Concentrating Photovoltaic Power System Technical Difficulties Analysis
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Solar photovoltaic technology refers to a kind of forward-looking technology that can directly convert the solar light energy into electric energy and make full use of it. Its broad application prospects allow the people of the world to constantly strive for development, innovation and application. In this issue, we will introduce the principles of solar power generation, solar cells, solar cell modules, photovoltaic controllers, and photovoltaic inverters.
Solar power generation principle
Solar cells are devices that respond to light and convert light energy into electricity. There are many kinds of materials that can produce photovoltaic effect, such as: monocrystalline silicon, polysilicon, amorphous silicon, gallium arsenide, selenium indium copper and so on. Their power generation principle is basically the same. The crystal is used as an example to describe the process of photovoltaic power generation. P-type crystalline silicon can obtain N-type silicon through doping with phosphorus to form a PN junction.
When the light shines on the surface of the solar cell, some of the photons are absorbed by the silicon material; the energy of the photons is transmitted to the silicon atoms, causing the electrons to migrate and become free electrons that accumulate on both sides of the PN junction to form a potential difference when the circuit is externally connected. When the voltage is applied, current will flow through the external circuit to generate a certain output power. The essence of this process is the process of converting photon energy into electricity.
Crystal silicon solar cell manufacturing process
"Silicon" is one of the most abundant materials on our planet. Since scientists discovered the crystalline nature of crystalline silicon in the 19th century, it has changed everything, even human thinking. At the end of the 20th century, "silicon" was seen everywhere in our lives, and crystalline silicon solar cells were the fastest industrialized in the past 15 years. The production process can be roughly divided into five steps: a, purification process b, pulling process c, slicing process d, battery production process e, and packaging process.
In the 1960s, scientists had already applied solar cells to space technology—communications satellites. At the end of the last century, in the process of human self-reflection, this kind of clean and direct form of energy for photovoltaic power generation has become more cordial. Not only in space applications, but also in many fields. Such as: solar garden light, solar power household system, independent system of village power supply, photovoltaic water pump (water or irrigation), communication power, cathodic protection of oil pipeline, power supply of optical cable communication pump station, seawater desalination system, road sign in town, high speed Highway signposts, etc. Advanced countries such as Europe and the United States have integrated photovoltaic power generation into the urban power system and the remote villages' natural village power supply systems in the development direction. The integration of solar cells and building systems has become an industrial trend. There are more and more applications of solar photovoltaic glass curtain wall components. With several projects in Shanghai and Beijing entering into substantive operation, this method will replace ordinary glass curtain walls. It has the characteristics of small reflected light intensity and good thermal insulation properties!
Solar module
Solar cell modules (photovoltaic modules) consist of a number of solar cells connected by a series of wires and connected in parallel and encapsulated. In a module, the standard number of solar cells is 36 (10cm x 10cm), which means that a solar cell module can produce about 17V voltage, which can effectively charge a battery with a nominal voltage of 12V. The current photovoltaic element output power is as large as several hundred watts.
Solar cells can provide sufficient mechanical strength, vibration resistance and impact resistance after being packaged into components; have good sealing properties, can be anti-corrosion, windproof, tamper-proof and moisture-proof; have good electrical insulation; and can resist UV radiation. Its potential quality issues may occur at the edge of the seal and the junction box on the back of the assembly.
According to the needs of photovoltaic engineering installation, when the application field requires higher voltage and current and a single component can not meet the requirements, multiple components can be assembled into a “solar cell square array†also called “photovoltaic array†through series connection and parallel connection. Get the required voltage and current, and its power can be determined according to the actual demand combination.
Solar Photovoltaic Controller
Photovoltaic charge controllers can basically be divided into five types: parallel photovoltaic controllers, series photovoltaic controllers, pulse width modulation photovoltaic controllers, smart photovoltaic controllers, and maximum power tracking photovoltaic controllers.
1. Parallel type photovoltaic controller. When the battery is full, the output of the photovoltaic array is diverted to the internal shunt resistor or power module using electronic components and then consumed as heat. Parallel-type photovoltaic controllers are generally used in small, low-power systems, such as voltages of 12V, 20A, and systems. This type of controller is very reliable and does not have mechanical parts such as relays.
2. Tandem photovoltaic controller. The use of mechanical relays controls the charging process and shuts off the photovoltaic array at night. It is generally used in higher power systems. The capacity of the relay determines the power level of the charge controller. It is easier to make a series-connected photovoltaic controller with a continuous current of 45A or more.
3, pulse width modulation type photovoltaic controller. It switches the input of the PV array in PWM pulses. When the battery tends to be full, the pulse frequency and time are shortened. According to the research of Sandia National Laboratories of the United States, this kind of charging process forms a relatively complete state of charge, which can increase the total cycle life of the storage battery in the photovoltaic system.
4, smart photovoltaic controller. Based on MCUs (such as Intel's MCS51 series or Microchip's PIC series), high-speed instant collection of operating parameters of the photovoltaic power system, and according to a certain control law by the software program to separate and connect single or multiple PV arrays control. For medium and large photovoltaic power systems, distance control can also be performed through the MCU's RS232 interface with a MODEM modem.
5, the maximum power tracking controller. The solar battery voltage V and current I are detected and multiplied to obtain the power P, and then determine whether the output power of the solar battery reaches the maximum at this time. If not at the maximum power point, just adjust the pulse width, modulate the output duty cycle D, and change the charge. The current is sampled again in real time and a judgment is made as to whether or not to change the duty ratio. Through this optimization process, the solar cell can always be operated at the maximum power point to fully utilize the output energy of the solar cell array. At the same time, the PWN modulation method is used to make the charging current a pulse current to reduce the polarization of the battery and improve the charging efficiency.
Photovoltaic inverter
As an independent photovoltaic system, its DC power generation voltage is relatively low, so power conditioning devices, that is, inverters, are absolutely indispensable.
In the grid-connected system, two types of inverters are mainly used to realize AC power generation.
1 Line rectification can use the signal in the grid as a reference for synchronization.
2 Self-rectification The signal waveform is determined by the internal circuit structure of the inverter and then input to the grid.
It can also be classified according to the application of the product.
1 The central inverter is used to rectify the output of a large-scale photovoltaic system whose rated power is in the range of 20 to 400 kWp. At this stage, mainstream products have a self-rectifying design and are realized by bipolar transistors and field-effect transistors.
The 2 series inverter only allows signals received through independent serial transmission, so the rated power is 1 to 3 kWp.
3 Duplex series inverters are equipped with various independent DC-DC inverters that feed back signals to a central inverter device. Such a design can be applied to a variety of different component connection structures so that the solar cells on each series line can output maximum power.
4 AC Component Inverter is installed on each PV element to convert the output of all components into AC.
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