WO2015193523A1

WO2015193523A1 - Heliostat

Info

Publication number: WO2015193523A1
Application number: PCT/ES2015/070405
Authority: WO
Inventors: Julián López Garrido; Emilio Murcia Pacheco; Pedro MURCIA PACHECO
Original assignee: Aplicaciones Renovables Integradas, Sl
Priority date: 2014-06-17
Filing date: 2015-05-25
Publication date: 2015-12-23
Also published as: CL2016003224U1; ES1114205U; ES1114205Y; MA39531A1

Abstract

Heliostat provided with an actuating shaft trained on the objective, reflection, refraction or direct solar sensors, closed-loop control, with the possibility of combination with open-loop control, irrespective of the main reflective optics solution, provision having been made for the closed-loop control system, which keeps the heliostat trained on the objective at all times, to be powered retroactively by the solar sensor signals.

Description

HELIOOSTATE

DESCRIPTION

Title

Heliostat with a drive shaft pointing to the target, solar sensor and closed loop control.

Object of the invention

The present invention relates to a heliostat belonging to a solar field that reflects the light beams that reach it, equipped with a solar tracking mechanism. It is an invention that belongs, within the area of thermotechnics, to the field of energy production from solar radiation.

This invention does not contemplate the typology or nature of the main reflective surface that supports it, so that this surface could be flat, spherical, parabolic, cylindrical, toroidal, tessellated or adopt any other geometric configuration.

This invention does not specify the defined structural execution of the system, but encompasses all structural executions that meet the conditions of movement and operation.

Background of the invention

The use of solar energy as a source of energy is made by man since ancient times. The Sun emits a huge amount of energy, a part of which reaches the Earth in the form of light and heat. Since the mid-twentieth century, research has been conducted to try to transform that energy into electricity: thus, plates have been developed photovoltaic that produce electricity directly when its surface is conveniently activated by light, and different types of heat collectors that concentrate light beams on a pipe or on a central receiver that contains a fluid manage to reach sufficient temperatures to produce large amounts of steam of water that generates electricity through a turbine, usually in a Rankine cycle. It is about this last type of installation that the present invention is about.

Given the low specific power per unit area of solar radiation, to use this energy properly it is necessary to concentrate a large number of light beams on the same point, which is traditionally done through mirrors oriented on a tank or on a pipe as a collector. In this case the radiation is by indirect concentration, since to reach its objective the rays must bounce previously in the mirror.

The state of the art has different internationally patented systems aimed at optimizing the concentration and use of solar energy reflected by heliostat systems for the production of electrical energy, as well as accessories and complements that are reflected in different headings of the International Patent Classification .

The solution adopted by the patent with publication number ES 8100499, is the so-called classic vertical or zenith axis solution. This mechanical solution requires extremely precise control and actuation and complex initial calibration to maintain the aiming for a short period of time until the next calibration. Astigmatic aberration (unwanted phenomenon of all lenses when viewed through them obliquely, in our case deformation of the reflected image of the Sun) tends to increase the apparent size of the Sun outside the optimal operating conditions. Since the objective is to obtain an image of the Sun as small as possible (concentration of the energy received), this phenomenon It is unwanted. The presented invention solves both inconveniences because the closed loop control system, which can be combined with the usual open loop control, eliminates the need for continuous recalibration, and constructively astigmatic aberration is minimal in spin-lift drive systems. .

Another patent with publication number ES 2244339, proposes a different constructive solution to the classical configuration. This, like the previous one, also has an open loop control conditioned to a multitude of recalibrations of the system, which, as already indicated, the presented invention solves by adding the advantage of cost reduction in both the monitoring system and the system. maintenance.

The first heliostats considered as industrial elements were developed at the beginning of the eighties for the experimental central solar thermal solar plants, with the purpose of testing the viability of solar thermal energy in the industrial scale electricity production processes. Table 1 summarizes the projects because of the international initiative (Data System name, year of installation, site installation, MWe electrical power installation, type of installed heliostats, No. number of heliostats m ^2):

Once the demonstration projects were completed, most of these plants were closed. In the USA, the Solar One plant was remodeled and, with the same field of heliostats, the Solar Two plant was put into operation, which has been in operation until April 1999.

In Europe, only the heliostat fields corresponding to the CRS and CESA-1 plants continued in service, thanks to a collaboration agreement between the German and Spanish governments, constituting the Almería Solar Platform (PSA).

The PSA continues to operate these heliostat fields today thanks to a great diversity of projects that have been carried out in recent years. The objective of these projects has been the development and evaluation of new solar components in this technology, mainly heliostats and solar receivers.

None of the heliostats developed and applied in these plants is similar to the one presented here, since all these are based on an azimuth-elevation tracking mechanism, while the one presented is based on a rotation mechanism around the aiming and elevation axis.

The azimuth-lift system consists of a vertical (constant) and a horizontal (rotating with the first) axis of rotation. This assembly involves problems associated with the optics in the reflection, decreasing the concentration of the rays reflected by the system and therefore the total efficiency of the solar plant.

The essential difference of the invention is the configuration of the axes of rotation, which allows, on the other hand, to introduce the control system in closed loop.

The invention described below has been developed after numerous studies and tests, and after understanding the possibilities of optimization of various solutions previously raised by various research teams. The general objective intended with the present invention is the development of an economical device in its installation, which minimizes maintenance needs and expenses, maximizes solar radiation and is quick and easy to install in any location.

Description of the invention

In the existing devices whose mission is to reflect the energy coming from the Sun towards an objective there are two main problems:

The control system is open loop, since by construction these devices are not able to obtain a signal that indicates to what extent they approach or move away from the desired state of operation. This is the cause of expensive control systems, apart from a reduction in accuracy.

The reflected energy varies the way of influencing the objective greatly over time. Because the angle with which the Sun is reflected in the heliostat varies greatly, this affects the reflection optics by varying the way in which the reflected energy affects the target over time, being able to double the size of the region of incidence of reflected rays.

The invention that is proposed to meet the objectives set and solve these problems consists of a device formed by a heliostat that reflects solar radiation with less astigmatic error (phenomenon explained above) as a function of time, and whose operation is done in a different configuration than the existing ones, with closed loop control that can be supported in combination with an open loop control.

All this is possible because the kinematics of the system is substantially different from that of the previous devices.

As in these devices, the system consists of two orthogonal turns along two axes of rotation of which one of them, the primary one, is fixed in the space and the other, the secondary, varies its position depending on the turn around the primary.

On the contrary, in the proposed invention the primary axis is kept aiming at the objective at all times, therefore the primary axis contains the objective. We call this configuration point to target. The plane formed by the primary axis and the Sun will be the reflection plane, since in that plane the solar energy is reflected to the objective. The secondary axis will be the axis perpendicular to the reflection plane.

This geometric condition, in which the plane perpendicular to the secondary axis must contain the Sun and therefore the rays coming from the Sun remain perpendicular to the secondary axis, is the one that offers the possibility of reducing the astigmatic error. How to do this falls within the scope of application referred to the reflective surface, and being outside the scope of this patent will not go deeper into this issue.

The geometric condition highlighted in the previous paragraph is also used to obtain the first of the two signals that allow closed loop control. For this, a possible configuration consists in placing a pointer or solar sensor on the outer end of the reflective surface, and contained in the plane perpendicular to the secondary axis. This solar sensor provides a signal that indicates whether the Sun is located on either side of the plane perpendicular to the secondary axis. This signal allows to know if the rotation of the primary axis is adequate to reflect the solar energy in the objective.

The ultimate purpose of the invention is to reflect the energy towards the objective, which means that the reflected energy moves towards the objective according to the direction indicated by the primary axis. This can mean that the reflected main beam is simultaneously in two perpendicular planes, which geometrically indicates that said direction is that of the line formed by the intersection of both planes. The first sensor of the presented configuration checks the first of these two conditions. The second condition is that the reflected main beam is contained in the plane formed by the primary axis and the secondary axis. The plane formed by the primary and secondary axis is the drive plane.

There are two methods to verify that the second condition is met:

Direct measurement: a sensor is placed in the path of the energy reflected to the target. A small amount of energy from the one destined to reach the receiver is intercepted to verify that it is pointing correctly.

Indirect measurement: a small amount of energy is diverted from that destined to reach the receiver in the opposite direction and parallel to its direction of travel by means of an optical system. It is this energy that is checked by the sensor.

There are two types of optical systems:

Reflective: reflects the incident energy through a secondary reflective surface that forms 90 ° with the reflective surface of the heliostat. By basic geometry, the angle formed by the main energy directions reflected by the main reflection system and this secondary one is 180 °. This system is represented in Figure 10.

Holographic: captures part of the incident energy through a surface with a special optical treatment that behind it forms a virtual image of the Sun that indicates when the reflected energy reaches the receiver or if the system is not properly aligned.

To complete the measurement system, a sensor is placed on the primary axis, after the optical system, which monitors the first condition and with its reference plane parallel to that formed by the primary axis and the secondary axis. Another possible configuration of the measurement system is to place a direct solar sensor, which will point to the incident beam in case of compliance with the two conditions set forth above. If this configuration is chosen, the closed loop control system used in the invention must be combined with an open loop control system.

The set of elements described and the movement and control strategy make up the invention to which this document is subject.

For a better understanding of what is stated here in the next section, all the terms used are clarified and illustrated by images.

Description of the drawings

First of all, a series of terms are listed and developed, with the meaning described and represented in a series of figures.

- Solar energy: radiant energy that comes from the Sun and that reaches the Earth's surface with a characteristic intensity and spectral composition.

- Heliostat: Mirror of great focal length, equipped with movement in two axes and whose mission is to reflect, concentrate and maintain static the image of the Sun in a certain focus throughout the day.

- Heliostat field: Also called primary concentrator or solar field, it is a set of heliostats arranged in a limited terrain and whose mission is the contribution of radiant energy to a target or receiver.

- Solar receiver or objective: Device that intercepts and absorbs the solar radiation provided by a field of heliostats, in order to transfer it through a heat exchanger to the power block of the plant. - Central receiver thermosolar plant: electric power production plant that bases its operation strategy on the contribution of heat to a certain conventional thermodynamic cycle, by concentrating solar radiation by a high number of heliostats on a single receiver.

- Main incident ray: the one that comes from the center of the solar disk and cuts at the central point of the heliostat optics.

- Reflected main beam: the one that comes from the central midpoint of the heliostat optics and results from the reflection of the main beam incident in the heliostat.

- Solar sensor or solar pointer: Device that by means of optical, photovoltaic, thermal or any other phenomena is able to discriminate the position of the Sun with respect to a reference plane, allowing to know if the Sun is on one side or the other of the same, generally with the purpose of leading this reference plane to coincide with the position of the Sun (point condition).

- Optical system: device installed in the heliostat whose purpose is to divert a small part of the incident energy so that it is possible to monitor thanks to it, and by means of a solar sensor, the incidence of the rest of the energy reflected in the solar receiver or target .

- First condition or condition 1: The plane perpendicular to the secondary axis must contain the Sun. It is one of the two geometric conditions that lead to the reflected main beam being directed correctly towards the objective, and in the proposed invention is achieved by a adequate rotation of the primary axis.

- Condition sensor 1 or sensor 1: Solar sensor that reports compliance with condition 1. - Second condition or condition 2: It can be stated as "the reflected main beam is contained in the plane formed by the primary and secondary axes". It is one of the two geometric conditions that lead to the correct reflection of the main beam towards the objective, and in the proposed invention it is achieved by an adequate rotation of the secondary axis.

- Condition sensor 2 or sensor 2: Solar sensor that reports compliance with condition 2.

- Secondary secondary beam: the one that comes from the center of the solar disk and cuts at the central point of the optical system.

- Deviated main beam: the one that comes from the central point of the optical system and results from the reflection of the incident secondary beam.

- Reflection plane: The one that contains the main incident beam and the main reflected beam.

- Primary axis: Axis of rotation of the heliostat that remains fixed in the space during its operation and with respect to which the mobile assembly rotates.

- Main plane of the optics: Plane of symmetry of the reflective surface, which in turn contains the primary axis.

- Secondary axis: Axis of rotation of the heliostat that is orthogonal to the primary axis, and to the main plane of the optics.

- Optical axis of a heliostat: virtual straight line that passes through the center of the optics, cuts orthogonally to the secondary axis of the heliostat and is contained in the main plane of the optics.

- Drive plane: plane containing the primary axis and the secondary axis. - Horizontal mount: Mechanical device of orientation in two axes of a heliostat with respect to a topocentric system of horizontal coordinates, called azimuth and height. The fundamental plane is the horizon of the observer and the fundamental point is the true North. The orientation of the heliostat, depending on the diurnal evolution of the Sun in this same coordinate system, is achieved by azimuthal turns (arcs of horizon from the fundamental point) and height or zeniths (arches orthogonal to the horizon plane in the direction of the zenith of the observer). The mechanical axis of azimuthal rotation is orthogonal to the plane of the horizon and of fixed orientation. On the contrary, the axis of zenith rotation is parallel to the plane of the horizon and of variable orientation, due to the existence of a mechanical ligation between both movements, which causes the "dragging" of the zenith axis each time the azimuthal rotation occurs.

- Spin-lift mount: Mechanical device constructively similar to the horizontal mount but whose primary axis is not vertical but is oriented in such a way that said axis points to the target or solar receiver. The axis system in this case is also orthogonal, which means that the secondary axis remains perpendicular to the primary one at all times. The orientation of the heliostat, depending on the diurnal evolution of the Sun, is achieved by turning around the primary axis and inclination with respect to the aiming axis.

- Facets: Individual specular elements of which the reflective surface of some heliostats is composed.

- Declination: Variation of the height of the Sun over the celestial equator when the earth, throughout the year, travels its trajectory (the ecliptic) around the Sun.

- Aiming strategy: Operation procedure of a solar thermal plant that consists of defining a set of coordinates on the receiver to which each of the heliostats of the field must aim to achieve the distribution of energy required on it. - Dynamic aiming strategy: It is an aiming strategy in which the coordinates on the receiver change over time, following certain control criteria.

To complete the description that follows and in order to help a better understanding of the features of the invention, a detailed description of a preferred embodiment will be made based on a set of drawings that accompany this specification, and where For the purposes of guidance only and not limitation, the following has been represented:

Figure 1 shows a central receiver solar thermal plant where the heliostat of the invention can be used. You can also see the main elements of the plant such as the tower (13) where the receiver (1 1), heliostats and other attached facilities are located.

Figure 2 shows a rear perspective view of the "horizontal" mount of a heliostat. In this figure you can see the zenith axis (9), which in this case coincides with the primary axis (3), and the secondary axis (5) in this case horizontal. This configuration is the most common, in a single-pole configuration where the structure is supported by a pedestal (7), where you can also observe a common element to any heliostat, the control device (8).

Figure 3 shows a rear perspective view of a "spin-lift" mount of a vain of the heliostat of the invention. This configuration is more similar to the "horizontal" mount configuration. The way to support the weight of the structure is by means of a pedestal (7), and also consists of a control device (8). In this mount, the primary axis (3) varies its inclination and orientation depending on the position relative to the target (1 1). The secondary axis (5), which in the position shown is in a horizontal position, varies its position within a plane perpendicular to the primary axis (3). The figure also shows the pivot points at which the inclination and orientation of the primary axis is regulated, in the pedestal joint mechanism (7) and the primary axis (3). Figure 4 shows a perspective of the heliostat object of the invention, in general configuration. It should be noted that in this one you can clearly see the primary (3) and secondary (5) axes, and a way of actuating them through the primary (4) and secondary (6) drives. The control system (8), common to all heliostats, is also represented. In the center of the reflective surface, the optical system (17) is located in front of the condition sensor 2 (15) which together with the condition sensor 1 (14) represented in the following figure form the collection system necessary for the closed loop control.

Figure 5 shows a side and front view of the heliostat. In this figure, apart from the elements highlighted in the previous figure, such as the primary axis (3), primary drive (4), secondary shaft (5), secondary drive (6) and the control system (8), You can observe other elements. The reflective surface (1) is mounted on the mobile support (2), and on this support the condition sensor 1 (14) is also located at one end.

Figure 6 shows a plan view of the reflection plane. In this view you can see the main characteristics of the reflection of solar energy in a correct pointing position. The reflective surface (1) is oriented along the optical axis (18). The incident main beam (22) and the reflected main beam (23) form at each moment both an angle γ with the optical axis (18), a direct consequence of the law of reflection. The reflected main ray (23) results from the reflection of the main incident ray (22) that comes from the Sun (12), and is reflected by the reflective surface (1), and so that it reaches the target (1 1), located in the tower (13), it must be fulfilled that it is coincident with the main axis (3), for which the system is operated by the main (3) and secondary (5) axes. Although not shown in this figure, the main plane of the optics (21) and the reference plane of the sensor of condition 1 will both be located in the reflection plane so that condition 1 is met. Figure 7 shows, schematically in perspective, the spatial geometry on which the invention is based. In this configuration, the two aiming conditions that allow the reflected main beam (23) to reach the objective (1 1) are being met. This representation clarifies the participation of some elements that do not appear in the previous figure, such as the drive plane (10).

Figure 8 is an elevation of Figure 6. This figure together with the previous two just clarified the spatial position of all the elements involved in the reflection.

Figure 9 represents the detail of a possible configuration of sensor 1 (14). This sensor is composed of an opaque surface (24) as a physical representation of the reference plane and two surfaces (25) sensitive to incident solar energy. The sensitive surface (25) on the side where the Sun is located (12) will produce a greater signal (the dotted part where the sensitive surface is not illuminated), which indicates the breach of condition 1. As soon as the Sun (12) is contained in the reference plane, the sensitive surfaces (25) will generate the same signal and it will be known that the position with respect to the rotation of the main axis is correct.

Figure 10 represents the detail of a possible configuration of the optical system (17) of the sensor 2 (15). In this case, the sensor 2 (15) is equal to the sensor 1 (14), with the proviso that only its position varies due to the action of the primary axis (3), the opaque surface (24) parallel to this axis remaining at all times. . The opaque surface (24) also remains parallel to the secondary axis (5), whereby said surface is located in the drive plane (10), which is perpendicular to the main plane of the optics (21) which is the plane to which the opaque surface (24) of the sensor 1 (14) is parallel. The secondary reflective surface (26) rotates around the secondary axis (5) reorienting the main beam deflected towards the sensor 2 (15). By the same phenomenon as in the sensor 1 (14), when the sensitive surfaces produce the same signal, the deflected main beam (19) will be parallel to the primary axis (3) and therefore the main reflected (23) will also be parallel to said axis and will therefore target the target (1 1).

Figure 1 1 presents a view of the reflection plane, once condition 1 is met, therefore both the Sun and the objective are in the reflection plane. This figure shows the arrangement of the sensor 2 (15) and its optical system (17) when the rotation around the secondary axis (5) leads to the fulfillment of condition 2. It should be emphasized here that the actuation of the rotation around the secondary axis (5) modifies the orientation in the plane of the figure of all heliostat elements represented with the exception of sensor 2 (15). This is because the sensor 2 (15) is located or attached to the T-piece that articulates the movement along the secondary axis (5), and therefore does not experience movement around this axis.

It is noted that Figures 1 to 3 correspond to the field of application of the invention, prior art and necessity of the invention, Figures 4 to 6 correspond to the structural description of the invention, Figures 7 and 8 correspond to the explanation of the mode of operation of the invention, while Figures 9 to 1 1 are a detail of a preferred embodiment of the system sensors.

In these figures the numerical references correspond to the following parts and elements:

one . Reflective surface.

2. Mobile support.

3. Primary axis.

4. Primary drive. 5. Secondary axis.

6. Secondary drive.

7. Pedestal.

8. Control device.

9. Zenith axis.

10. Drive plane.

eleven . Target or solar receiver.

12. Sun

13. Tower.

14. Sensor condition 1.

15. Sensor condition 2.

16. Ground.

17. Optical system

18. Optical axis

19. Deviated main beam

20. Plane of reflection.

twenty-one . Main plane of the optics 22. Main beam incident.

23. Main beam reflected.

24. Opaque surface

25. Sensitive surface

26. Secondary reflective surface

27. Incident secondary beam

Preferred Embodiment of the Invention

Figure 1 shows a central receiver solar thermal plant, where a detail of the area of the tower in which the solar receiver is located has been represented.

Figure 2 shows the conventional assembly of a heliostat. Note how the primary axis (3) is inserted into the pedestal (7), while the secondary axis (5) is "dragged" along the primary axis (3) itself.

The proposed solution involves tilting the primary axis so that it points to the objective (1 1).

The preferred embodiment is shown in Figure 3, where it can be seen that the system consists of a fixed structure formed by a pedestal (7) that can be made of steel or concrete, and the main axis (3), which is adjustable in elevation and horizontal orientation to aim at the objective (1 1). This regulation is carried out for each heliostat and on a single occasion when the system is installed, since from this initial regulation the main axis (3) remains fixed in space over time. It also consists of a reflective surface (1), which is supported by a mobile support (2) that prevents deformation of said surface and in turn allows the movement through which the reflection of solar energy reaches the receiver. These movements are produced by a drive system composed of two independent actuators (4) and (6), of which in this preferred and non-limiting embodiment the main actuator (4) is a linear actuator while the secondary actuator is a rotary actuator, both of which allow the heliostat to be pointed. The system is completed by a set of reflection sensors (14) and (15), represented in detail figures 9, 10 and 1 1, and a control device that ensures that at all times the energy reflected by the heliostat reaches the receiver (1 1).

The system bases its operation on making a turn around a fixed axis (main axis (3)) that has the peculiarity of aiming at the solar receiver or objective (1 1).

The second turn made by the heliostat to be able to control the aim of the system is carried out along an axis perpendicular to the main axis called the secondary axis (5).

The first aiming condition to be fulfilled by the system is that the main plane of the optics (21) contains the main incident ray (22), or what is the same, that the main plane of the optics (21) is coincident with the reflection plane (20). In figures 6 to 8 this condition is fulfilled, the drawing plane being also in the case of figure 6 the main plane of the optics (21). If this condition is not fulfilled, the reflected main beam would deviate from the target (1 1).

This condition is satisfied by the primary drive (4) arranged along the primary axis (3). The second condition is that the reflected main beam (23) is parallel to the primary axis (3). This condition is achieved by the secondary drive (6) along the secondary axis (5), and is only possible if the first condition is satisfied.

The operation of both drives follows an independent strategy, but finally both conditions must be met.

The sensor system detects whether or not the aiming conditions are met, and if not met, warns the control system to what extent or in what way the conditions are not met.

The system consists of two types of sensors that measure whether:

- The main plane of the optics (21) contains the main incident beam (22).

- The reflected main beam (23) is parallel to the primary axis (1 1).

The first of the conditions is monitored by a sensor arranged at the intersection of the main plane of the optics (21) and the outer edge of the reflecting surface (1) and detects in which of the two spatial regions of those defined by the main plane from the optics (21) is the main incident beam. For greater clarity of this system, Figure 5 clarifies the referred location, and Figure 9 presents a preferred embodiment of this sensor.

The second of the conditions is monitored by a sensor arranged along the main axis that detects in which region of the space defined by the drive plane (10) the image of the Sun is, after being redirected by an optical system (17) located in the preferred embodiment in the center of the reflective surface (1) and in front of the condition 2 sensor (15). This system is represented in Figure 10, where the detail is extracted from the central area of the reflective surface (1). Here there is a hole through which lightning Main deflected is directed to condition sensor 2 (15) which for this case is identical to condition sensor 1 (14) but oriented its opaque plane (24), which is its reference plane, parallel to the drive plane (10).

In another configuration, not shown in the figures, the fulfillment of the two conditions can be performed with a single direct sensor, which will point to the main incident beam (22) when these conditions are verified. In such a case, the control device (8) will necessarily house an open loop control system that will support the closed loop system described in the invention.

Figure 5 shows a preferred embodiment from the type of constructive view, in which no restriction has been introduced regarding the orientation of the objective. The heliostat object of the invention comprises a reflective surface (1), capable of rotating by means of a primary drive (4) around a primary geometric axis (3) integral with a movable support (2) which, in turn, is capable of rotate around a secondary geometric axis (5) perpendicular to the primary geometric axis (3), using a secondary drive (6). Both drives (4) and (6) are governed by a control device (8). The assembly is supported by a pedestal (7) whose design allows the movement of the reflective surface (1) and the mobile support (2) without interfering with the pedestal itself (7).

In a particular embodiment, called a single-pole assembly and described in Figure 3, the objective (1 1) is arranged on the receiver of a tower (13), the primary axis (3) being aligned so that it crosses the objective (1 one ).

The sensor system allows to determine independently the behavior of the reflection conditions expressed above, which by independent drive (both control variables are not linked which greatly facilitates the control of the invention) will lead to the control system by closed loop to constantly meet the conditions of reflection. Also, the control device (8) can house an open loop control system that will work in combination with the closed loop control system. The main function of this open loop system will be to perform the control functions in case of eventuality, weather or any other type, during which the sensors of the closed loop control system do not provide the necessary information. It will also support if the heliostat has a single direct solar sensor.

This open loop system will, in turn, be recalibrated by the closed loop control system in order to eliminate errors, cumulative over time, characteristic of this type of control system.

The mobile support structure (2) is a simple reticular structure with longitudinal sections perpendicular to the drive and support axis that is the secondary axis (5). A detail of the preferred embodiment can be seen in Figure 3. The secondary axis (5) is a circular section beam driven by the secondary actuator (6), a linear actuator, rotating this system around the holes of the corresponding lugs. to a piece in T, the axis of said T (the arm perpendicular to the axis formed by the centers of the lugs) being the primary axis (3). At a certain point in its length, the axis of the T will be divided into two sections, which will have relative rotation with respect to this primary axis (3) by means of a bearing connection. This rotation of the primary shaft (3) will be driven by the primary actuator (4).

This T in turn is articulated along a horizontal axis perpendicular to the primary axis (3) and at a point lower than the joint by bearings that allows the rotation around the primary axis (3). The mentioned T-piece is articulated to allow varying the elevation of the primary axis (3) at the initial point, on a second T-piece similar to that already mentioned, consisting of two lugs and an axis (arm perpendicular to the axis formed by the lugs ). In this case the shaft is a single piece unlike the T-piece mentioned above. The axis formed by the center of these lugs is the horizontal axis mentioned, around which the initial T-piece is articulated. This second T-piece rotates around a vertical axis with respect to the pedestal (7) to allow azimuth orientation of the primary axis (3). Both turns, around this vertical axis and around the lugs of the second T-piece, are those that allow the initial orientation of the primary axis (3) so that it always points to the target (1 1). These last two turns are prevented in the normal operation of the system being used simply for aiming at the objective at the time of installation and adjustment of the system.

Claims

one . - Heliostat characterized by having a drive shaft pointing to the target, solar reflection, refraction or direct sensors, closed loop control, with the possibility of combination with open loop control, regardless of the solution of the main reflective optics, having been provided that the closed loop control system, which keeps the heliostat pointing at all times to the target, is fed retroactively by the solar sensor signals.

2. Heliostat according to claim 1, characterized by having a mobile support (2), which rotates under the action of a primary drive (4) relative to a primary axis (3) coinciding with the direction of aiming at the target ( 1 1), and on which the reflective surface (1) of very high reflectivity is mounted, which rotates under the action of a secondary drive (6) with respect to a secondary axis (5) perpendicular to both the primary axis (3) and the main plane of the optics (21).

3. Heliostat according to claim 1, characterized by having a solar sensor (14) that is preferably located on the contour of the reflective surface (1) and is integral with it, and has an opaque surface (24) which acts as a reference plane and two sensitive surfaces (25) to incident solar energy.

4. Heliostat according to claim 1, characterized in that it has a solar sensor (15) that is located in the center of the reflective surface (1) rotating exclusively around the primary axis (3), at all times remaining its opaque surface ( 24) parallel to this axis and the secondary axis (5). The sensor receives solar radiation after its reflection in an optical system (17), formed by a secondary reflecting surface (26). This secondary reflective surface (26) is perpendicular to the reflective surface (1) of the heliostat, and contains the secondary axis thereof.