Solar photovoltaic (PV) modules, also known as solar cell modules or photovoltaic modules, are composed of a series of solar cells arranged in different arrays. A single solar cell cannot be used directly as a power source. To use it as a power source, several individual cells must be connected in series and parallel and tightly packaged into a module. Solar photovoltaic modules (also called solar panels) are the core and most important part of a solar power generation system. Their function is to convert solar energy into electrical energy, which is then either stored in batteries or used to power loads.
Main raw materials and components of solar photovoltaic cell modules
Photovoltaic Glass: The panel glass used in solar cell modules is low-iron, ultra-clear, textured tempered glass. The typical thickness is 3.2mm and 4mm. Building-grade solar cell modules sometimes use tempered glass with a thickness of 5-10mm, but regardless of thickness, a light transmittance of over 90% is required. Low-iron, ultra-clear means that this type of glass has a lower iron content than ordinary glass, thus increasing its light transmittance. Additionally, this glass appears whiter than ordinary glass when viewed from the edges, which tend to have a greenish tint. Tempering is used to increase the glass's strength, resisting the impact of wind, sand, and hail, thus providing long-term protection for the solar cells. After tempering, the strength of the panel glass can be increased by 3-4 times compared to ordinary glass.
EVA film: A copolymer of ethylene and vinyl acetate, it is a thermosetting, film-like hot melt adhesive, and is currently a widely used bonding material in the encapsulation of solar cell modules. Two layers of EVA film are added to the solar cell module, sandwiched between the panel glass, the solar cells, and the TPT backsheet film, bonding the glass, cells, and TPT together. After bonding with the glass, it increases the light transmittance of the glass, acting as an anti-reflective agent, and also enhances the power output of the solar cell module.
Backsheet Material: The backsheet material for solar cell modules can be chosen from various options depending on the specific requirements of the module. Common choices include tempered glass, acrylic glass, aluminum alloy, and TPT composite film. Tempered glass backsheets are primarily used to manufacture double-sided translucent building material type solar cell modules for photovoltaic curtain walls and roofs; these are more expensive and heavier. Besides tempered glass, TPT composite film is currently the most widely used. TPT composite film is characterized by its airtightness, high strength, good weather resistance, long service life, no change at lamination temperature, and strong bond with adhesive materials. These characteristics make it ideal for encapsulating solar cell modules, effectively preventing the corrosion and impact of various media, especially water, oxygen, and corrosive gases, on the EVA and solar cells. In addition to TPT, common composite materials include TAT (a composite of Tedlar film and aluminum film) and TIT (a composite of Tedlar film and iron film), which have a metal film interlayer structure. These composite films also possess properties such as high strength, flame retardancy, durability, and self-cleaning. The white composite film can also reflect sunlight, which can improve the conversion efficiency of the battery module. Furthermore, it has a strong reflective effect on infrared rays, which can reduce the operating temperature of the battery module under strong sunlight.
Junction box and bypass diode
A dedicated junction box for solar cell modules is a component that connects the internal output lines of the module to external lines. Positive and negative busbars leading from the solar panel enter the junction box and are plugged in or soldered to their corresponding positions. External leads are also connected to the junction box using methods such as plugging, soldering, and screw crimping. The junction box also has space for a bypass diode, or a bypass diode may be directly installed inside.
Basic knowledge of solar cell modules
When a number of solar cell modules are connected in series to form a cell array or a branch of a cell array, a diode needs to be connected in reverse parallel at the positive and negative output terminals of each cell panel. This diode connected in parallel at both ends of the module is called a bypass diode.
The function of a bypass diode is to prevent a component or part of a component in the array from being shaded or from failing and stopping power generation. When this happens, a forward bias voltage is formed across the bypass diode of the component, causing the diode to conduct. The operating current of the array bypasses the faulty component and flows through the diode bypass, without affecting the power generation of other normal components. At the same time, it protects the bypassed component from being damaged by high forward bias voltage or by overheating due to the "hot spot effect".
battery cells
Crystalline silicon solar cells are divided into monocrystalline silicon cells and polycrystalline silicon cells. Each cell has a voltage of approximately 0.5V, and the main specifications are 125mm×125mm, with a current of approximately 5-6A and a power of approximately 2.5-3W; and 156mm×156mm, with a current of approximately 8-9A and a power of approximately 4-5W. The thickness is generally 170-220um. The surface of the cell has a blue anti-reflective coating and silver-white electrode grid lines. Many of the fine grid lines are leads from the surface electrodes to the main grid lines, while the two wider silver-white lines are the main grid lines, also called electrode lines or upper electrodes. There are also two silver-white main grid lines on the back of the cell, called lower electrodes or back electrodes. The connection between cells is achieved by soldering interconnects to the main grid lines. Generally, the electrode lines on the front are the negative electrode lines of the cell, and the electrode lines on the back are the positive electrode lines. The size of the solar cell is directly proportional to the output current and power generation; the larger the area, the greater the output current and power generation.
