WO2010000108A1

WO2010000108A1 - Concentrating photovoltaic cell system, wiring and aranging methods thereof

Info

Publication number: WO2010000108A1
Application number: PCT/CN2008/071516
Authority: WO
Inventors: Yingtian Chen
Original assignee: Yingtian Chen
Priority date: 2008-07-01
Filing date: 2008-07-01
Publication date: 2010-01-07

Abstract

A concentrating photovoltaic array system, wiring and arranging methods thereof are disclosed to minimize the effect of shading. The array system contains a plurality of arrays, each of which includes multiple rows of horizontal modules wired in series. Corresponding rows from different arrays, shaded or in the sun simultaneously, can be wired in series. Then plural series rows are connected in parallel to generate solar energy.

Description

CONCENTRATING PHOTOVOLTAIC CELL SYSTEM, WIRING AND ARRANGING METHODS THEREOF

BACKGROUND OF THE INVENTION

[001] Photovoltaic cells, also known as solar cells, are finding increasing use for power generation. Such cells are generally made of silicon or other semiconductor material processed to provide a p-n junction near an illuminated surface of the cell.

[002] For most applications, a single photovoltaic cell does not provide enough power. Instead, a group or array of cells are generally formed on a single substrate and wired together to produce a desired electrical output. Such flat panel arrays can include just a few cells (e.g., for a solar powered calculator) or thousands of cells (for a solar power generator). In some cases, multiple arrays are mounted in a single location.

[003] One of the more important considerations for placement of such arrays is shading. Partial shading can have a disproportionate impact on the output of a solar array. For example, just 0.28% shading of an array can result in an output loss of 7.5%. Thus, if possible, arrays are arranged to avoid any shading. In the case of solar farms having multiple photovoltaic arrays, land is usually cleared of any obstacles that could cause shading (e.g., trees). However, shading between adjacent arrays within a solar farm may still result in power losses.

SUMMARY OF THE INVENTION

[004] Disclosed herein are systems of concentrating photovoltaic cell devices and methods of use. In one aspect, a system includes a group of interconnected arrays that are densely packed and configured to minimize the effects of shading. [005] In one embodiment, a system of concentrating photovoltaic modules comprises a first, second, and third array. Each of the photovoltaic modules comprises a single photovoltaic cell. The first array includes at least a first and a second row of concentrating photovoltaic modules, the first and second rows comprising multiple concentrating modules connected in series with one another. The second array comprises at least a first and a second row of concentrating photovoltaic modules, the first and second rows comprising multiple concentrating modules connected in series with one another. The third array comprises at least a first and a second row of concentrating photovoltaic modules, the first and second rows comprising multiple concentrating modules connected in series with one another.

[006] In one aspect, the first rows of the first, second, and third arrays are connected in series with one another and the second rows of the first, second, and third arrays are connected in series with one another. In addition, the serial connected first and second rows are connected in parallel with one another. The first, second, and third arrays can be spaced from one another such that a shadow from the first array is cast on the first row of the second array, and simultaneously, a shadow from the second array is cast on the first row of the third array. Thus, serially connected modules are simultaneously shaded and modules in the sunlight are connected to the shaded modules in parallel.

[007] In one aspect, the first and second rows extend horizontally. In addition, the rows can be positioned parallel to the horizon. The system can also include a sun tracking device. In one aspect, each array is separately mounted on a sun tracking device. In another aspect, two or more arrays are mounted on a single sun tracking device.

[008] The modules can each include a solar concentrating surface. For example, the modules can include a funnel-type solar concentrator positioned adjacent to the photovoltaic cells. However, each module includes only one solar cell.

BRIEF DESCRIPTION OF THE DRAWINGS

[009] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate exemplary embodiments of the invention and, together with the description, serve to explain the principles of the invention.

[0010] FIG. 1 is a perspective view of one embodiment of a system described herein;

[0011 ] FIG. 2 is a side view of one array in the system of FIG. 1 ; and

[0012] FIG. 3 is a side view of the system of FIG. 1.

DETAILED DESCRIPTION [0013] Described herein are interconnected arrays of concentrating photovoltaic cells arranged in a densely packed configuration. Instead of spacing the arrays from one another to avoid any shading, the systems described herein allow arrays to be positioned more closely together with a minimum impact on energy output.

[0014] In one embodiment, a first array includes multiple rows of concentrating photovoltaic modules, where the modules within the rows are wired in series with each other. A second and third array similarly each comprise multiple rows of serially connected concentrating photovoltaic module. The spacing of the arrays is such that the first array shades the second array during at least a portion of the day and the second array shades the third array during at least a portion of the day. The spacing of the arrays and layout of the modules is such that a row of modules in the second array enters the shade simultaneously with a row of modules on the third array. The simultaneously shaded rows of the second and third arrays are wired in series with one another. The non-shaded rows are wired in parallel with the shaded rows. While shading is usually avoided between adjacent arrays, the systems described herein minimize the effects of shading and thereby allow more efficient use of land.

[0015] While a variety of solar cells can be used with the systems described herein, in one embodiment, the photovoltaic cells are concentrating photovoltaic cells. Each cell can comprise a module having at least one photovoltaic cell and a reflective member for directing solar energy onto the at least one photovoltaic cell. Thus, the term "module," as referred to herein, includes a solar-concentrating reflective structure and only one photovoltaic cell.

[0016] Depending on the configuration of the reflective surface, the solar concentrator can provide 1 to 20 suns, in another aspect 2 to 8 suns, and in a further aspect 3 to 8 suns. In one aspect, the reflecting surface can include a funnel-type concentrator that surrounds the photovoltaic cell. In another aspect, the reflective surface can have an octagonal shape and a geometry similar to that disclosed in Chinese Patent Application Publication No. 1780136, the specification of which is hereby incorporated herein by reference in its entirety. One skilled in the art will appreciate that a variety of solar concentrator sizes, shapes, and intensities can be chosen depending on the power generation needs, local insolation, and design requirements.

[0017] FIG. 1 illustrates one exemplary embodiment of a system of concentrating photovoltaic modules. System 10 comprises a plurality of solar photovoltaic modules disposed in three individual arrays, 12, 13, 14. Each of the arrays includes modules 16 arranged in rows and columns. For example, array 12 includes three rows, 20(a), 20(b), and 20(c) and each row includes multiple modules. While the illustrated embodiment includes three arrays, each array having three rows of ten modules, it should be appreciated that each array can include one or more rows having one or more modules, and the number of arrays is limited only by the available space.

[0018] In one embodiment the arrays are independently mounted. For example, the arrays can be independently fixed to the ground or mounted on devices having sun tracking capabilities in one or more axes. Alternatively, two or more arrays can be mounted on a common platform. As illustrated in FIG. 1 , arrays 12, 13, 14 are mounted on a platform 22 via one or more pedestals 18. The platform can rotate around a common azimuth axis 19 and in turn each array can be elevationally adjusted for tracking the sun.

[0019] FIG. 2 illustrates a side view of array 12. Each row, 20(a), 20(b), and 20(c), can have common shade characteristics. As the sun begins to set, the modules of row 20(c) will first fall into the shade at substantially the same time. As the sun continues to fall, the modules of row 20(b) are then shaded followed by the modules of row 20(a). Similarly, as the sun rises, the modules in each row will enter the sunlight at the same time. Thus, each row of modules extends horizontally and is positioned substantially parallel to the horizon. In addition, each row can be positioned parallel to the other rows.

[0020] As mentioned above, the modules within a row are electrically connected in series. The serially connected modules within a row fall into the shade/sunlight together. At some point during the day, one serially connected row is positioned in the shade and the other rows are positioned in the sun. To reduce the impact of shading on the output of the array, the row of modules in the shade is connected in parallel with the row(s) of single cell modules in the sun. This configuration results in an array where shading produces a generally proportional impact on the output of the array and minimizes energy losses from shading.

[0021 ] In one embodiment, rows of modules from adjacent arrays sharing common shading characteristics are connected in series with one another. FIG. 1 , for example, illustrates rows of different arrays within system 10 wired in series. In particular, the top or first row 20(a) of array 12 is connected in series with the first row 20(a)' of array 13 and the first row 20(a)" of array 14. Similarly, the second rows 20(b), 20(b)', and 20(b)" of arrays 12, 13, 14 can be wired in series. The series connected rows can be wired in parallel with rows having different shading characteristics. For example, the first rows 20(a), 20(a)', and 20(a)" are wired in parallel with second rows 20(b), 20(b)\ and 20(b)".

[0022] One drawback of parallel connections between modules is that the produced voltage is not additive. However, by wiring rows from different arrays together in series, where the rows have common shade characteristics, a desired voltage output can be achieved without the disproportionate effect of shading. [0023] In one aspect, the parallel connections between the rows occurs at a DC- AC inverter. FIG. 1 , for example, illustrates inverter 15 connected separately with each of the rows. The rows having common shading characteristics are connected in series by a wire or wires 17, while connections from different levels of rows are connected in parallel to the inverter 15 to generate sufficient open circuit voltage to match the voltage range of the input for the DC-AC inverter.

[0024] In one embodiment, the systems described herein can include arrays spaced from one another such that shade from one array falls on another array. While such dense packing is usually avoided, the series and parallel connections between the concentrating photovoltaic modules minimizes the impact of such shading.

[0025] FIG. 3 illustrates arrays 12, 13, 14 spaced by a distance L such that the arrays partially shade each other. As the sun sets or rises, array 12 shades row 20(c)' of array 13 and array 13 shades row 20(c)" of array 14. Because row 20(c)' of array 13 and row 20(c)" of array 14 are wired in series with each other and are wired in parallel with the other rows, the output drop from the shading of rows 20(c)' and 20(c)" is minimized. As the sun continues to set, a second row of series wired modules (20(b)', 20(b)") simultaneously falls into the shade. Again, the output drop from power generation system 10 is minimized because the single cell modules in the sunlight are wired in parallel with the modules in the shade.

[0026] In one embodiment, the arrays have identical heights and module positioning, and the spacing "L" between adjacent arrays 12, 13, 14 is constant. However, the height of the arrays, the angle of the modules, and/or the array spacing need not be the same, as long as at least some of the rows having common shade characteristics are wired together in series and those having different shade characteristics are wired in parallel.

[0027] This arrangement can provide a more densely packed solar generation system and make more efficient use of available land. The series and parallel wiring results in the output loss due to partial shading being proportional to that of the shaded area. If it is assumed that the incident solar altitude angle is α, and the height of the module is /, the instantaneous percentage of the output loss during the sun blocking time would be:

/ - D sin a _0/

[0028] A calculation is included below in order to demonstrate the efficiency of the above disclosed arrangement.

[0029] For a series wired system allowing for an average annual energy loss of 15% due to shading, the distance between adjacent arrays would be double the height of the array, i.e.,

Ϊ- - 2.

[0030] Using above defined equation, the annual loss for system 10 can be estimated to obtain a comparison figure for demonstrating the efficiency of system 10. It may be assumed that in order to achieve a good content, the tracking system may be started from solar altitude angle of an acceptable value of 20°; and from the above equation, the shading will end at a solar altitude angle of

. / a = arcsin — . D [0031 ] Therefore, if it is assumed that the radiation at all altitudes is the same, which is too conservative in most cases, the estimated loss in percentage caused by the shade would be 15%, using the ratio:

[0032] From this comparison, it is shown that by the disclosed arrangement, at least 25% of available land use may be saved.

[0033] Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims.

Claims

1. A system of concentrating photovoltaic modules, each comprising a single photovoltaic cell, for converting sunlight into electrical energy, comprising: a first array comprising at least a first and a second row of concentrating photovoltaic modules, the first and second rows comprising multiple concentrating modules connected in series with one another; a second array comprising at least a first and a second row of concentrating photovoltaic modules, the first and second rows comprising multiple concentrating modules connected in series with one another; and a third array comprising at least a first and a second row of concentrating photovoltaic modules, the first and second rows comprising multiple concentrating modules connected in series with one another; wherein the first rows of the first, second, and third arrays are connected in series with one another and the second rows of the first, second, and third arrays are connected in series with one another, and the serial connected first and second rows are connected in parallel with one another, and wherein the first, second, and third arrays are spaced from one another such that sunlight incident on the first array casts a shadow on the first row of the second array, and simultaneously, sunlight incident on the second array casts a shadow on the first row of the third array.

2. The system of claim 1 , wherein the first and second rows extend horizontally.

3. The system of claim 1 , further comprising a sun tracking device.

4. The system of claim 1 , wherein each module includes a solar concentrating surface.

5. The system of claim 1 , wherein each module includes a funnel-type solar concentrator.

6. The system of claim 1 , wherein the arrays are spaced by a distance that is less than twice their height.

7. The system of claim 1 , wherein the arrays are spaced by a distance that is less than 1.5 times their height.

8. The system of claim 1 , wherein the arrays are spaced by a distance between 1 and 1.8 times their height.

9. A system of concentrating photovoltaic modules, each comprising a single photovoltaic cell, for converting sunlight into electrical energy, comprising: a first array comprising at least a first and a second row of concentrating photovoltaic modules, the first and second rows comprising multiple concentrating modules connected in series with one another; a second array comprising at least a first and a second row of concentrating photovoltaic modules, the first and second rows comprising multiple concentrating modules connected in series with one another; and a third array comprising at least a first and a second row of concentrating photovoltaic modules, the first and second rows comprising multiple concentrating modules connected in series with one another; wherein the first, second, and third arrays are spaced from one another such that sunlight incident on the first array casts a shadow on the first row of the second array, and simultaneously, sunlight incident on the second array casts shadow on the first row of the third array, and wherein the first row of the second array and the first row of the third array are connected in series with one another and are connected in parallel with the second row of the second array and the second row of the third array.

10. The system of claim 9, wherein the second row of the second array is connected in series with the second row of the third array.

11. A method of arranging a system of concentrating photovoltaic modules for converting sunlight into electrical energy, comprising: providing a first, second; and third array of concentrating photovoltaic modules, the first array comprising at least a first and a second row of concentrating photovoltaic modules, the first and second rows comprising multiple concentrating modules connected in series with one another, the second array comprising at least a first and a second row of concentrating photovoltaic modules, the first and second rows comprising multiple concentrating modules connected in series with one another, and the third array comprising at least a first and a second row of concentrating photovoltaic modules, the first and second rows comprising multiple concentrating modules connected in series with one another; positioning the first, second, and third arrays such that sunlight incident on the first array casts a shadow on the first row of the second array, and simultaneously, sunlight incident on the second array casts a shadow on the first row of the third array; and wiring the first rows of the first, second, and third arrays together in series and wiring the serially connected first rows in parallel with the second rows from the first, second, and third array.

12. The method of claim 11 , wherein the step of positioning the arrays includes positioning the arrays such that the arrays are spaced less than twice their height from one another.

13. The method of claim 11 , wherein the step of positioning the arrays includes positioning the arrays such that the arrays are spaced between 1 and 1.5 times their height from one another.

14. The system of claim 11 , wherein the step of positioning the arrays includes positioning the arrays such that the arrays are spaced between 1 and 1.8 times their height.

15. The method of claim 11 , wherein the step of positioning the arrays includes positioning the arrays such that the arrays are spaced equally.