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The basic knowledge of solar photovoltaic power generation
- May 22, 2018 -

1. The composition and principle of solar photovoltaic system


The solar photovoltaic system consists of the following three components: solar cell modules; charge and discharge controllers, inverters, test instruments, and computer monitoring and other power electronic equipment and batteries or other energy storage and auxiliary power generation equipment.


Solar photovoltaic systems have the following characteristics:


- No rotating parts, no noise;


- No air pollution, no discharge of wastewater;


- No combustion process, no fuel;


- Simple maintenance and low maintenance costs;


- Operational reliability and stability;


- Long service life of solar cells as key components, crystal silicon solar cells can reach 25 years of life;


It is easy to expand the scale of power generation as needed.


Photovoltaic systems are widely used. The basic forms of photovoltaic system applications can be divided into two major categories: independent power generation systems and grid-connected power generation systems. The main areas of application are mainly household power supply in space aircraft, communications systems, microwave relay stations, television differential transmissions, photovoltaic pumps, and areas with no electricity or electricity. With the development of technology and the need for sustainable development of the world economy, developed countries have begun to systematically promote urban photovoltaic grid-connected power generation, mainly by constructing household rooftop photovoltaic power generation systems and MW-level centralized large-scale grid-connected power generation systems, etc. The use of solar photovoltaic systems is strongly promoted in such areas as transportation and urban lighting.


Photovoltaic systems vary in scale and application. For example, they range in size from 0.3 to 2W solar garden lights to MW solar photovoltaic power plants, such as 3.75kWp home-type rooftop power generation equipment and the Dunhuang 10MW project. Its application forms are also varied and can be widely used in many fields such as home, transportation, communications, and space applications. Although the PV system is of different sizes, its composition and working principle are basically the same. Figure 4-1 is a schematic diagram of a typical PV system that supplies DC loads. It contains several major components in the photovoltaic system:


Photovoltaic module: It is made up of solar modules (also called photovoltaic modules) that are connected in series and in parallel according to the system requirements. It converts solar energy into electricity output under the sunlight. It is the core component of the solar photovoltaic system.


Batteries: Store the electrical energy generated by the solar cell modules. When the light is insufficient or at night, or when the load demand is greater than the amount of electricity generated by the solar cell modules, the stored electrical energy is released to meet the energy requirements of the load. It is a storage system of solar photovoltaic systems. Can parts. At present, the solar photovoltaic system is commonly used lead-acid batteries, for the higher requirements of the system, usually used deep-discharge valve-regulated sealed lead-acid batteries, deep-discharge liquid-absorbing lead-acid batteries.


Controller: It regulates and controls the charging and discharging conditions of the battery, and controls the solar module and battery power output to the load according to the power demand of the load. It is the core control part of the entire system. With the development of the solar photovoltaic industry, controllers have become more and more powerful. There is a trend to integrate traditional control parts, inverters, and monitoring systems. For example, the AES SPP and SMD series controllers integrate the above three. Functionality.


Inverter: In a solar photovoltaic power supply system, if an AC load is included, an inverter device is used to convert the direct current generated by the solar cell module or the DC discharged by the battery into the alternating current required by the load.


The basic working principle of the solar photovoltaic power supply system is that under the irradiation of sunlight, the power generated by the solar cell module is charged by the control of the controller to charge the battery or directly to the load when the load demand is satisfied, if the sunshine is insufficient or at night Then, the battery supplies the DC load under the control of the controller. For the photovoltaic system containing the AC load, an inverter needs to be added to convert the DC power into AC power. Photovoltaic systems have many applications, but their basic principles are very similar. For other types of photovoltaic systems, the control mechanism and system components are different depending on the actual needs. The different types of photovoltaic systems will be described in detail below.

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2. Classification and introduction of photovoltaic systems


This paper has written the principle of solar photovoltaic, and also classified and introduced the classification and introduction of photovoltaic systems. Generally, photovoltaic systems are divided into independent systems, grid-connected systems and hybrid systems. According to the application form, application scale and type of the PV system, the photovoltaic power supply system can be divided into six types: Small solar power system (Small DC) and Simple DC system (Simple) DC); Large-scale solar energy supply system (Large DC); AC, DC power supply system (AC/DC); Grid-connected system (Utility Grid Connect); Hybrid power supply system (Hybrid); Grid-connected hybrid system.


Photovoltaic power generation is an electronic component technology that utilizes the photovoltaic effect of the semiconductor interface to convert light energy directly into electrical energy. The key component of this technology is solar cells. After the solar cells are encapsulated and protected in series, a large area solar cell module can be formed, and a photovoltaic power generation device can be formed by combining the power controller and other components. Photovoltaic power generation has the advantage of being less restricted by geography because the sun shines on the earth. Photovoltaic systems also have the advantages of being safe, reliable, noise-free, low-pollution, energy-efficient, and energy-efficient.


Photovoltaic power generation is based on the principle of photovoltaic effect, using solar cells to convert solar energy directly into electrical energy. Regardless of whether it is used independently or connected to the grid, the photovoltaic system is mainly composed of solar panels (components), controllers and inverters. They are mainly composed of electronic components and do not involve mechanical components. Therefore, photovoltaic power generation equipment Extremely refined, reliable and stable, long life, easy installation and maintenance. In theory, photovoltaic technology can be used in any application where power is needed, from spacecraft, down to home power, up to megawatts of power stations, to toys, and photovoltaic power is everywhere. The basic components of solar photovoltaic power generation are solar cells (sheets), monocrystalline silicon, polysilicon, amorphous silicon, and thin-film batteries. At present, the single crystal and polycrystalline batteries are the most used, and amorphous batteries are used in some small systems and calculators as auxiliary power sources.


Solar photovoltaic related terms


Air Mass The path length of the air mass through the atmosphere, abbreviated as AM, outer space is AM 0, and the sunlight is AM1 when the sunlight is perpendicular to the earth (very much spring/autumn centimeter vertical spectrum of sunlight on the equator), solar cell The standard test condition is AM 1.5 (equivalent to the spring/easter sun exposure to the spectrum at about 48.2 degrees south/north latitude).


Irradiance Intensity of solar radiation per unit area, generally expressed in units of W/m2 or mW/cm2, intensity of sunlight in AM0 exceeding 1300 W/m2, standard test conditions for solar cells at 1000 W/m2 (equivalent to 100 mW/cm2). ).


Radiating Radiating total energy per unit area per unit time, generally in million joules/year. square meters (MJ/Y.m2) or million joules/month. square meters (MJ/M.m2) 1 Joule is 1 Watt of power accumulated in 1 second (1J=1W.s).


Solar Cell Photovoltaic Effect A component that converts light into electricity (Voltaic), also known as a photovoltaic cell (PV Cell). Solar cells generate electricity as direct current.


Photovoltaic is abbreviated as PV (photo=light light, voltaics=electricity). Because this type of power generation does not generate nitrogen oxides, harmful gases and radioactive waste, it is called “clean power generation technology. "." The PV System is a system that converts solar energy into a complete electrical energy system called a solar photovoltaic system or a photovoltaic system, and is classified into an independent type, a parallel type, and a hybrid type.


PV Module (PV Module) A series of solar cells are connected in series to increase the voltage and are packaged in a solid external material for application, also known as a module (PV Pannel or PV Module).


PV string (PV String) A series of modules are serially connected in series. The purpose of grouping is to increase the voltage. Ten template voltages are connected in series of 20 volts and 5 amps. The group voltage is 200 volts and the current is 5 amps.


PV Arrays Arrays multiple group columns in parallel. The purpose of the array is to increase the current. The 5-string group voltage is 200 volts and 5 amps in parallel. The array voltage is 200 volts and the current is 25 amps. An array consisting of a group of columns, the array corresponds to the group column.


Stand along system (Stand Along System) A plurality of solar cells are connected in series to increase the voltage, and are packaged in a firm external material for application, also referred to as a module (PV Pannel or PV Module).


Gridded System (PV Grided System) PV array output is converted into AC and AC mains or self-provided generators in parallel by the inverter, the system does not need to configure the storage device.


Hybrid System Standalone and parallel hybrids, when the electricity supply to the disaster-suppressed city is stopped, the parallel system will stop operating, and the hybrid type may switch to the independent type and continue to supply power. Therefore, it is also called a disaster prevention type.


瓩 (kW) kilowatts, the calculation unit of the capacity of the power generation equipment; 1瓩=1000 watts (Watt).


Peak (kWp) P Table peak, which represents the peak value. Refers to the installation of the solar cell template under standard conditions (ie, the template temperature is 25°C, conversion


Conversion efficiency 15%) The sum of the maximum power generation. Usually 1 peak can send 3-5 kWh.


瓩 瓩 ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( ( (.


MW (Mega Watt) megawatts, usually measured in units of solar photovoltaic company.


Ampere Hour Another type of electrical energy representation, usually used for battery capacity, 50Ah means 5Amp 10 hour capacity or 1Amp 50 hour capacity, but battery capacity cannot be fully utilized.


Load The power or current output per unit time for a specific period of time.


BIPV (Building Integrated Photovoltaics) An energy-saving building material product combining solar photovoltaic systems with architectural design, which can directly replace traditional roofs, windows, exterior walls, and shade (rain) shelters. It can greatly improve the bulky appearance of traditional solar photovoltaic systems. It can not only enhance the aesthetic benefits but also increase the space benefits; it can create another market opportunity for solar photovoltaic building industry.


Power Conditioner The general name for the power conditioning function device, the controller for the battery charge/discharge adjustment, or the inverter that converts DC to AC regulation.


The charge controller (Charger) has a battery charge control function, which can control the charge current, and can cut off the charge controller when the battery voltage reaches the saturation voltage. This is the necessary equipment for independent configuration of the battery.


Discharge Controller (Charger)


Battery discharge control function, can limit the discharge current size or time, when the battery in the cut-off voltage can be cut off the discharge function of the controller, which is a separate configuration battery necessary equipment.


Charger/Discharger


Battery discharge control function, can limit the discharge current size or time, when the battery in the cut-off voltage can be cut off the discharge function of the controller, which is a separate configuration battery necessary equipment.


Charger/Discharger


Controllers with charge and discharge functions are often used on stand-alone systems.


Inverter


The conversion of DC power into AC equipment, also known as inverters, is a proprietary specification for grid-connected PV system converters and is not commercially available.