Classifications of Solar Cells (Part One)

Classifications of Solar Cells (Part One)


There are many types of solar cells, but currently, there is no generally accepted nomenclature for most mass-produced and developed solar cells. Photovoltaic systems are divided into independent systems, grid-connected systems and hybrid systems. If the photovoltaic power supply system is divided more carefully according to the application form, application scale and load type of the solar photovoltaic system, the photovoltaic system can also be subdivided into the following six types: small solar power supply systems, simple DC systems, large solar power systems, power supply systems, AC and DC power supply systems, grid-connected systems, hybrid power supply systems and grid-connected hybrid systems. 
 
1.1 Small solar power supply system
The characteristics of this system are that there is only DC load in the system and the load power is relatively small. The entire system has a simple structure and is easy to operate. Its main uses are general household systems, various civilian DC products and related entertainment equipment. This type of photovoltaic system has been widely promoted and used in western China. The load is a DC lamp to solve the problem of household lighting in areas without electricity.
 
1.2 Simple DC systems
The characteristic of this system is that the load in the system is a DC load and there is no special requirement for the use time of the load. The load is mainly used during the day, so there is no battery used in the system and no controller is needed. The system has a simple structure and directly uses photovoltaic components to power the load, eliminating the need to store and release energy in the battery as well as the energy loss in the controller, and improving energy utilization efficiency. It is commonly used in PV water pump systems, some temporary equipment during the day, and some tourist facilities.
 
1.3 Large-scale solar power supply systems
Compared with the above two photovoltaic systems, this photovoltaic system is still suitable for DC power supply systems, but this kind of solar photovoltaic system usually has a greater load power. In order to ensure that it can reliably provide a stable power supply to the load, its corresponding system scale is also larger, requiring larger photovoltaic module arrays and larger battery packs. Its common applications include power supplies for communication, telemetry, and monitoring equipment, centralized power supply in rural areas, navigation beacons, lighthouses, street lights, etc.
 
1.4 AC and DC power supply systems
Different from the above three solar photovoltaic systems, this photovoltaic system can provide power for both DC and AC loads at the same time. The system structure has inverters to convert DC power into AC power to meet the needs of AC load. Usually, the load power consumption of this kind of system is relatively great, so the scale of the system is also large. It is used in some communication base stations with both AC and DC loads and other photovoltaic power stations with AC and DC loads.
 
1.5 Grid-connected systems
The greatest feature of this solar photovoltaic system is that the DC power generated by the photovoltaic array is converted into AC power that meets the requirements of the mains power grid through a grid-connected inverter and then directly connected to the mains power grid. In addition to supplying AC power, the power generated by the PV array in the grid-connected system, excess power is sent to the grid. On rainy days or at night, when the photovoltaic array does not generate electrical energy or the generated electrical energy cannot meet the load, it is powered by the grid. Because electric energy is directly input into the grid, there is no need to configure a battery, and the process of battery energy storage and release is eliminated. The power generated by the PV array can be fully utilized, thereby reducing energy loss and system costs. 
 
However, a dedicated grid-connected inverter is required in the system to ensure that the output power meets the requirements of the grid power for voltage, frequency and other indicators. There will still be some energy loss due to the efficiency of the inverter. Such systems are often able to use mains electricity and solar photovoltaic module arrays in parallel as power sources for local AC loads, reducing the load shortage rate of the entire system. Moreover, grid-connected PV systems can play a peak-shaving role on the public grid. However, as a distributed power generation system, the grid-connected photovoltaic power supply system will have some adverse effects on the power grid of the traditional centralized power supply system, such as harmonic pollution, islanding effect, etc.