First, characteristics:
Solar power is a device that uses a battery pack to convert solar energy directly into electrical energy. Solar cells are solid-state devices that use the electronic properties of semiconductor materials to realize PV conversion. In a large area without electricity grids, the device can be conveniently used for lighting and living for users. Some developed countries can also use the regional grid. Grid to achieve complementarity. In China, the company mainly researches and produces small-scale solar power generation systems suitable for home lighting in areas where power is not available.
Second, the system consists of:
â—† Power System: Solar modules and batteries.
â—† Control protection system: controller and inverter.
â—† System Terminal (Load): The user's electrical equipment.
Third, the principle of solar power:
â—† Solar Power System
The solar battery and the battery constitute the power supply unit of the system, so the battery performance directly affects the system operating characteristics.
(1) Battery unit:
Due to technical and material reasons, the amount of electricity generated by a single battery is very limited. In practice, a solar battery is a battery system in which a single battery is composed of strings and parallels, and is called a battery module (array). The single cell is a silicon crystal diode. According to the electronic characteristics of the semiconductor material, when the sun shines on the pn junction made of p-type and n-type homogenous semiconductor materials of different conductivity types, under certain conditions Solar radiation is absorbed by the semiconductor material, resulting in non-equilibrium carriers, electrons and holes, in the conduction band and valence band. Similar to the PN junction barrier region, there is a strong built-in electrostatic field, so that the current density J, the short-circuit current Isc, and the open-circuit voltage Uoc can be formed under illumination. If the electrodes are drawn on both sides of the built-in electric field and connected to the load, the circuit formed by the PN junction, the connecting circuit, and the load theoretically has a “photo-generated current†flowing therethrough, and the solar cell module realizes the power to the load. P output.
(2) Electrical energy storage unit:
The direct current generated by solar cells enters the battery first, and the characteristics of the battery affect the efficiency and characteristics of the system. The battery technology is very mature, but its capacity is affected by the amount of power required at the end of the day and the duration of the sunshine (power generation time). Therefore, the battery watt-hour capacity and ampere-hour capacity are determined by the predetermined continuous no-sunlight time.
â—† Controller
The main function of the controller is to make the solar power system always in the vicinity of the maximum power point of power generation in order to obtain the highest efficiency. The charge control usually adopts pulse width modulation technology, ie, PWM control mode, so that the entire system always runs in the area near the maximum power point Pm. Discharge control mainly refers to the lack of electricity in the battery, system failure, such as the battery open or reversed switch off. Currently, Hitachi has developed a "sunflower" type controller that can both track the control point Pm and track the sun's movement parameters, which increases the efficiency of fixed battery modules by about 50%.
â—† DC-AC inverter
The inverter can be divided into self-excited oscillation inverter and he-excited oscillation inverter according to the excitation method. The main function is to reverse the direct current of the battery into alternating current. Through a full-bridge circuit, SPWM processors are generally used to modulate, filter, boost, etc., to obtain sinusoidal alternating-current power supply system end users that match the lighting load frequency f and rated voltage UN.
â—† The efficiency of solar power systems
In a solar power system, the total system efficiency ηesee consists of the PV module conversion rate, controller efficiency, battery efficiency, inverter efficiency, and load efficiency. However, compared to solar cell technology, it is much more mature than the technology and production levels of other units such as controllers, inverters, and lighting loads, and the current system conversion rate is only about 17%. Therefore, improving the conversion rate of battery modules and reducing the unit power cost is the key and difficult point in the industrialization of solar power generation. Since the advent of solar cells, crystalline silicon has maintained its dominance as the leading material. The current research on the conversion rate of silicon cells mainly revolves around increasing the energy-absorbing surface, such as double-sided batteries, to reduce reflections; using gettering technology to reduce the recombination of semiconductor materials; thinning the battery; improving theory and establishing a new model; Spotlight batteries.