A typical solar photovoltaic (PV) power generation system consists of solar cell arrays (modules), cables, power electronic converters (inverters), energy storage devices (batteries), and loads (users). The solar cell arrays and energy storage devices constitute the power supply system, the controller and power electronic converter constitute the control and protection system, and the loads are the system terminals.
1. Solar cell array
The smallest unit used for photoelectric conversion is the solar cell. Its size ranges from 4 to 100 cm², its operating voltage is 0.45 to 0.50 V, and its operating current is 20 to 25 mA/cm², therefore it cannot be used as a standalone power source. In a photovoltaic power generation system, solar cells need to be connected in series and parallel and encapsulated to form solar cell modules. Their power output can range from a few watts to hundreds of watts, and they can be used as standalone power sources. A solar cell array, on the other hand, consists of solar cell modules connected in series and parallel and mounted on a support structure. It can output hundreds of watts, kilowatts, or even greater power, serving as the power generator of a photovoltaic power generation system.
Solar cell modules come in a wide variety of types, which can be categorized based on the type of solar cell: monocrystalline silicon modules, polycrystalline silicon modules, gallium arsenide modules, and amorphous silicon thin-film modules, among which crystalline silicon (including monocrystalline and polycrystalline silicon) solar cell modules account for approximately 80% to 90% of the market. The encapsulation materials and processes for crystalline silicon also differ, mainly including epoxy resin encapsulation, lamination encapsulation, and silicone encapsulation. Currently, vacuum lamination encapsulation is the most widely used method, suitable for the industrial encapsulation of large-area solar cells.
2. Solar storage battery
Stand-alone photovoltaic (PV) power generation systems rely on batteries to store excess electrical energy, making batteries crucial. As the price of solar cell modules decreases, the proportion of battery costs in the total system investment will gradually increase. Furthermore, battery failures account for a significant proportion of system disruptions during operation. Therefore, selecting the appropriate battery type and capacity during system design, precise installation and operation, and meticulous maintenance are essential for the normal operation of stand-alone solar PV power generation systems.
3. Power electronic converter (photovoltaic inverter)
An inverter in a photovoltaic power generation system is a converter circuit that transforms the direct current (DC) generated by the solar cell array into alternating current (AC) with various required frequencies and voltage values. Inverters can be further divided into passive and active types. Passive inverters directly supply energy to the load from DC power, while active inverters supply AC power from DC power to the AC source.
The necessity of DC-to-AC conversion is also reflected in the fact that when the power supply system needs to raise or lower the voltage, an AC system only requires adding a transformer, while the technology and equipment in a DC system are much more complex. Therefore, except for special users, inverters are required in photovoltaic power generation systems.
In addition, inverters also have automatic or manual voltage regulation functions, which can improve the power supply quality of photovoltaic power generation systems. Clearly, inverters are an indispensable and important supporting device in photovoltaic power generation systems.
