Independent photovoltaic power system is relative to the grid-connected power system. It belongs to the isolated power generation system. The isolated system is mainly used in remote areas without electricity, and its main purpose is to solve the problem of no electricity.
The reliability of power supply is greatly affected by meteorological environment, load and other factors. The stability of power supply is relatively poor, so energy storage and energy management equipment are often needed.
The independent photovoltaic power system is also called fully off-grid solar system, which is mainly composed of solar cell modules, controllers and batteries. To supply power for AC loads, an AC inverter needs to be configured. Independent photovoltaic power systems can be divided into DC photovoltaic power systems and AC photovoltaic power systems.
1. DC photovoltaic power systems
The characteristic of the DC photovoltaic power system without battery is that the electric load is DC load. There is no requirement for load usage time, and the load is mainly used during the day.
The solar cell is directly connected to the electrical load. When there is sunlight, it generates electricity for the load to work. When there is no sunlight, it stops working. The system does not require controllers, and there is no battery storage device.
The DC photovoltaic power system without battery saves the loss caused by the energy passing through the controller and the storage and release of the battery, improving the efficiency of solar energy utilization. The most typical application of such systems is solar photovoltaic water pumps.
The DC photovoltaic power system with battery is composed of solar cells, charge and discharge controllers, batteries and DC loads. With sunlight coming in, the solar cell converts light energy into electricity for the load and simultaneously stores electricity to the battery.
At night or on rainy days, the battery supplies power to the load. This system is widely used, ranging from solar lawn lights and garden lights to mobile communication base stations and microwave transfer stations that are far from the power grid and power supply in remote rural areas. When the system capacity and load power is large, it is necessary to equip the solar cell module array and battery.
2. AC photovoltaic power systems
Compare the AC photovoltaic power system and AC-DC hybrid photovoltaic power system with the DC photovoltaic power system, we can find that the AC photovoltaic power system has an AC inverter, which is used to convert direct current into alternating current to provide electricity for AC load. The AC-DC hybrid photovoltaic power system can supply power for both DC and AC loads.
The municipal complementary photovoltaic power system is based on solar photovoltaic power generation in the independent photovoltaic power generation system, and supplemented by ordinary 220 V AC power.
So the capacity of solar cells and batteries in photovoltaic power systems can be designed to be smaller. Basically, when there is sunshine in the day, electricity generated by solar energy is used, and when there is rain, mains supply is used to supplement it.
It is suitable to establish independent photovoltaic power stations in towns and islands without electricity but with good lighting conditions and relatively large load demands, and in regions without electricity but with relatively concentrated users within a few kilometers.
At present, the capacity of independent photovoltaic power stations ranges from several kilowatts to tens of kilowatts. The power station consists of solar panel arrays, batteries and converters, energy managers, and distribution and transmission systems.
During the day, the photovoltaic power system charges the battery and provide power to photovoltaic water pumps, processing machines and other machines at the same time, so the machine can finish water pumping, storage and processing operations. At night, the photovoltaic power system realizes the load power supply by the inverter discharge control of the battery.
When designing an independent power station, it is very important to consider the reasonable use of battery, especially for the dynamic load of electric motors with high ratio of power consumption at night.