PV module is the smallest indivisible solar cell assembly device with encapsulation and internal connection that can independently provide direct current output. It is also called solar cell module.
Photovoltaic modules are the core part of the entire photovoltaic power generation system, and their function is to convert solar energy into DC power output through the photovoltaic effect. When sunlight shines on the solar cell, the cell absorbs light energy and generates photo-generated electron-hole pairs. Under the action of the built-in electric field of the battery, the photogenerated electrons and holes are separated, and the accumulation of different signs of electric charge appears at both ends of the battery, that is, a “photogenerated voltage” is generated, which is the “photovoltaic effect”. If the electrodes are drawn on both sides of the built-in electric field and the load is connected, the load will have “photo-generated current” flowing through it, thereby obtaining power output. At the same temperature, the greater the light intensity, the greater the open circuit voltage and short-circuit current of the solar panel, and the greater the maximum output power.
In addition to the conventional module types that occupy a dominant position in industrial applications, with the continuous breakthrough of photovoltaic technology in recent years, a variety of new photovoltaic modules or solar cells have gradually emerged and developed rapidly. Among them, the more representative development direction is the double-sided photovoltaic module that reflects the more optimized module structure design.
Double-sided photovoltaic modules generally use a special battery structure and transparent backsheet materials to achieve the effect of generating electricity on both front and back sides. Since the backplane of the module is generally made of glass, it is also called a double glass module. The light that can be received and used on the back of this type of module includes not only the reflected light from the ground, but also the scattered light in the atmosphere, the reflected light of dust in the air, and the reflected light of surrounding buildings. At present, there are three types of bifacial photovoltaic modules on the market: single crystal N-type bifacial photovoltaic modules, monocrystalline PERC bifacial photovoltaic modules, and N-type heterojunction (HIT or HJT) bifacial photovoltaic modules.
Compared with conventional single-sided modules, double-sided modules also have the following features:
(1) The back can generate electricity. The back of the double-sided photovoltaic module mainly uses the reflected light from the ground to generate electricity. The higher the ground reflectivity, the stronger the light received on the back of the battery and the better the power generation effect. Common ground reflectivity is 15% to 25% for grass, 25% to 35% for concrete, and 55% to 75% for wet snow. The application of double-sided photovoltaic modules on the grassland can increase the power generation by 8%-10%, and the maximum power generation on the snow can be increased by 30%.
(2) Speed up the snow melting of winter components. After the front side of the double-sided photovoltaic module is covered by snow, the back side of the module can receive the reflected light from the snow to generate heat, accelerate the melting and sliding of the snow, and increase the power generation.
(3) Flexible installation methods and site adaptability. Double-sided modules can reduce the amount of combiner boxes, cables, etc. in most 1500V photovoltaic systems, and reduce the initial system investment cost. At the same time, the water permeability of the glass is almost zero, so there is no need to consider the drop in output power caused by water vapor entering the module to induce PID. This feature makes the double-sided module more adaptable to the environment, and is suitable for photovoltaic power plants built in areas with more acid rain or salt fog. In addition, the requirements for the installation direction of the double-sided module are more flexible.
(4) Special support form requirements. The conventional support form will block the back of the double-sided photovoltaic module, which not only reduces the back light, but also causes a series mismatch between the cells in the module, which affects the power generation effect. The bracket of the double-sided photovoltaic module can be designed in the form of a “mirror frame” to avoid blocking the back of the module (see Figure 1).