Introduction to photovoltaic panel
Photovoltaic cells and applications

Introduction to photovoltaic panel. 1 article accurate make it clear!

Photovoltaic panel, also known as solar panel, is an assembly composed of several solar cell components assembled on a board in a certain way, usually as a unit of a photovoltaic array.

A single solar cell cannot be used directly as a power source. To make a power supply, several single cells must be connected in series, parallel and tightly sealed into components.

Solar cell components (also called solar panels) are the core part of the solar power generation system and the most important part of the solar power generation system. Its function is to convert solar energy into electrical energy, or send it to the battery for storage, or promote load work. The quality and cost of solar panels will directly determine the quality and cost of the entire system.

Photovoltaic panel characteristics

A: The main function of photovoltaic cells (PVcells) is to convert the sun’s light energy into electrical energy. Currently, they are silicon solar cells based on silicon materials, including monocrystalline silicon, polycrystalline silicon, amorphous silicon, and multi-component compound cells. Monocrystalline silicon and polycrystalline silicon are superior to amorphous silicon in terms of efficiency and lifespan. Polycrystalline silicon has lower conversion efficiency than monocrystalline silicon, but polycrystalline silicon is cheaper.

Crystal solar cells, thin film solar cells, silicon heterojunction (HIT) solar cells, etc. Photovoltaic modules are composed of multiple solar cells. According to the actual power demand, the voltage level is achieved by photovoltaic cells connected in series, and the current output is achieved by photovoltaic cells connected in parallel. The photovoltaic array is composed of several photovoltaic modules according to the size of the power station.

B: The characteristics of photovoltaic cells include photoelectric characteristics and photochemical characteristics. The photochemical characteristics are still in their infancy. We will not study the working of energy-saving batteries based on the principle of photoelectric effect. When materials come into contact, an internal potential is generated so that electrons can only move from area B to area A.

When sunlight hits a photovoltaic panel, the photons carry enough energy to cause electrons to break away and form holes, or electron-hole pairs. At this time, the internal potential will send the electrons released by the photons to area A and the holes to area B, breaking the initial balance. There are more and more electrons in area A. When a loop is connected outside the PN junction, a current can be formed .

In fact, it’s just the electrons that are moving. This also depends on the characteristics of the semiconductor material. The bandgap of semiconductor materials is narrow. The electrons require only a small amount of energy to escape from their bonds, leaving holes, which allows the surrounding electron areas to fill the holes and form an electric current. (Note: From physics, Hertz discovered and Einstein correctly explained that certain substances can generate electrons when exposed to light)

C: PV and IV characteristics of photovoltaic panels

Photovoltaic cell arrays generally consist of parallel and series connections, as shown in the figure below: There are also other more complex connection methods such as SP structure, TCT structure, and CTCT connection method. There are two main aspects that affect the output characteristics of the photovoltaic cell array: light intensity and ambient temperature. These two factors will in turn affect the power output of the photovoltaic cell array. The V-I characteristics and V-P characteristics of the photovoltaic panel are analyzed below:

Photovoltaic panel types and applications

When the junction temperature remains unchanged, the short-circuit current gradually increases with the increase of illumination, the maximum power point also gradually increases, and the open-circuit voltage does not change much; the output voltage corresponding to the maximum power point is basically stable, about 0.8 times the open-circuit voltage.

When the light intensity is constant, temperature changes have little impact on the short-circuit current, but have a greater impact on the open-circuit voltage. The open circuit voltage becomes smaller as the temperature increases, the maximum power point decreases as the temperature increases, and the maximum power point voltage decreases accordingly.

Types of photovoltaic panels

To maximize energy output, it's crucial to angle the photovoltaic panel towards the sun's trajectory
To maximize energy output, it’s crucial to angle the photovoltaic panel towards the sun’s trajectory

Monocrystalline silicon photovoltaic cells

The photoelectric conversion efficiency of monocrystalline silicon solar cells is about 15%, with the highest reaching 24%. This is the highest photoelectric conversion efficiency among all types of solar cells currently, but the production cost is so high that it cannot be widely used and used in large quantities. commonly used. Since monocrystalline silicon is generally encapsulated with tempered glass and waterproof resin, it is strong and durable, with a service life of generally up to 15 years and up to 25 years.

Polycrystalline silicon photovoltaic cells

The manufacturing process of polycrystalline silicon solar cells is similar to that of monocrystalline silicon solar cells, but the photoelectric conversion efficiency of polycrystalline silicon solar cells is much lower, and its photoelectric conversion efficiency is about 12%. In terms of production cost, it is cheaper than monocrystalline silicon solar cells.

The material is easy to manufacture, saves power consumption, and has a low overall production cost, so it has been widely developed. In addition, the service life of polycrystalline silicon solar cells is shorter than that of monocrystalline silicon solar cells. In terms of battery performance/price ratio, monocrystalline silicon solar cells are slightly better.

Amorphous silicon photovoltaic cells

Amorphous silicon solar cells are a new type of thin-film solar cells that appeared in 1976. They are completely different from monocrystalline silicon and polycrystalline silicon solar cells in manufacturing methods. The process is greatly simplified, silicon material consumption is very small, and power consumption is lower. Its main The advantage is that it can generate electricity even in low light conditions.

However, the main problem of amorphous silicon solar cells is that the photoelectric conversion efficiency is low, the international advanced level is about 10%, and it is not stable enough. As time goes by, its conversion efficiency decays.

Multi-compound photovoltaic cells

Multi-compound solar cells refer to solar cells that are not made of single element semiconductor materials. There are many varieties studied in various countries, and most of them have not yet been produced industrially. The main ones are as follows:

a) Cadmium sulfide solar cells

b) Gallium arsenide solar cells

c) Copper indium selenide solar cell (new multi-band gap gradient Cu (In, Ga) Se2 thin film solar cell

Photovoltaic panel types and applications

The role of tempered glass is to protect the main body of power generation (such as cells), and there are requirements for its light transmission. 1. The light transmittance must be high (generally above 91%); 2. Ultra-white tempered glass.

EVA is used to bond and fix tempered glass and the main body of power generation (such as battery cells). 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, which affects the light transmittance of the module and thus affects the power generation quality of the module. In addition to the quality of the EVA itself, the lamination process of the module manufacturer also has a great impact. If the EVA bonding degree is not up to standard, and the bonding strength between EVA, tempered glass, and backplane is insufficient, it will cause premature aging of EVA and affect the life of the 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 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, such as the solar cells on calculators.

EVA mainly bonds and encapsulates the power generation body and 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. Component manufacturers have a 25-year warranty. Tempered glass and aluminum alloys are generally no problem. The key lies in whether the backplane and silicone can achieve the desired effect. Require.)

Aluminum alloy protective laminate 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. Silica gel is commonly used in China. The process is simple, convenient, easy to operate, and the cost is very low. .

Photovoltaic panel application fields

User solar power supply: (1) Small power supply ranging from 10-100W, used for military and civilian life in remote areas without electricity, such as plateaus, islands, pastoral areas, border posts, etc., such as lighting, TVs, radios, etc.; (2) 3-5KW Home roof grid-connected power generation system; (3) Photovoltaic water pump: solve the problem of deep water well drinking and irrigation in areas without electricity.

Transportation field: such as navigation beacon lights, traffic/railway signal lights, traffic warning/sign lights, Yuxiang street lights, high-altitude obstacle lights, highway/railway wireless phone booths, unattended road shift power supply, etc.

Communication/communication field: solar unattended microwave relay station, optical cable maintenance station, broadcast/communication/paging power supply system; rural carrier telephone photovoltaic system, small communication machine, soldier GPS power supply, etc.

Petroleum, ocean, and meteorological fields: cathodic protection solar power systems for oil pipelines and reservoir gates, life and emergency power supplies for oil drilling platforms, ocean detection equipment, meteorological/hydrological observation equipment, etc.

Household lighting power supply: such as garden lights, street lights, portable lights, camping lights, mountaineering lights, fishing lights, black light lights, rubber tapping lights, energy-saving lamps, etc.

Photovoltaic power stations: 10KW-50MW independent photovoltaic power stations, wind and solar (diesel) complementary power stations, various large parking plant charging stations, etc.

Solar buildings: Combining solar power generation with building materials will enable future large-scale buildings to be self-sufficient in electricity, which is a major development direction in the future.

Other fields include: (1) Supporting automobiles: solar vehicles/electric vehicles, battery charging equipment, automobile air conditioners, ventilation fans, cold drink boxes, etc.; (2) Regenerative power generation systems for solar hydrogen production and fuel cells; (3) Seawater desalination equipment Power supply; (4) Satellites, spacecraft, space solar power stations, etc.

The efficiency of the photovoltaic panel depends on various factors such as sunlight intensity and temperature
The efficiency of the photovoltaic panel depends on various factors such as sunlight intensity and temperature