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Mobile WebSiteWith the rapid development of science and technology, photovoltaic power generation technology has been widely used at home and abroad. Its application forms are various, and its application places are widely distributed. It is mainly used for roofing and building photovoltaic of large-scale ground photovoltaic power stations, residential and commercial buildings. Building integration, photovoltaic street lights, etc. In these places, buildings, shades, chimneys, dust, clouds, etc., are inevitably blocked from solar cells. Therefore, people are concerned about how much such a situation affects the power generation efficiency of solar cells, and how to solve them.
In practical applications, a solar cell is generally connected in series or in parallel by a plurality of battery modules to obtain a desired voltage or current. In order to achieve higher photoelectric conversion efficiency, each cell in the battery pack must have similar characteristics. During use, one or a group of batteries may not match, such as cracks, internal connection failure or shading, which may cause the characteristics to be inconsistent with the whole.
Under certain conditions, the solar cell module that is shielded in a series branch will be used as a load to dissipate the energy generated by other illuminated solar cell modules. The shaded solar cell component will heat up at this time, which is the hot spot effect. This effect can seriously damage the solar cell. Part of the energy generated by a solar cell with light may be consumed by the obscured battery. In order to prevent the solar cell from being damaged by the hot spot effect, it is preferable to connect a bypass diode between the positive and negative terminals of the solar cell module to prevent the energy generated by the illumination component from being consumed by the shielded component.
About the cause of the hot spot of the component, the source of the problem battery and the corresponding countermeasures
(1) Causes of component hot spots
The core component of a photovoltaic module is a solar cell. Generally speaking, the electrical characteristics of the solar cells used in each component are substantially the same, otherwise a so-called hot spot effect will be generated on a battery (problem battery) having poor electrical performance or being blocked.
In order to prevent hot spot generation, a bypass diode should be connected in parallel with each battery. When the battery is faulty or blocked, the current generated by other batteries larger than the problem battery will be bypassed by the bypass diode.
In fact, it is unrealistic to have a diode connected in parallel on each cell. Typically on the assembly are 18 (36 or 54 cells in series) or 24 (72 cells in series). The cells are connected in series with a diode in parallel.
It is conceivable that when the currents generated in the 18 or 24 cells are inconsistent, that is, when the problematic battery is present, the current through the string of cells will cause hot spots on the problematic battery. If the current between the battery string and the string does not match, a so-called step curve or an abnormal curve can be seen on the component characteristic curve of the bypass diode.
If the solar cell performance in the component is inherently inconsistent, it will inevitably lead to hot spots in the component. We can see the presence of hot spots in the component through the output characteristics of the component and infrared imaging.
If the efficiency of the solar cell is attenuated after the solar cell is attenuated, the solar cell performance in the component is inconsistent. We can see the changes in the component before and after illumination by testing the output characteristic curve before and after attenuation of the component and infrared imaging.
If the component is not connected to the bypass diode, even if there is a problem with the battery, the output characteristic curve of the component does not see the step curve, but the short-circuit current should be smaller than the normal component, which indicates that the hot spot phenomenon exists.
(ii) The source of the problem battery
1. Defects in silicon material itself
2. Reasons for battery manufacturing
1) Incomplete edge, short edge
2) Going over the head, the P-type layer extends toward the center of the N-type layer, and the edge gate line causes a partial short circuit.
3) Sintering is poor, the positive electrode or the back electrode is in poor contact with the silicon wafer, and the series resistance is increased.
4) Excessive sintering, which will burn the PN junction and short circuit
The above several types may not be exposed during the sorting test, but after being made into components, they gradually change over the long-term use process and become more and more intense.
3. The performance of the same grade of battery is inconsistent
1) Misjudgment during battery sorting test
a) Sorting the tester's own error
b) Difference between tester and tester
c) Misoperation of the sorting tester
2) The battery's own attenuation is inconsistent
3) Artificial blends
If the information on the battery is inaccurate, it may be mislabeled, mixed, and mixed when the battery is inspected.
4. Reasons for component manufacturing
1) Mixing before mixing or patching before soldering
2) The crack of the battery itself
3) The splint or cracked piece caused by the manual welding process, the proportion of abnormal welding curve of the machine is generally smaller than that of manual welding.
4) There are almost no reports of poor soldering in the daily inspection report.
5) Cracks generated during the production of components, such as glass bending caused by cracks or overheated fashion frames, universal ball cracking batteries
6) Poor soldering when reworking components, overlap between interconnecting strips, large contact resistance
7) Foreign matter in the component causes a short circuit
8) When the back side is soldered, the front interconnect strip is disengaged, so that tin particles are present between the interconnect strip and the battery, and the battery is broken due to lamination.
(iii) Measures taken
1. The battery production line uses a 72-pack package to avoid the mixing of several parts of the assembly line.
2. The battery production line is first visually inspected and post-tested and sorted to prevent the appearance inspection after the test sorting.
3. When the components are produced, use the whole package of battery chips, do not use bulk bags to prevent mixing
4. The principle of component patching must be supplemented with the same grade of battery (it is preparing to test 75 packs of one pack)
5. Check the cracks before welding
6. The weld string template is regularly inspected to prevent the interconnect strip from being desoldered
7. Strictly check foreign objects
8. Strengthen the virtual welding inspection to prevent the cold welding
9. Minimize glass bending during handling
10. Large components use 4mm glass to reduce bending and increase strength
11. Move the turnover car to the glass vertically
12. Not allowed >50 ° C fashion box
13. Interconnecting strips are not allowed during rework
14. Bulk batteries must be re-sorted and tested.
15. Batteries that have been in stock for more than a certain period of time should undergo a second sorting test before being assembled.
16. When testing, the components must be within the specified temperature range
17. Give the treatment method after finding the curve abnormality to prevent the bad components from flowing to the customer.
18. The battery is first attenuated and then sorted and tested (in trial implementation)
Although the above measures have been taken, the current curve anomalies still exist. Many components have different degrees of hot spots. Some measures are difficult to implement, progress requires time and related equipment, and measures are not implemented thoroughly. How to ensure that each component uses a pack of 72 or 54 batteries of the same grade without attenuation, and still needs continuous improvement.
