MX2008002410A - Fresnel solar collector arrangement - Google Patents

Abstract

The invention relates to a Fresnel solar collector arrangement consisting essentially of a receiver (1) and a mirror arrangement associated with the receiver (1). Said arrangement is temperature-compensated by the use of materials with the same temperature expansion coefficient for the receiver mast (2) and the mirror supporting framework (4), and the adjustment of the primary mirror (6, 6') in relation to the sun by a mechanical coupling of the mirror is simplified by means of an electromotive connecting rod.

Description

ARRANGEMENT OF SOLAR COLLECTOR FRESNEL DESCRIPTION OF THE INVENTION The invention relates to a Fresnel solar collector arrangement. By this is meant a line focusing system in which several specular bands arranged parallel to a receiver follow the solar position and deflect the solar radiation over a fixed absorption tube in which a means of heat accumulation flows. Additionally, a secondary reflector associated with the absorption tube guides the radiation to the focal line formed substantially by the absorption tube. The absorption tube and the secondary reflector constitute the receiver that is arranged high with respect to the specular bands. A Fresnel solar collector is currently in operation, for example, in Australia for research in the field. The heat produced can be used as process heat or can be converted into electric current, for example, by means of a Stirling engine. The advantage of the Fresnel solar collectors compared to the usual parabolic trough collectors lies in their remarkably simplified structure. The parabolic duct collectors consist of a reflector that has the shape of a parabolic cylinder. Also in this case the light is focused on a line, the focal line. In this line is the absorption tube of the parabolic duct collector, which absorbs the concentrated radiation and transmits it to the circulating medium. The medium is typically heated to values of about 400 ° C. To improve the degree of effectiveness the absorption tube can be surrounded by a glass tube. In the intermediate space between the absorption tube and the glass tube there is a vacuum for insulation. The "solar vapor" produced in this way can also be used directly for process heat applications, or for conventional, steam and combined power plants. Alternatively, flat collectors and CPC collectors are known as additional types of collectors. The degree of effectiveness of the Fresnel solar collector depends substantially on how well the reflected solar radiation is focused on the absorption tube. For this purpose it is reasonable to follow the sun with the primary mirrors associated with the absorption tube. Only in this way is it possible to obtain acceptable degrees of effectiveness of the installation. Usually this occurs through an electric motor associated with each of the primary mirrors. Electric motors are usually provided with a time control, so that monitoring is more of a control than a regulation. An essential problem of the Fresnel solar collectors is that these arrangements obtain the best degrees of effectiveness in areas of greater solar radiation, that is, for example, in desert areas where extreme variations in temperature are not unusual in any case , much higher than 40 ° C, from degrees below zero to degrees above zero. The materials and support structures that are used are exposed to considerable stress, being that thermal deformations of the material are almost inevitable and that consequently they can cause angular deviations of the total arrangement that can be reflected in a two-digit percentage range as far as possible. regarding the degree of total effectiveness of the installation. Already a small angular deviation in the support structure of the mirror array can cause a large part of the radiation reflected by the primary mirrors not to focus on the absorption tube but the reflection simply passes long to the absorption tube. In addition, the control or also regulation and individual adjustment of the various electric motors for the monitoring and control of rotation of the mirrors has combined a considerable expenditure of regulation and control that causes the installation to be quite prone to failures. From this state of the artThe object of the invention is to design the most robust installation in its entirety and thereby improve its degree of effectiveness as far as possible. The solution of this problem is possible by means of a Fresnel solar collector arrangement in accordance with the main claim. Favorable embodiments can be derived from the subordinate claims 2 to 11. By virtue of the fact that in accordance with the main claim, the mirror support frame is stationary mounted in the region of the support frame of the receiver and / or connected to the support frame of the receiver, and is otherwise mounted slidable, thus free of compression, it is ensured that the mirror support frame compensates for the corresponding variations in the case of an inevitable thermal expansion of the support frame by virtue of the effects of heat. This is most successful if the receiver support frame and the mirror support frame are made essentially of the same material and mounted stationary substantially in the same place. In the case of thermal expansions of the material or of vibrations it can be assumed at least approximately that the reciprocal expansions of the supporting frames take place to the same extent. For example, as a result of the effect of heat, the mast of the receiver expands approximately the same as, say, the support rails of the primary mirrors arranged as a support frame for the mirrors. By virtue of the mutual arrangement at least substantially orthogonal of the support frame of the receiver and the support frame of the mirrors and the coefficient of expansion as it results because the same material is used, it is again ensured that the angular relations do not undergo mutual changes or changes. in any case very mild. However, this is only possible if both the receiver support frame and the mirror support frame are assembled compression-free, ie, only one of the minimum of two necessary supports is stationary. This amazingly simple solution saves the complex subsequent regulation of expansions and contractions of material or carrying out the considerably useless attempt to use materials that are more or less independent of temperature. The use of this type of material most of the time is already eliminated for reasons of cost. In concrete configuration, the receiver of the Fresnel solar collector arrangement can be mounted as an absorption tube on a series of receiver masts, being that in the same place, optionally using the same concrete base, the support framework can also be stationary of the mirrors. The mast of the receiver and the support frame of the mirrors are advantageously made in each case of steel 37 and therefore have considerably the same coefficient of expansion. In favorable refinement, some of the primary mirrors mounted on the mirror support frame are brought together in a group of primary mirrors which, for mechanical tracking, are themselves coupled by means of a common mechanical adjustment element, and thus continue in Sun. By virtue of the use of a common adjustment element, the complex adjustment and the complicated control and mutual regulation of the used electric motorization are dispensed with, at least within the group of primary mirrors in question. Rather, it is possible, by means of a common adjusting element, to adjust the group of primary mirrors in their entirety, provided that the relative angular relationship of one to the other of the primary mirrors is always ensured. This in turn is based on the trivial knowledge of the optical theorem that the relative angular deviation that in the course of tracking the sun is required from the primary mirrors, which in front of the absorption tube arranged at a distance and high are arranged in successive form in an imaginary orthogonal line with respect to the absorption tube is relatively relative to each other. Otherwise, this would also be applicable for the primary mirrors grouped in an imaginary parallel line with respect to the absorption tube. The explanation given above of the arrangement of the manifold with a mechanical coupling for the common rotation of the primary mirrors by means of a common adjustment element is also favorable independently of the compression-free assembly of the mirror support frame. This common rotation is achieved through a connection of the primary mirrors of a group of primary mirrors by means of a tracking tree. Due to the movement of the connection bar when orienting the primary mirrors, a rotation of the tracking tree is effected which, through the connection, is transmitted uniformly to the entire group of primary mirrors. 'Conveniently, the tracking shaft is mounted at regular intervals on roller bearing stands, which surround the shaft but only mount it with the aid of rolling elements. These rolling elements allow an axial rotation of the tracking shaft and their configuration is barrel-shaped, ie they are substantially cylindrical, their casing surfaces being bulged. This shape makes it possible to arrange the tracking tree not only along flat surfaces but optionally also to guide it on height variations. The shaft can be placed inclined on the rolling elements so that it is possible to do without simultaneously placing the inclined roller carrier. In a specific embodiment, the mechanical coupling of the primary mirrors assembled in a group can be carried out by means of a common connecting rod by means of which the primary mirrors rotatably mounted on the mirror support frame are rotated or rather said to the sun in relation to the absorption tube depending on the position of the sun or the hour. In a favorable embodiment, the connecting rod is driven electrically motorized with a linear motor, being that by means of the linear motor the connecting rod which is arranged orthogonal to the longitudinal extension of the absorption tube is pressed inwards or outwards in function of the position of the sun. In a favorable embodiment, a water vapor or a thermal oil flows into the absorption tube, which is heated to a temperature of approximately 400 ° C by the reflected radiation. The thermal medium heated in this way can then be fed to the subsequent use in a known manner or be used for the generation of electric current. For however the best angular fidelity of the arrangement also improve the degree of effectiveness of the arrangement, the absorption tube is additionally associated with a secondary reflector that substantially overlaps the absorber tube in the manner of an umbrella, and in this way captures any scattered radiation of the primary mirrors and deflects it so that also this scattered radiation is focused on the absorption tube. That is, also the secondary reflector is arranged so that the absorption tube is substantially in the focal line of the secondary reflector. In another embodiment of the electrically motorized drive, the linear motor is also arranged substantially centrally, that is to say approximately in the area of the imaginary line formed by the receiver poles arranged in a row. With the use of a corresponding inverter it is possible to drive with one and the same linear motor one or several groups of primary mirrors driven by one or more connection bars to the left of the absorption tube as well as one or more groups of primary mirrors driven by means of one or several connection rods to the right of the absorption tube, so that a regulated rotation of the primary mirrors takes place in relation to the absorption tube by time control or by tracking the sun. The necessary opposite movement of the primary mirrors to the right of the absorption tube compared to the primary mirrors to the left of the absorption tube is carried out by means of an inverter of the linear movement of the connecting rod that is only associated with one of both sides . In a favorable embodiment, the linear motors can be connected with a common control and / or regulator, since the relative movements to be executed by the connecting rods are exactly identical over the entire length of the absorption tube and therefore a common regulation for the entire installation is possible. In the following, the invention is explained in more detail by means of an exemplary embodiment which is only schematically represented in the drawing. They show: Figure 1: a Fresnel solar collector arrangement in cross section, Figure 2: a detail of the Fresnel solar collector array in a beginning sketch, and Figure 3: a regulation diagram for the Fresnel solar collector arrays shown in the Figure 1 and 2. According to the representation of Figure 1, the Fresnel solar collector arrangement is constituted by a receiver 1 which is mounted on the tip of a receiver mast. The mast 2 of the receiver is housed for this in a fixed support 3, which simultaneously constitutes the central axis of a mirror support frame 4 which is arranged angularly symmetrical. The mirror support frame 4 consists essentially of support rails 5 which are made of the same material as the mast 2 of the receiver, in the present example of embodiment specifically of steel 37 and which in each case extend away orthogonally from the longitudinal axis of the receiver 1. The receiver 1 consists essentially of an absorption tube in which a thermal medium flows acting as a thermal accumulator. In this respect, it can simply be water vapor or a thermal oil. The absorption tube is usually overlapped by a secondary reflector that captures any scattered radiation from the cluster of mirrors and deflects it towards the absorption tube. The primary mirrors 6, 61 are mounted rotatable on the support structure on both sides thereof, that is, as mirror trains grouped substantially with mirror symmetry relative to the receiver 1 which is placed higher. The mirror trains are mounted on the mirror support frame 4 substantially so that the solar radiation incident on the Fresnel solar collector array is reflected and deflected so that it focuses on the absorption tube in the receiver region 1. The absorption tube ideally constitutes the focal line of the primary mirrors 6, 6 'mounted on the mirror support frame 4. In this aspect, several primary mirrors 6, 6 'are associated to each receiver 1 at a different distance, that is to say, at a progressively greater orthogonal distance from the central axis of the mirror support frame 4, defined by the absorption tube. The mirror support frame 4 itself is mounted separately from the floor, placing it on base elements 7, since these are only connected by means of bearings with the support rails 5 extending fixed orthogonal to the longitudinal extension of the receiver. 1. In other words, in particular the mast 2 of the receiver as well as the support rails 5, which in the longitudinal direction of the receiver 1 are disposed one after the other, are only fixed in the stationary fixed support 3 and otherwise slide-mounted free of compressions. Since both the receiver mast 2 and the support rails 5 are made of steel 37 and therefore have a substantially identical coefficient of expansion, any possible thermal expansion of both support frames also substantially corresponds to each other. That is, the longitudinal expansion of the receiver mast 2 is substantially compensated for by the fact that by means of a similar expansion of the support rail 5 a possible angular error of the array is compensated with the possible consequence that the absorption tube moves out of the focal line of the grouping of mirrors. Accordingly, the Fresnel solar collector array according to FIG. 1 substantially has an automatic temperature compensation by virtue of which the expansions and contractions of material due to the extreme temperature variations of any point usual in the regions of the territories of use compensate each other. By this, dispersion losses of reflected radiation are avoided at least considerably, which have a very negative effect on the performance factor of the installation. Therefore it is possible to omit considerably the complex techniques to compensate the variation of the length due to the temperature of the materials used. According to FIG. 2, the arrangement is favorably complemented so that the primary mirrors 6, 6 'associated with the individual support rails 5 are connected with the respective support rail 5 in a tilting manner by means of a mirror support 8, 8'. . It is known from the state of the art to dedicate to each mirror 6, 6 'a separate electric motor, and with the help of this electromotor drive to obtain a follow-up of the primary mirrors 6, 6' in relation to the receiver 1 as a function of the position of the sun. According to FIG. 2, several primary mirrors 6, 6 'are combined to form a group of primary mirrors characterized by being mechanically coupled to each other by means of a common adjustment element, specifically a connecting rod 10, 10'. The adjustment bar 10, 10 'is driven electrically motorized for linear movement with a linear drive 11, the movement of the connecting bars 10, 10' being opposite to the left and right of the receiver mast 2 and consequently of receiver 1 by means of an inversion element that is not represented mostly here. That is, the connecting bars 10 and 10 'which are to the left and right of the receiver 1 are both retracted or both are pushed outwards. By this it is understood that one of both connection bars 10 or 10 'only indirectly attacks the primary mirrors 6, 6', namely through an inversion element such as the one leading to the aforementioned opposite movement. This in turn has the effect that the mirrors that are grouped to the right and to the left retain an exactly equal angular relation with respect to the reflector or absorption tube centrally arranged when they are turned towards them or they turn towards the other side with about them. In other words, the solution shown according to FIG. 2 makes it possible to create a mechanical coupling by means of a simple connecting bar 10, 10 'with a single electric motor, presently by means of a linear drive, and consequently saving a complicated reciprocal adjustment of several individual electric motors, at least along the support rail 5, that is, within a group of primary mirrors, and instead through the rigid mechanical coupling and by virtue of the angular fidelity of the arrangement, allow an exact tracking of according to the position of the sun with a single common linear drive. According to the representation of the principle of Figure 3 it can be a control and / or regulation. According to the representation of FIG. 3, a regulator 12 common to the linear motors 11, 11 ', 11"is associated, to which one or more connection bars 10, 10' or respectively rails 5 are associated. of support. This regulator 12 can be controlled in the simplest case in the sense of a time control according to a predefined program that at all times associates the determined solar position and with it a certain angular position of the primary mirrors 6. For this purpose the regulator 12 has a data connection with a time recording device 14. However, alternatively, the regulator 12 can be connected to a real / theoretical value comparator 13, where the real and theoretical value either compares the actual position of the sun with the preset theoretical value or is fed back to the control value as actual value the degree of effectiveness of the installation, for example by evaluating the radiation intensity reached or the current current performance to determine a possible deviation of the regulation. By means of the adjustment element it is then possible to readjust the angular position of the mirrors 6, 6 'primary *. In other words, the connection bar 10, 10 'constitutes more or less the adjustment element in the case of a correct understanding for the regulation or monitoring of the grouping of primary mirrors, since the motor 11 also belongs to this adjustment element. 11 ', 11' 'electric. The control or regulation of the linear motors 11, 11 ', 11"is carried out by means of a common regulator 12. Figures 4 and 5 show a roller bearing stand 15 in which a tracking shaft 17 is guided. The tracking tree 17 connects the primary mirrors 6, 6 'of a group of primary mirrors and ensures a parallel rotation of all the mirrors of this group as a result of a follow-up initiated by the movement of a connecting rod 10, 10'. The roller carrier trestle 15 surrounds the tracking shaft 17, the shaft being mounted on the roller bearing stand 15 on rolling elements 16, 16 ', 16' '. These rolling elements 16, 16 ', 16' 'are essentially cylindrical, but nevertheless have concave shell surfaces on which the tracking shaft 17 rests. By means of the barrel-shaped formation, it is possible, as shown in FIG. 5, to place the inclined tracking shaft 17, where the roller-holder trestle 15 is kept in its perpendicular position. This allows a positioning of the tracking shaft 17 along inclined surfaces, "for example in hills or uneven terrain In this aspect it is naturally necessary to ensure that a covering of the receiver with respect to the primary mirrors 6, 6 'is avoided. Accordingly, a Fresnel solar collector arrangement considerably thermally compensated is disclosed herein in that for the support rails 5 of the mirror support frame 4 and the masts 2 of the receivers materials with the same expansion coefficients are used. In addition, the mast 2 of the receiver as well as the mirror support frame 4 is assembled without compression, and the tracking of the primary mirrors 6, 6 'is simplified substantially according to the position of the sun by means of a mechanical coupling of the 6, 6 'primary mirrors.

List of reference symbols 1 Receiver 2 Receiver mast 3 Fixed support 4 Mirror support frame 5 Support rail 6, 6 'Primary mirror 7 Base elements 10, 10' Connection bar 11 Linear motor 12 Controller 13 Comparison of actual value / Theoretical 14 Time recording device 15 Roller stand 6 '' Rolling elements Tracking tree

Claims (13)

1. CLAIMS 1. Fresnel solar collector arrangement with at least one receiver that is mounted on a higher receiver support frame in relation to several primary mirrors that are arranged on both sides of the receiver, tilting on a mirror support frame in a manner that the solar radiation reflected by the primary mirrors focuses at least substantially on the receiver and the primary mirrors follow the sun in each case, characterized in that the mirror support frame that extends to both sides from the support frame to the receiver it is mounted stationary in the area of the support frame of the receiver and / or connected to the support frame of the receiver and otherwise sliding, at least considerably free of compression.
2. 2. Fresnel solar collector arrangement according to claim 1, characterized in that the support frame of the receiver and the mirror support frame are made of a material having expansion coefficients * of material at least substantially identical, preferably in each case. steel case 37.
3. 3. Fresnel solar collector arrangement according to claim 1 or 2, characterized in that the receiver comprises an absorption tube that is mounted high by a series of receiver masts preferably arranged in an imaginary line, which substantially constitute the support frame of the receiver, and the mirror support frame comprises support rails spaced apart from each other which optionally are connected in the form of lattice by corresponding tie rods, these support rails extending away at least substantially orthogonal line of an imaginary line of the receiving masts They are arranged in a row, and these support rails are fixed stationary connected with the masts of the receivers or in the area of the base of the masts of the receivers and otherwise mounted sliding. .
4. Fresnel solar collector arrangement according to any of the preceding claims, characterized in that the primary mirrors which are grouped on a common support rail in an imaginary line parallel or perpendicular to the longitudinal extension of the absorption tube of the receiver, are grouped in a group of primary mirrors, being that the primary mirrors of the group of primary mirrors are mechanically coupled by a common adjustment element and follow the sun together.
5. 5. Fresnel solar collector arrangement according to claim 4, characterized in that the primary mirrors associated with one or more of the support rails arranged in imaginary extension relative to each other are combined to form a group of primary mirrors.
6. 6. Fresnel solar collector arrangement according to claim 5, characterized in that the primary mirrors of the group of primary mirrors are mounted on each swingarm on the support rail (s), since these primary mirrors are rigidly connected to one another by means of a connecting rod which is preferably driven by an electric motor and can swing together by a linear movement of the connecting rod in the direction of the longitudinal extension of the connecting rod to adjust its respective angle of incidence relative to the absorption tube of the receiver.
7. 7. Fresnel solar collector arrangement according to claim 6, characterized in that the primary mirrors of a group of primary mirrors are firmly connected to each other for common tilting by means of a tracking shaft that is rotatably disposed with respect to the rails of support, substantially parallel to the longitudinal extension of the absorption tube.
8. 8. Fresnel solar collector arrangement according to claim 7, characterized in that the tracking shaft is housed in a roller bearing stand that surrounds the shaft. Being that the tree is retained in the roller bearing stand by a crowd, preferably three barrel-shaped rolling elements so as to allow an axial rotation of the tracking shaft.
9. 9. Fresnel solar collector arrangement according to any of claims 5 to 8, characterized in that the connecting rod is motorized by means of a linear motor in the direction of its longitudinal extension.
10. 10. Fresnel solar collector arrangement according to any of claims 6 to 9, characterized in that the linear motor is preferably arranged in the region of the receiver mast and the linear motor drives one or more connection rods, being that for the purposes The primary mirrors grouped to the right of the receiver are moved in the opposite direction to the primary mirrors grouped to the left of the receiver, whereas the movement in the opposite direction is carried out by means of a corresponding inversion element that is provided on only one side of the receiver. receiver.
11. 11. Fresnel solar collector arrangement according to any of the preceding claims, characterized in that a thermal accumulation medium, preferably water vapor or thermal oil, flows into the absorption tube.
12. 12. Fresnel solar collector arrangement according to claim 10 or 11, characterized in that the receiver further comprises a secondary reflector associated with the absorption tube that substantially receives the scattered radiation reflected by the primary mirrors and deflects it on the absorption tube.
13. 13. Fresnel solar collector arrangement according to any of the preceding claims, characterized in that the dimensions and distances of the primary mirrors are calculated such that at least the primary mirrors mutually shadow each other considerably.