Method and system for monitoring the quality of photovoltaic cells
A method and system for monitoring the quality of photovoltaic cells is described, the method including for each cell: an excitation step, during which the cell to be monitored is subjected to excitation at a predetermined level of excitation; a step of acquiring at least one luminescence image of the cell to be monitored after excitation; and a step of processing the acquired image. The invention is characterized in that, for each cell, there is provided a preliminary step for determining an excitation level adjusted to the cell, the respective adjusted excitation levels of the different cells to be monitored being adapted such that the luminescence intensities of the signals emitted by the different cells are equal at a given reference luminescence intensity.
1. Method for monitoring the quality of a plurality of photovoltaic cells, the method comprising, for each cell:
subjecting the cell to be monitored to an excitation;
acquiring at least one luminescence image of the cell to be monitored after excitation; and
processing the acquired image;
wherein, for each cell to be monitored, the processing, comprises decomposing the luminescence image of the cell to be monitored into a first image corresponding to the cell without defects and a second image corresponding to defects of the cell,
wherein the first image corresponds to the luminescence of the cell without defects taking into account the luminescence of a plurality of local areas of the cell, and
wherein the second image is obtained based on the acquired luminescence image taking into account the first image.
2. The method according to claim 1 , comprising, to decompose the luminescence image of the cell to be monitored, the luminescence image of the cell being composed of a set of pixels to which respective luminescence intensity values are assigned:
selecting a plurality of pixels of said luminescence image;
assigning to each of the selected pixels a value which is representative of a local environment of said pixel; and
assigning a new value to each pixel of the image from the values of the selected pixels in order to obtain the first image corresponding to the cell without defects.
3. The method according to claim 2 , comprising, in order to obtain the second image, calculating a mean of the luminescence intensity values associated with the pixels of the second image in order to determine a parameter for quantification of the defects of the cell.
4. The method according to claim 3 , comprising correcting the defect quantification parameter by a correction factor determined from a mean of the pixel values of the first image.
5. The method according to claim 2 , comprising in order to obtain the first image, assigning a new value to each pixel of the luminescence image by interpolation of the values of the selected pixels.
6. The method according to claim 2 , wherein the selected pixels of the luminescence image are situated at periodically spaced-apart locations.
7. The method according to claim 1 , comprising obtaining the second image by forming a ratio or a subtraction between the luminescence image of the cell and the first image.
8. System for monitoring the quality of a plurality of photovoltaic cells comprising hardware and software configured for implementing, for each cell:
subjecting the cell to be monitored to an excitation;
acquiring at least one luminescence image of the cell to be monitored after excitation, and
processing the acquired image;
wherein, for each cell to be monitored, the processing, comprises decomposing the luminescence image of the cell to be monitored into a first image corresponding to the cell without defects and a second image corresponding to defects of the cell,
wherein the first image corresponds to the luminescence of the cell without defects taking into account the luminescence of a plurality of local areas of the cell, and
wherein the second image is obtained based on the acquired luminescence image taking into account the first image.
9. System for monitoring the quality of a plurality of photovoltaic cells comprising:
an excitation device adapted to apply an excitation to a cell to be monitored;
an acquisition device for acquisition of a luminescence image of the cell after excitation; and
an image processing module;
wherein the image processing module is adapted to decompose the luminescence image of each cell to be monitored into a first image corresponding to that cell without defects and a second image corresponding to defects of that cell,
wherein the first image corresponds to the luminescence of the cell without defects taking into account the luminescence of a plurality of local areas of the cell, and
wherein the second image is obtained based on the acquired luminescence image taking into account the first image.
10. The system according to claim 9 , wherein the image processing module is designed to select a plurality of pixels of said luminescence image, assign to each of the selected pixels a value which is representative of a local environment of said pixel, and assign a new value to each pixel of the image from the values of the selected pixels in order to obtain the first image.
11. The system according to claim 10 , wherein the image processing module is designed, in order to obtain the second image, to calculate a mean of the luminescence intensity values associated with the pixels of the second image in order to determine a parameter for quantification of the defects of the cell.
12. The system according to claim 11 , wherein the image processing module is designed to correct the defect quantification parameter by a correction factor determined from a mean of the pixel values of the first image.
13. The system according to claim 10 , wherein the image processing module is designed, in order to obtain the first image, to assign a new value to each pixel of the luminescence image by interpolation of the values of the selected pixels.
14. The system according to claim 10 , wherein the image processing module is designed to situate the selected pixels of the luminescence image at periodically spaced-apart locations.
15. The system according to claim 9 , wherein the image processing module is designed to obtain the second image by forming a ratio or a subtraction between the luminescence image of the cell and the first image.