Due to the above characteristics of Solar Power System, Solar Energy System can be classified according to different compositions and purposes of use. For example, according to whether the electric energy generated by photovoltaic power generation systems is sent back to the power system, they can be divided into grid connected systems with reverse current (power system with reverse energy transmission), grid connected systems without reverse current (power system without reverse energy transmission), switched grid connected systems, direct and AC grid connected systems, Mixed system and regional system. Figure 8-1 shows the main types of grid connected photovoltaic power generation systems.
1、 With countercurrent grid connected system
If there is residual electric energy after the power of the solar cell is supplied to the load and it flows to the power system, the system is called a grid connected power generation system with countercurrent. For the grid connected power generation system with countercurrent, because the residual electric energy can be used by other loads, it can give full play to the power generation capacity of solar cells and make full use of electric energy. When the power of the solar cell can not meet the needs of the load, the power can be obtained from the power system. The grid connected system with countercurrent can be widely used in household, industrial power supply and other occasions, and it is generally used at present.
In grid connected photovoltaic power generation systems, batteries are generally omitted, which can not only save investment, greatly reduce the cost of the system, facilitate the popularization of photovoltaic power generation systems, but also save the cost of battery maintenance and overhaul, so the system is very economical.
2、 Non countercurrent grid connected system
Even if there is residual electric energy after the power of the solar cell is supplied to the load, the residual electric energy does not flow to the power system, which is called the grid connected system without countercurrent. In this system, if the power of the solar cell cannot meet the needs of the load, the power can be obtained from the power system.
3、 Switching grid connected system
Switched grid connection systems can be divided into systems used in general and self operating switched grid connection systems, which are mainly used in disaster prevention and other situations.
(1) Switched grid connected photovoltaic power generation system Figure 8-4 shows the switched grid connected photovoltaic power generation system. The system is mainly composed of solar cells, batteries, inverters, switchers and loads. Under normal circumstances, the photovoltaic power generation system is separated from the power system and directly supplies power to the load. When the sunlight is insufficient, at night, in rainy days or the battery is insufficient, the switch automatically switches to the side of the power system and the power system supplies power to the load. The characteristic of this system is that smaller capacity batteries can be selected when designing the capacity of batteries, saving investment.
(2) Self operation switching grid connected system (disaster prevention type) Self operation switching grid connected photovoltaic power generation system is generally used in disasters, disaster relief and other situations. Generally, the system is connected to the power system through the system grid connection device. The electrical energy generated by the photovoltaic power generation system supplies the load. When a disaster occurs, the system grid connection protection device (in the power regulator) acts to separate the photovoltaic power generation system from the power system. The self running switching grid connected photovoltaic power generation system with batteries can be used as the power supply for economic communication, shelter, medical equipment, gas station, road indication, lighting, etc, Supply power to emergency loads in disaster situations.
4、 Direct and AC grid connected system
Figure 8-6 (a) shows the DC grid connected photovoltaic power generation system. As the power supply of information and communication equipment is DC power, the DC power generated by photovoltaic power generation system can be directly provided for information and communication equipment. In order to improve the reliability of power supply, photovoltaic power generation system can also be used with the power system. Figure 8-6 (b) shows the AC grid connected photovoltaic power generation system, which can provide electrical energy for AC loads.
5、 Hybrid grid connected system
The system composed of photovoltaic power generation system and other power generation systems, such as wind power generation and fuel cell power generation, is called hybrid system. If it is connected to the power system, it is called hybrid grid connected power generation system. This system is applicable to the case where the power output of solar cells is unstable and other energy sources are needed as a supplement.
(1) Wind solar complementary grid connected power generation system The power generated by wind power and photovoltaic power is not stored by the battery, but is connected to the grid through the inverter. Generally, this system is called wind solar complementary grid connected power generation system. Figure 8-7 shows the wind solar complementary grid connected power generation system. In this system, taking advantage of the complementarity between wind power generation and photovoltaic power generation, the load preferentially uses the electric energy generated by wind power and photovoltaic power generation. When the power supply is insufficient, the power system will supply power (buy electricity), while when there is surplus electricity, it will send it to the power system (sell electricity) through the grid connection protection device.
(2) Solar PV and fuel cell grid connection system Figure 8-8 shows the solar PV and fuel cell grid connection system. It is composed of solar photovoltaic system, fuel cell system, heating system and load. The fuel cell uses gas as fuel. The system can comprehensively utilize energy, improve the comprehensive utilization rate of energy, and can be used as power supply for personal residence in the future. Solar photovoltaic and fuel cell grid connected systems use fuel cells to generate electricity, so they can save electricity charges, significantly reduce carbon dioxide emissions, and reduce environmental pollution.
6、 Regional grid connected system
The system is mainly composed of solar cells, power regulators and loads. It is characterized by that each photovoltaic power generation system is directly connected with the distribution line of the power system, and the residual electric energy of each system is directly sent to the power system. When the required electric energy of each load is insufficient, the electric energy is directly obtained from the power system.