Field of the Invention

This invention relates to a solar panel for a solar tracking system, and a solar tracking system having a plurality of panels.

Background to the Invention

An increasingly common type of solar panel is a solar panel for use in a photovoltaic system. Such a panel typically carries an array of series connected photovoltaic cells which are arranged in an array of a plurality of rows and columns across the face of the panel. Many such panels are mounted on the parts of building roofs which face the arc described by the sun as it travels across the sky during any given day. For example, such panels would normally be south facing if installed on a roof of a northern hemisphere home. The panels are ideally at an angle to the horizontal which corresponds to the latitude of their location, so that at midday sunlight is incident on the panels at approximately 90 ⁰ to the panel faces. In reality, (in the case of roof- mounted panels) the angle relative to the horizontal will normally be determined by the pitch of the roof on which the panels are installed.

Such installations are relatively simple and cheap, but can only offer optimal performance in the portion of the day when the sun is directly overhead and in particular are relatively very inefficient in mornings or evenings, times when (coincidentally) demand for electrical power tends to peak.

A tracking solar system provides an arrangement of one or more panels which are moved throughout the day so that the or each panel directly faces the sun, and can thus provide a significantly higher output, especially at mornings and evenings, than a fixed panel. A relatively simple tracking system is a "single axis" system in which a number of louvre-like rectangular panels are arranged in a linear array on a framework, with each of the panels being pivotable about its respective elongate pivot axis. The pivot axes are arranged in a parallel array. These panels will typically be connected to a drive system comprising a stepper motor and simple transmission which pivots the panels about their axes over the course of a day so that the panels always face the sun. As well as exposing the panels to a larger amount of the sun's energy, compared with a fixed panel arrangement, the single axis tracking array also allows air to circulate behind the panels and thus avoids or ameliorates problems of overheating (which can drastically affect the performance of the panels). However, problems can arise if one of the panels casts a shadow on the adjacent panel.

More specifically, if that shadow completely shades one of the cells on the adjacent panel, then not only will that cell generate no solar electricity, but it will also be rendered non-conductive, as the cell is essentially a semiconductor. Since the cells are connected in series, this impairs the performance of the whole of the shaded panel.

Consequently, the individual panels tend to be spaced apart by a distance significantly greater than the panel width so as to reduce or avoid the problems of one panel fully shading the cells on another. This results in the array occupying significantly more area than arrangement of fixed solar panels having the same area of solar cells, and thus gives rise to a sub-optimal use of the base, e.g. a roof, on which the cells are mounted. Even with this greater spacing the performance of conventional arrays is still reduced in the mornings and evenings, when significant shading still occurs.

Summary of the Invention

According to a first aspect of the invention, there is provided a solar panel for a solar tracking system having an array of tracking panels, the solar panel comprising mounting means for mounting the panel on tracking apparatus so that, in use, opposite sides of the panel move in opposite directions as the array tracks the sun and one or more photovoltaic cells, wherein the or each cell extends substantially all the way from one of the said sides to the other.

Thus, if a panel is partially shaded by another panel in the array, at least part of the cell will not be shaded in this way. This means that the cell can continue to generate power or at least will act less of a drag (compared to a fully shaded cell) on the power output of the panel.

This enables the panels of the array to be more closely spaced than is the case with an array of conventional panels in which, for example, each panel carries cells arranged in a plurality of rows and columns. Alternatively, the panels can have similar spacings to those of a conventional array. In this case an array of panels in accordance with the invention achieves improved performance in mornings and evenings compared with an array similarly spaced conventional panels.

For example, a conventional 'single axis' tracking array of panels may have the panels so arranged that the spacing between the adjacent edges of neighbouring panels (when co-planar) is 25-30% of the panel width. In such a case the distance between the pivot axes of the two panels will be 1.25-1.3 times the panel width. By contrast, a single axis tracking array of panel in accordance with the invention can be arranged with the spacing between adjacent edges of neighbouring panels to be 5 to 10% of the panel width (when the panels are co-planar), the distance between adjacent pivot axes thus being 1.05-1.1 times the width of each panel.

Alternatively the spacing between the adjacent edges of neighbouring panels, in an array of panels in accordance with the invention, may be in the range of 10% to 50% of the panel width, if enhanced performance of the array in mornings and evenings is desired.

Preferably the or each cell extends as close to the sides of the panel as is practicable, so that the cell can still be properly sealed within the panel. Preferably the distance between each side of the panel and an adjacent edge of the cell is not more than 3mm, more preferably approximately 2mm.

Preferably, the mounting means, in use, pivotally mounts the panel on the tracking apparatus to enable the tracking apparatus to pivot the panel about a pivot axis, said opposite sides of the panel being on opposite sides of the axis. Thus, if the panels are arranged in a linear array, and are always positioned to face the sun, the only condition in which one of the panels would completely shade a cell on an adjacent panel will be when the panels are vertical.

Preferably, the mounting means comprises pivot pins which are coaxial with said pivot axis.

Preferably, the panel is elongate, the elongate axis of the panel lying on the pivot axis and the cell extending in a direction generally perpendicular to the elongate axis.

Preferably the cell is one of a respective single row or column of such cells, which row or column extends along the elongate axis of the panel.

Preferably, the panel is rectangular, said opposite sides being the longer sides of the rectangle, the cell thus extending across substantially the whole width of the panel.

According to a second aspect of the invention, there is provided a solar tracking system comprising a plurality of panels, each as aforesaid, mounted on tracking apparatus.

Preferably, the panels are mounted on the tracking apparatus in a linear array, the tracking apparatus being moveable to pivot each panel about a respective axis of a corresponding array of parallel axes, wherein the panels are rectangular, having longer sides parallel to said axes, and the spacing between adjacent panels corresponds to the panel width.

According to a further aspect of the invention, there is provided a solar tracking system comprising a linear array of solar panels, each pivotable about a respective one of a corresponding array of pivot axes, to track the sun, each panel having at least one photovoltaic cell that extends from one side of the axis to the other, the arrangement of cells and panels being such that if any one of the panels partially shades another of the panels, said one panel will not fully shade the cell on the other panel. Preferably, each panel has a plurality of cells, none of which on at least one panel can be fully shaded, from the sun, by another panel which only partially shades said one panel.

Brief description of the Drawings

The invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 is a plan view of a solar tracking system in accordance with the invention, having an array of four panels, each of which is also in accordance with the invention;

Figure 2 is an end elevation of the system;

Figure 3 shows three of the panels and the tracking apparatus of the system in side elevation, when the panels are in a co-planar configuration; and

Figure 4 is a view which corresponds to Figure 3, but shows the panels when tilted to face morning or evening sun.

Figure 5 shows three panels of the system, without the connecting linkage, when facing the morning or evening sun at a slightly steeper angle; and

Figure 6 is a corresponding view of a modified version of the system, in which there is a greater spacing between adjacent panels.

Detailed Description

Figure 1 shows a single axis solar tracking system having a linear array of four solar panels 1-4, each of which is rectangular, and has a pair of mounting pins, each of which is positioned in the centre of a respective one of the shorter sides of the panel, so that the two pins are opposed to each other and coaxial. The pins for the panels 1-4 are denoted by the reference numerals 6-13. The panels are flanked by a pair of frame uprights 16 and 18, on which the panels are pivotally mounted via the pins 6-13. The frame uprights 16 and 18 are shown in simplified form in the drawings, but are in fact L-shaped plates each having a vertical side portion which has apertures through each of which a respective one of the pins 6-13 passes and a base portion which is perpendicular to the side portion and which includes connecting formations (such as bolt holes) via which the system can be mounted on a roof. The frame includes a pair of cross beams, one of which is shown at 20 in Figure 2, which connect the uprights 18 and 16. The cross beam 20 is at one end of the uprights 16 and 18, whilst the other cross beam is at the opposite end of the uprights.

The pins 6-13 are retained in the side plates of the uprights 16 and 18 in a conventional way so as to be rotatable about the axis of the pins. Thus, the pins define a respective pivot axis for each of the panels 1-4, which is coaxial with the pins that hold that panel in position (e.g. the pins 6 and 7 for the panel 1), is parallel with and centrally positioned between the two opposed longer sides of the respective panel, such as the sides 22 and 24 of the panel 1.

Turning to Figures 3 and 4, the tracking apparatus for the system runs along one end of the panels, and comprises three connecting arms 25-27 each of which is attached at one end, at the top of the arm, to a respective one of the pins 7, 8 and 10 so as to rotate with that pin about the pivot axis for the respective panel. The opposite, lower end of each arm 25-27 is pivotally attached to a coupling rod 28 of the tracking apparatus. The rod 28 has been shown in simplified form, but is in fact a thin metal strip that defines a face through which pivot pins 30-32 pass in order to provide the pivotal connection between the arms 25-27 and coupling rod 28. The end of the rod 28 is pivotally mounted via an end pin 34 to a connecting rod 36, that is, in turn, pivotally attached at its opposite end to an arm 38 rotationally secured to the output shaft of a stepper motor 40. Figure 3 shows the three panels 1-3 in a central position in which they substantially co-planar with each other. However, operation of the motor will cause each of the panels to pivot around the axis defined by its respective pivot pins. For example, Figure 4 shows the position of the panels after the motor 40 has rotated the arm 38 in an anti-clockwise direction compared to Figure 3. As can be seen, this has caused the arm to pull on the coupling rod 28 via the connecting rod 36 which in turn causes the arms 25-27 to swing about the pivot axes of the corresponding panels and thus to rotate the panels into the position shown in Figure 4.

The rod 36 and motor 40 have been omitted from Figure 2 for the sake of clarity.

The position of the panels as shown in Figure 3 would be appropriate around midday when the sun would be shining directly onto the panels, substantially at right angles. Figure 3 shows the relative position of the panels and the sun's rays, reference 42, at another time of day. As can be seen from the Figure, the rays 42 strike the panels at an oblique angle. This means that each panel receives a lower flux of solar photons that would be the case if the rays were striking the panels at right angles. By contrast, when the panels are in the position shown in Figure 4, the sun's rays will intersect the panels substantially at right angles.

Referring back to Figure 1, each of the panels includes a respective column of three substantially identical photovoltaic cells, for example the cells 44-46 on the panel 1. In this example, each cell is square, and has a side length of between 125 and 156 mm. Since the arrangement of solar cells on the panels is identical, only the arrangement on the panel 1 will be described. As can be seen from Figure 1, each of the cells extends substantially across the entire width of the panel 1, from adjacent the side 22, over the pivot axis defined by the pins 6 and 7 and to a position adjacent the side 24. The distance between each of the sides 22 and 24 and the adjacent side of each cell (for example the spacing indicated by the arrow d in Figure 1) is approximately 2mm.

As can be seen from Figure 4, when the panel 1 is tilted into the position shown in that Figure, so as to be substantially perpendicular to the rays 42, it will cast a shadow on the panel 2 which, similarly will cast a shadow on the panel 3.

If the panels 2-4 were conventional, having a number of rows and columns of identical solar cells, then some of the cells (specifically on the left-hand side of the panels 2-4 as viewed in Figure 1) would be completely shaded by the adjacent panel (1, 2 or 3), and would therefore be rendered substantially non-conductive, which would adversely affect all of the cells on the shaded panel. However, with the panels in accordance with the present invention, at least the right-hand portion of each cell of a partially shaded panel will still be exposed to the sun. The portions in question are indicated by the arrows 48 in Figure 4. This means that the cells on the partially shaded panels will still continue to work.

For the sake of simplicity, only three of the panels 1-3 are shown in Figures 3 and 4, but it will be appreciated that the panel 4 is also connected to the coupling rod 28 (by respective arm and pivot) in the region between the pins 32 and 34.

In the arrangement shown in Figures 1-5, the spacing between the neighbouring panels is 10% of the panel width (when the panels are co-planar), the distance between adjacent pivot axes of the panels thus being 1.1 times the width of each panel. In Figure 5, the panels are shown tilted at a shallower angle to the horizontal than is the case in Figure 4, and the mounting frame and linkage for pivoting the panels , along with the panel 1, have been omitted for the sake of clarity. As can be seen, when the rays 42 of sunlight are perpendicular to the panels 2, 3 and 4 in Figure 5, then the panel 2 will shade approximately half of the panel 3 which, in turn, shades approximately half of the panel 4. Although none of the photovoltaic cells on any of the panels 2, 3 and 4 is rendered non-conductive by this shading, for the reasons explained above, Figure 5 does illustrate a situation in which the power generated by the array is significantly reduced by the shading. In situations where there is a high demand for electricity around the middle part of the day, the arrangement in Figure 5 is still highly advantageous because the array substantially optimises the use of the area (for collecting solar energy) over which the array is installed.

However, there are situations in which electricity generated in mornings and evenings is more valuable, in which case the embodiment shown in Figure 6 may be advantageous.

The embodiment shown in Figure 6 is identical in all respects to the embodiment shown in Figures 1-5 save in that the spacing between the panels (52, 53 and 54) is around 50% of the panel width, so that the distance between the pivot axes of two adjacent panels is 1.5 times the panel width. As can be seen from Figure 6 (which illustrates a position 2 hours after sunrise), the sun's rays illuminate about ¾ of each of the panels (other than the end panel which is not shaded), so the arrangement generates more power than the first embodiment. Although the spacing between the adjacent panels is not less than the spacing that would be used for a conventional array, the second embodiment is still advantageous to a convention array because shading of one of the panels in the conventional array would lead to the cells of one row being completely shaded, so that the panel becomes substantially non-conductive. Consequently, standard multi-cell panels can only generate useful power for about 6 hours during a day having 12 hours of daylight whereas the arrangement shown in Figure 6 can generate useful power for 9 or 10 hours over the course of such a day.