ES1264624U - SOLAR PLANT THAT INCLUDES A CENTRAL TOWER AND A FIELD OF HELIOSTATS, AND HELIOSTATE FOR USE IN SUCH SOLAR PLANT (Machine-translation by Google Translate, not legally binding) - Google Patents

Abstract

Solar plant comprising a central tower (48) and a set of heliostats (3), the central tower (48) being provided with a receiver (1) intended to receive solar radiation reflected by the heliostats (3) and equipped of an active part (10) of total height (Δ H) comprised between a lower height (H0) and a higher height (H1), the plant being solar characterized by: The heliostats (3) are arranged around the central tower forming radii (9) that start from the central point (2) of the base of the tower and define isochronous groups (11) in which: - the line of focus (LE10, LEn0) of the first heliostat of each isochronous grouping (11) runs from the center of said first heliostat to the lowest point of height (H0) of the receptor (1); - the focus line (LE11, LEn1) of the last heliostat of each isochronous grouping (11) runs from the center of said last heliostat to the highest point of height (H1); - the focus lines (LE10, LEn0) of the first heliostat and the focus lines of the last heliostat (LE11, LEn1) of each isochronous grouping (11) are parallel to each other; and - for each isochronous grouping the relationship is fulfilled: {IMAGE-01} where (R10) is the distance from the radius origin to the center of the first heliostat of the first isochronous grouping (11) of a predefined radius (9); (R11) is the distance from the radius origin to the center of the last heliostat of the first isochronous grouping (11) of said radius (9); (Rn0) is the distance from the origin of radii to the center of the first heliostat of the nth isochronous grouping (11) of said radius (9); (Rn1) is the distance from the radius origin to the center of the last heliostat of the nth isochronous grouping (11) of said radius (9). (Machine-translation by Google Translate, not legally binding)

Description

DESCRIPTION

SOLAR PLANT THAT INCLUDES A CENTRAL TOWER AND A FIELD OF

HELIOSTATS, AND HELIOSTAT FOR USE IN SUCH SOLAR PLANT

TECHNICAL SECTOR

The invention belongs to the technical field of solar thermal energy and is applicable, especially but not limited to, in thermal solar installations capable of reaching radiation concentrations with an intensity greater than the natural one, by a factor of 100 and higher.

TECHNICAL PROBLEM TO BE SOLVED and BACKGROUND OF THE INVENTION

The solar radiation that reaches our planet has a low intensity, being usually less than 1.4 kW per square meter facing the sun. Such energy input is very good for our life, and particularly for the meteorology of our environment, but it is too low to extract heat flows from it at a sufficient temperature to carry out industrial applications.

To be able to materialize these industrial applications, for example, with boiling water at 100 bar pressure and 311 ° C, the heat flow must be much higher than that obtainable from solar radiation that directly affects our planet, for example, of the order of 150 kW / m2. In view of this, a solution known in the state of the art consists in concentrating the original solar radiation using optical means, typically reflection.

If the concentration factor that is sought is much lower than 100, the optical means of reflection can be designed so that they concentrate the solar radiation in a single axis, as happens, for example, with parabolic trough concentrators; but if the required heat flux requires concentration factors above 100, it is necessary to use optical means that concentrate the solar radiation in two different axes, typically called the azimuth axis (or rotation in the horizontal plane of the place) and the elevation axis.

A public example of optical media capable of concentrating solar radiation in two different axes are the heliostats of the solar plant of the company "Gemasolar", located in Fuentes de Andalucía, Province of Seville (Spain) and of which it can be found information at https://es.wikipedia.org/wiki/Gemasolar; and more precisely at http://www.poweroilandgas.sener/es/proyecto/gemasolar.

Said Gemasolar solar plant is of the central tower type and comprises a set of reflective optical means, called heliostats, capable of tracking and concentrating the sun on two axes, which reflect sunlight and concentrate it on a central receiver installed in a tower.

Although some of Gemasolar's heliostats are arranged along a radius that emanates from the base of the tower, their surface area (120 m2) and the separation they must keep between them, do not allow to take advantage of certain geometric properties. Therefore, in the sector, there is a need to improve the arrangement of heliostats in the solar plant to optimize their ability to concentrate solar radiation.

The most common in central tower solar plants is to arrange the heliostats in circular tracks around the tower, forming a field of heliostats, as disclosed in the US patent application US201562200570 (or in the corresponding PCT application WQ2017024038).

One of the serious problems in this technology is losing focus to the sun throughout its diurnal and seasonal movement; which generally requires having a digitized procedure that starts from the position of the sun, either measured or given by astronomical tables, and comes to determine the value that the azimuthal and elevation angles, or zenith, must have in order to that the focus to the sun is correct. Hence, there are some documents, such as MX2013014689, that disclose methods to correct the drift experienced by heliostats in terms of their focusing results.

On the other hand, the larger the size of the heliostat, the cheaper its structure is usually per square meter of mirror. This tendency has, however, a limit, above which the heliostat is excessively large and the structural requirements necessary to withstand the action of gravity and the effects of the wind are remarkably expensive. Large heliostats can also present focusing problems, since the vibrations and oscillations that appear at their ends can lead to the appearance of very severe focus disturbances.

Small heliostats have the advantage of lower structural requirements, but have the drawback that to cover the surface of the solar plant intended for the reflective optical means it is necessary to build a large number of different heliostats. For example, at the Gemasolar plant, the specular surface of a heliostat is 120 m2, which roughly corresponds to 120 mirror tiles, each of which receives a small twist in mounting to center the focus.

One could think of 6 m2 heliostats, to alleviate structural stress, but that would mean 20 times more heliostats in number, which only compensates if a way is found to improve the overall focus of all reflected light, which is simpler to do. treat in small units, without making everything more expensive.

There is, therefore, the need to design a solar plant whose heliostat field has a configuration that reduces the need for focusing devices and that, in addition, the heliostats that form said field are cheap to assemble, easy to install on the ground and easy to install. simple focus orientation.

EXPLANATION OF THE INVENTION

A first object of the present invention refers to a solar plant comprising a central tower and a set of heliostats, the central tower being provided with a receiver intended to receive the solar radiation reflected by the heliostats and equipped with an active part of total height AH comprised between a lower height (H0) and a higher height (Hi), the solar plant being characterized by:

The heliostats are arranged around the central tower forming radii that start from the central point of the base of the tower and define isochronous groups in which:

- the line of focus of the first heliostat of each isochronous grouping runs from the center of said first heliostat to the lower height point of the receiver;

- the focus line of the last heliostat of each isochronous grouping runs from the center of said last heliostat to the highest point of height;

- the focus lines of the first heliostat and the focus lines of the last heliostat in each isochronous array are parallel to each other; Y

- for each isochronous grouping the relationship is fulfilled:

Ho_

River

where

(R10) is the distance from the radius origin to the center of the first heliostat of the first isochronous grouping of a predefined radius;

(R11) is the distance from the radius origin to the center of the last heliostat of the first isochronous grouping of said radius;

(Rn0) is the distance from the radius origin to the center of the first heliostat of the nth isochronous grouping of said radius; Y

(Rn1) is the distance from the radius origin to the center of the last heliostat of the nth isochronous grouping of said radius.

The solar plant object of the invention is a structure with two degrees of freedom, corresponding to the two turns that must be made to focus on the active part of the receiver, which is at the top of the central tower; and said active part is comprised between a height H0 and a higher height, H1; taking as 0 the origin of the three-dimensional reference system that is adopted to express the prescriptions of the invention.

The distribution of the heliostats around the central tower is done following selected radii for this purpose, and within all the heliostats installed following a determined radius, a plurality of them, consecutive, and having the same angle of angle, is called isochronous grouping. visual to the central receiver, said angle being the one formed by a horizontal line that goes from the central point of the heliostat, to the vertical axis of the central receiver; and another line, called the focus line, which goes from said central point of the heliostat, to a point on the vertical axis of the central receiver, at a height that corresponds to the so-called active zone of the receiver; both lines forming a vertical plane, which contains the vertical axis of the central receiver, and the central point of each and every one of the heliostats that are part of a given isochronous grouping; the focus lines of all its heliostats being parallel to each other, going the one of the heliostat closest to the tower, from the central point of its traverse to the point of the active part of the receiver at the height H0, and going that of the heliostat more far from the tower, from the center point of its traverse to the point of the active part of the receiver at height H1.

The focus of the heliostats of an isochronous grouping is determined for all at once, using the essential definition of the field and the central tower, which are fixed, and the position of the sun, which varies, and is characterized by its three directing cosines , cx, cy, and cz.

It has already been stated that in solar plants according to the present invention, the heliostats are deployed in a distribution along virtual radii that start from the central point of the base of the tower, in the upper part of which is the receiver, whose active part, where the reflected radiation is truly concentrated, it is at a height that goes from H0, which is its lower level, to Hi, which is its upper level, with AH being the height of the active part; grouping into groups, which we call isochronous groupings, the heliostats that are along the same virtual radius and have parallel lines of focus, which are those that go from the center of the heliostat, to a given point of a virtual vertical line, in the active part of the receiver, specifying that, for a certain isochronous grouping of radially arranged heliostats (which we will designate with the generic reference n), the first of said heliostats they have their line of focus (LEn0) from their center to the point height H0 and the last heliostat of the isochronous grouping has its line of focus (LEn1) from its center to the point of height H1; fulfilling that, if Rn0 is the distance from the origin of radii to the center of the first heliostat of said isochronous grouping, and Rn1 is the distance from the origin of radii to the center of the last heliostat of the isochronous grouping, the quotient H0 / Rn0 is equal H1 / Rn1; and both focus lines are parallel.

According to the nomenclature used, if the isochronous grouping selected is the first one (that is, it is the closest to the central tower along a certain radius), then n = 1; if the selected isochronous cluster is the second, then n = 2, if the selected isochronous cluster is the third, then n = 3, and so on.

In a preferred embodiment of the invention, the radio segment comprised between the first heliostat and the last heliostat of at least one isochronous grouping is divided into m equal parts, a different heliostat being housed at the end of each of said parts.

Thanks to this distribution of heliostats within the isochronous grouping, it is possible to accommodate m-1 intermediate heliostats, at the end of each part, and in all of them keep the ratio H / R constant, which is equivalent to all the focus lines of the heliostats of an isochronous grouping are parallel to each other. As well as the solar rays that affect the center of each heliostat, the planes generated by each focus line and the aforementioned solar ray are also parallel to each other; and the angle bisector of reflection, will be contained in said plane; and it will be the line that marks the normal to the heliostat position, which in principle we can associate with a flat virtual plate, whose center coincides with the central pivot of two-dimensional rotation, the normal to said plate coinciding with the aforementioned bisector.

To determine the unit vector or three-dimensional direction of the bisector, it is enough to calculate the azimuth angle and the elevation angle (or its complement, which is the zenith angle), for which the invention is expressed in a three-dimensional Cartesian system, in which It uses as the x plane, and the horizontal plane of the place, with the x axis pointing to the East; and the y-axis pointing North, and its normal being the z-axis, pointing to the local zenith.

The geography of the northern hemisphere is used in this description, in which the heliostat field is to the north of the receiver, whose active part faces north; and for most of the daytime solar path, the sun is further south than the vertical east-west plane. Only in summer, early in the morning or late in the afternoon, do you have the sun to the north of the vertical plane that contains the local parallel.

Preferably, in solar plants according to the present invention, the focus of the heliostats of an isochronous grouping is determined for all at once, using the essential definition of the field and the central tower, which are fixed, and the position of the sun, It varies, and is characterized by its three director cosines, cx, cy, and cz. It is interesting to determine, from them, the trace of the Sun in the plane y = 0, taking into account that the ray in question will hit the central point of the heliostat, which is located at the coordinates (x0, y0, 0). In turn, the point of the tower receiver where the radiation reflected from the central point of the reference heliostat has to hit is (0, 0, z0).

The sun will have a mark or trace in the horizontal plane, with the equation z = 0, which will coincide with the coordinates of the central point of the heliostat, x0 and y0.

It remains to determine the solar trace when crossing the vertical plane that contains the parallel, that is, y = 0; for which we need the directing cosines of sunlight as it reaches us. Take into account that the advancement of light along each axis is proportional to its directing cosine; and that the advance along the y-axis goes from y = 0 to y = y0.

Thus, we have that the elevation zs of the solar trace is

zs = i-cz / cy

and the value of the East West abscissa.

Xs = Xo i-cx / Cy

To determine the bisector (or more exactly its directing cosines) it is taken into account that it starts in the center of the heliostat, and goes to a trace in the y = 0 plane that is in the straight line segment that joins the focal point of the receiver with the solar trace, being the distances from the bisector trace to both points, proportional to the distances from each extreme point of the segment, to the central point of the heliostat. This is applicable to each coordinate separately.

The distance from the focal point to the center of the heliostat, which we call DB, is

DB = (xo2 yo2 zo2) 1/2

And the distance from the solar trace to the center of the heliostat, DC

DC = ((Xs - xo) 2 yo2 zs2) 1/2

The coordinates of the bisector trace in the y = 0 plane are, in addition to this (yb = 0),

zb = z ⁰ + (zs - z ⁰ ) - (DB / (DB + DC))

xb = xs- (DB / (DB + DC))

The distance from the center of the heliostat to the bisector trace, which we call LB, obeys

LB = ((xb - x0) 2 y02 zb2) 1/2

And the directing cosines are

Bx = (xb - x0) / LB

By = y0 / LB

Bz = zb / LB

And from them, the angles that have to be carried out for the focus are established. To do this, first define the reference position, position 0 of all heliostats, which is perfectly vertical, looking south. The azimuth is therefore 0o in that position, and the elevation is also 0o, since the normal to the mirror is a horizontal one.

The azimuth is considered negative when the rotation of the normal of the mirror points to the east, and positive in the opposite case.

Thus, in a preferred embodiment of the invention, in at least one isochronous grouping, the focusing azimuth (Az) and the elevation angle (Ae) of the heliostats that make up said isochronous grouping are determined by:

Az = arc tg ((X ⁰ - Xb) / y ⁰ ),

Y

Ae = arc tg (zb / ((Xb - X ^{0) 2} + y ⁰ 2) 1/2)

where

^x 0 is the abscissa (coordinate in the East-West direction) of the central point of the heliostat of the isochronous grouping being considered,

xb is the abscissa of the trace, in the virtual plane y = 0, of the bisector of the angle of reflection at the center of said heliostat,

y0 is the ordinate, in a North-South direction, of the central point of the heliostat of the isochronous grouping considered,

Y

zb is the elevation of the trace, in the virtual plane y = 0, of the bisector of the angle of reflection at the center of said heliostat.

The invention takes advantage of these trigonometric properties to incorporate the mechanisms with which to make the turns, azimuth and elevation, required at all times.

A second aspect of the present invention refers to a heliostat for use in a solar plant such as those described above. Said heliostat comprises:

- a central vertical rotating staff, inserted at its lower end in a cylindrical sheath driven into the ground, and ending at its upper end in a double fork open upward;

- a main cross member housed in the double fork open upwards, which is attached to a plurality of beams, on which mirror modules are fixed, the mirror modules being arranged on either side of the central plane of symmetry of the heliostat , where the vertical staff is located;

- Turning means arranged in the central area of the cross member, selected from a central wheel fixed to the central part of the cross member and a pair of arms perpendicular to and fixed to the cross member, said turning means being configured to rotate with the cross member when said crossbar rotates on the double fork; Y

- a horizontal platform integral with the central pole in its lower part, said horizontal platform being configured to rotate with the central pole and to rest in its peripheral part on a plurality of freely rotating wheels, whose axes of rotation are supported on a structure in fork fitted with a stem driven into the ground, or supported on a foundation piece, so that the upper edge of all the wheels is arranged at the same height.

In this particular embodiment of the invention, the center of the heliostat coincides with the center point of its crossbar.

The method of driving the turns of each heliostat can be, -preferably electrical or mechanical. In case the drive is electric (referred to as "electric mounting"), each heliostat is provided with at least one electric motor; Whereas in the event that the drive is mechanical (designated as “mechanical mounting”), all heliostats in an isochronous array are provided with an azimuth actuator (responsible for azimuth rotation) and a zenith actuator (responsible for allowing elevation or elevation rotation). zenith), being further provided mechanical transmission cables from each actuator to each heliostat of the isochronous array. In this embodiment of the invention, the azimuthal actuator is preferably located on the line of the radius of the isochronous array in a position closer to the central tower than the first heliostat of said isochronous array, and the zenith actuator is located in a position further away from the central tower than the last of the heliostats of said isochronous grouping.

In the mechanical assembly, there is an actuator that allows the azimuthal turns of the heliostats of an isochronous grouping and an actuator that allows the turns zeniths. Such actuators preferably operate either by controlled electric motor or by pressure in a hydraulic circuit.

Also, preferably in mechanical assembly:

- the azimuth actuator is connected to a right-hand drive cable, and a left-hand drive cable, which act antagonistically to each other; Y

- the zenithal actuator is connected to an agonist cable and an antagonist cable that act antagonistically to each other, each of said cables being attached to an arm perpendicular to the cross member (of the turning means); the agonist wire being configured to raise the normal of the mirror modules; and the opposing cable being attached to an elongation spring (or dynamometer) fixed to the rear of the platform being free end, so that the action of the spring is configured to bring the heliostat to a resting position, defense against meteors and against the production of undue reflections.

In this embodiment of the heliostat according to the present invention, if the agonist cable is left without tension, the action of the counter spring becomes dominant, and when the spring is fully contracted, the mirrors remain in the resting position, horizontal, looking down; and precisely the opposing cable is mounted by putting the mirrors in the rest position, and the spring without tension, and the cable is attached at one end to the spring, and at the other to the end of the opposing arm, in such a way that its successive segments remain straight, but without mechanical tension; and it will be the spring that comes into tension and lengthens, when it begins to pull the actuator cable, agonist; maintaining the tension in this cable until reaching, with the spring antagonism, the zenith rotation in said normal, which is necessary to make the normal coincide with the focus bisector.

Throughout the present description it is understood that the first heliostat of an isochronous grouping is the one that is closest to the central tower, while the last heliostat of an isochronous grouping is the one that is furthest from the central tower.

In the electrical assembly of the heliostat, a single electric motor can be used, which alternately, and by means of a clutch, jumps to attend the azimuth and zenith turns. Likewise, in another embodiment of the invention, the heliostat may comprise: - an azimuth electric motor anchored in the ground, provided with a drive pulley that moves jointly with a chain or belt, which in turn is integral in its rotation with a horizontal wheel fixed to the pillar or to the central rotating staff; Y

- a zenith electric motor, arranged at the rear of the platform and connected to the vertical wheel fixed to the central part of the crossbar, by means of a belt or chain.

EXPLANATION OF THE FIGURES

The figures, in general, are not to scale, since the relative sizes of the elements are very different; but they are representative of the invention and its principles of operation.

Figure 1 schematically shows the coordinate system that characterizes the reflection of a heliostat of a solar plant according to the present invention;

Figure 2 shows the fundamental triangle of reflection, in the plane created by the incident ray and that reflected in a heliostat of a solar plant according to the present invention;

Figure 3 shows the simplified profile of a solar plant according to the present invention, along one of its radii;

Figure 4 is a plan view showing in a schematic and simplified way (only in one sector), the radial distribution of heliostats in a solar plant according to the present invention;

Figure 5 is a partial schematic view along a radius of a solar plant according to the present invention, showing the separation that must exist between successive heliostats of the same isochronous grouping, to avoid blocking of the reflected radiation. A reference (not to scale) to the location of the central tower is included;

Figure 6 is a profile view of a first embodiment of a heliostat according to the present invention, with electrical mounting of two motors, one azimuthal and the other zenith;

Figure 7 is a plan view of the heliostat of Figure 6;

Figure 8 is a profile view of a second embodiment of a heliostat according to the present invention, in the rest position and with mechanical mounting;

Figure 9 is the heliostat of the previous figure, in the turn where the greatest elevation occurs, almost looking at the zenith;

Figure 10 corresponds to the heliostat of Figure 8, in a working position;

Figure 11 is a plan view of the heliostat of Figure 8, mechanically mounted;

Figure 12 shows a detail of the upper part of the central staff, where the main cross member of a heliostat according to any of claims 6 to 11 is seated.

To facilitate understanding of the figures of the invention, and its modes of implementation, the relevant elements thereof are listed below:

1. Central tower receiver;

2. Central point of the base of the central tower that is taken as the origin of the spatial coordinate system, (x, y, z);

3. Heliostat. The location of point (3) corresponds to the two-dimensional center of rotation of said heliostat, which in heliostats according to the present invention coincides with the center of the heliostat's cross-member (30);

4. Point that represents the trace of the Sun in the vertical plane that passes through the origin of coordinates (2) and is perpendicular to the local meridian, or North-South line, and corresponds to the equation y = 0. Said trace is the intersection of said plane y = 0 with the central solar ray incident, at a given moment, on the heliostat characterized by point 3;

5. Point that marks the intersection with the plane y = 0, of the bisector of the angle formed by the lines that go from point 3 to point 1, and from point 3 to point 4, with vertex at point 3, logically. Point 5 'is the projection of point 5 on the x-axis (8, 8' axis);

6. Z axis, vertical over point 2, and in which point 1 is located, at a generic height H (which is required for various cases);

7. Y coordinate axis, which goes in a South-North direction;

8. X axis, which marks the local tangent of the parallel at point 2, and goes from the West (referenced with 8 ') to the East (8);

9. Radius on which a set of heliostats is arranged;

10. Active part of the central tower receiver;

11. Isochronous grouping. Represents the set of heliostats along a radius, whose mirrors have their focus lines parallel on the active part (10) of the receiver (1) of the central tower;

12. Sheath embedded in the ground intended to house the central rotating pillar (14) of the heliostat (3);

13. Ball or bearing that allows the rotation of the rotating pillar (14);

14. Pillar or vertical rotating staff of the heliostat, located in the central part of it;

15. Shoe or foundation piece that supports an inverted wheel (17);

Structure that supports the inverted wheel (17) and is fixedly supported on a piece or shoe (15);

Inverted wheels on which the horizontal heliostat platform rotates;

Electric motor (or azimuth motor) that allows the azimuth rotation of the rotating part of the heliostat (pillar, more structure, more mirrors);

Shoe or foundation piece on which the azimuth motor (18) sits;

Chain or transmission belt from the motor 18 to the fixed disk (28) on the rotating pillar (14);

Platform or horizontal plate that rotates with the pillar (14);

Lifting motor support structure (23);

Elevation motor (or zenith motor), which raises the heliostat mirrors, in the zenith direction;

Transmission belt from the zenith engine (23) to the vertical disk (27) fixed to the main cross member (30) of the heliostat structure;

Stringers of the heliostat structure on which the mirrors sit (at least there is one on each side of the central plane of symmetry of the heliostat), the focus bisector (line LB) being contained in said plane;

Heliostat mirrors;

Vertical disk fixed to the main cross member (30) of the structure, with which the zenith movement is carried out, since said cross member rotates on the fork of the rotating pillar (14);

Horizontal disk fixed to the pillar (14) that rotates by the action of the belt or chain (20) of the azimuth motor (18).

Circumference in which the zenith movement of the heliostat mirrors and their structure are inscribed (adjustable panel);

Main cross member of the heliostat structure;

Virtual circumference in which the zenith movement of the rear arms of the heliostat is inscribed, which only exist in the purely mechanical assembly;

Azimuthal actuator of an isochronous grouping, which is located closer to the central tower, than the closest of the heliostats of said grouping;

Horizontal disk fixed to the pillar (14) that rotates by the action of the left-handed (34) or right-hand (35) traction belt from an azimuth actuator that is used for the entire isochronous grouping; in mechanical assembly said belts extend from one heliostat to the next;

Left-hand drive belt for the disc (33);

Right-hand drive belt for the disc (33);

Lift rotation actuator (or zenith actuator) of an isochronous array. In the mechanical assembly, said actuator is located further from the central tower, than the farthest of the panels of said grouping;

Guide through which the mechanical tension cable of the zenith rotation (39) is channeled, which goes from the actuator (36) to each of the heliostats of an isochronous group (11);

Cable gland with trumpet inlet and outlet, through which the mechanical tension cable (39) of the heliostat's zenith movement is channeled;

Mechanical tension cable that pulls the agonist arm (40);

Rear arm of the heliostat or agonist arm, which only exists in the purely mechanical assembly, and serves to effect the zenith movement of focus by raising the normal to the panel, of all the heliostats in unison, of the same isochronous grouping;

Rear arm of the heliostat or antagonist arm, which only exists in the purely mechanical assembly, and serves to counteract the tension of the agonist arm, in the zenith movement of focus, of all the heliostats in unison, of the same isochronous grouping);

Cable connecting the free end of the counter arm (41) with the free end of the counter spring (44).

Support structure, with pulley, of cable 42;

Counter spring to fix the zenith elevation of the focus;

Legs of the upper fork of the central staff (14) where the slots to mount the main cross member (30) are located. The opposing arm (41) must pass through the space between said legs in its rotation, accompanying the panel in its lifting movement for focus;

Fork leg grooves;

Land;

Central tower;

Normal to the heliostat mirrors;

50. Focus bisector. For the heliostat to be focused, the normal to the mirrors (49) must coincide with this bisector;

In addition to the numeric labels, other alphabetic labels are used, starting with A, if they are angles:

Aa: half-angle of the bisector at point 3 (figure 2);

Ab: angle, at point 4, opposite side DB;

Ac: angle at point 1, opposite side DC;

Ad: auxiliary angle, in figure 2, to determine the bisector trace ;.

Ae: elevation angle from normal (49) to heliostat mirrors, to produce correct focus;

Av: angle of the focus line, above the radius. (Av1 and Avn represent in FIG. 3 two specific values of Av that correspond, respectively, to the first isochronous grouping of heliostats and to the nth grouping of heliostats in a given radius);

Az: azimuth angle, which indicates the horizontal rotation that the normal (49) has to adopt to the heliostat mirrors, when they are correctly focused. It is measured from the south direction (looking south). It is negative if the deviation is towards the East, and positive if it is towards the West.

Regarding distances, lengths or heights, we have:

DA: distance between point 1 and point 4;

DB: distance between point 1 and point 3;

DC: distance between point 3 and point 4;

Dp: physical height of the adjustable panel of the heliostat, which rotates about its center, sweeping a circle of diameter Dp;

Dr1: distance between point (1) and the bisector line;

Dr2: distance between point (4) and the bisector line;

LB: length of the bisector, from its origin at (3) to its trace at (5) in the y = 0 plane;

LE = line of focus that goes from the central point (3) to the corresponding point of incidence on the receiver. Sometimes it goes under-indicated, to refer to a particular case, so LE10 and LEn0 are -respectively- the focus lines of the first heliostat of the first isochronous cluster and of the first heliostat of the nth isochronous cluster. Similarly, LE-n and LEn1 are -respectively- the focus lines of the last heliostat of the first isochronous cluster and of the last heliostat of the nth isochronous cluster; H0: lower height, or height of the lowest point of the active part of the receiver;

H1: upper height, or height of the highest point of the active part of the receiver;

R10: radial distance in which the central point of the first heliostat of the first isochronous grouping is located, identified by (Av1);

R11: radial distance in which the central point of the last heliostat of the first isochronous grouping is located, identified by (Av1);

Rn0: radial distance in which the central point of the first heliostat of the nth isochronous cluster is located, identified by (Avn);

Rn1: radial distance in which the central point of the last heliostat of the nth isochronous cluster is located, identified by (Avn);

From: total height of the mirrors plus structure, which is the diameter of the circle (29).

MODE OF EMBODIMENT OF THE INVENTION

For the correct implementation of the invention, it is necessary to take into account the properties that emerge from an arrangement of the heliostats in a radial field, that is, grouped by isochronous groupings 11 that offer uniform geometric characteristics, and that in particular present the same values. azimuth and zenith orientation at any given time. Hence, it is very important to analyze how the field is constituted, and what advantages it brings with regard to the construction of heliostats, which also have to consume modest and cheap resources, given the need to reduce costs in this energy source.

To this end, Figures 1 and 2 show the basic relationships between the geometric elements of the solar plant according to the present invention, which are essentially the heliostats 3 and the receiver 1, at a certain height, plus the sun. Note that in theory, the maximum concentration of solar radiation that can be achieved with two-dimensional concentration is a factor 46,000 (in round numbers) which drops to 215 for the concentration in a single axis, which is the most common. But the thermal applications available, such as those that use synthetic oil as heating fluid, and the Rankine cycle in power generation, do not require thermal fluxes above 50 kW / m2, which justifies that parabolic-trough installations, the most extended today, do not exceed a maximum factor of 100, and in the mean of the useful concentration zone it does not exceed 70.

Likewise, figure 3 shows the simplified profile of a solar plant according to the present invention, along one of its radii 9. Figure 4 is, in turn, a plan view which shows in a schematic and simplified way (only in one sector), how the heliostats 3 are radially distributed defining isochronous groups 11 in a solar plant according to the present invention.

Furthermore, figure 5 is a partial schematic view along a radius 9 of a solar plant according to the present invention, showing the separation that must exist between successive heliostats 3 of the same isochronous grouping 11, to avoid radiation blockages reflected. A reference (not to scale) to the location of the central tower 48 is included.

Although central tower 48 applications should be aimed at developing and operating higher temperature and more efficient cycles, and with better starting and transient performance, it does not seem necessary to go above 300 kW / m2, which makes concentration factors unnecessary. above 500; for example, 250. This is achieved by concentrating on 1 m2 of receiver surface, the total surface of mirrors that will reflect 250 m2 of straight section oriented to the sun. This implies taking into account the cosine effect both in incidence in the mirror, in reflection, and in incidence in the receiver, which would have to be calculated in annual mean values according to latitude. The mean values for 35-40 ° latitude can be taken as a series of these cosines 0.7, 0.8 and 0.75, whose product gives 0.42. That is, it would be necessary to have 600 m2 per m2 of receiver; and if one considers that the active part of the tower could be 10 m high, 6,000 m2 would have to be located in the circular sector assigned to that meter of horizontal receiver length; To which 0.2 radians of sector aperture could be assigned, between circular crown radii of 200 to 500 m. This trapezoid (with two curved sides) would have a little more than 20,000 m2, which would mean a fill factor of 0.3 (mirror surface on floor surface).

This is very easy to achieve with small heliostats (especially in height) with less than 10 m2 of mirrors per unit. This has an enormous advantage, and that is that as the suspended useful weight (that of the mirrors) is small, the structural part is very light, and its associated cost is reduced.

The trade-off is that you need a focus system for each heliostat, and if there are many of them, that game is triggered. In Figs. 6 to 11 different examples of possible embodiments of heliostats according to the present invention are given both electrically (Figs. 6 and 7), and mechanically (Figs. 8 to 11).

As a prototype heliostat 3, in said figures one of four mirror modules 26 is illustrated, two on each side; and on each side, one above the crossbar and the other hanging from it, supported from behind by two stringers on each side, also fitted with the frames to bend the mirrors with the appropriate curvature, for which the prescriptions given in the Patent ES2596294 B2, "Device for bending flat plates and method of use" (of which the first author of this application is the inventor). The mirror modules are 1.5 m high by 1 m wide. Its thickness is 3 mm, with a density of 2.8 g / cm3. That gives a mass per module of 12.6 kg; which means a useful weight hanging on each side of 25.2 kg (with a total of 50.4).

The structural elements are in the embodiments of the invention shown here the following, in the mechanical assembly:

Central staff (14): cylindrical piece with an external diameter of 125 mm, 4 mm thick, 3 m high; mass of 36 kg;

Ground driving pod (12): 1m, 155mm outside diameter = 18kg;

Horizontal platform (21): 2.2 m in diameter, 1mm thickness of the spokes and ribs = 44 kg;

Cross member (30): 2m piece of rectangular section of 70x50 mm, 3mm thick, 10 kg; Stringers and frames (25): 36 m of pieces of section 40x30 mm, thickness 2 mm, 54 kg Horizontal disc (28): 2 kg

Rear arms (40, 41): 4 kg

Assembly of pulley (43) and counter spring (44); 12 kg

Inverted wheels (17): 5, with a total weight of 8 kg

Total structural mass: 188 kg

Total mass per heliostat (3), approximately 240 kg

Compared to the usual large panels, the structural weight can be greatly reduced, since it must be remembered that for a constant linear weight on the cross member, the relationship between the deflection deflection in a beam and the length of the beam increases according to the length. to the cube, which forces the use of heavier support structures, which in turn increase the total linear weight to be supported, which ultimately overloads the weight, the assembly and the price.

The counterpart is that the number of heliostats increases, and therefore that of focusing equipment, which must be compensated with much simpler types of equipment, either electrical or mechanical. Specifically, in the mechanical case, the approach of a whole isochronous grouping of synchronized heliostats is done with one actuator per turn type, plus cables and pulleys, which is very simple and cheap.

Bear in mind that the cables to be used in the mechanical assembly are like those of bicycles, and must also be guided by sleeves.

The force to be transmitted is that necessary to overcome the opposition of the opposing spring, and that of the mirrors' rotation, although they will be mounted balanced, and their moment of inertia to rotation will be very moderate. Crossbar, according to what was said in the chosen example, is about 120 kg, which occupies about 6 m2 of surface, giving a surface density of 20 kg / m2, which is a modest value.

Assimilating the mirrors and their structures to two 3x1-meter plates, the geometric moment of inertia with respect to the crossbar axis is one twelfth of the product of the base times the cube of the height, which leads to 4.5 m4; and the mass moment of inertia can be estimated assuming uniform weight distribution in all the plates, so that multiplying the last figure by 20 kg / m2 gives a value of 90 kg-m2.

The torque needed to move it depends on the angular acceleration to be given. If we think of a unit turn (discontinuous) traveling 2 milli-radians, half moving uniformly accelerated in 2 seconds, and the other half decelerating in another 2 s, the angular acceleration to be printed is 0.5-10-3 radians / s2. The necessary pair would be this last value, multiplied by 90; which gives 0.045 N-m, which is a very modest value, which requires relatively little, mechanically speaking. If this torque is to be found with a 5 cm arm, the required force would be slightly less than 1 N.

The elongation of the spring (44) would require a force equal to the product of its elastic constant and the maximum deformation, which is the increase in the length of the cable 42 in the segment that goes from the end of the arm to the pulley (at its tangent point) in figure 8, up to the length from said point to the end of the opposing arm in its most extreme position, figure 9, which in this case represents a rotation of 166 °.

The relevant dimensions in the proposed example are:

-length of opposing arm = 1.1 m

-length of cable (42) from end of arm to pulley, rest position = 0.9m

-length of the spring (44) collected, = 40 cm

-length of cable on the side of the dock, collected = 2.60 m (3.00 m if the dock is counted) -maximum arm swing = 166 ° (supplementary angle = 14 °)

-length of cable at maximum lift position, Lmax = (a2 c2) 1/2

a = 1.1 sin 14 ° = 0.266

c = b + 0.9

b = 1.1 1.1 cos 14 ° = 2.17

Lmax = 3.08m

Elongation = 2.18 m

The available cable to pass through the pulley from the rest position to the maximum elongation is 2.40 m (assuming that we leave 20 cm for anchoring the spring to the platform (21); that is, almost the entire cable would pass , minus 22 cm.

With these figures, it is forced to go to a spiral spring that governs a cable drum, which is released as the spring force is overcome.

It remains to justify that all the heliostats of a synchronized grouping have the same focusing conditions, for a position of the sun, which is the same as showing that the values of Az and Ae are equal, which correspond to:

AZ ⁰ = arc tg ((x ⁰ - xw,) ^)

And the elevation angle, Ae,

Ae ⁰ = arc tg (Zb ⁰ / ((xb - x ⁰ ) 2 y ⁰ 2) 1/2)

To do this, previously, it is necessary to show that the coordinates of the location of the bisector trace in the plane y = 0 are valid; which is shown in figure 2, which shows the plane formed by the rays of incidence and reflection. It can be written

Drl sine ( Aa) ■ DB

D r2 sine ( A a) ■ DC

On the other hand, using the angle Ad on either side of the bisector, it can be seen that the segments into which the base of the triangle is divided, on one side and the other of the bisector trace, are proportional to Dr1 and Dr2 ; that is, proportional to the lengths of the adjacent sides of the triangle, so we can write

zb0 = z0 (zs0 - z0) - (DB0 / (DB0 + DQ)))

xb0 = xs0 '(DB0 / (DB0 + DC0))

and in turn the coordinates of the solar trace are

Zs0 = y0-CZ / Cy

Xs0 = Xo i'Cx / Cy

At any given time, the directing cosines of sunlight are the same for all heliostats in a synchronous array. From one heliostat to another, the coordinates of the focal point, which we now call (0, 0, z1) and those of the center point of the heliostat, which are (xi, yi, 0) change.

Because it belongs to the same radial, it is fulfilled

And by the definition of focus points that has been prescribed

zo _ zi

V * or I V * i and í

And if we take into account the previous equation, with the proportionality between x and y, it remains

These proportionalities suggest referring to an enlargement relation as

x1 = m x0

And from it, we can write

and i = ray

^{z - j =} mz0

Zsi = yi-cz / cy = mzs0

Xsi = Xi yi-cx / cy = mxs0

For the plane that passes through x1, y1, all distances and segments are enlarged by a factor m, with respect to the plane that passes through x0, y0.

The bisector trace values are now

zbi = zi (zsi - zi) - (DBi / (DBi + DCi))

xb ⁰ = xs ⁰ - (DBi / (DBi + DCi))

The quotient (DBi / (DBi + DCi) is equal to (DB0 / (DB0 + DC0) since m affects the numerator and denominator).

zbi = mzb0

xbi = mxb0

The value of the azimuth angle is

Azi = are tg ((xi - xbi) / yi) = Az0

since the mat is equal to the numerator and denominator of the argument of the tangent area. And similarly happens with the angle of elevation

Aei = are tg (zM / ((xi - xi) 2 y2) i / 2) = Aeo

Thus, all the heliostats of the same isoerone group move according to the same values of azimuthal and eenital spin, which is the geometric basis of the invention.

Once the form of the invention has been determined, it must be confirmed that the particular realizations previously desired are susceptible to modifications of detail as long as they do not alter the fundamental principle and the essence of the invention.

Claims (1)

1 - Solar plant comprising a central tower (48) and a set of heliostats (3), the central tower (48) being provided with a receiver (1) intended to receive solar radiation reflected by the heliostats (3) and equipped of an active part (10) with a total height (AH) comprised between a lower height (H ⁰ ) and a higher height (H ¹ ), the solar plant being characterized in that: The heliostats (3) are arranged around the central tower forming radii (9) that start from the central point (2) of the base of the tower and define isochronous groups (11) in which: - the focus line (LE ¹⁰ , LE ⁿ⁰ ) of the first heliostat of each isochronous grouping (11) runs from the center of said first heliostat to the lower height point (H ⁰ ) of the receiver (1); - the focus line (LE -n , LE ⁿ¹ ) of the last heliostat of each isochronous grouping (11) runs from the center of said last heliostat to the highest point of height (H 1 ); - the focus lines (LE ¹⁰ , LE n0) of the first heliostat and the focus lines of the last heliostat (LE ¹¹ , LE ⁿ¹ ) of each isochronous cluster (11) are parallel to each other; Y - for each isochronous grouping the relationship is fulfilled: H1 = Hi_ Ho_ = _Hi_ Rio Rll RnO Rnl where (R10) is the distance from the origin of radii to the center of the first heliostat of the first isochronous grouping (11) of a predefined radius (9); (R11) is the distance from the radius origin to the center of the last heliostat of the first isochronous grouping (11) of said radius (9); (Rn0) is the distance from the origin of radii to the center of the first heliostat of the nth isochronous grouping (11) of said radius (9); (Rn1) is the distance from the origin of radii to the center of the last heliostat of the nth isochronous grouping (11) of said radius (9). 2 - Solar plant according to the first claim, in which the radio segment comprised between the first heliostat (R10, Rn0) and the last heliostat (R11, Rn1) of an isochronous grouping is divided into m equal parts, a heliostat being housed different at the end of each of these parts. 3 - Solar plant according to any of the preceding claims in which, in at least one isochronous grouping (11) of heliostats, the focus azimuth (Az) and the elevation angle (Ae) of the heliostats (3) that make up said grouping (11) are determined by: Az = arc tg ((x o - x b ) / y o ), and Ae = arc tg (Z b / ((X b - x o ) ² + y o ² ) ^1/2 ); where x ⁰ is the abscissa (coordinate in the East-West direction) of the central point of the heliostat of the isochronous grouping considered, x b is the abscissa of the trace, in the virtual plane y = 0, of the bisector of the angle of reflection at the center of said heliostat, and ⁰ is the ordinate, in a North-South direction, of the central point of the heliostat of the isochronous grouping, Y z b is the elevation of the trace, in the virtual plane y = 0, of the bisector of the angle of reflection at the center of said heliostat. 4 - Heliostat (3) for use in a solar plant according to any of claims 1 to 3, comprising: - a central vertical rotating staff (14), inserted at its lower end in a cylindrical sheath (12) driven into the ground, and ending at its upper end in a double fork (45, 46) open upward; - a main cross member (30) housed in the double fork (45, 46) open upwards, which is connected to a plurality of beams (25), on which mirror modules (26) are fixed, the modules being arranged of mirrors (26) on one side and the other of the plane of central symmetry of the heliostat, where the central staff (14) is located; - Turning means arranged in the central area of the cross member, selected from a central wheel (27) fixed to the central part of the cross member and a pair of arms (40, 41) perpendicular to the cross member and fixed on it, said means being configured of rotation to rotate with the main cross member (30), when said cross member (30) rotates on the double fork (45, 46); Y - A horizontal platform (21) integral with the central pole (14) in its lower part, said horizontal platform (21) being configured to rotate with the central pole (14) and to rest in its peripheral part on a plurality of wheels (17 ) of free rotation, whose axes of rotation are supported on a fork structure (16) provided with a stem driven into the ground, or supported on a foundation piece (15), so that the upper edge of all the wheels (17 ) is arranged at the same height. 5 - Heliostat (3) according to claim 4, further comprising an azimuth actuator (32), a zenith actuator (36) and mechanical transmission cables arranged between said heliostat (3) and each actuator (32, 36). 6 - Heliostat (3) according to claim 5, in which the azimuth actuator (32) is located in the radius (9) of the isochronous grouping (11) in a position closer to the central tower than the first heliostat of said isochronous grouping (11), and in which the zenith actuator (36) is located in a position further from the central tower than the last of the heliostats of said isochronous grouping (11). 7 - Heliostat (3) according to any of claims 5 and 6, wherein: - the azimuth actuator (32) is connected to a right-hand drive cable (35) and a left-hand drive cable (34), which act antagonistically to each other; Y - the zenith actuator (36) is connected to an agonist cable (39) and an antagonist cable (42) that act antagonistically to each other, each of said cables (39, 42) being connected to an arm (40, 41 ) perpendicular to the cross member (30); the agonist cable (39) being configured to raise the normal (49) of the mirror modules (26); and the opposing cable (42) being attached to an elongation spring (44) fixed to the rear of the platform (21), so that the action of the spring (44) is configured to bring the heliostat (3) to a resting position, defense against meteors and against the production of undue reflections. 8 - Heliostat (3) according to claim 4, comprising: - an azimuth electric motor (18) anchored in the ground (19), provided with a drive pulley that moves jointly with a chain or belt (20), which in turn is jointly rotated with a horizontal wheel ( 28) fixed to the pillar (12) or to the central rotating staff (14); Y - a zenith electric motor (23), arranged at the rear of the platform (21), and connected to the fixed vertical wheel (27) by means of a belt or chain (24).