A brief introduction to solar photovoltaic cells. 1 article accurate make it clear!

A brief introduction to solar photovoltaic cells

Solar photovoltaic cells (referred to as photovoltaic cells) are used to convert the sun’s light energy directly into electrical energy. At present, ground photovoltaic systems use a large number of silicon solar cells based on silicon, which can be divided into monocrystalline silicon, polycrystalline silicon, and amorphous silicon solar cells.

In terms of comprehensive performance such as energy conversion efficiency and service life, monocrystalline silicon and polycrystalline silicon cells are superior to amorphous silicon cells. Polycrystalline silicon has lower conversion efficiency than monocrystalline silicon, but is cheaper. On September 6, 2012, the EU filed an anti-dumping case against China’s photovoltaic industry.

basic introduction

Solar photovoltaic cells (referred to as photovoltaic cells) are used to convert the sun’s light energy directly into electrical energy. At present, ground photovoltaic systems use a large number of silicon solar cells based on silicon, which can be divided into monocrystalline silicon, polycrystalline silicon, and amorphous silicon solar cells.

In terms of comprehensive performance such as energy conversion efficiency and service life, monocrystalline silicon and polycrystalline silicon cells are superior to amorphous silicon cells. Polycrystalline silicon has lower conversion efficiency than monocrystalline silicon, but is cheaper.

According to the application requirements, a group of photovoltaic cells that reaches a certain rated output power and output voltage after a certain combination of solar cells is called a photovoltaic module. Depending on the size and scale of the photovoltaic power plant, photovoltaic modules can be composed into arrays of various sizes.

Photovoltaic modules are made of high-efficiency monocrystalline silicon or polycrystalline silicon photovoltaic cells, high transmittance tempered glass, Tedlar, corrosion-resistant aluminum polyframes and other materials, and are manufactured using advanced vacuum lamination processes and pulse welding processes. Guaranteed long service life even in the harshest environments.

The installation and erection of components is very convenient. A waterproof junction box is installed on the back of the component, through which it can be easily connected to external circuits. Each solar cell module is guaranteed to have a service life of more than 20 years.

Solar energy development history

The term “Photovoltaics” comes from the Greek, meaning light, volts and electricity, and comes from the name of the Italian physicist Alessandro Volta. After Alessandro Volta, “Volt” ” is used as the unit of voltage.

Looking at the history of solar energy development, the “photoelectricity” behavior caused by light shining on materials was discovered as early as the 19th century.

The term “photo-voltaic” only appeared in English in 1849, which means the electromotive force generated by light, that is, light generates volts.

In 1839, the photovoltaic effect was first discovered by French physicist A.E. Becquerel.

The first solar cell was successfully prepared in 1883 by Charles Fritts. Charles used a selenium semiconductor covered with an extremely thin gold layer to form a semiconductor metal junction, and the device had an efficiency of only 1%.

By the 1930s, photoelectric behavior was widely used in camera exposure meters.

In 1946, Russell Ohl applied for a patent for the manufacture of modern solar cells.

In the 1950s, with the gradual understanding of the physical properties of semiconductors and the advancement of processing technology, in 1954, when Bell Labs in the United States was conducting experiments on semiconductors, it was discovered that silicon becomes more sensitive to light after a certain amount of impurities are added to it. Later, the first solar cell with practical application value was born at Bell Labs in 1954. The era of solar cell technology has finally arrived.

Since the 1960s, artificial satellites launched by the United States have used solar cells as their energy source.

During the energy crisis in the 1970s, countries around the world realized the importance of energy development. The oil crisis occurred in 1973, and people began to shift the application of solar cells to general livelihood purposes.

At present, in the United States, Japan, Israel and other countries, solar energy devices have been widely used and are moving towards the goal of commercialization.

Among these countries, the United States built the world’s largest solar power plant in California in 1983, with a power generation capacity of up to 16 million watts. South Africa, Botswana, Namibia and other countries in southern Africa have also set up projects to encourage the installation of low-cost solar photovoltaic power generation systems in remote rural areas.

The most active country in promoting solar power generation is Japan. In 1994, Japan implemented a subsidy and incentive scheme to promote a “mains parallel-connected solar photovoltaic system” with a power of 3,000 watts per household. In the first year, the government subsidizes 49% of the funds, and subsequent subsidies will decrease year by year.

The “mains parallel solar photovoltaic system” uses solar cells to provide power to your own loads when the sunshine is sufficient, and if there is excess power, it is stored separately. When power generation is insufficient or no power is generated, the required power will be provided by the power company.

By 1996, 2,600 households in Japan had installed solar power generation systems, with a total installed capacity of 8 million watts. A year later, there were 9,400 installations and the total installed capacity reached 32 megawatts. In recent years, due to the rise in environmental awareness and the government subsidy system, the demand for residential solar cells in Japan is expected to increase rapidly.

In China, the solar power generation industry has also received strong encouragement and funding from the government. In March 2009, the Ministry of Finance announced plans to subsidize large-scale solar projects such as solar photovoltaic buildings.

Photovoltaic cells convert sunlight into electricity through the photovoltaic effect
Photovoltaic cells convert sunlight into electricity through the photovoltaic effect

working principle

A solar cell is a device that directly converts light energy into electrical energy through the photoelectric effect or photochemical effect. Thin-film solar cells that work on the photoelectric effect are the mainstream, while solar cells that work on the photochemical effect are still in their infancy. Sunlight shines on the semiconductor p-n junction, forming new hole-electron pairs. Under the action of the p-n junction electric field, holes flow from the n region to the p region, and electrons flow from the p region to the n region. After the circuit is turned on, a current is formed.

Implementation process:

Solar panels on the roof convert sunlight into DC current. An uninterruptible power supply (UPS) converts this DC energy to AC 220V/50Hz.

This electricity can be used completely for local equipment, or it can be used partially, and the remaining electricity is sold to utilities, or it can be sold entirely.

It is strongly recommended that this expensive facility be protected from lightning strikes.

Battery composition and function

The role of tempered glass is to protect the main body of power generation (battery cells). There are requirements for its light transmission. 1. The light transmittance must be high (generally more than 91%); 2. Ultra-white tempered treatment

EVA is used to bond and fix tempered glass and the main body of the power generation (battery sheet). The quality of the transparent EVA material directly affects the life of the component. EVA exposed to the air is prone to aging and yellowing. This affects the light transmittance of the component, thereby affecting the power generation quality of the component in addition to the quality of the EVA itself. The lamination process of component manufacturers also has a great impact. For example, if the adhesion of EVA is not up to standard, and the bonding strength between EVA and tempered glass and backplane is insufficient, it will cause premature aging of EVA and affect the life of components.

The main function of cells is to generate electricity. The mainstream in the power generation market are crystalline silicon solar cells and thin film solar cells. Both have their own advantages and disadvantages. Crystalline silicon solar cells have relatively low equipment costs, but high consumption and cell costs, but the photoelectric conversion efficiency is also high.

Thin-film solar cells are more suitable for generating electricity under outdoor sunlight. The relative equipment cost is high, but the consumption and battery costs are very low. However, the photoelectric conversion efficiency is slightly more than half that of crystalline silicon cells, but the low-light effect is very good, and it can also generate electricity under ordinary light. Like the solar cells on a calculator.

EVA functions as above, mainly bonding and encapsulating the power generation body and the backplane

The function of the backplane is sealing, insulation, and waterproofing (usually TPT, TPE and other materials are used and must be resistant to aging. Now component manufacturers have a 25-year warranty. Tempered glass and aluminum alloys are generally no problem. The key lies in whether they can be used with the backplane and silicone. Meet the requirements.)

Aluminum alloy protects laminated parts, plays a certain sealing and supporting role

The junction box protects the entire power generation system and plays the role of a current transfer station. If a component is short-circuited, the junction box automatically disconnects the short-circuited battery string to prevent burning of the entire system. The most critical thing in the junction box is the selection of diodes. According to the type of battery cells in the component Different, the corresponding diodes are also different.

Silicone sealing function is used to seal the junction between components and aluminum alloy frames, components and junction boxes. Some companies use double-sided tape and foam to replace silica gel. Nowadays, silica gel is commonly used in China. The process is simple, convenient, easy to operate, and the cost is very low. Low.

Variety classification

Monocrystalline silicon photovoltaic cells

Monocrystalline silicon photovoltaic cells are a type of photovoltaic cell that was developed earlier, has the highest conversion rate, and has a large output.

At present, the conversion efficiency of monocrystalline silicon photovoltaic cells has reached an average of 16.5% in my country, and the highest conversion efficiency recorded in the laboratory exceeds 24.7%. This kind of photovoltaic cell generally uses high-purity monocrystalline silicon rods as raw materials, with a purity requirement of 99.9999%.

Polycrystalline silicon photovoltaic cells

Polycrystalline silicon photovoltaic cells are photovoltaic cells based on polycrystalline silicon materials. Since polycrystalline silicon materials are mostly cast instead of the drawing process of single crystal silicon, the production time is shortened and the manufacturing cost is greatly reduced. In addition, monocrystalline silicon rods are cylindrical, and photovoltaic cells made from them are also wafers, so the plane utilization rate after forming photovoltaic modules is low. Compared with monocrystalline silicon photovoltaic cells, polycrystalline silicon photovoltaic cells appear to have certain competitive advantages.

Amorphous silicon photovoltaic cells

Amorphous silicon photovoltaic cell is a new type of thin film cell made of amorphous silicon as raw material. Amorphous silicon is a semiconductor with an amorphous crystal structure. Photovoltaic cells made with it are only 1 micron thick, equivalent to 1/300 of monocrystalline silicon photovoltaic cells. Compared with monocrystalline silicon and polycrystalline silicon, its manufacturing process is greatly simplified, silicon material consumption is less, and unit power consumption is also reduced a lot.

Copper indium tin photovoltaic cells

Copper-indium-selenide photovoltaic cells are semiconductor films made of copper, indium and selenium ternary compound semiconductors deposited on glass or other cheap substrates. Due to the good light absorption performance of copper indium selenide cells, the film thickness is only about 1/100 of that of monocrystalline silicon photovoltaic cells.

Gallium arsenide photovoltaic cells

Gallium arsenide photovoltaic cell is a III-V compound semiconductor photovoltaic cell. Compared with silicon photovoltaic cells, gallium arsenide photovoltaic cells have high photoelectric conversion efficiency. The theoretical efficiency of silicon photovoltaic cells is 23%, while the conversion efficiency of single-junction gallium arsenide photovoltaic cells has reached 27%. It can be made into thin films and ultra-thin solar cells, which also absorb 95% of sunlight. Gallium arsenide photovoltaic cells only need a thickness of 5-10 μm, while silicon photovoltaic cells need to be greater than 150 μm.

Cadmium telluride photovoltaic cells

Cadmium telluride is a compound semiconductor with a band gap most suitable for photoelectric energy conversion. Photovoltaic cells made of this semiconductor have high theoretical conversion efficiency. At present, the highest conversion efficiency that has been actually obtained reaches 16.5%. Cadmium telluride photovoltaic cells are usually manufactured on a glass substrate. The first layer on the glass is a transparent electrode, and the subsequent thin layers are cadmium sulfide, cadmium telluride and a back electrode. The back electrode can be carbon paste or It’s a thin layer of metal.

There are many deposition techniques for cadmium telluride, such as electrochemical deposition, near-space sublimation, short-range vapor transport, physical vapor deposition, screen printing and spraying. The thickness of the cadmium telluride layer is usually 1.5-3um, and a thickness of 1.5um is enough for cadmium telluride to absorb light.

Polymer photovoltaic cells

Polymer photovoltaic cells utilize the different redox potentials of different redox polymers to perform multi-layer composites on the surface of conductive materials to create a unidirectional conductive device similar to an inorganic P-N junction.

The output voltage of photovoltaic cells varies with changes in light intensity and temperature
The output voltage of photovoltaic cells varies with changes in light intensity and temperature
Author: admin