angular deviations in the overall arrangement to lead can, the efficiency of the entire plant in the double-digit percentage range can knock down. An already small angular deviation in the support structure of the mirror assembly can lead to, that much that of the primary mirrors reflected radiation is not focused on the absorber tube, but simply be reflected past the absorber tube. Furthermore is the individual control or regulation and coordination the various electric motors for tracking or controlling the pivoting the mirror accompanied by a considerable regulatory or control effort, the the plant reasonably become susceptible to failure leaves.

to solution this problem strikes the prior art, the mirror structure in the receivables area and / or in connection with the receivables infrastructure stationary and otherwise sliding, thus constrained, to store. This ensures that the mirror frame in the case of a due to the heat unavoidable thermal Expansion of the structure compensates for the corresponding changes.

This is even better achieved if the receiver support structure and the mirror support structure are essentially made of the same material and are essentially stationarily supported in the same place. In the case of thermal material expansion or material shrinkage, it can at least approximately be assumed that the mutual expansions of the structures take place to the same extent. For example, as a result of the action of heat, the receiver mast is stretched approximately as well as, for example, the mounting rails of the primary mirrors arranged as a mirror support structure. Due to the mutually at least substantially orthogonal arrangement of Receivertragwerk and mirror structure to each other and the same expansion coefficient resulting from the same material used is again ensured that the angular relationships do not change or at most slightly. However, this is only possible if both the Receivertragwerk, and the mirror structure are mounted without jamming, so only one of at least two necessary supports is stationary. This amazingly simple solution saves you the trouble of expanding or shrinking material or to make the largely hopeless attempt to use materials that are more or less temperature-independent. The use of such materials is usually eliminated for reasons of cost.

In a concrete embodiment, the receiver of the Fresnel solar collector arrangement can be mounted as an absorber tube on a number of receiver masts, wherein at the same place, optionally using the same concrete base, and the mirror frame can be stored stationary. Receivermast and mirror structure are hereby advantageously made of steel 37 manufactured and thus have largely the same expansion coefficient.

In Advantageous development are some of the on the mirror structure superimposed primary mirror to a primary mirror group summarized, in turn, by means of a common, mechanical Actuator for Nachfüh tion mechanically coupled and so the sun are tracked. Due to the use of a common actuator eliminates the cumbersome Tuning, complicated control and regulation of the electromotive used among themselves at least within the affected primary mirror group. Rather, by means of a common actuator, the primary mirror group be adjusted in total, the relative angle of the primary mirror is always maintained among each other. That, in turn, is in itself trivial knowledge of the set of rays underlying that in the course the tracking required relative to the sun relative angle adjustment of the primary mirror, the opposite spaced and elevated arranged Absorber tube in an imaginary orthogonal line to the absorber tube are arranged one behind the other, is the same relative to each other. This would, by the way also for arranged on an imaginary parallel line to the absorber tube primary mirror be valid.

The explained above execution the collector assembly with a mechanical coupling to the common Pivoting of the primary mirror By means of a common actuator is also independent of the constraint-free Storage of the mirror structure advantageous.

These Joint pivoting is achieved by connecting the primary mirror a primary mirror group by means of a tracking shaft reached. By the movement of the push rod in the alignment the primary mirror becomes a rotation of the tracking shaft which transmits through the compound evenly to the entire primary mirror group becomes.

With Advantage is the tracking shaft at regular intervals in roller blocks stored, which encircle the shaft, but they only using store rolling elements. These rolling elements allow an axial Rotation of the tracking shaft and are formed in their shape barrel-like, so are essentially cylindrical, with their lateral surfaces bulging are bulging. This shape allows the tracking shaft not only along flat surfaces to arrange, but also to guide over height changes if necessary. The Wave can be made obliquely on the rolling elements, so that a simultaneous oblique Employment of the roller block can be omitted.

In concrete embodiment, the mechanical coupling of a Group of combined primary levels be realized by means of a common push rod, over which the pivotally mounted on the mirror frame primary mirror relative to the absorber tube as a function of Swung the sun or the time of the sun or better said followed by the sun become.

In Advantageous embodiment is the push rod with a linear motor driven by electric motor, wherein by means of the linear motor, the orthogonal to the longitudinal extent of the absorber tube, depending on the position of the sun, or disengaged becomes.

In advantageous embodiment flows while in the absorber tube, a steam or a thermal oil through heated the reflected radiation to a temperature of up to about 400 ° C. becomes. The thus heated heat medium can then be supplied in a conventional manner further use or used for power generation.

Around despite the improved angular accuracy of the arrangement and the efficiency To further improve the arrangement, the absorber tube is also a secondary reflector assigned, which engages over the absorber tube substantially umbrella-like and so any stray radiation of the primary mirror fields and so deflected that even this scattered radiation on the absorber tube is focused.

Of the secondary reflector is therefore also arranged so that the absorber tube substantially in the focal line of the secondary reflector lies.

In a further refinement of the electromotive drive, the linear motor is also essentially arranged centrally, that is to say approximately in the region of the imaginary line which is formed by the receiver masts arranged in a row. In this case, when using a corresponding deflection with one and the same linear motor both one or more driven by one or more push rods primary mirror groups left of Absor berrohrs, as well as one or more driven by one or more push rods primary mirror groups are driven to the right of the absorber tube such that a timed or the sun's position tracked controlled pivoting of the primary mirror is relative to the absorber tube.

The necessarily counter-rotating Movement of the primary mirror right of the absorber tube compared to the primary mirrors To the left of the absorber tube is through one of only two sides associated deflection of the linear movement of the push rod realized.

In advantageous embodiment can the linear motors with a common control and / or regulation be connected, as to be carried out by the push rods Relative movements over the entire length of the absorber tube are exactly identical and thus a common Regulation for the entire facility possible is.

However, after this, from the EP 06002605 Previously known, solution a control circuit produced by the fact that the actual value of the inclination of the primary mirror in turn can be determined from the position of the push rod. This is still an inaccuracy.

In front The background of this prior art is thus the invention the object of the invention to provide a Receivertragwerk, which Improves the accuracy of the actual value determination.

This succeeds by a Fresnet solar collector arrangement according to the features of claim 1. Further embodiments of these arrangements, the dependent claims be removed.

According to the invention is a every primary mirror or at least one of each primary mirror group associated with a tilt sensor, which is a determination of the inclination the primary mirror against the vertical. The inclinometer or sensors provide an exact actual value of the Tilt, which conveys to the regulator and is available as an actual value. It can be omitted, the Actual value of the inclination to determine from the position of the push rods. A closed loop is thus realized.

One such tilt sensor can be electronically such as by means of a mercury chamber be realized whose wall is designed as a resistance path. Depending on the position of the inclination sensor is contained by the in the chamber Mercury applied to a part of the resistance path in a characteristic manner. As a result of this imposition of resistance can on the location of mercury and thus on the inclination of the tilt sensor deduced become. This ensures a electronic signal, which directly into a position value for detection the inclination can be implemented.

In meaningful development is the controller with a plurality of Linear drives or a plurality of tilt sensors via a shared bus.

The Invention will be described below with reference to a in the drawing only schematically illustrated embodiment explained in more detail.

It demonstrate:

1 : a Fresnel solar collector arrangement in cross section,

2 : a detail of the Fresnel solar collector arrangement in a schematic diagram,

3 : a regulatory picture to that in the 1 and 2 shown Fresnel solar collector arrangements,

4 : a roller block for supporting a push rod in a perspective view,

5 : the in 4 shown roller block in a side plan view,

6 : a schematic diagram of a control arrangement for controlling the tracking by means of a tilt sensor, and

7 : a control loop, which the in 6 used controller shows.

As shown in 1 the Fresnel solar collector arrangement consists of a receiver 1 standing on a receiver mast 2 is elevated. The receiver mast 2 is this in a fixed camp 3 at the same time the central axis of an angular symmetrically arranged mirror structure 4 represents. This is the mirror structure 4 essentially from carrier rails 5 made of the same material as the receiver mast 2 , namely steel in the present embodiment 37 , are made and each orthogonal to the longitudinal axis of the receiver 1 forterstrecken. There is the receiver 1 essentially from an absorber tube, in which a heat medium acting as a heat storage medium flows. This can be simple steam or thermal oil. The absorber tube is usually overlapped by a secondary reflector, the eventual Streustrah catching the mirror assembly and deflects it onto the absorber tube. On the support structure are on both sides, that is essentially mirror-symmetrical to the raised receiver 1 arranged, mirror tracks, the primary mirror 6 . 6 ' , pivoted. The mirror tracks are on the mirror frame 4 essentially stored so that the solar radiation acting on the Fresnel solar collector arrangement is reflected and deflected so that they are in the range of the receiver 1 , is focused on the absorber tube. The absorber tube ideally forms the focal line on the mirror frame 4 superimposed primary mirror 6 . 6 ' , There are each receiver 1 several primary mirrors 6 . 6 ' with different spacing, ie in increasing orthogonal distance from the central axis of the mirror structure defined by the absorber tube 4 ,

The mirror structure 4 itself is in turn opposite the floor with foot elements 7 elevated, with these being orthogonal to the longitudinal extent of the receiver 1 firmly extending carrier rails 5 only connected by plain bearings. Specifically, therefore, are the receiver mast 2 as well as the carrier rails 5 in the longitudinal extension of the receiver 1 are arranged one behind the other, only in the stationary fixed bearing 3 fixed and otherwise slip-free sliding. After both the receiver mast 2 as well as the carrier rails 5 from steel 37 are manufactured and thus have a substantially identical coefficient of expansion, also corresponds to a possible thermal expansion of the two structures essentially each other. The length extension of the receiver mast 2 is thus compensated essentially by the fact that by a similar extent of the support rail 5 a possible angular error of the arrangement with the possible consequence that the absorber tube moves from the focal line of the mirror assembly, is compensated.

The Fresnel solar collector arrangement according to 1 is thus substantially self-regulating temperature compensated by any material strains and material shrinkage due to the quite common in the field of applications of Fresnel solar collector arrays extreme temperature fluctuations compensate each other. As a result, the scattering losses of the reflected radiation, which have a very negative effect on the yield factor of the system, at least largely avoided. Elaborate techniques to compensate for the temperature-induced change in length of the materials used can therefore be largely eliminated.

According to 2 the arrangement is advantageously supplemented so that the individual carrier rails 5 associated primary mirror 6 . 6 ' each by means of a mirror carrier 8th . 8th' pivotable with the respective support rail 5 are connected. It is known from the prior art, each primary mirror 6 . 6 ' Assign a separate electric motor and with the help of this electric motor drive tracking the primary mirror 6 . 6 ' depending on the position of the sun relative to the receiver 1 to reach. According to 2 are several primary levels 6 . 6 ' to a primary mirror group, which is characterized by a common actuator, namely a push rod 10 . 10 ' mechanically coupled to each other. The push rod 10 . 10 ' is with a linear drive 11 linearly displaceable electromotive driven, the movement of the push rods 10 . 10 ' left and right of the receiver mast 2 and thus the receiver 1 are in opposite directions by means of a deflection not shown here. The push rods 10 . 10 ' left and right of the receiver 1 So either both are indented or both are disengaged. By this is meant that one of the two push rods 10 or 10 ' only indirectly at the primary levels 6 . 6 ' , namely acts on a deflection, which leads to the mentioned opposite movement. This, in turn, causes the mirrors arranged on the right and left to be turned in or out at exactly the same angle ratio as the centrally arranged reflector or absorber tube. The according to 2 The solution shown thus makes it possible, by means of a single electric motor, above by means of a linear drive 11 , a mechanical coupling via a simple push rod 10 . 10 ' to create and thus a complicated coordination of several individual electric motors with each other at least along a carrier rail 5 , ie within a primary mirror group, save and instead by the mechanical rigid coupling and due to the angular accuracy of the arrangement an exact tracking to the state of the sun with a single common linear drive 11 to enable.

It may be in accordance with the schematic representation in 3 to act a controller and / or regulation. As shown in 3 is the linear motors 11 . 11 ' . 11 '' , each one or more push rods 10 . 10 ' or carrier rails 5 are assigned, a common controller 12 assigned. This controller 12 can in the simplest case in the sense of a control time-controlled according to a predefined program, the at any time the specific position of the sun and thus a certain angular position of the primary mirror 6 . 6 ' be assigned, controlled. This is the controller 12 with a time recording device 14 data-connected. Alternatively, however, the controller 12 also with a real actual / nominal value comparison 13 be interconnected, comparing the actual and setpoint comparison either between the real position of the sun and setpoint specification or directly the efficiency of the system, for example by evaluating the achieved Radiation intensity or the current output is fed back as the actual value to the controlled variable, to determine a possible control deviation. About the actuator can then the angular position of the primary mirror 6 . 6 ' be readjusted. The push rod 10 . 10 ' Thus, if the understanding is correct, it also represents, more or less, the actuator for regulating or tracking the primary mirror arrangement, with the linear drive still being connected to this actuator 11 . 11 ' . 11 '' is proper. The control or regulation of the linear drives 11 . 11 ' . 11 '' is via a common regulator 12 realized.

The 4 and 5 show a roller block 15 in which a tracking shaft 17 is guided. The tracking shaft 17 connects the primary mirror 6 . 6 ' a primary mirror group and ensures a parallel rotation of all mirrors of this group as a result of a movement of a push rod 10 . 10 ' initiated tracking. The roller block 15 surrounds the tracking shaft 17 , wherein the shaft in the roller block 15 on rolling elements 16 . 16 ' . 16 '' is stored. These rolling elements 16 . 16 ' . 16 '' are substantially cylindrical, but have concave lateral surfaces on which the Nachführwelle 17 supported. The barrel-shaped design makes it possible, as in 5 shown, the tracking shaft 17 inclined to make, with the roller block 15 remains in its vertical position. This allows a laying of the tracking shaft 17 along sloping surfaces, such as on hills or on uneven terrain. It must of course be ensured that a concealment of the receiver 1 opposite the affected primary mirrors 6 . 6 ' is avoided.

6 shows a schematic diagram in which the controller 12 over a bus 19 , such as a CAN bus, with linear drives 11 . 11 ' as actuators and tilt sensors 18 . 18 ' is connected as an actual value transmitter. The inclination sensors detect the inclination of the primary mirrors connected to them 6 . 6 ' and thus give the control the actual value. In the event of a deviation between the actual value and the setpoint value ascertained as described above, the controller provides 12 a control signal to the linear drives 11 . 11 ' output, which causes a correction of the mirror tilt.

In principle, according to 7 that of the inclination sensors 18 . 18 ' exactly determined actual value of the mirror inclination compared with the target value and the difference value Δφ to the linear drive 11 . 11 ' forwarded. This takes place until the difference Δφ is equal to zero.

In the foregoing, therefore, a Fresnel solar collector arrangement is described that is largely temperature compensated by the fact that for the carrier rails 5 of the mirror structure 4 and the receiver masts 2 Materials with the same thermal expansion coefficients are used and also the receiver mast 2 , as well as the mirror structure 4 is stored without constraint. In addition, the tracking of the primary mirror 6 . 6 ' according to the position of the sun by a mechanical coupling of the primary mirror 6 . 6 ' considerably simplified.

1

receiver

2

receiver mast

3

fixed bearing

4

Mirror structure

5

support rail

6 6 '

primary mirror

7

foot elements

8th, 8th'

mirror support

10 10 '

pushrod

11 11 ', 11' '

linear motor

12

regulator

13

PV / SV Comparison

14

Time recording device

15

Rollenbock

16 16 '

rolling elements

17

tracking shaft

18 18 '

tilt sensor

19

bus

Claims (6)

Fresnel solar collector arrangement according to the European patent EP 06002605 , characterized in that a tracking of the primary mirror ( 6 . 6 ' ) is realized automatically on the basis of a desired-actual value comparison, wherein the inclination of the primary mirror ( 6 . 6 ' ) using at least one inclination sensor ( 18 . 18 ' ) can be detected and the determined value can be supplied to the control loop as an actual value. Fresnel solar collector arrangement according to claim 1, characterized in that a plurality of inclination sensors ( 18 . 18 ' ) as well as several linear drives ( 11 . 11 ' . 11 '' ) via a bus ( 19 ) with at least one controller ( 12 ) are connected. Fresnel solar collector arrangement according to claim 2, characterized in that each primary mirror group at least one inclination sensor ( 18 . 18 ' ) assigned. Fresnel solar collector arrangement according to one of the preceding claims, characterized in that the inclination sensor ( 18 . 18 ' ) has a chamber which, preferably in the region of the inner wall, provided with at least one resistance path and only partially with a conductive liquid, such as mercury, is filled. Fresnel solar collector arrangement according to Claim 4, characterized in that on the basis of the position of the conductive liquid in the chamber, a resistance value uniquely assignable to a tilt position can be measured. Fresnel solar collector arrangement according to claim 5, characterized in that the resistance value as an output signal is applied to the tilt sensor.