Solar photovoltaic power generation system performance and principle

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 achieve PV conversion. In a vast 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 that are suitable for home lighting in areas without electricity.

Second, the system consists of:

Power system: solar modules and batteries.

Control protection system: controller and inverter.

System terminal (load): The user's power equipment.

Third, the principle of solar power:

The solar energy system solar battery and 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, short-circuit current Isc, and 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 through, and the solar cell module realizes the power to the load. P output.

(2) Electrical energy storage unit: The DC electricity generated by the solar cell enters the storage battery first, and the characteristics of the storage battery affect the working 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 daylight (power generation time). Therefore, the battery watt-hour capacity and ampere-hour capacity are determined by the predetermined continuous no-sunlight time.

The main function of the controller 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 when the battery is lack of electricity, system failure, such as the battery open or reversed switch off. At present, Hitachi has developed a “sunflower” controller that can both track the control point Pm and track the sun's movement parameters, which increases the efficiency of the fixed battery assembly by about 50%.

DC-AC inverter 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 the full-bridge circuit, the SPWM processor is generally used to modulate, filter, boost, etc., to obtain the sinusoidal alternating-current power supply system end users that match the lighting load frequency f and rated voltage UN.

Solar Power System Efficiency In a solar power system, the total efficiency of the system consists of the PV module conversion rate, controller efficiency, battery efficiency, inverter efficiency, and load efficiency. However, compared with 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 enlarging energy-absorbing surfaces, such as double-sided cells, and reducing reflections; using gettering technology to reduce the compounding of semiconductor materials; ultra-thin cell modeling; improving theory and establishing new models; Spotlight batteries.