1. Working principle of solar photovoltaic system
During the day, under light conditions, the solar cell modules generate a certain electromotive force, and the solar cell square array is formed through the series and parallel connection of the modules, so that the square array voltage meets the requirements of the input voltage of the system, and then the battery is charged through the charge and discharge controller, which will be charged by the battery. The electrical energy converted from light energy is stored. At night, the battery pack provides input current for the inverter, and through the action of the inverter, the DC power is converted into AC power, and sent to the power distribution cabinet. The power supply is supplied by the switching function of the power distribution cabinet. Control to ensure the normal use of the battery. The photovoltaic power station system should also have limited load protection and lightning protection devices to protect the system equipment from overload operation and avoid lightning strikes, and maintain the safe use of system equipment.
2. Components of solar photovoltaic system
The solar photovoltaic system is composed of solar cell array, storage battery, charge and discharge controller, inverter, AC power distribution cabinet and other equipment. The functions of each part of the equipment are as follows.
(1) Solar cell array
When there is light (whether it is sunlight or light generated by other illuminants), the battery absorbs light energy, and the accumulation of opposite-signal charges occurs at both ends of the battery, that is, a “photo-generated voltage” is generated, which is the “photovoltaic effect” .Under the action of photovoltaic effect, electromotive force is generated at both ends of the solar cell, which converts light energy into electrical energy. It is an energy conversion device. Solar cells are generally silicon cells, which are divided into monocrystalline silicon solar cells, polycrystalline silicon solar cells and Three types of amorphous silicon solar cells.
(2) battery pack
Its function is to store the electric energy emitted by the solar cell array when it is illuminated and to supply power to the load at any time. The basic requirements of solar cell power generation for the battery pack used are:
①Low self-discharge rate
② long service life;
③ Strong deep discharge capability;
④High charging efficiency;
⑤ Less maintenance or maintenance free;
⑥ Wide operating temperature range;
⑦The price is low.
At present, the batteries used in the solar power generation system are mainly lead-acid batteries and cadmium-nickel batteries. For lead-acid batteries above 200A.h, fixed or industrial sealed maintenance-free lead-acid batteries are generally used. The rated voltage of each battery is 2V (DC). For lead-acid batteries below 200A.h, small sealed lead-acid batteries are generally used. Maintenance-free lead-acid batteries, each with a rated voltage of 12V (DC).
(3) Charge and discharge controller
It is a device that can automatically prevent the overcharge and overdischarge of the battery. Since the number of cycles of charge and discharge and the depth of discharge of the battery are important factors that determine the service life of the battery, a charge and discharge controller that can control the overcharge or overdischarge of the battery pack is an essential device.
A device that converts direct current to alternating current. Since solar cells and batteries are DC power sources, and the load is an AC load, an inverter is indispensable. According to the operation mode, the inverter can be divided into independent operation inverters and grid-connected inverters. Stand-alone inverters are used in stand-alone solar cell power systems to power stand-alone loads. The grid-connected inverter is used for the solar cell power generation system running on the grid. The inverter can be divided into square wave inverter and sine wave inverter according to the output waveform. The square wave inverter has a simple circuit and low cost, but has a large spectral wave component. It is generally used in systems below a few hundred watts and does not require high harmonics. The sine wave inverter has a high cost, but it can be applied to various loads. Inverter protection functions: overload protection; short circuit protection; reverse connection protection; undervoltage protection; overvoltage protection; overheating protection.
(5) AC power distribution cabinet
Its main function in the power station system is to switch the standby inverter, ensure the normal power supply of the system, and also measure the line power.