EP2756235A2

EP2756235A2 - Concentration-type solar panel with bi-axial seeking and managing system comprising such panel

Info

Publication number: EP2756235A2
Application number: EP12773388.9A
Authority: EP
Inventors: Marco Zangirolami; Mauro Rossi
Original assignee: Fandis Lab SRL
Current assignee: Fandis Lab SRL
Priority date: 2011-08-25
Filing date: 2012-08-09
Publication date: 2014-07-23
Also published as: ITTO20110777A1; WO2013027229A2; WO2013027229A3

Abstract

A concentration-type solar panel (1) with bi-axial seeking is described, comprising an external containing structure (3) defining therein at least one first room and having in its upper surface an opening covered with a layer of highly transparent material (5) adapted to allow the passage of a solar radiation inside such room, further comprising at least one solar absorbing device, inserted inside a Dewar tube (7) and arranged inside the first room and a respective plurality of parabolic concentrators (9), which rotate through handling means around a rotation axis coaxial with an axis of symmetry of the absorbing device and the Dewar tube (7) and with an axis of the focus of the parabolic concentrator (9), and further comprising means for recognising a direction of an incident radiation of a sun light cooperating with at least one concentrator (9) and processing means cooperating with the handling means and the means for recognising a direction of an incident radiation. A managing system for the operation of such solar panel is further described (1).

Description

CONCENTRATION-TYPE SOLAR PANEL WITH BI-AXIAL SEEKING AND MANAGING SYSTEM COMPRISING SUCH PANEL

The present invention refers to a concentration-type solar panel with bi-axial seeking and to a managing system comprising such panel.

As known, the art proposes different types of solar devices, that allow converting the solar radiance into thermal energy by means of components aimed to pick up the solar radiation. In general, the operation of such devices provides that the solar radiation, once arrived onto the pick-up device, is absorbed by an absorbing device and transferred to a thermo-vector fluid, that can be water, air or a diathermal fluid.

The part of radiance that directly reaches the ground is the direct radiation, while the remaining part is the diffused radiation. To these ones, finally, the reflected radiation or albedo must be added, which represents the percentage of direct and diffused radiation that is refleceted by the ground or the surrounding surfaces on the considered surface: some of the solar devices are able to exploit only the direct radiation, while others allow using the three components (direct, diffused and reflected) of the radiation itself.

The solar devices can also be classified depending on the temperature of the thermovector fluid and on the concentration ratio Cr, defined as the ratio between the admission surface of the non-concentrated solar radiance and the absorption surface of the device.

Currently, solar devices are substantially represented by solar panels, concentrators and solar plants .

Solar panels are generally composed of:

an absorbing surface;

a network of pipes in which the thermovector fluid flows ;

a highly transparent cover, typically made of glass, able to pass visible and near-infrared rays, but to stop the far-infrared radiation;

an insulating coating;

a containing structure that makes the external envelope .

The plane solar panels use the three components of the solar radiation and exploit the greenhouse effect. The transparent cover is in fact made of materials that are transparent to the incident solar radiation, but opaque to the re-irradiated infrared radiation. The thermal energy coming from the sun is then captured inside the panel and transferred to the thermovector fluid. In order to limit the heat losses towards outside, the side and rear areas are then protected with insulating material.

Moreover, inside the containing strutture, there is a slab, typically made of copper, coated with a selective absorbing device, which in turn has the feature of absorbing with high yields the visible and near-infrared radiations, limiting the emissivity on the thermal infrared emitted by the same slab with hot vault.

The back of this slab is insulated from outside through a panel, typically made of mineral wools, to avoid as much as possible the heat losses.

The advantages of a plane panel are those of being easily installed on a roof and, due to its shape, not allow an easy deposit of snow.

Moreover, since the optical path between glass and absorbing device arranged immediately adjacent to the glass itself, is reduced to a minimum, the optical efficiency (at ΔΤ = 0) is the highest one among the solar devices .

The greatest disadvantage however is having a great radiating, in addition to absorbing, surface, and from this surface, both due to radiance and due to conduction with the above air and the lower insulating panel, and due to convection with the above air and through the glass slab, the panel loses heat when the temperature difference with the outside starts getting important, lowering thereby immediately the efficiency. In practice, the plane solar panels cannot be used for high temperature jumps, and also their adoption for integration to heating in cold areas is not always possible, and anyway requires the installation of low- temperature radiating elements (typically radiating floors) , which is not always possible (and anyway is costly) when new buildings are involved.

In order to optimise the efficiencies, it is further necessary to orient them in the best possible way, which in the majority of cases does not correspond to the inclination of the roof pitch (even less the walls), making the advantage of snow sliding moot.

The art further proposes solar panels equipped with vacuum tubes composed of a plurality of Dewar thermos with the external vase transparent and the internal vase coated with highly selective absorbing materials. Since, through the vacuum hollow space existing between the two vases, heat is transmitted only through radiance, the degree of thermal insulation of the absorbing device is very high. Putting many of these pipes side by side and making a tube, inside which the thermovector fluid flows, pass thereinto, a panel is obtained with good efficiency even at high temperature differences.

The circuit for removing absorbed heat can be made with an U-bent tube, with a heat pipe or even by circulating water by natural convection inside the glass tube. This latter solution, though having advantages for the thermal exchange, does not however allow operating the manifold under pressure, and, in case of accidental breakage even of a single tube, causes the plant to be emptied, thereby preventing, due to pollution reasons, to easily use antifreeze fluids.

The advantage of the solar panels with vacuum tubes is that they have a higher operating temperature that allows using them in more severe climates.

The main disadvantages of the solar panels with vacuum tubes however are their higher technical complexity, with the risk that the Dewar tube, for example due' to a minimum crack, loses its inside vacuum, becoming inefficient, the difficulty of freeing them from snow that gets entangled between the tubes and the fact that, since only the internal tube has to be absorbed, they have a useful orthogonal surface that is lower than the one of the plane panels.

The art further proposes solar panels with CPC vacuum tubes that comprise concentrator mirrors arranged below the Dewar tubes to concentrate light, reducing the number of tubes with the same picked-up energy (and therefore the losses that are in direct proportion with the number of used tubes) . Since however such mirrors are arranged in fixed positions, they could have a high merit factor Q, otherwise they would lose their efficacy even for very small offsets. Moreover, since such mirrors are exposed to bad weather, the loss of reflectivity due to dirt lowers system efficiency with time.

Concentrators are instead composed of a mirror or optical lenses with high merit factor, which converge sunrays towards the absorbing device in which the thermovector fluid flows. Since they exploit the only direct radiation, they need devices suitable to keep at any time the reflecting surface orthogonal to the direction of sunrays. This allows concentrating light onto small surfaces, thereby obtaining, in addition to a temperature- increase, an efficiency increase at high ΔΤ due to the mere form factor. In fact, the amount of radiating energy collected and made pass through the surface of the absorbing device (smaller than a factor equal to the concentration ratio) depends on the projected mirror surface, while the radiated energy depends only on the temperature of the absorbing device and on its surface. It is however necessary to limit the heat loss due to air convection motions that could be very high even in case of light wind.

Moreover, concentrators are distinguished into "image"-type systems, the most common ones, that reproduce the sun image on the focal plane, and "non- image" type systems, that randomly concentrate the sunrays onto the absorbing device.

Image concentrators can in turn be of the punctual or linear types, if they converge sunrays onto the focal point or into an axis passing for the focus.

The main image concentrators of the punctual type are the parabolic concentrators, characterised by a parabolic reflecting surface and by an absorbing device placed in the focal area.

Among them, the two main types are different due to the solar seeking: the first type has its absorbing device fixed and integral with the reflector that instead is moving and seeks the sun; the second type instead has its reflector fixed and the absorbing device moving and going to the area in which the reflector converges the solar radiation.

Cylindrical-parabolic concentrators instead are image systems of the linear type: they are composed of a reflecting surface obtained translating a parabola along an axis passing through its focus and orthogonal to the plane that contains it. In the focal area of the reflecting surface, the linear absorbing device is placed, generally composed of a copper or stainless steel piping inside which the thermovector fluid flows. In order to reduce the convection losses and to favour the greenhouse effect, this piping can be placed inside a glass tube.

As regards sun seeking, the system can have its absorbing device fixed and its parabola rotating, or have its absorbing device integral with the parabola in turn subjected to a rotation motion. Seeking finally can be on an axis (and in such case the absorbing device will have to be oriented according to the east-west direction) or on two axes .

The art further proposes systems that adopt mixed solutions among the previously described ones, such as for example the solar panels with linear concentration with plane screen and/or with vacuum tubes.

The linear concentration-type solar panel with plane screen is in fact equipped with a plane glass that covers the concentrator or a plurality of concentrators if they are very small. The efficiency improvement is given by the only form factor and the presence of the plane glass, in addition to creating an area with unmoving insulating airs, and preserves the parabolic mirror from dirt and bad weather. Such solution is typically adopted for small and medium systems (with parabolas up to about one meter of width) .

The linear concentration-type solar panel with vacuum tubes instead adopts the insulation of the collecting tube with vacuum systems similar to the previously mentioned ones, in order to obtain the maximum temperatures for industrial use (typically for producing energy through turbines or anyway thermal machines operating on the Rankine cycle) . In this way, temperatures of several hundreds degrees are reached with good efficiencies. The system is in practice adopted only in big plants with mirrors whose width is 4 meters or more and with lengths of hundreds of meters, therefore dedicated to producing energy and that cannot be used on a household scale, for example to integrate heating.

O2008130838 discloses a linear concentration-type solar panel with screen on which the cylindrical- parabolic concentrators arranged along each linear absorbing device are rotating along a rotation axis to remain substantially perpendicular to the sun, such rotation being performed with a motor supplied in energy by solar cells.

In order to make solar plants, instead, tower-type systems are normally used, whose major elements are:

a mirror field, composed of a high number of reflecting surfaces that automatically follow the sun path and that concentrate sunrays instant by instant towards a receiver;

an energetic received (punctual boiler) , placed on a tower arranged in a central position with respect to the mirror field;

a system for converting prime thermal energy into mechanical energy (steam turbine) and afterwards into electric energy (electric generator) ;

a regulating system aimed to keep the mirrors orthogonal to the direct radiation.

Seeking can be performed by a computer or by photosensitive elements, which, instant by instant, measure the orientation error of the individual mirror.

US-A1-2008/257335, US-A-4375807 and WO-A1-

2005/066553 disclose a solar panel according to the preamble of- Claim 1.

Object of the present invention is solving the above prior art problems by providing a concentration-type solar panel with bi-axial seeking equipped on board with processing means, such as for example a microprocessor intelligence, and with a series of sensors cooperating with such processing means that allow extremely accurately using such panel.

Another object of the present invention is providing a concentration-type solar panel with bi-axial seeking that can be easily cleaned, can allow easily removing snow, and protecting internal absorbing and reflecting surfaces .

Moreover, an object of the present invention is providing a concentration-type solar panel internally equipped with a bi-axial seeking system which allows removing the disadvantage of the compulsory positioning, and allows installing such concentration-type solar panel on various building surfaces, being them differently- oriented pitches (East-West-South or on a plane) or vertical walls, without excessivley lowering their efficiencies .

Another object of the present invention is providing a concentration-type solar panel with bi-axial seeking that allows obtaining the advantages of the better efficiency ' (due to the form factor) and the higher temperatures of known concentration systems.

Moreover, an object of the present invention is providing a concentration-type solar panel that allows obtaining the advantages of insulation of known vacuum systems coupled with the concentration system.

Another object of the present invention is providing a managing system comprising a plurality of concentration-type solar panels with bi-axial seeking that allows optimising the output temperature of the thermovector fluid from such panels depending on the specific request of the building together with the other panels, managing the modes of seeking, stagnation safety and active thermostating of the delivery due to a dedicated electronics that can be remotely managed through a dedicated network.

The above and other objects and advantages of the invention, as will appear from the following description, are obtained with a concentration-type solar panel with bi-axial seeking as claimed in claim 1.

Preferred embodiments and non-trivial variations of the present invention are the subject matter of the dependent claims.

It will be immediately obvious that numerous variations and modifications (for example related to shape, sizes, arrangements and parts with equivalent functionality) could be made to what is described, without departing from the scope of the invention, as appears from the enclosed claims.

The present invention will be better described by some preferrend embodiments thereof, provided as a non- limiting example, with reference to the enclosed drawings, in which:

Figure 1 shows a top, partially sectioned perspective view of a preferred embodiment of the concentration-type solar panel with bi-axial seeking according to the present invention;

Figure 2 shows a top, partial perspective view of the concentration-type solar panel with bi-axial seeking of the present invention, partially disassembled;

Figures 3 to 5, 7 to 9 and 13 are detailed perspective views of the concentration-type solar panel with bi-axial seeking according to the present invention;

Figure 6 is an enlarged view of box A in Figure 5;

Figure 10 shows a top perspective view of the concentration-type solar panel with bi-axial seeking of the present invention in an operating position thereof;

Figure 11 shows a perspective view of a preferred embodiment of a component of the concentration-type solar panel with bi-axial seeking of the present invention;

Figure · 12 shows a perspective view of an alternative embodiment of the component of Figure 11; and

Figures 14, 15 and 16 show block diagrams respectively of some variations of the managing system according to the present invention.

With reference to the Figures, it is possible to note that the concentration-type solar panel 1 with bi- axial seeking according to the present invention comprises at least one external containing structure 3 defining therein at least one first room and having at least in its upper surface an opening at least partially covered with at least one layer of highly transparent material 5, such as for example glass, adapted to allow the passage of the solar radiation inside such room. The solar panel 1 according to the present invention further comprises at least one solar absorbing device, each one of which is inserted inside at least one Dewar tube 7, arranged inside such first room and at least one respective plurality of parabolic concentrators 9, each one of such concentrators 9 rotating through handling means, described below, aroung a rotation axis coaxial, as is possible to note in particular in Figure 2, at least both with the axis of symmetry of the respective absorbing device and Dewar tube 7, and with the focus axis of such parabolic concentrator 9. Obviously, the rotation axis can also be coaxial with the ducts 21' for removing heat picked up by such absorbing device and transporting the thermovector fluid in order to address it to users through at least one manifold connecting such ducts 21' and described below.

Advantageously, il solar panel 1 according to the present invention further comprises means for recognising a direction of an incident radiation of a sun light cooperating with at least one of such concentrators 9 and processing means cooperating with such handling means and such means for recognising a direction of an incident radiation.

Preferably, as is possible to note notare in particular in Figures 8 and 9, the handling means are composed of a kinematic chain comprising at least one motor 23 and at least one control rod 27, such control rod 27 being moved by such motor 23, possibly by interposing at least one gear-type reducer 25, to drive each screw-type reducer 29 adapted to take and rotate its respective parabolic concentrator 9 with slow rotation axis coaxial with the corresponding absorbing device 23.

Possibly, the control rod 27 can be inserted inside at least one protecting tube, for example made of aluminium.

The handling means can further comprise at least one incremental^' encoder cooperating with the motor 23 and managing means 31 adaoted to drive such motor 23 depending on the position read by such incremental encoder and the measures performed and transmitted by other sensors, such as, for example, a temperature sensor placed in contact with the absorbing device, and indications of means for recognising a direction of an incident radiation placed as moving equipment on the parabolic concentrators 9 and described below in more detail .

Preferably, the control rod 27 has a not circular but constant section, and is therefore free of longitudinally sliding in the worm screws 33 of the reducers 29.

Such screws 33 engage slow gears 35 integral with their respective parabolic concentrators 9 with minimum play and the gears 35 themselves have mechanical limit switches integrated therein. A similar kinematic chain allows reaching every possible position of the parabolic concentrators 9 (this not being possible for example with a system with connecting rods) included the total protection position in case of resting the panel 1 (for example during summer) with the parabolic concentrators 9 completely overturned, that operate as protecting umbrella for the Dewar tubes and the respective absorbing devices, as- shown for example in Figure 10.

Due to this train of reducers 29 integrated in the kinematic chain itself, it is possible to easily reach a high reduction ratio and drive a high number of screw- type reducers with a minimum effort.

Obviously, the external containing structure 3 can be made of any material suitable for this purpose, such as, for example, sheet. Preferably, such external containing structure 3 is made of a single slab of a composite of aluminium and polyethylene (ACP) known with the commercial trademark Alucobond® and the like. In this way, it is possible to perform working on such slab, such as shape cropping, drilling and bend facilitations, and transfer them into their plane shape (and therefore without wasting space during transports), performing the bending of the structure 3 for its formation only upon its final assembly. The application of common tear-type •rivets, screws or any other suitable fastening means will obviously consolidate the structure 3. It must be noted however how, advantageously, the external containing structure 3 is not insulated, since insulation is guaranteed by the Dewar tubes. Inside the external containing structure 3, also having a supporting function of the internal mechanical parts, at least one second room can be obtained, suitable to contain the hydraulic manifold, the control electronics, all the kinematic chain composing the handling means adapted to transfer the motion from the motor to the parabolic concentrators 9 and the thermal insulation in foamed materials and/or mineral wools (according to the working temperature at which the panel 1 is made operate) .

As can be noted from the Figures, advantageously,. the parabolic concentrators 9 are slightly spaced and can rotate around their own rotation axis to follow, wihout shadow overlapping, the sun position till angles of plus or minus 30°, possibly going on following, till a unitary concentration factor is obtained for angles of plus or minus 70°, over which it makes not any more sense to continue .

Preferably, as it is possible to note in particular in Figures 3 and 4, each parabolic concentrator 9, obviously equipped with at least one reflecting surface 11 oriented towards the respective absorbing device and Dewar tube 7 to which it is associated, is made of a reflecting slab of aluminium, curved in order to make it self-bearing in addition to its correct shape. Each head 13 of the parabolic concentrator 9 is equipped with a respective supporting bush 15 for the rotation of such parabolic concentrator 9, such bush 15 being coaxial with the rotation axis of the concentrator 9 itself, and in particular such rotation axis being coaxial with the main major axis of inertia of the sysytem composed of the parabolic concentrator 9 and the supporting bush 15 passing through the barycenter of the moving equipment, in such a way as to be able to rotate such parabolic concentrator 9 with a minimum effort. Preferably, such heads 13 are made of a plastic material resisting to UV, but not necessarily to the high temperatures that can be reached, since, being the focus of the parabolic concentrators 9 concentrated on the absorbing device inside the Dewar tubes 7, outside them no high temperatures are reached. In this way, it is possible to make particularly light parabolic concentrators 9, as advantage regarding both cost and their easy handling even with small motors.

Moreover, it is possible to provide that also the heads 13 are in turn coated with a reflecting material, with the double purpose of protecting plastics from the concentrated radiation and of reflecting this radiation again in the focus of the respective parabolic concentrator 9, inverting its direction. By doing this, one improves the self-aligning performances of focusing along the major axis of the parabolic concentrator 9, since a length is recovered which is equal to the projection of the parabola height per the incidence angle in turn projected along the direction of the major axis of the parabola itself.

Preferably, the means for recognising a direction of an incident radiation are those disclosed in WO9818100. Synthetically, as it is possible to note in Figures 5 and 6, such means for recognising comprise at least one tracking device 17, preferably arranged in a suitable position on at least one head 13 of at least one parabolic concentrator 9, and composed of at least two photosensitive elements 19 (minimum two in case the direction on a fixed axis has to be identified, and minimum three in case of two axes) and at least one overlapping element 21 interposed between such photosensitive elements 19, such overlapping element 21 being adapted to project a shadow onto such photosensitive elements 19. This shadow is made so that, when the angular position of the device 17 on at least one photosensitive element 19 changes, it changes as coverage differently in intensity and/or direction on at least one of the others. By acquiring the intensity values and by processing them, it is always possible to find the relative angular position of the group of photosensitive elements 19 with respect to the incident direction, provided that the degrees of freedom to identify are at least one less with respect to the number of active photosensitive elements 19 (under a linearity situation) at that time. In the particular case of the panel 1 according to the present invention, being it necessary to identify a single axis, two photosensitive elements 19 will be enough, with a single overlapping element 21 that throws its shadow on both of them.

However, in order to be able to reach the declared angles of incidence with an integrated system constrained to the mirrors, it is necessary to provide a particular arrangement. In fact, there is no point of the surface of the parabolic concentrators 9 that is always illuminated by the sun in order to be able to house the tracking device 17. Preferably therefore, at least one parabolic concentrator 9, for example the central one, is equipped with at least two separate tracking devices 17, arranged at the opposite ends of the respective head 13.

In fact, as it is possible to note in Figure 7, the movement of the motor 23 is controlled by a PID regulator that takes the error signal from a direction sensor of the incident radiation 25 valid in such angular position, such angular position being known since the motor 23 itself that moves the parabolic concentrators 9 is equipped with the incremental encoder that is reset upon turning on the panel 1, for example on mechanical limit switches. The count value of the above encoder informs the processing means about the leftward or rightward banking of the parabolic concentrator 9 with respect to the position with axis of the parabola normal to the plane of the panel 1 and consequenty which photosensitive element 19 is surely in the directly illuminated area. From the same encoder, the processing means can obtain the speed signal on which a first feed-forward loop can_. be closed in order to make the behaviour of the motor 23 virtual, simply by deriving the position signal with respect to the time, thereby allowing, with ample margins, to replace the motor 23 with similar models without incurring in control anomalies.

The tracking device 17 as described above takes care of pointing out not only the perfectly aligned position, but also a signal proportional to the offset of the parabolic concentrators 9 with respect to such position. Such signal advantageously allows the processing means to perform the position control of the parabolic concentrators 9 in order to thermostate (within the limits that the available input power is over-abundant with respect to the request) the temperature of the absorbing device. The individual signal coming from a photosensitive element 19 is however affected, in addition to the width of the illuminated area, also by the intensity of the incident radiation that unfortunately is not constant. Therefore, even if next to the central position, the value is always null, the slant with which these values change, also depends on the instantaneous insulation. This can generate instabilities of the control performed by the processing means, if not adequately filtered, since it introduces an uncontrolled gain in the feed-forward loop of the system. However, if the geometric arrangement of the photosensitive elements 19 is such that the shadow areas are inversely proportional one to the other, the sum of the two signals is proportional to the incident power at that time. The processing means therefore can use this value to normalise the error signal, stabilising the motor 23 control, and to evaluate the incident radiation, stopping the seeking when the irradiated power is below a threshold value. The necessary dynamics for such recognition is about 50, since the maximum possible radiation is about 1 W per square meter, while it makes no sense to go on seeking for values lower than 20 W per square meter. If a signal dynamics of 25 for the control is enough (equivalent to identify an angular variation under the worst conditions, assuming to have a maximum angle of 150°, equal to 6 degrees), it is enough to have processing means comprising at least one controller with 8-bit TO inputs. However, it is now normal to use controllers^' with 12-bit inputs or more, without increasing costs, which allow easily going on till angular resolutions equal to 0.3°, more than enough for any seeking device.

The panel 1 according to the present invention is devised to work at high temperatures (up to 250 °C) or to produce boiling water also under low radiance (winter) conditions and low external temperature. In order to reach this result, it is necessary to minimise the losses proportional to the temperature difference towards the outside. The first advantage directly comes from the intrinsic geometry of the joining manifold of the ducts 27', since the radiating surface, in case of concentration-type manifolds, is reduced. Moreover, the panel 1 according to the present invention is advantageously equipped with absorbing devices arranged inside a vacuum environment generated by the Dewar tubes 7 that is based on the principle that, in vacuum, heat is propagated only by radiance (not by convection nor by conduction) , since there are no molecules that are able to absorb and transfer heat in the hollow space. Moreover, advantageously, the absorbing surface internal to the Dewar tube 7 and in contact with the ducts 27' that remove heat to take it to users, is coated with at least one layer of selective pigment having the feature of being · highly absorbing regarding the incoming wavelengths (visible and near infrared) and reflecting (and threfore scarcely emissive) regarding the long wavelenghts, such as the thermal infrared corresponding to the working temperature. Preferably, such layer of selective pigment is composed of:

- at least one reflecting substrate, typically metallic and deposited by vacuum evaporation, with a sufficient thickness to totally reflect the thermal wavelength typical of the maximum temperature at which one wants to operate;

- at least one thin layer of absorbing pigment arranged above such reflecting substrate and deposited with similar techniques (and consequenty of a dark colour) in the frequencies that have to be picked up and that are necessarily shorter (arriving from a surface, the sun one, at about 6000 K) . The thickness of such pigment must be sufficiently low as to become transparent regarding the thermal wavelengths corresponding to temperatures of about 500 K (that are quite higher) .

Such layer of selective pigment is suitable to operate in an evacuated environment and, instead, it is protected, while a normal paint would create many problems due to its high vapour tension.

According to the desired concentration factor, the Dewar tube 7 can be, alternatively and preferably:

- integrally made of glass;

- with through-glass/metal.

In particular, Figure 11 shows an example of Dewar tube 7 integrally made of glass, composed of an external tube 37 made of boron-silicate glass on which the above layer of selective pigment is deposited, inside which the ducts 27' of the absorbing device pass, and a getter 41 having the function of chemical pump for vacuum, and of loss indicator (since it changes colour from silver to white being oxidised and points out the vacuum loss and therefore the insulating power loss). These two tubes 37, 39 are coaxial and inside them vacuum is made, preferably, of at least 10^"3 Torr.

At least one slab of conducting material 43 (for example aluminium) is inserted inside the internal tube 39, and has the purpose of picking up heat from the internal tube 39 and transfer it to the thermovector fluid circulating inside the ducts 27' that extract it to take it to users.

As an example, Figure 11 shows a transport of the thermovector fluid with double ducts 27', but this can obviously be performed with other equivalent arrangements, such as for example through a system with coaxial tubes like the one described below or with a heat pipe.

Figure 12 instead shows an example of Dewar tube 7 with through- glass/metal composed of an external tube 45 made of glass directly containing a metallic tube 47 on which the above layer of selective pigment is applied. The external tube 45 made of glass and the metallic tube 47 are mutually sealed in an end 49 thereof (for example by means of a glass/metal welding) and after having made vacuum with the same features as previously described. A further tube 51 is inserted in a central position, and its purpose is inserting the fluid into the metallic tube 47 and make the circulation for removing heat.

Obviously, it cannot be excluded that, for example due to the transport or due to production defects, one of the Dewar tubes 7 has leakages. As is possible to note in particular in Figures 1 and 13, at least one of the edges of the external containing structure 3 is therefore equipped with suitable through-openings 53 inside each one of which a respective Dewar tube 7 is inserted, in order to be taken to its operating position, each one of such openings being equipped with a respective protecting cover 55. It is therefore possible to be aware of the failure by examining the getter colour, which changes from silver to white, and to replace the damaged tube 7 through the opening 53, by preliminarily removing the cover 55, without having to completely disassemble the panel.

The solar panel 1 according to the present invention can reach very high temperatures, so that it can be used for producing electric energy through a Rankine cycle with a low boiling organic thermovector fluid, such as, for example, with hydrocarbon (hexane, isopentane) or a. freon, making it therefore potentially dangerous if not well controlled. The present invention therefore also deals with a managing system for such . solar panels 1 suitable to make its operation safe and adapted to be easily interfaced with any other system that needs heat. In particular, the system according to the present invention allows managing both the autonomous operation of every single solar panel 1, and the operation of a plurality of solar panels 1 arranged in a network.

With particular reference to Figure 14, it is possible to note that, for the autonomous operation of every single solar panel 1, the system according to the present invention comprises at least processing means 57, composed of at least one microprocessor, cooperating with the handling means, in particular the motors 23, the means for recognising a direction of an incident radiation of a sun light and the processing means of each panel 1 and, towards the outside, with at least one communication network 59 (for example of the CAN type).

The system further comprises electric supply means

61, preferably with low voltage, whose continuity is guaranteed by accumulators placed as buffer (not shown) .

Under normal operation, the solar panel 1 according to the present invention can work under four operting modes, according to the time of the day, the measured radiance and the temperature readings performed by the temperature sensor 63 arranged in strict contact with the absorbing device.

A first operating mode with thermostatic seeking can be activated by an internal clock to the system according to the present invention and helped by the reading of the incoming radiation intensity. Typically, this mode starts from the position of the parabolic concentrator 9 with parabola axis normal to the plane of the layer 5.

The processing means 57 then read the unbalance of the position of the parabolic concentrator 39 with respect to the incoming radiation 65 and supply the motor 23 in order to reduce the error signal. Once having reached the alignment, the processing means 57 start taking into account the temperature of the absorbing device read by the temperature sensor 63 and, if the value of reached temperature exceeds the set one, they introduce in the control an error proportional to the temperature- excess by thermostating it.

In fact, such error signal will cause a partial disalignment of the optical system reducing the picked-up energy and avoiding further overheating.

A second operating mode for resetting the position can provide that, upon the first start up, the system does not know the position of the parabolic concentrators 9 and therefore autonomously takes care of performing an initialising procedure of such concentrators 9. Such procedure consists in reaching the two limit positions of the concentrators 9 and, after having evaluated that the distance between the two limit switches is the correct one, the internal counter that keeps track of the position is reset. The procedure ends with the concentrators 9 completely overturned (total protection) .

A third standby operating mode can provide that, during the night period (evaluated depending on local time and/or perceived brightness) the concentrators 9 are taken to their "ready" position, namely with parabola axis normal to the main plane of the panel 1. From this position, the position of best alignment can be reached, upon activating the above thermostatic seeking mode.

A fourth operating mode for total protection can provide that, if the panel 1 is deactivated for a long time (for example during summer in case heat is not used for producing electric energy or conditioning) , the system can be totally protected. This mode can be activated in three ways:

- through bus command;

- through straightforward contact;

- through reading the supply voltage.

In fact, the battery voltage is significantly lower than the normal supply voltage and points out a malfunction .

With particular reference to Figures 15 and 15, it is possible to note that, for the network operation of a plurality of solar panels 1, the system according to the present invention comprises at least master processing means 67 able to communicate to the panels 1, individually or in a group, the various operating modes, of being occasionally connected to a PC 69 for the configuration, the failure search and for downloading the operating history, and for managing, through dedicated I/O 71, the coordination with any coupled thermohydraulic plant .

Among the above components of the system according to the present invention, at least the communication network 59 (for example a CAN network) and at least the electric supply means 61 are laid. It is moreover possible to provide that the system according to the present invention comprises one .or more battery packs 73 arranged in any network point and at least one power supply 75. The line voltage given by the power supply 74 is significantly higher than the voltage of the battery pack 73 in order to allow this latter one to be charged during the normal operation, and the panels 1 to recognise, by measuring the line voltage, whether they are supplied by mains or in emergency. Therefore, the reached safety degree is very high, since every single panel 1 can be put under protection, both from a central unit command and autonomously, in case of electric mains shortage, since the mains shortage makes one suppose that also the circulation of the cooling fluid is impaired.

Obviously, the control and supply elements of the system according to the present invention can be grouped in a single unit or widespreaded . In particular, it is possible to increase the number of battery packs 73 to increase the safety level of the system according to the present invention.

Claims

1. Concentration-type solar panel (1) with bi-axial seeking comprising:

- at least one external containing structure (3) defining therein at least one first room and having at least in its upper surface an opening covered at least partially with at least one layer of highly transparent material (5) adapted to allow the passage of a solar radiation inside said room,

- at least one solar absorbing device, each one of said solar absorbing devices being inserted inside at least one Dewar tube (7), arranged inside said first room;

at least one respective plurality of parabolic concentrators (9), each one of said concentrators (9) being rotating through handling means around a rotation axis coaxial with an axis of symmetry of a respective absorbing device and with an axis of the focus of said parabolic concentrator (9), the rotation axis of said concentrators (9) being coaxial with said Dewar tube (7); and

- means for recognising a direction of an incident radiation of a sun light cooperating with at least one of said concentrators (9) and processing means cooperating with said handling means and said means for recognising a direction of an incident radiation; characterised in that each one of said parabolic concentrators (9) is equipped with at least one reflecting surface (11) oriented towards a respective absorbing device and said Dewar tube (7), and is made of a self-bearing slab.

2. Solar panel (1) according to claim 1, characterised in that said handling means comprise at least one motor (23) and at least one control rod (27), said control rod (27) being moved by said motor (23), preferably by interposing at least one gear-type reducer (25), in order to drive each screw-type reducer (29) adapted to rotate a respective parabolic concentrator (9) with slow rotation axis coaxial with a corresponding absorbing device (23) .

3. Solar panel (1) according to claim 2, characterised in that said handling means comprise at least one incremental encoder cooperating with said motor (23) and managing means (31) adapted to drive said motor (23) in cooperation with said incremental encoder and/or at least one temperature sensor (63) placed in contact with said absorbing device and/or with said means for recognising a direction of an incident radiation.

4. Solar panel (1) according to claim 2, characterised in that said control rod (27) has a not circular and constant section in order to freely longitudinally slide into worm screws (33) of said reducers (29), said screws (33) engaging slow gears (35) integral with respective parabolic concentrators (9) and said gears (35) having mechanical limit switches.

5. Solar panel (1) according to claim 1, characterised in that said external containing structure (3) is made of a single slab of a composite of aluminium and polyethylene, ACP.

6. Solar panel (1) according to claim 1, characterised in that said self-bearing slab is a curved, reflecting slab of aluminium.

7. Solar panel (1) according to claim 6, characterised in that each head (13) of said parabolic concentrator (9) is equipped with a respective supporting bush (15) for a rotation of said parabolic concentrator (9), said bush (15) being coaxial with said rotation axis of said concentrator (9), said head (13) being made of a UV- resistant plastic material and coated with a reflecting material .

8. Solar panel (1) according to claim 7, characterised in that said means for recognising a direction of an incident radiation comprise at least one tracking device (17) arranged on at least one head (13) of at least one of said parabolic concentrators (9).

9. Solar panel (1) according to claim 8, characterised in that said tracking devices (17) are two, separated and arranged at the opposite ends of a respective head (13) .

10. Solar panel (1) according to claim 1, characterised in that an absorbing surface internal to said Dewar tube (7) and in contact with ducts (27') suitable for removing is coated with at least one layer of selective pigment composed of at least one reflecting substrate, preferably metallic, deposited by vacuum evaporation, and at least one thin layer of absorbing pigment arranged above said reflecting substrate and depositated by vacuum evaporation.

11. Solar panel (1) according to claim 10, characterised in that said Dewar tube (7) is composed of an external tube (37) made of boron-silicate glass containing an internal tube (39) made of boron-silicate glass on which said layer of selective pigment is deposited, inside which said ducts (27) of the absorbing device pass, and a getter (41), at least one slab of conducting material (43) being inserted inside said internal tube (39) .

12. Solar panel (1) according to claim 10, characterised in that said Dewar tube (7) is composed of an external tube (45) made of glass directly containing a metallic tube (47) on which said layer of selective pigment is applied, said external tube (45) and said metallic tube (47) being mutually sealed at an end (49) thereof, a further tube (51) adapted to insert a fluid into said metallic tube (47) being inserted in a central position.

13. Solar panel (1) according to any one of the previous claims, characterised in that at least one of the edges of said external containing structure (3) is equipped with through-openings (53) inside each one of which a respective Dewar tube (7) is inserted to be taken to its operating position, each one of said openings (53) being equipped with a respective protecting cover (55) .

14. Managing system for an autonomous operation of at least one solar panel (1) according to any one of claims

1 to 13, characterised in that it comprises at least processing means (57) cooperating with said handling means, said means for recognising a direction of an incident radiation of a sun light and said processing means of each panel (1) and, towards the outside, with at least one communication network (59).

15. Managing system for a network operation of a plurality of solar panels (1) according to any one of claims 1 to 13, characterised in that it comprises at least master processing means (67) adapted to communicate to said panels (1), individually or in a group, various operating modes, to be connected to a PC (69) and to manage through dedicated I/O (71) a coordination with a coupled thermohydraulic plant, and at least one communication network (59) .

16. Managing system according to claim 14 or 15 characterised in that said communication network (59) is a CAN network.