The solar cell is the smallest unit for photoelectric conversion. After the solar cell is connected in series, parallel and packaged, it becomes a solar cell module. The solar cell modules are connected in series, in parallel and mounted on the bracket to form a solar cell array. It can meet the output power required by the load.
(1) Packaging of solar cell modules
①The connection method of the unit cell of the module.
There are mainly two ways to connect single cells in series and parallel, and two ways can also be used at the same time to form a series-parallel hybrid connection, as shown in Figure 1.
If the performance of each single cell is consistent, the series connection of multiple single cells can increase the output voltage proportionally without changing the output current;
The parallel connection method can increase the output current proportionally without changing the output voltage; while the series-parallel hybrid connection method can not only increase the output voltage of the component, but also increase the output current of the component.
② package structure of components.
Structure of a crystalline silicon solar cell module. Conventional solar cell modules have the following structural forms: glass shell type structure, bottom box type module, flat plate type module, and fully glue-sealed module without cover plate.
Structure of thin film solar cell modules. The packaging of thin film photovoltaic cells and crystalline silicon cells is somewhat different, the type of substrate is different, the packaging method is different, and the relative position of the semiconductor material and the substrate will affect the structure of the module. For front wall type CdTe cells and most amorphous silicon cells using non-tempered glass substrate, the glass substrate can be used as the upper cover to protect the cell, any type of glass can be used on the back, and tempered safety glass can be used if required.
For rear wall type CIS cells and some amorphous silicon cells using non-tempered substrates, a cover plate needs to be added to protect the cells.
In addition to the above two structures, if other types of substrates are used, another encapsulation method is used. This encapsulation method has three layers and is suitable for both front-wall and rear-wall thin-film photovoltaic cells.
③ The packaging material of the component.
The working life of a solar cell module has a lot to do with the packaging material and packaging process.
Upper cover. The upper cover plate covers the front of the solar cell and constitutes the outermost layer of the module. It should not only be light-transmitting, firm, and resistant to wind, frost, rain and snow, but also withstand the impact of sand, gravel and hail, so as to protect the battery for a long time. The materials used for the upper cover include tempered glass, polyacrylic resin, fluorinated ethylene propylene, transparent polyester, and polycarbonate. At present, low molten iron white tempered glass is the most common top cover material. After adding a micro-pyramid structure to the glass surface, it can also increase the absorption of diffuse reflection light and reduce the light pollution caused by the glass surface.
Binder. Adhesive is the key material for fixing solar cells and ensuring the tightness of the upper and lower cover plates. The requirements for it are: high light transmittance in the visible light range and anti-ultraviolet aging; it has a certain elasticity to buffer thermal expansion and contraction between different materials; it has good electrical insulation properties and chemical stability, and does not produce gas or liquid that is harmful to solar cells; it has excellent air tightness and can prevent the erosion of solar cells by external moisture or other harmful gases; it can be applied to automated component packaging. Adhesives mainly include room temperature curing silicone rubber, polyvinyl fluoride (PVF), polyvinyl butyral (PVB) and ethylene vinyl acetate (EVA).
Bottom plate. The bottom plate also has a protective effect on the battery, and sometimes also has a supporting effect. The general requirements for the bottom plate are: good weather resistance, can isolate moisture or other harmful gases from the back; no change in the lamination temperature; strong bond with the bonding material. The materials used for the bottom plate are generally glass, aluminum alloy, plexiglass, TPF composite film, etc. At present, TPF composite film is more widely used.
Border. The flat panel assembly must have a frame to protect the assembly and facilitate the connection and fixation of the assembly to the phalanx bracket. The frame and the adhesive form a seal on the edge of the component, and the main materials are stainless steel, aluminum alloy, rubber, and reinforced plastic.
④The process flow of component packaging.
Components of different structures have different packaging processes.
(2) Electrical connection and arrangement of solar cell array
The solar cell array requires cables, blocking diodes, and bypass diodes to electrically connect the solar cell modules, in addition to brackets to hold the many solar cell modules together, and need to be equipped with special branch junction box and main junction box with built-in arrester. Sometimes in order to prevent birds from contaminating the surface of the solar cell array and causing the hot spot effect, it is also necessary to install a bird repellent on the top of the array.
When assembling solar cell modules in series and parallel to form a square array, the principles that need to be paid attention to in series and parallel connection of solar cells should be referred to, and special attention should be paid to the following points:
①When connecting in series, components with the same operating current are required, and a bypass diode is connected in parallel for each component. ②When in parallel, components with the same working voltage are required, and a blocking diode is connected in series with each parallel line.
③ Try to consider the principle of the shortest interconnection wiring of components.
④ It is necessary to strictly prevent individual solar cell modules with deteriorated performance from being mixed into the solar cell array.
Figure 2 shows that the same 64 solar cell modules are formed into a square array in 4 parallel and 8 series, but there are two different electrical connections (a) vertical and horizontal and (b) horizontal and vertical. As can be seen in the figure, when there is a partial shadow, the bus voltage connected in (a) drops, the output battery also drops significantly, and the system may not work properly; while the bus voltage connected in (b) can remain the same, although one less current is required, but the system can work normally.