1. Installation of photovoltaic modules
For large-scale grid-connected photovoltaic power stations with conventional ground-fixed supports, the installation inclination angle of the modules should be comprehensively considered based on the latitude value of the area and the actual situation on site. Before installing the components, the installer must be familiar with the mechanical and electrical requirements of the components. The back of the module is equipped with a terminal junction box. The junction box is equipped with a certain length of cable and terminal (divided into male and female) to facilitate the electrical connection between the components.
When sunlight or other light sources illuminate the surface of the module, the module generates electricity. When the components are connected in series, the voltage accumulates; when the components are connected in parallel, the current accumulates. Therefore, a large-scale photovoltaic module string can generate very high voltage and current, and improper operation may cause serious electric shock and personal injury.
(1) The component mounting hole is installed with bolts.
The components can be fixed on the bracket through the mounting holes reserved for the frame, as shown in Figure 1. The components are fixed with 4 mounting holes, and all fasteners used for installation are made of stainless steel.
(2) Installation of component pressing block.
In the clamp installation mode, according to the relative position relationship between the long side of the module and the mounting bracket, it can be divided into two ways: the long side of the module is parallel to the mounting bracket or the long side of the module is perpendicular to the mounting bracket.
When the long side of the module is parallel to the mounting bracket, it is necessary to further distinguish whether the mounting clamp is located on the long side of the module or whether it is located.
There are two cases for the short side of the component:
1 ) .The mounting clamp is located on the long side of the module, as shown in Figure 2(a). In this case, the distance from the edge of the component to the centerline of the pressure block must be between 300mm and 350mm. The two long sides of the module are supported by the bracket, and the bracket and the aluminum frame of the module overlap by at least 20mm. The installation clamp should meet the minimum size shown in Figure 2(c) (the overlapping part should be at least 5mm in width and 30mm in length). The brackets of the array must be continuous.
2) .The mounting clamp is located on the short side of the module, as shown in Figure 2(b). The installation clamp must also meet the minimum size shown in Figure 2(c). If only four pressure blocks are used to fix the component, and the distance from the edge of the component to the center line of the pressure block is between 200mm and 300mm.
When the long side of the module is perpendicular to the mounting bracket, the pressure block should be further distinguished between the long side of the module or the short side of the module supported by the bracket:
①.The mounting clamp is located on the long side of the module, as shown in Figure 2(a). In this installation mode, the distance from the edge of the module to the centerline of the pressure block must be between 300mm and 350mm. The support of the array must support the bottom of the component and must be continuous.
②. The two short sides of the module are supported by the mounting bracket, as shown in Figure 2(b). The mounting bracket and the aluminum frame of the module overlap at least 20mm. The bracket of the array must support the bottom of the module and must be continuous. The distance from the edge of the module to the centerline of the pressure block (four) is between 200mm and 300mm. If two pressure blocks are added to the center of the two long sides of the module to strengthen the fixation (the middle of the module is also equipped with a mounting bracket to support the module).
2. Electrical connection of pv modules
The connection mode of a single module in the string is positive and negative connection. That is, during electrical connection, the negative electrode of the first component is connected to the positive electrode of the second component, the positive electrode of the second component is connected to the negative electrode of the third component, and so on. After the string connection is completed, the positive pole of the first component and the negative pole of the last component are not connected, and the remaining positive and negative poles need to be connected to the DC combiner box or the DC side of the string inverter. The connection method is not a series connection method, but a connection method where the positive electrode is connected to the positive electrode and the negative electrode is connected to the negative electrode, as shown in Figure 3.
On the common bracket of photovoltaic power station, a set of brackets can be placed 2 strings. At this time, there are two wiring methods. One is to connect according to the above-mentioned form, and the factor of saving cables is also considered to be a cross-over wiring method. For example, a certain set of brackets can place 2 strings, each string has 22 modules, that is, 44 modules, and the cross-span connection means that the first module and the second module each have a positive and negative connector to connect to the confluence. In a box or string inverter, the odd-numbered components are connected positively and negatively, the even-numbered components are positively negatively connected, and the remaining positive and negative electrodes of the last two components are connected. Figure 4 is the connection schematic diagram.
When photovoltaic modules receive light, they generate voltage and current. Although the output voltage of one or a small number of components is lower than the safety voltage of the human body, when multiple or a large number of components are connected in series (voltage addition) or parallel (current addition)
When connected, a high voltage that is sufficient to pose a threat to personal safety is generated. In order to effectively prevent electric sparks, arcs and even fires during component installation, especially when replacing male and female connectors or other related electrical connection operations, operation and maintenance personnel should pay special attention to the following matters:
(1) When plugging and unplugging the male and female plugs and wiring, be careful and use safety protection equipment to the greatest extent, including but not limited to various insulating tools, insulating gloves, etc.
(2) When the system circuit is not disconnected and there is a load at that time, the male and female plugs of the components will generate arcs. During operation, the upper-level fuse should be disconnected first to ensure that the string is in the state of disconnected positive and negative poles. .
(3) DC current will be generated when the component has cracks, stains or is exposed to light. An electric arc occurs when the circuit is connected and disconnected. Therefore, it is generally necessary to cover a light-shielding cloth on the module during installation to ensure the personal safety of the installer.