WO2008110477A1

WO2008110477A1 - Method and device for the operative control of the orientation of photovoltaic capturing surfaces directed to equipment for the production of electrical energy

Info

Publication number: WO2008110477A1
Application number: PCT/EP2008/052569
Authority: WO
Inventors: Alessandro Chiorlin
Original assignee: Alessandro Chiorlin
Priority date: 2007-03-09
Filing date: 2008-03-03
Publication date: 2008-09-18
Also published as: ITPD20070082A1

Abstract

There is described a method for the operative control of the orientation of a capturing surface (2a) of at least one photovoltaic panel (2), in which provision is made to orient the at least one panel, relative to a support structure (1) for the panel, with a rotational movement about at least a first axis (X), and in which at least one irradiation sensor means (12) associated with the at least one panel (2) is provided, the sensor means including a respective sensor surface (12a) capturing the light radiation, the sensor capturing surface being capable of being rotationally oriented about at least a second axis (X'). The method comprises a detection step during which the sensor means (12) is shifted into a sequence of angular positions, spaced apart from one another, about the second axis (X'), there being detected in each position a respective signal related to the irradiation incident upon the sensor capturing surface (12a), a step for comparing the signals detected during the detection step, to identify the angular position corresponding to the signal related to the point of maximum energy production, a panel orientation control step during which the at least one panel (2) is oriented, with rotation about the first axis (X), in order to arrive at the angular position of maximum energy production identified in the comparison step, in which during the detection step the capturing surface (12a) of the sensor means (12) is shifted into the sequence of angular positions with a movement that is independent of the capturing surface (2a) of the photovoltaic panel (2), so that the panel is shifted solely during the control step in order to arrive at the preselected orientation resulting from the step for detecting and comparing the signals detected by the sensor means (12). There is also described a control device operating according to the abovementioned method.

Description

Method and device for the operative control of the orientation of photovoltaic capturing surfaces directed to equipment for the production of electrical energy Technical field The present invention relates to a method for the operative control of the orientation of photovoltaic panel capturing surfaces, having the features set out in the preamble of main Claim 1. The invention also relates to a control device operating according to the abovementioned method. Technological background In the technical field of reference, relating to equipment for the production of electrical energy by conversion of light radiation through the photovoltaic effect, elements capturing the radiation are used as is known (photovoltaic or photosensitive cells), produced in the form of panels which are mounted on support structures and are capable of being controlled in an orientation movement about one or more axes. The movement of the panel enables the capturing surface to be oriented with respect to the direction of the incident light radiation, on varying the relative positioning between the Earth and the sun during daily sunlight hours, in order to maximize the production of energy. Typically, in this situation, control methods are set up for moving the panel, seeking to obtain a relative positioning with the capturing surface perpendicular to the rays of light radiation, in order to have the maximum light intensity directed onto the surface. A first known methodology provides for the photovoltaic panel to be shifted, in its orientation movement, into a sequence of positions that are precalculated, and determined taking into account the geographic position of the panel (latitude and longitude), which determines a certain relative positioning with respect to the sun, which can vary during the solar year. In other words, by means of appropriate algorithms, for each unit of time, for example for every hour of the day of every day of the solar year, the respective positioning of the panel, with respect to the light radiation, is identified, thereby ensuring the best angle of incidence. In this case tracking controls for orienting the panel as a function of the sequence of precalculated positions are set up.

This method exhibits a major limitation in the fact that, due to the effect of the variability of climatic conditions, for example related to the different degrees of cloudiness in the sky, the theoretical position of best incidence often does not correspond to the position of maximum energy production, really because the weather conditions disturb and can alter the theoretical ideal conditions, with phenomena of reflection or refraction of the light radiation which can lead to positions of maximum effectiveness that are different from the theoretically calculated positions. In this sense technical solutions have been proposed which provide for the use of sensors of the light radiation mounted on board the photovoltaic panels. These sensors, by means of rotation movements allowed by the panel, are shifted along certain rotation sequences at preselected angular pitch, acquiring, in each angular positioning, a signal related to the light radiation incident upon the sensor. By comparing the acquired signals the positioning corresponding to the best effectiveness level is then preselected and consequently the panel is oriented into this position. At certain time intervals, the known method provides for the abovementioned scans to be repeated, in a certain pre-established angular space (in order to explore a significant part of the celestial arc), so as to vary in time the positioning of the panel during the day. For every point of orientation of the panel, the abovementioned scanning is therefore executed beforehand in order to enable the sensor to acquire the signals and, by comparing the signals, to select the optimal positioning. While on the one hand this method exhibits the advantage of enabling orientation of the panel to be chosen as a function of real irradiation conditions, by the scanning performed by the sensor, on the other hand it exhibits the limitation of having to require the shifting of the whole panel capturing surface during the step of acquisition of the signals by the sensor, which is a penalizing aspect in terms of the time required, the energy required in shifting the entire panel, and the stresses induced in the structure of the panel when it is repeatedly moved, which can compromise its effectiveness and life. Furthermore, in order to improve the effectiveness of the apparatus it is necessary to reduce as far as possible the angular scanning pitch in the movement of the sensor, requiring, however, an increase in the number of shifts of the panel, giving rise to further drawbacks related to the abovementioned limitations.

Otherwise, technical solutions are known in which the methodology of precalculated positionings is integrated with the methodology of the detection sensors on board the panels, which solutions however bring out the abovementioned limitations and do not avoid the drawbacks mentioned.

It is also to be noted that the sensor means provided on the photovoltaic panels can in turn exhibit functional limitations and therefore make the identification of the point of maximum energy production uncertain. Indeed, this identification process is generally based on the comparison of signals acquired by the sensor during orientation movements, for example about a pair of axes (an azimuthal axis and an axis of oscillation about an axis perpendicular to the azimuthal axis), the choice being made on the basis of the equality of signals detected in the two rotations, or on a pre-established threshold value within which the difference of the signals acquired at the same point of positioning must fall, the criterion then, by introducing a certain level of approximation and compromise in the choice of the point of maximum effectiveness, consequently brings about a certain degree of uncertainty in this identification. Disclosure of the invention One main object of the present invention is to make available a method and a device to control the orientation of the capturing surface of photovoltaic panels, structurally and functionally designed to overcome the limitations highlighted with reference to the cited prior art.

This and other aims which will be described clearly below are achieved by a method and by a device produced in accordance with the claims that follow. Brief description of the drawings

Other features and advantages of the invention will become clear from the following detailed description of one of its preferred example embodiments illustrated, by way of indication and in a non-limiting manner, with reference to the appended drawings in which : - Figures 1 to 3 are perspective views, in front elevation and as a plan from above respectively, of a device operating with the method of the invention,

Figure 4 is a partial perspective view of a photovoltaic panel set up to be oriented with a control device operating with the method of the invention, - Figure 5 is a front elevation view of the panel of Figure 4, Figure 6 is a large-scale perspective view of a detail of the panel of Figures 4 and 5,

Figure 7 is a view corresponding to that of Figure 1 in a variant embodiment of the device of the invention, - Figure 8 is a schematic view of the panel orientation control system using the method of the invention,

Figure 9 is a view corresponding to that of Figure 8 in a further variant embodiment.

Preferred embodiment of the invention With reference to the cited drawings, the label 1 indicates in an overall sense a support structure (only partly represented) of a plurality of photovoltaic panels, all indicated by the label 2, housed in a pair of frames 3a, 3b rotatably supported on the structure, about an axis of rotation X. The support structure is formed as a stand with a pair of legs Ia (only one of which is represented) between which is rotatably supported a shaft 5, at its axial ends.

The frames 3a, 3b are secured to the shaft 5 by laterally opposed parts, in a configuration which is such that the light radiation capture surfaces of the panels 2 are coplanar with each other. Furthermore by rotating about the axis X, the whole capture surface of the panels 2, indicated by the label 2a, can be oriented with respect to the support structure 1, this orientation operation being required to position the capturing surface 2a at the most appropriate tilt with respect to the direction of incidence of the light rays, this direction varying during the day due to the effect of the relative movement between the sun and the Earth, in order to obtain the maximum energy production in the photovoltaic panels 2. For rotationally controlling the shaft 5, about the axis X, in the orientation movement of the capturing surface 2a, a kinematic transmission is provided comprising a motor 6, operatively connected to the shaft 5, a reducer 7, with orthogonal shafts, the output shaft of which is coaxially connected to the shaft 5. To shift the capturing surface 2a in the orientation about the axis X, a control device is provided, indicated as a whole by the label 10, operating according to the method of the invention, which will be described in detail below. The device 10 comprises a stationary support 11, on which there is rotatably supported an irradiation sensor 12 for the light radiation, about an axis indicated as X'. More specifically, the sensor 12, in itself conventional, comprises a plane capturing surface 12a, able to be struck by the light radiation and transducer means to convert the quantity of energy detected by the sensor into a voltage signal (mVolt) produced as output at terminals 13 of the sensor. This sensor is conveniently an analogue irradiation sensor, able to measure the quantity of energy produced by the radiation that is incident upon capturing surface 12a. There is also operatively associated with the sensor 12 an angular position sensor 14 able to detect the angle of rotation swept through following a rotation about the axis X' by the surface 12a. Preferably the sensor 14 is of an analogue type, for example potentiometric. Furthermore, the label 15 indicates an electric motor, with reversible rotation, preferably a DC motor, set up to rotationally control the irradiation sensor 12, resulting in orienting the surface 12a about the axis X'.

The label 16 indicates a circuit assembly, for example produced in the form of a printed circuit board, set up for the functions which will be explained in detail in the description of the method set out below, which circuit assembly is designed to control the orientation of the photovoltaic panels. The circuit assembly is provided with circuit means 17 for acquiring signals from the device 10, signal storage means 18, signal comparison means 19 and means 20 for generating control signals to the motors 6 and 15. Signal transmission means, in the form of electrical conductors 21, are provided between the device 10 and the printed circuit board 16, and between the latter and the control motor means for the panels 2.

The method of the invention provides for a first preliminary "calibration" step during which the surface 12a of the sensor 12 is oriented so as to be coplanar with the overall capturing surface 2a of the photovoltaic panels. In this regard, conventional equipment can be used such as levels or similar devices. To appropriately orient the sensor 12, the latter can be oscillated about the axis X' and, in addition, about an axis Y', orthogonal to X', at which the sensor is mounted in an articulated manner on the support 11. On this axis Y' there are provided screw-operated locking means to hold the sensor 12 in relation to the support 11, once the position of coplanarity with the surface 2a is identified. At the calibration step there follows a detection step, in which the surface 12a of the sensor is oscillated, about the axis X', in a sequence of consecutive angular positions, spaced apart angularly, and in each of these positions the corresponding irradiation incident upon the surface 12a is detected. The quantity of energy produced through the photovoltaic effect has a proportional relationship with the voltage signal V produced as output at the terminals 13 of the sensor, which signal is sent to and acquired by the printed circuit board 16, by the means 17. With reference to Figure 2, a preferred choice provides for the capturing surface 12a to be oscillated at constant angular pitch, for example equal to 1°, from an angular position of -60° with respect to a theoretical horizontal axis, indicated by P, to an angular position of +60° with respect to this plane, as illustrated in the drawing. In each of the angular positions contained in the abovementioned angular portion, and which are important for an appropriate scanning of the celestial arc, a signal V is therefore detected which corresponds to the production of energy related to the radiation incident upon the surface, this value being dependent on the direction of incidence of the radiation and on the effects of disturbance on the intensity of the radiation (weather conditions) that are present at the time of the detection. To control the rotation of the surface 12a, provision is made for the motor 15 to be actuated by a signal controlled by the angular position sensor 14, by means of which the motor is stopped every time the preselected angular pitch is swept through, in the rotation about X'.

The method also provides for a comparison step which is alternated at the detection step at each pair of consecutive detections performed by the sensor 12. In other words, provision is made such that for each pair of consecutive angular positions, the signals acquired are compared with each other and the value of the pair, relating to the signal of greater energy production, is stored together with its corresponding angular position. This comparison is executed for each successive detection, such that the storage means 18 preserve in memory the highest (Vmax) of the signals V acquired in the scanning operation. Once the scanning is completed, the angular position of the sensor 12 corresponding to the point of maximum energy production is then maintained in memory. Using this information, during a successive step, identified as the orientation control step for the panels, provision is made for the motor 6 to be rotated, until the surface 2a is oriented with the same angle of orientation of the sensor corresponding to the maximum energy production. In other words, the surface 2a is rotated about the axis X in order to arrive at a configuration that is coplanar with the surface 12a corresponding to the point of maximum energy production. Control of the rotation about the axis X is transferred to an angular position sensor 6a, associated with the motor 6, in its entirety similar to the position sensor 14, by means of which the motor 6 is stopped when, with a feedback signal sent to the printed circuit board by the sensor 6a, the preselected angular positioning is arrived at. The method provides for all the steps of detection, comparison and orientation control of the panels to be repeated at pre-established time intervals, during the day, for example, according to a preferred choice, with intervals of 15-20 minutes. Thus at the end of each interval, with the detection and comparison steps executed, the relative angular positioning at the point of maximum energy production is identified and the capturing surface 2a of the panels 2 is rotated as a result. It is deduced from this that this surface is conveniently rotated solely to arrive at the positioning identified at each time interval, while the rotation operations required at the scanning of the celestial arc, during the detection step, are carried out by the irradiation sensor 12, which is shifted independently of the photovoltaic panels. Furthermore, the control device 10, with the sensor 12, can be placed in a position that is remote from the structure 1 of the panels 2, since it is only necessary to ensure coplanarity of the capturing surfaces 2a of the panels and 12a of the sensor, prior to the orientation step. In a variant embodiment of the device 10, illustrated in Figure 7, provision is also made for the rotation of the sensor 12 about the axis Y' to be controlled by an angular position sensor 22, operated to control the rotation of a motor 23 able to rotational Iy drive the sensor about the axis Y'. The angular position sensor 22 is conveniently chosen to be of an analogue type, for example potentiometric, and can be in its entirety similar to the angular position sensors 6a and 14. In another variant of the invention, provision can be made for the device 10 to be equipped with a third motorized axis Z of rotation, directed orthogonally to the axes X' and Y' described above, so as to form a tern of orthonormal axes. This third degree of freedom with which the device can be equipped can be controlled by a sensor for measuring the corresponding angular position (similar to those described previously) in such a way as to ascertain its orientation with respect to the abovementioned vertical-orientation third axis (azimuthal). This motorized axis enables the device described above to become a three- dimensional scanner of irradiation from the celestial arc and therefore it can lend itself to the mapping of the irradiation, finding the maximum level thereof wherever it may be and enabling any biaxial tracker systems (rotation about two orthogonal axes, the first an azimuthal one and the second about a horizontal axis) to move completely autonomously. The advantages described above for the monoaxial tracker are transferred directly and in the same way onto biaxial trackers which can be moved in a more rational way reducing stresses and able to use one inverter, as described elsewhere in greater detail, to control their motors, reducing costs.

In the diagram of Figure 8, it may be noted how with a single device 10 the orientation of capturing surfaces 2a belonging to a plurality of support structures 1 of panels 2 can be controlled. The diagram of Figure 9 illustrates a preferred configuration of the device 10 according to the invention, designed to control the orientation of a plurality of capturing surfaces 2a, obtained by arranging in a modular manner groups of panels 2 associated with respective support structures Ia placed adjacent one to the other. For clarity, the motors 6 associated with each structure Ia are indicated as 6', 6", 6'",... etc. The label 25 indicates an inverter device integrated in the printed circuit board 16 and set up to supply the power control signal to the abovementioned motors. Provision is made such that on the power connection line of each motor 6', 6", 6'",... to the board 16 there is placed a respective line switch 26', 26", 26'",. ■■ which can be opened/closed by a signal sent by the board. Thus, it is possible to actuate the motors in sequence, by closing the switches 26', 26", 26'",... one by one, to orient the structures in a preselected time sequence. This form of actuation is conveniently acceptable and advantageously provides for dimensioning the inverter 25 on the power rating of a single motor 6, even though the inverter can provide for actuating all the motors present. It is also possible to provide sequences of orientation of structures that are different from each other (still by operating a single motor at a time) for specific requirements related to the area covered by the panels. The invention thus achieves the aims proposed, attaining a number of advantages over the known solutions.

A first advantage is associated with the fact that by virtue of the device and the method of the invention, there is first of all the certainty that the identified positioning is that of maximum energy production, because of the fact that the celestial arc is scanned in real time under actual irradiation conditions as well as under real weather conditions. Furthermore, using the method of the invention, the need to move the entire capturing surface of the panels during the scanning step, to search for the most effective positioning, is eliminated, since that shifting operation is carried out by the remote irradiation sensor. This provides for energy savings in the shifting operation, due to the reduced mass and inertia of the sensor with respect to the structure of the photovoltaic panels, greater speed, a longer life of the structure of the panels, due to lower dynamic stresses related to the smaller number of shifts required, for a higher overall effectiveness of the apparatus. Also to be noted is the advantage that with a single control device it is possible to control the orientation of a plurality of structures of photovoltaic panels that are structurally independent from one another. With such configurations another advantage gained is that the panels of the plurality of structures have their orientation controlled by a device having a single irradiation sensor, according to desired and preselected sequences, as well as programmable ones. Furthermore, by using an inverter, as highlighted above, with which the power supply voltage for a motor is frequency-controlled, very gradual startups are possible, thus reducing stresses. The use of a single inverter with a switch-based system, set up to control the motors of a plurality of structures of panels, in the end proves to be advantageous since it entails significant cost reductions. In other words, the advantage of the scanning and control device is that of providing for the exact position into which to orient to be stored (this position being valid for all the capturing areas), and to scan quickly and using an independent remote structure having low inertia and mechanical criticality. Furthermore, since control can be given to the trackers sequentially, one inverter can advantageously be provided, such a solution resulting in a two-fold reduction of mechanical stresses, the first arising from the fact that the tracking structures and their actuations are moved precisely for positioning purposes and the second arising from the fact that one inverter can be used.

Claims

1. A method for the operative control of the orientation of a capturing surface

(2a) of at least one photovoltaic panel (2), in which provision is made to orient the at least one panel, relative to a support structure (1) for the panel, with a rotational movement about at least a first axis (X), and in which at least one irradiation sensor means (12) associated with the at least one panel (2) is provided, the sensor means (12) including a respective sensor surface (12a) capturing the light radiation, the sensor capturing surface (12a) being capable of being rotationally oriented about at least a second axis (X'), the method comprising :

- a detection step during which the sensor means (12) is shifted into a sequence of angular positions, spaced apart from one another, about the second axis (X'), there being detected in each position a respective signal related to the radiation incident upon the sensor capturing surface (12a), - a step for comparing the signals detected during the detection step, to identify the angular position corresponding to the signal related to the point of maximum energy production,

- a panel orientation control step during which the at least one panel (2) is oriented, with rotation about the first axis (X), in order to arrive at the angular position of maximum energy production identified in the comparison step, characterized in that during the detection step the capturing surface (12a) of the sensor means (12) is shifted into the sequence of angular positions with a movement that is independent of the capturing surface (2a) of the photovoltaic panel (2), so that the panel (2) is shifted solely during the control step in order to arrive at the preselected orientation resulting from the step for detecting and comparing the signals detected by the sensor means (12).

2. A method according to Claim 1, in which during the detection step provision is made for the values of the signals detected in each pair of consecutive angular positionings to be compared with each other, and both the value of the pair, relating to the signal of greater energy production, and its corresponding angular position are stored in respective storage means (18), this comparison being repeated for each successive angular position assumed by the sensor capturing surface (12a), so that, once the preselected angular rotation of the sensor (12) is completed, the value of the signal associated with the maximum energy production is held in memory with the corresponding angular positioning of the sensor capturing surface (12a).

3. A method according to Claim 2, in which the signal associated with the angular positioning of the point of maximum energy production is transferred to means (20) for controlling motor means (6) set up to control the orientation of the panel (2) by rotation about the first axis (X), so that the panel (2) is shifted into the corresponding angular positioning of maximum energy production.

4. A method according to Claim 3, in which the rotation of the capturing surface (12a) of the irradiation sensor (12), about the second axis (X'), is controlled by a respective first angular position sensor (14), the first sensor detecting the angular position arrived at by the capturing surface (12a) of the irradiation sensor (12) in order to stop respective first rotation control motor means (15) of the irradiation sensor (12) in each of the angular positions.

5. A method according to Claim 4, in which the first angular position sensor (14) is of an analogue type.

6. A method according to either Claim 4 or Claim 5, in which the rotation of the panel capture surface (2a), about the first axis (X), is controlled by a respective second angular position sensor (6a), this second sensor detecting the angular position arrived at by the capturing surface (2a) of the panel (2) in order to stop respective second rotation control motor means (6) of the panel in the preselected angular position corresponding to maximum energy production, which means are separate and distinct from the first motor means (15).

7. A method according to Claim 6, in which the second angular position sensor (6a) is of an analogue type.

8. A method according to any one of the preceding claims, in which prior to the detection step, a calibration step is provided during which the spatial orientation of the sensor capturing surface (12a) is adjusted to make the sensor surface coplanar with the capture surface (2a) of the photovoltaic panel (2).

9. A method according to any one of the preceding claims, in which the sensor capturing surface (12a) can be oriented about a respective third axis (Y') perpendicular to the second axis (X').

10. A method according to Claim 9, in which the rotation about the third axis (Y') is controlled by a respective third angular position sensor (22).

11. A method according to any one of Claims 8 to 10, in which during the calibration step the capturing surface (12a) of the irradiation sensor (12) is rotated about one or both of the second (X') and third (Y') axes in order to arrive at complanarity with the panel capturing surface (2a).

12. A method according to any one of the preceding claims, in which the detection step is conducted by rotating the sensor capturing surface (12a) about the second angular rotation axis through 120° with angular positions in which the irradiation signal is detected that are angularly spaced apart from each other by 1°.

13. A method according to any one of the preceding claims, in which an electronic circuit assembly (16) is provided in which the signals detected by the irradiation sensor are acquired as input, the signal values associated with each pair of consecutive angular positions are compared, the irradiation signal value and angular positioning value of the point of maximum energy production are stored, and from which a control signal is sent to the first panel control motor means in order to rotate the panel by a corresponding angle in order to reach the position of maximum energy production.

14. A method according to Claim 13, in which the irradiation sensor (12) is placed in a position that is remote from the corresponding photovoltaic panel (2) with which it is operatively associated, means (21) for transmitting the signals being provided between the irradiation sensor (12) and the circuit block (16), and between the latter and the photovoltaic panel (2).

15. A device for controlling the orientation of a capturing surface of at least one photovoltaic panel, operating according to the method of one or more of the preceding claims.

16. A device according to Claim 15, in which the at least one panel (2) is supported rotatably, about at least a first axis (X), on a carrying structure (1), the device comprising at least one irradiation sensor means (12) associated operatively with the panel (2), the sensor means including a respective sensor surface (12a) capturing the light radiation, the sensor surface being supported rotatably about at least a second axis (X'), characterized in that the sensor (12) is arranged in a position that is remote from the panel (2) and is controlled, in the orientation movement about the second axis (X'), independently of the panel (2).

17. A device according to either Claim 15 or Claim 16, comprising an angular position sensor (14) operatively associated with the sensor capturing surface (12a) in order to control the angular positioning of the surface about the second axis (X').

18. A device according to Claim 17, comprising motor means (15) to rotationally control the sensor capturing surface (12a) about the second axis (X').

19. A device according to any one of Claims 15 to 18, in which the sensor capturing surface (12a) can also be oriented about a third axis (Y') perpendicular to the second axis (X').

20. A device according to Claim 19, comprising a further angular position sensor (22) to control the angular positioning of the sensor capturing surface (12a) about the third axis (Y').

21. A device according to Claim 20, in which the angular positioning sensors are of analogue types.

22. A device according to any one of Claims 15 to 21, comprising a reversible DC electric motor (15) for the rotational control of the sensor surface (12a) about the second axis (X').

23. A device according to any one of Claims 15 to 22, in which means (21) for transferring signals between the device and an electronic circuit assembly (16) and between the circuit assembly and respective panel capturing surface control means are provided.