ES2244339B1 - LINEAR FOCUS HELIOSTATE AND OPERATING METHOD. - Google Patents

Abstract

Linear focus heliostat and operation method. It comprises a reflective surface (1), cylindrical or parabolic trough, capable of rotating around a primary axis (3) integral with a movable support (2) which, in turn, is capable of rotating around a secondary axis (5 ) perpendicular to the primary axis (3). The secondary axis (5) has a particular orientation, perpendicular to a main image plane (10) that contains a fixed linear target (11), in addition to the primary axis (3). With this structure and arrangement the confinement of the linear focus on the linear target (11) is achieved, without the reflection of the light outside the optical axis being able to pick it throughout the day. The movements are achieved by a primary drive (4) and a secondary drive (6) governed by a control device (8). In the particular case where the linear target (11) is vertical, so will the main image plane (10), so that the secondary axis (5) will be horizontal.

Description

Linear focus heliostat and method of operation.

Object and field of application

The present invention relates to the realization of a new cylindrical optic heliostat and mount pseudo-horizontal, whose mission is to distribute and stabilize the sunlight reflected on its surface along a defined direction on a certain target along the day. This direction of concentration of solar radiation is what results from projecting the central generatrix of the cylindrical optics of the heliostat on the surface of the target.

The scope of the invention would be the central receiver thermo-solar plants whose design demands that the distribution of solar energy reflected by the heliostat field follows a preferred direction on said receiver. Since the image of the Sun given by a heliostat conventional on a white is circular, this distribution Directional energy has traditionally been achieved in conventional thermo-solar plants through operation techniques based on group targeting strategies of heliostats.

Power plants tower-type thermo-solar, or central receiver, base their operation strategy on the heat input to a certain conventional thermodynamic cycle, through concentration of solar radiation by a high number of heliostats Among the functional characteristics of the heliostats is its ability to concentrate radiation solar in the receiver or boiler, for which they are provided with a reflective surface of spherical geometry and mechanical mount of the type called horizontal. Except for some requirements very basics about the optical quality of its reflective surface, its pointing ability or its land occupation factor, the rest of the design parameters of a heliostat, such as geometry, size, control, or type of drive mechanism, have come traditionally imposed by essentially economic criteria. The fact that the heliostat design has not come is striking so far, in none of its parameters, conditioned by the type of solar receiver on which to distribute the radiant energy It reflects from the sun.

However, large solar receivers have a geometry in which at least one of its dimensions is much larger than the others, such as tubular or volumetric cylindrical receivers. In all these projects the fact that the image of the Sun generated by spherical heliostats is much smaller than the dimensions of the solar receiver itself has been verified, which is a serious inconvenience, since the complete irradiation of this requires pointing the heliostats to the along its entire surface with some specific criteria or strategy, which are entrusted to the control system of the heliostat field. Since it is no longer aimed at a single place on the receiver, the control algorithms basically have to strategically disperse the radiation that has previously been concentrated by each heliostat. This essentially contradictory fact and of questionable success, since it jeopardizes the performance and the integrity of the solar receiver itself, has led to reflect on the advisability of reviewing the heliostat design parameters, so that the irradiance distribution given by each heliostat on the solar receiver it adapts in origin to the geometric shape of the latter and, consequently, the point control strategies are minimized or even suppressed. The revision of these design parameters involves the optics, the pointing mechanism and the orientation of its location within the field of heliostats. As an alternative to the conventional design, the linear focus and pseudo-horizontal mount heliostat is proposed, object of the present invention.

Throughout the document the following terms, with the meaning described:

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

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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 place throughout the day.

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Cylindrical optics : Reflective surface of revolution obtained by rotating a segment of arbitrary length around an axis parallel to it, called the axis of revolution of the cylindrical optics.

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Cylindrical heliostat: heliostat provided with cylindrical optics.

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Geometric axis of a cylindrical heliostat : It is the axis of revolution of its cylindrical optics.

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Optical axis of a cylindrical heliostat : virtual straight line that passes through the centers of the cylindrical optics, white and Sun, assumptions aligned, and cuts orthogonally to the geometric axis of the heliostat.

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Central plane of a cylindrical heliostat : plane containing the geometric and optical axes.

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Central generator of a cylindrical heliostat : Of all the generatrices of the cylindrical heliostat, that which is contained in its central plane.

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

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Reflected main beam : the one that comes from the midpoint of the central generatrix of the heliostat optic and cuts at the midpoint of the target.

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

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Main plane object of a cylindrical heliostat : Plane containing the central generatrix and the main incident beam.

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Main plane image of a cylindrical heliostat : Plane containing the central generatrix and the reflected main beam.

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Focal line of a cylindrical heliostat : Geometric place of intersection with the central plane of the solar rays reflected on its optical surface, assuming the incidence paths of said rays parallel to the optical axis. In incidence not parallel to the optical axis, the focal line moves to the main image plane and modifies its genuine characteristics due to astigmatism, becoming a pseudo-focal line.

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Primary axis of a cylindrical heliostat : Axis of rotation of the heliostat coinciding with its central generatrix.

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Secondary axis of a cylindrical heliostat : Axis of rotation of the heliostat that is orthogonal to the primary axis.

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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 towards 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 "drag" of the zenith axis every time the azimuthal rotation occurs.

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Pseudo-horizontal mount: Variant of the horizontal mount, whereby the orientation of the heliostat is achieved through turns around the primary and secondary axes of the heliostat, orthogonal to each other but arbitrarily oriented with respect to the plane of the horizon, and assuming the position of the Sun given in horizontal coordinates. The position of the mechanical axis of zenith rotation is fixed and its orientation does not refer to the plane of the horizon, but to the main image plane of the heliostat, with respect to which it must necessarily be orthogonal. The mechanical axis of azimuthal rotation must be orthogonal to the aforementioned zenith axis and, therefore, is fully contained in the main image plane of the heliostat, its orientation being variable in said plane due to the existence of a mechanical bond between both movements, which causes the "drag" of the azimuthal axis every time the zenith turn occurs.

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

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Alignment or edging of a heliostat : Action to orient the facets in such a way that the intersection of all the optical axes of these is on the optical axis of the heliostat, at a distance to the vertex of this double of its focal. The alignment gives focal to the heliostat, supposedly faceted its reflective surface.

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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.

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Field of heliostats : Also called primary concentrator, 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.

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Solar receiver : 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.

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Linear target : Solar receiver that must receive radiant energy along a line (or at least one of its dimensions is much larger than the others).

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Thermo-solar plant of central receiver : plant of production of electrical energy that bases its strategy of operation in the contribution of heat to a certain conventional thermodynamic cycle, by means of the concentration of the solar radiation by a high number of heliostats on a single receiver.

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Aiming strategy : Operation procedure of a thermo-solar plant that consists of defining a set of coordinates on the receiver where each of the heliostats of the field must aim to achieve the required energy distribution on it.

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Dynamic aiming strategy: It is an aiming strategy in which the coordinates on the receiver change over time, following certain control criteria.

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Confined focal line : Condition determined by the optics and orientation mechanism of the heliostat with respect to the apparent movement of the Sun, whereby the orientation of the main image plane of the heliostat remains invariant and, consequently, the orientation of its focal line is stabilized on the target. That is, by guiding the optics to follow the Sun in its daytime movement, it can be achieved that the radiation reflected by the heliostat, grouped around its focal line, is permanently distributed over a linear target.

Background of the invention

The first heliostats considered as industrial elements were developed at the beginning of the decade of the eighties for experimental plants central receiver thermo-solar, with the purpose to prove the viability of solar thermal energy in processes of industrial scale electricity production. Table 1 summarizes the projects carried out due to the international initiative:

TABLE 1 International plant projects central receiver thermo-solar

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one

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Once the demonstration projects were completed, most of these plants were closed. 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).

In the USA, the Solar One plant was remodeled and, with the same heliostat field, the plant was put into operation Solar Two which has been running until April 1999.

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

Table 2 summarizes the prototypes of heliostats developed today and its optical characteristics and mechanical

TABLE 2 Heliostat model and its optical characteristics and mechanical

2

As shown in table 2, all described heliostats have had spherical optics, that is, any beam of rays parallel to the optical axis converges once reflected in a single point, called focus or focal point. its objective is, therefore, the reproduction of the image of the Sun in a certain white, in contrast to the optical heliostat cylindrical, object of the invention, whose purpose is not the reproduction of the image of the Sun, but the distribution of its radiant energy along a preferred direction. Disappears thus the concept of focal point, replacing the concept of line focal; that is, any beam of rays parallel to the optical axis converges once reflected along a line, called focal line

But the cylindrical focal line heliostat confined needs two additional requirements, which are the immobility and specific orientation of the secondary axis. Saying axis, as such, does not exist in any of the heliostats reviewed, since all are spherical. However, table 2 shows that only the HELLAS spherical heliostat has a mechanical shaft fixed zenith of non-specific orientation for each heliostat, but general East-West for all field heliostats; since the secondary axis as such does not exist, its immobility responds only to mechanical criteria, without impact on optical performance, which is the purpose of the present invention

The problems posed by the use of spherical heliostats are perfectly reflected in the US 3,892,433 by Martin Marietta, which describes an installation to produce electricity using the solar energy concentrated by a field of spherical heliostats on a circular target. In order to follow the sun during its daytime variation of height and azimuth, the reflective surface of each heliostat must be able to pivot around a horizontal axis, which is adjustable in turn around a vertical axis. How I know shows in figure 4 of said document, such a solution introduces various astigmatism errors due to incidence of the light outside the optical axis of the heliostats which causes, on the one hand, a dispersion of energy as a result of the focus does not match the plane of the receiver, and on the other hand, a image picking throughout the day. It is understood that this selection will be especially harmful if it is intended to pass from concept of focal point to that of focal line, replacing spherical reflectors by cylindrical reflectors.

Proposals for use are also known of cylindrical heliostats with orientation movement in a single axis in solar plants with linear type receiver, both small scale (US 3,861,379) as large scale (US 4,141,626).

Thus, the linear focus concentrator device described in Anderson patent document 3,861,379 to Anderson, comprises a plurality of rectangular flat reflectors arranged with different angles of inclination to concentrate the sunlight on a domestic hot water collector located by above and a short distance from the reflectors. The angle of Reflector incidence varies simultaneously during the day so that the reflected image of the sun always affects the manifold. Since high performance is not pursued, the inclination of the device with respect to the plane of movement The sun's apparent is fixed. That is to say, the variation of the decline of the sun during the year, anticipating at most two positions, winter and summer, among which switch manually. As a consequence, the linear focus shifts longitudinally over the receiver throughout the year, although without serious consequences given the small focal length. A solution can only work for low power devices and very short focal length, such as water applications domestic hot.

It has also been proposed to correct the errors of astigmatism through the use of geometry optics variable such as that described in US Pat. 4,141,626 of FMC Corporation in which the day is modified curvature of the reflective surface of the heliostat. This modification will be maximum during the summer solstice and minimum in the winter one, due to the extreme positions (maximum and minimum, respectively) of the azimuth and height angles of the Sun over the horizon. The cited document uses a certain type of heliostat with deformable cylindrical reflective surface, which point to a horizontal white, oriented East-West, the primary axes of said heliostats being parallel thereto, while the secondary axis as such does not exist, and the deformation of the image by astigmatism is compensated by an action on the cylindrical reflective surface, varying its focal length. A solution eliminates image scattering, improving considerably the focus and, given the orientation of the axis heliostat primary parallel to the target, suppresses the selection, but cannot prevent the linear focus from shifting longitudinally over the target throughout the day. This displacement is very important when working with distances high focal points, so that the length of the target is limited, the number of hours of operation of the device. Note that if we provide this device with a second vertical axis to follow the sun's hourly movement, such as recommended by Martin Marietta, we would get the longitudinal immobilization of the linear focus on the target at throughout the day but, in return, there would be a burning of the linear focus because the parallelism of the primary axis is no longer maintained of the heliostat with the target.

In certain cases the use is proposed of cylindrical heliostats with associated linear mobile target, and Two-axis orientation movement for sun tracking.

Thus, US 5,253,637 of Maiden states the problem of fixed reflector and white solar collectors, which present high losses and a severe limitation of number of hours of use The proposed solution consists of couple a linear receiver on a cylindrical shaft reflector horizontal primary capable of rotating with respect to an axis vertical secondary In this way the linear focus does not present picking since it is a mobile target device attached to the reflector. While it is true that in Maiden there is a plane main image (the primary axis and the linear target are parallel by construction), this is a mobile plane, necessarily inclined, and consequently it can never be perpendicular to the secondary axis vertical. Maiden solves the problem of selection in exchange for make the linear target mobile, which implies that it can only carry a single reflector associated, with the consequent limitation of the power absorbed by it.

Finally, in GB 2 063 465 of Jubb, the problem posed is the low performance of the photoelectric cells as a power generating device electric The proposed solution is to divide the spectrum luminous by means of a diffraction groove, making each stretch of wavelength over different groups of cells Photoelectric systems specially adapted to each wavelength. How in the previous document, it is a reflector set cylindrical with associated mobile target, in horizontal arrangement.

In conclusion, none of the heliostats known previously has the requirements to a cylindrical of high performance and simplicity of construction and operation like the one that is the object of the invention.

The problem posed is the selection of the focal line on a fixed target independent of the heliostat, and could be solved by a three-axis drive, of such way we would need two axes to follow the sun in its diurnal variation of height and azimuth, and a third axis to correct the burning One such solution is expensive and complex of realization.

Consequently, it is an objective of the present invention having a heliostat of such a constructed and operated that is able to follow the sun in its daytime movement, maintaining a linear image without burning on a white Fixed linear located at considerable distance.

It is another objective of the present invention the have a heliostat that, fulfilling the conditions above, can be operated by its operation in two axes

Description of the invention

To achieve the proposed objective the plan main image of the heliostat object of the invention should remain motionless in space and contain the linear blank, which It can be achieved by combining the following elements:

one.

A reflective surface of cylindrical optics or parabolic trough, indistinctly, that must be able rotate around a primary axis coinciding with the generatrix central reflective surface.

2.

A structure consisting of a mobile support that can rotate with respect to a secondary axis perpendicular to the primary axis, being the primary axis of solidarity of the mobile support.

3.

Specific axis orientation secondary, perpendicular to a main image plane, motionless in the space, which contains at all times the linear target and the axis primary.

Four.

A primary drive to rotate the reflective surface around the primary axis and a secondary drive to make rotate the mobile support around the secondary axis, governed both by a control device.

As relevant aspects of the realization of the invention we will stop especially in the geometry of the reflective surface, its daytime orientation, the structure that relates the primary axis and the secondary axis, and the confinement of the focal line

Geometry of the reflective surface . The reflective surface of the heliostat object of the invention has cylindrical or parabolic trough geometry instead of the conventional spherical, which concentrates the solar radiation not on a focal point but on a focal line, of length consistent with the preferred direction dimension of distribution of the intended energy over a certain target. This surface can be of a piece or faceted, in which case the facets are also cylindrical or parabolic trough and with foreseeable focal length that is predictably identical to that of the enveloping surface that results from aligning them cylindrically. The central generatrix of this reflective surface (faceted or not) must be coincident with the primary axis of the heliostat and, therefore, orthogonal to its secondary axis. For practical purposes it can be admitted that the central generatrix and the primary axis are not exactly coincident if they are parallel and very close and in this sense the word "coincident" will be used in this document. The purpose of this geometry is to replace the focal point of conventional heliostats with a focal line, parallel by construction to the central generatrix of the cylinder, and whose length, at normal incidence, coincides with its dimension. The result is a distribution of the radiant energy of the Sun reflected by the heliostat along a preferred direction over the target.

Daytime orientation of the reflective surface to achieve the aim . Like any heliostat, the confined focal line cylindrical needs to be oriented in space in order for the rays from the Sun and reflected on its surface to hit the target. This is achieved through the intervention of two drive mechanisms, which rotate said surface a certain angle around the primary and secondary axes, after calculating the solar vector and direction of the beam reflected by a control device.

Structure of the set . The special arrangement of the primary and secondary axes just described constitutes a radical change with respect to the arrangement used in conventional heliostats. In these, the primary axis of azimuthal orientation of the reflective surface is vertical and remains motionless in space. The reason is fundamentally economic, since it is very favorable to support said primary axis on the heliostat pedestal itself, which holds it to the ground. Said pedestal is usually constituted by a vertical metal tube, which can accommodate inside the rotating bearings of the primary shaft, which is thus hidden in the pedestal itself. Such an arrangement is absolutely inadequate to meet the condition of confinement on the target of the focal line. The proposed solution is to relate directly to the pedestal not the primary axis but the secondary axis, with which the primary axis of azimuthal movement is freely dragged during the zenithal movement around the secondary axis, which now remains in a fixed orientation in space .

Focal line confinement . The confinement (immobility) of the focal line of the cylindrical surface described above is achieved by immobilization of the orientation of the secondary axis of the heliostat in its systematic procedure of targeting a target during the day. This immobilization of the secondary axis also immobilizes the main image plane and, therefore, its intersection with the surface of the target, which is the geometric place where irradiance is distributed (focal line). Since the position of the focal line on the target depends on the intersection of the main image plane with the target plane, and that the orientation of said main image plane depends on the orientation of the secondary axis of the heliostat, it follows that the orientation from it it can be modified at will by simply orienting (and immobilizing) said secondary axis.

In summary, the confinement of the focal line (i.e. immobility and orientation of the secondary axis) by previous means will enable the focal line of the reflective surface is oriented according to the direction where it is intends to distribute the light concentrated by it on an element receiver (linear white) and, more importantly, than the keep static in that direction, without the reflection of the light off the optical axis I managed to pick it since, at all times, the focal line lies on the main image plane, motionless, remaining "confined" throughout the day.

The cylindrical heliostat object of the invention, clearly outperforms conventional spherical heliostat in those applications in which the radiant energy of the Sun reflected on a certain receiver needs to be specifically concentrated at along a preferred line or address. In this case the form of The flow distribution over the receiver is no longer Gaussian circular or elliptical, but will have a Gaussian profile in a direction and straight in the orthogonal direction, which coincides with that of the focal line of the heliostat. The advantages that derive from this done are basically:

one.

Individual irradiance profile by defect of each heliostat on the target coinciding with that of design for the entire field, which prevents the construction of the latter through a composition of Gaussian profiles individual irradiance (aiming strategy).

2.

Global irradiance distribution more stable on the receiver, because there is no picking (turn on the white plane of each of the distributions individual irradiance) throughout the day, due to the immobility and orientation of the secondary geometric axis of the heliostats

3.

Adjustable irradiance profile, already that the mechanism allows to orientate the secondary geometric axis of the heliostat in any direction.

Four.

Damping of the classic irradiance peaks due to various causes during the operation, such as spurious blurring of heliostats (breakdowns, loss of control), presence of clouds partially shading the heliostat field, loss of communications, etc. This is because the default profile of each heliostat does not support the presence of abrupt concentration peaks.

5.

Absence of dynamic strategies of point, which will allow a relaxed and safer operation of the plant, since each heliostat will aim throughout the operation Routine to one place.

6.

Simplification of the alignment procedure or edging of the faceted heliostat since there are no two directions of alignment but one. This reduces the set-up time of the heliostat in the field.

7.

Relief of surface tensions heliostat reflective, since, being cylindrical, we eliminate One of the curvatures. This fact will foreseeably extend life average of said surface.

Brief description of the drawings

To complete the description above and with in order to help a better understanding of the characteristics of the invention, a detailed description of a preferred embodiment based on a set of drawings that accompany this descriptive report, and where with character merely indicative and not limiting what has been represented next:

Figure 1 shows a plant central receiver thermo-solar where you can the heliostat of the invention be used.

Figure 2 represents a detail of the receiver showing the circular image of the sun produced by a heliostat Conventional spherical reflective surface.

Figure 3 represents a detail of the receiver showing the elongated image of the sun produced by a surface cylindrical reflective at noon.

Figure 4a shows the image of the sun produced by a cylindrical reflective surface in conventional mounting, in the morning.

Figure 4b shows the image of the sun produced by a cylindrical reflective surface in conventional mounting, at noon.

Figure 4c shows the elongated image of the sun produced by a cylindrical reflective surface in assembly Conventional, in the afternoon.

Figure 5a shows the image of the sun produced by a cylindrical reflective surface in the assembly of the invention, in the morning.

Figure 5b shows the image of the sun produced by a cylindrical reflective surface in the assembly of the invention, at noon.

Figure 5c shows the image of the sun produced by a cylindrical reflective surface in the assembly of the invention, in the afternoon.

Figure 6 shows a perspective view rear of the "horizontal" mount of a heliostat with cylindrical reflective surface.

Figure 7 shows a perspective view rear of a "pseudo-horizontal" mount of a variant of the heliostat of the invention with surface cylindrical reflective.

Figure 8 shows an elevation of the heliostat object of the invention, in general configuration.

Figure 9 shows an elevation of the heliostat object of the invention in a preferred embodiment in which the Linear white is arranged vertically and the mobile stand is of type fork.

Figure 10 shows an elevation of the heliostat object of the invention in a preferred embodiment in which the Linear white is arranged vertically and the mobile stand is straight, giving place to a reflective surface configuration in "clapper".

Figure 11 shows a side view of the heliostat of figure 9.

Figure 12 shows a plan view of the heliostat of figure 9.

Figure 13 shows, schematically, the positions of the earth with respect to the sun during the solstices.

Figure 14 shows, schematically, one of the devices known in the prior art and their arrangement in relation to the apparent path of the sun with respect to the plane of the soil for solstices and equinoxes,

Figure 15 shows, schematically in perspective, the spatial geometry on which the invention.

Figure 16 is an elevation of Figure 15.

Figure 17a shows, schematically in perspective, the spatial geometry of a mounting heliostat conventional.

Figure 17b shows schematically in perspective, the spatial geometry of a heliostat with mounting of the invention.

Figure 18a shows, schematically in perspective, the azimuthal movement of a mounting heliostat conventional.

Figure 18b shows, schematically in perspective, the azimuth motion of a heliostat with the mount of the invention.

Figure 19a shows, schematically in perspective, the zenith movement of a mounting heliostat conventional.

Figure 19b shows, schematically in perspective, the zenith movement of a heliostat with the assembly of the invention.

It is noted that figures 1 to 7 correspond to the field of application of the invention, prior art and necessity of the invention, figures 8 to 12 correspond to the structural description of the invention, and figures 13 to 19 correspond to the explanation of the mode of operation of the invention.

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

one.

Reflective surface.

2.

Mobile support.

3.

Axis primary.

Four.

Primary drive.

5.

Axis secondary.

6.

Secondary drive

7.

Pedestal.

8.

Control device.

9.

Axis zenithal

10.

Main plane image.

eleven.

Linear white.

12.

Sun.

13.

Earth.

14.

Axis of north-south turn of the earth.

fifteen.

Ecliptic.

16.

Ground.

17.

Apparent plane in the Equinoxes

18.

Apparent plane in the solstice of summer.

19.

Apparent plane in the solstice of winter.

twenty.

Main plane object.

twenty-one.

Bisector plane.

22

Thunderbolt main incident

2. 3.

Thunderbolt Main reflected.

24.

Reflection plane

25.

Axis optical.

26.

Tower.

27.

Flat reflectors.

28.

Manifold.

Detailed description of a preferred embodiment

Figure 1 shows a plant central receiver thermo-solar, where it has represented a detail of the area of the tower in which the White. In a conventional installation, with heliostats of spherical reflective surface, the image projected by each of them on the target is circular, as seen in figure 2. If, as is the case, a dimension of this is considerably greater than the transversal dimension it will be necessary to resort to a aiming strategy of the different heliostats to cover the White. Alternatively, and as seen in Figure 3, the use of a cylindrical reflective surface allows to cover the entire target with a single heliostat. In this way everyone field heliostats point to the same place, simplifying considerably the operation of the plant.

However, if we just equip a conventional mounting heliostat with a reflective surface cylindrical we will only get a vertical image at noon such as It is represented in Figure 4b. In the morning the image will appear selected in one direction (figure 4a), while in the afternoon the image will choose in the opposite direction (figure 4c). Since the objective is that the image does not sting throughout the day, as it is represented in figures 5a, 5b and 5c, we must modify the Reflective surface mount.

Figure 6 shows the assembly conventional of a heliostat that has been equipped with a cylindrical reflective surface. The image projected on the white corresponds to what is represented in figures 4a, 4b and 4c. Note how the primary axis (3) is inserted into the pedestal (7), while the secondary axis (5) is "dragged" by the own primary axis (3). We will call such a configuration as "7-3-5" according to references Numeric used.

The proposed solution, to obtain an image without screening, as a precondition, it passes by immobilizing the secondary axis as explained above. In the figure 7 shows the new assembly used in the heliostat of the invention, in which the secondary axis (5) is related directly with the pedestal (7), while the primary axis (3) it is "dragged" by the secondary axis itself (5). We will name to such a configuration as "7-5-3" to distinguish it from the configuration "7-3-5" conventional, highlighting that it presents a functional behavior radically different. Later we will justify the need to this choice to achieve the proposed objective.

Even when the assembly of figure 7 is functionally correct, it is not very practical from a point of constructive view In addition, the mismatch between the primary axis (3) and the central generatrix of the cylindrical reflective surface You can enter certain focus aberrations. Finally such as can be seen in figure 7, a interference of the pedestal itself (7) in the movement of the reflective surface.

An embodiment is shown in Figure 8 preferred from the type of constructive view, in which it has not been introduced any restriction regarding the orientation of the White. The heliostat object of the invention comprises a reflective surface (1), cylindrical or parabolic trough, capable of rotating through a primary drive (4) around a primary geometric axis (3) supportive of a mobile support (2) which, in turn, is capable of rotate around a secondary geometric axis (5) perpendicular to the primary geometric axis (3) and forming an angle of inclination α with the zenith axis (9), by means of a drive secondary (6). Both drives (4) (6) are governed by a control device (8). The set is supported by a pedestal (7) whose design must be such that it allows the movement of the reflective surface (1) and the mobile support (2) without interfering with the pedestal itself (7). The reflective surface (1) is, preferably, cylindrical optics or cylindrical-parabolic.

In a particular embodiment, which we will call zenith mount, linear target (11) is placed in position vertical on a tower (26) so that the focal line, when match it, it will also be vertical, which leads to a arrangement as shown in figures 9, 10, 11, 12, 15 and 16, in which the secondary axis (5) is horizontal and the primary axis (3) this content in the so-called main image plane (10), vertical.

Figure 10 shows a variant of the heliostat of the invention with a single surface support point reflective (1), to constitute a type configuration "clapper" as opposed to type setting "fork" shown in figure 9. One such solution, very simple, however, it presents some major requests in the only fastening point of the primary shaft (3) to the mobile support (2).

Referring now to figures 12, 15 and 16 we can see how the primary axis (3) is contained in the main plane image (10), which in turn contains the focal line of the heliostat, and the linear blank (11). So that the primary axis (3) this content at all times in the main image plane (10), the secondary axis (5) must be perpendicular to the plane main image (10), and therefore horizontal, so it remains defined during the initial assembly of the heliostat, not depending its orientation rather than the relative position of the heliostat Regarding the target.

The initial assembly of a heliostat like the described is very simple, just in a first phase with having vertical the primary axis (3) so that it is contained in a plane vertical that passes through the linear blank (11) for, in a second phase orient the secondary axis (5) perpendicular to said flat.

In order to explain the method of operation of a such heliostat and referring to figures 13 and 14 we will perform a brief introduction to the apparent movement of the sun with respect to the land, which in any case will be well known by the skilled. In figure 13 it has been represented, very schematically, the position of the earth (13) in its movement around the sun (12) when it travels the ecliptic (15). Due to the tilt of the north-south axis of rotation of the earth (14), with respect to the plane of the ecliptic (15) at an angle of 23 degrees 27 minutes, the sun's rays (12) hit a point of the earth's surface with an angle of incidence variable at throughout the year This angle of incidence will be maximum at the solstice summer (position A) and minimum in the winter solstice (position B). The position of the earth (13) for the equinoxes would correspond in this figure to an axis perpendicular to the plane of the same about the position in which the sun has been represented (12). In Figure 14 shows, very schematically, the movement apparent of the sun with respect to the ground (16), having represented the apparent plane in the equinoxes (17), the apparent plane in the summer solstice (18) and the apparent plane in the solstice of Winter (19) The observer O will see the ortho and the sunset of the sun diverted to the north (N) at the summer solstice (V) and diverted heading south (S) in the winter solstice (I), while in the equinoxes the sun rises in the east and sets in the west with an apparent 180 degree travel. In figure 14 it has also represented the Anderson solar concentrator as It is described in US 3,861,379. If the set of flat reflectors (27) is arranged perpendicular and centered with respect to the apparent plane in the equinoxes (17), the image of the sun converted into a line it will be projected on the collector (28) only in the equinoxes, suffering for the other days of the year a longitudinal displacement on the same that will be maximum in solstices. This penalty it is the inevitable result of single axis control, and in the case of the Anderson concentrator is admissible due to the small focal length "d".

Referring now to figures 11, 12, 15 and 16, for a heliostat as described in the present invention the operation method lies basically in governing the two drives (4) (6) in such a way as to ensure that the energy radiant reflected by the heliostat at all times affects the linear white (11) throughout each day and for every day of the year. According to the law of specular reflection, the main ray incident (22) and the reflected main beam (23) are in the same reflection plane (24), and the optical axis (25) of the heliostat must be also on the bisector line of both main rays, defined this bisector as the intersection of the reflection plane (24) with the bisector plane (21) of the main object plane (20) and of the main image plane (10). This requires:

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A drive movement primary (4) to carry the optical axis (25) of the surface reflective (1) a lateral angle? on the bisector plane (twenty-one). See figure 12.

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A drive movement secondary (6) for, taking into account that the positions of the sun and of the target are predefined, vary the angle of elevation? of the mobile support (2), in order to carry the optical axis (25) of the reflective surface (1) on the reflection plane (24). Watch figure 11.

Next we will analyze, in an example Simplified, step-by-step operation of a heliostat conventional and heliostat of the invention highlighting the reasons that lead to the special structure and layout of this latest.

Figure 17a schematically shows a cylindrical optic heliostat and conventional horizontal mount , of the type shown in Figure 6, in the rest position, with the vertical primary axis, oriented its reflective surface towards the South which is where it is also assumed that the white (the orientation of said surface is fixed by the direction and direction of the normal unit vector \ hat {n} that passes through its center). The central generatrix g of said cylindrical surface is contained in the plane \ pi of the meridian of the place and is, by construction, normal to the plane of the local astronomical horizon. According to Figure 17a, if we projected said central generatrix in the South direction on a plane π 'normal to the horizon, the resulting line would remain contained in the meridian of the place . Let's see how the orientation movement of the heliostat affects this projection of its central generatrix and its consequences from an optical point of view. Due to the nature of its mechanical mount , the heliostat is oriented in the Euclidean space by means of two turning mechanisms: a) the azimuth turning mechanism \ Omega_ {acim}, which runs around a vertical axis to the plane of the plane horizon, called the primary axis (3), and which normally coincides with the axis of the heliostat pedestal ; and b) the zenith \ Omega_ {cen} mechanism, which runs around an axis parallel to the plane of the horizon, called the secondary axis (5) and normally coincides with the horizontal support arm of the heliostat. Suppose the Sun is now, in the morning, somewhere on the plane of the horizon, so that the heliostat - obeying the laws of Geometric Optics - needs to orient itself in this coordinate system to reflect and maintain the image of the Sun on a fixed solar receiver, with an elongated and vertical shape , located on top of a tower throughout the day. As stated above, the heliostat must necessarily reach the orientation for the correct aim at the fixed target by executing two well-defined turns. The first of these, according to Figure 18a, is the azimuth turn \ Omega_ {acim} around the primary axis, whose angle of rotation we assume a magnitude w_ {acim}. It also follows from the figure that the orientation of the primary axis is not altered with the rotation but, due to a mechanical bond between them, as a consequence of this first rotation the secondary axis leaves its initial orientation and rotates exactly an angle of magnitude w_ { acim} . In the new orientation, the family of solar rays reflected in the central generatrix of the reflective surface of the heliostat will project on the base of the tower, still with all its rays contained in the plane \ pi of the meridian of the place. Since the solar receiver is on top of the tower, the heliostat should now execute the second turn that is still missing to raise the image to the desired point. Figure 19a shows the zenith turn \ Omega_ {cen} of magnitude w_ {cen} that must be executed around the secondary axis to achieve the objective. The fundamental question is now: in what position is the central generatrix g of the heliostat found after this second turn? When the orientation of the secondary axis has been altered due to the azimuthal rotation, and now the reflective surface is rotated around it, the central generatrix g bends over the plane of the horizon while also leaving the plane of the meridian of the place . From an optical point of view, the family of solar rays reflected in the central generatrix of the cylindrical surface will be projected on the solar receiver at the top of the tower, but its rays are no longer fully contained in the plane of the meridian of the place . In summary, the heliostat aiming procedure has had as a geometric consequence the removal of both the central generatrix and its projection on the target from the meridian plane and, consequently for optics, that of selecting the focal line on said target, thus losing the requirement of verticality That is, the linear image given by the heliostat adapts to the solar receiver in terms of shape (elongated) , but not in terms of the orientation requirement (vertical) . The consequences on the distribution of solar irradiance on the linear receiver are shown in Figure 4 through the analysis of the energy isoflow lines.

Figure 17b schematically shows a particular case of cylindrical optic heliostat and pseudo-horizontal mount , similar to that of Figure 10, in rest position, with the vertical primary axis, oriented its reflective surface towards the South (the orientation of said surface it is fixed by the direction and direction of the normal unit vector \ hat {n} that passes through its center). The central generatrix g of said cylindrical surface is contained in the plane \ pi of the meridian of the place and is, by construction, normal to the plane of the local astronomical horizon. According to Figure 17b, if we projected this central generatrix in the South direction on a plane \ pi 'normal to the horizon, the resulting line would remain contained in the meridian of the place . Let's see again how the orientation movement of the heliostat object of the invention affects this projection of its central generatrix and its consequences from an optical point of view. Due to the nature of its pseudo-horizontal mechanical mount , the heliostat is oriented in the Euclidean space by means of two turning mechanisms: a) the azimuthal rotation mechanism \ Omega_ {acim}, which runs around an orthogonal axis to the horizon plane, called the primary axis (3) and whose orientation coincides with that of the central generatrix of the heliostat; and b) the zenithal rotation mechanism \ Omega_ {cen}, which runs around an axis parallel to the plane of the horizon, called the secondary axis (5) and which coincides in this case with the horizontal support arm of the heliostat. Suppose the Sun is now somewhere on the horizon plane, so that the heliostat - obeying the laws of Geometric Optics - needs to be oriented in this coordinate system to reflect and maintain the image of the Sun on a fixed solar receiver. , with an elongated and vertical shape , located on top of a tower. As with the conventional model, the proposed heliostat must necessarily achieve the proper orientation by executing two well-defined turns. The first of these, according to Figure 18b, is the azimuth turn \ Omega_ {acim}, whose angle of rotation we assume of a magnitude w_ {az}. It also follows from the figure that the orientation of the primary axis is not altered with the rotation ; also, due to the special mechanical relationship between both axes, the secondary axis does not alter its initial orientation as a result of the first turn \ Omega_ {acim}. The family of solar rays reflected in the central generatrix of the reflective surface of the heliostat will be projected on the base of the tower, but with all its rays still contained in the plane \ pi of the meridian of the place .

Since the solar receiver is on top of the tower, the heliostat should now execute the spin that is still missing to raise the image to the desired point. Figure 19b shows the zenith turn \ Omega_ {cen} of magnitude w_ {acen} that must be executed around the secondary axis to achieve the objective. The essential question is now: in what position is the central generatrix of the heliostat after this second turn \ Omega_ {cen}? Since the orientation of the secondary axis has not been altered , and the cylindrical surface is now rotated around it, the central generatrix tilts with respect to the horizon, but remains fully contained in the plane \ pi of the luqar meridian . From an optical point of view, the result is that the family of solar rays reflected in the central generatrix of the cylindrical reflecting surface will project on the solar receiver at the top of the tower, but with all its rays contained in the plane of the meridian of the place . In summary, the geometric result of the heliostat pointing procedure has been to confine on the meridian of the place both the central generatrix of the reflective cylindrical surface and its projection on the target and , consequently, the focal line of the optical system remains vertical on this one for any solar position . That is, the image given by the heliostat, adapts to the solar receiver both in shape (elongated) and orientation (vertical) for any time of the day. The consequences on the distribution of solar irradiance on the linear receiver, for an arbitrary position of the Sun , are shown in Figures 5a, 5b and 5c through the analysis of the energy isoflow lines.

They will be evident to an expert in the field a series of realization alternatives that allow adapting the design to the specific technical and economic conditions of each concrete realization Thus, for example, in the description of a preferred embodiment, shown in Figure 9, the mobile support (2) is shaped like a "fork" but it is clear that obtain the same practical result with any other assembly of clamping of the primary and secondary axes, including the surface reflector hung in a "clapper" arrangement, such as depicted in figure 10.

Likewise, the expert knows the relative movement of the earth and the sun throughout the year, so which may determine the performance of the control device (8) to ensure that the reflected image of the sun affects at all times on the linear target (11), throughout each day and for all days of the year.

Claims (3)

1. Linear focus heliostat of the type used to form heliostat fields in central receiver solar thermal plants consisting of a linear target (11) fixed on a tower (26), characterized by understanding;

a surface reflective (1), cylindrical or parabolic trough, capable of rotating with respect to a primary axis (3), coinciding with the central generatrix of the reflective surface (1).

a mobile stand (2), capable of rotating with respect to a secondary axis (5) perpendicular to the primary axis (3), the primary axis (3) being solidarity of the mobile support (2), and the secondary axis being arranged (5) perpendicular to a main image plane (10), motionless in the space, which contains at all times the linear target (11) and the axis primary (3),

a drive primary (4) to rotate the reflective surface (1) around the primary axis (3),

a drive secondary (6) to rotate the mobile support (2) around the secondary axis (5),

a device control (8) to govern the primary drive (4) and the secondary drive (6).

2. Linear focus heliostat according to claim 1, characterized in that the linear target (11) is vertical. 3. Method of operation of the heliostat of claims 1 to 2 characterized by comprising the following maneuvers;

movement of primary drive (4) for, taking into account that the positions of the sun (12) and the linear target (11) are predefined, bring the optical axis (25) of the reflective surface (1) at an angle lateral γ on a bisector plane (21) of the main plane image (10) and the main object plane (20) defined as those contain the primary axis (3) and the main reflected beam (23) or to the main incident beam (22) respectively,

movement of secondary drive (6) for, taking into account that the positions of the sun (12) and the linear target (11) are predefined, vary the angle of elevation? of the mobile support (2), with object to carry the optical axis (25) of the reflective surface (1) on the reflection plane (24), defined as the plane that contains the reflected main beam (23) and the main beam incident (22);

in such a way as to ensure that the reflected radiant energy affects the target at all times linear (11), throughout each day and for every day of the year.