A photovoltaic power generation system uses solar cells to directly convert solar energy into electrical energy. Its main components are solar cells, batteries, controllers and inverters.
It is characterized by safety and reliability, no noise, low pollution, no fuel consumption, independent power generation and grid-connected operation. Let's take a look at the classification and application fields of photovoltaic power generation systems.
1. Classification of photovoltaic power generation system
Photovoltaic power generation systems are divided into independent photovoltaic power generation system, grid-connected photovoltaic power generation system and distributed photovoltaic power generation system.
● Independent photovoltaic power generation system
It is also called off-grid photovoltaic power generation. It is mainly composed of solar cells (off grid solar batteries), controllers, batteries, and AC inverters, which are also required to supply power to AC loads. Stand-alone photovoltaic power plants include photovoltaic power generation system with batteries that can operate independently.
● Grid-connected photovoltaic power generation system
It is the direct current generated by solar modules that is converted into alternating current by the grid-connected inverter and directly connected to the public grid. It can be divided into two types.
- Grid-connected photovoltaic power generation system with storage battery
Grid-connected photovoltaic power generation system with accumulators are dispatchable and can be integrated into or exited from the grid as needed. It also has the function of a backup power supply, which can provide emergency power when the power grid is cut off for any reason. Grid-connected photovoltaic power generation system with batteries are often installed in residential buildings.
- Grid-connected photovoltaic power generation system without storage battery
It does not have the functions of dispatchability and backup power, and is generally installed on larger systems.
● Distributed photovoltaic power generation system
This system can be divided into centralized large-scale, grid-connected photovoltaic power stations and distributed photovoltaic systems. The main feature of centralized large-scale grid-connected photovoltaic power stations is that the power generated can be directly transmitted to the power grid, and the grid will uniformly allocate power to users.
This kind of power station has large investment, a long construction period and large footprint. The distributed pv system has the advantages of low investment, fast construction and small footprint.
2. Disadvantages of photovoltaic power generation system
● Low conversion efficiency
The conversion efficiency of pv power generation refers to the efficiency of converting light energy into electrical energy. It is precisely because of the low photoelectric conversion efficiency that the power density of pv power generation is also very low, so it is difficult to form a high-power power generation system. Low photoelectric conversion efficiency is an important factor hindering the development of pv power generation.
● Can only work during the day
PV power generation has light to generate electricity, so it can only generate electricity during the day, can not generate electricity at night, and we usually use most of the electricity at night, the working characteristics of pv power generation do not match our living habits.
● Greatly affected by the environment
Long-term rain, snow, cloudy, foggy and even cloud changes will affect pv power generation. The solar cell plates must not be covered by debris.
● Strong geographical dependence
The geographical location is different, the climate is different, and the sunshine resources in different regions vary greatly. Photovoltaic power generation system will only be effective if they are applied in areas rich in solar energy resources.
Photovoltaic grid-connected power generation is to directly input electrical energy into the grid, eliminating the process of battery storage and release. Compared to off-grid photovoltaic power generation system, pv power generation is connected to the grid without the configuration of batteries, which can make full use of the power generated by the photovoltaic array, thereby reducing energy loss and system costs. How many grid-connected modes of pv power generation are there? Let's find out.
3. Grid-connected vs off-grid photovoltaic power generation system
● Grid-connected photovoltaic power station
Grid connection is a power generation system that must rely on the existing power grid to operate. It is mainly composed of solar panels and inverters, which can be applied to home energy storage.
When solar energy generates more electricity than used by household appliances, excess electricity is sent to the public grid. When the power generation of solar energy cannot meet the use of household appliances, it is automatically replenished from the grid. And this whole process is intelligently controlled and does not require manual operation.
Advantages: Since this photovoltaic power generation system does not need to use batteries, it also greatly saves costs. If you want to save electricity bills and the power supply is convenient, choose a grid-connected solar power system, which is also the mainstream way.
Disadvantages: When the public grid is powered off, pvpower generation cannot be operated. However, if the grid-connected inverter is replaced with an intelligent microgrid inverter, the power station can operate normally.
So, how can you store the electricity generated during the day and use it at night? This requires the addition of controllers and batteries, etc. During the day, the controller stores the power generated by the photovoltaic in the battery, and at night, the controller releases the power stored in the battery for use.
● Off-grid photovoltaic power station
Also known as independent photovoltaic power stations, it is a power generation system that operates independently without relying on the power grid. When the electricity generated by the solar panel flows directly into the battery and is stored, when it is necessary to supply power to the appliance, the DC current in the battery is converted into 220V alternating current through the inverter, which is a repetitive cycle of charging and discharging process.
Advantages: not limited by geography, widely used, as long as there is sunlight in the place, it can be installed and used.
Disadvantages: Must be equipped with batteries, and account for 30–50% of the cost of the power generation system. And the service life of the battery is generally 3-5 years, and then it has to be replaced, which increases the cost of use. In terms of economy, it is difficult to get a wide range of promotion and use, so it is not suitable for use in places where electricity is convenient. Simply, grid-connected batteries are not needed, off-grid batteries are required.
4. Grid-connected photovoltaic power generation modes
● Completely spontaneous self-consumption mode
This model is generally applied when the power load on the user side is large, and the power load is continuous, and there are few or semi-shutdowns in a year. Or the user's electricity maintenance load is also enough to absorb most of the electricity generated by the photovoltaic power station.
This kind of system, because the low-voltage side is connected to the grid, if the user's electricity cannot be absorbed, it will be sent back to the upper power grid through the transformer. The distribution transformer design is not allowed to be used for reverse transmission of electrical energy, and its initial power flow direction design is fixed. Therefore, it is necessary to install an anti-reverse flow device to avoid the reverse transmission of electricity.
● Spontaneous self-consumption surplus power network mode
For most users who are optimistic about distributed generation, choosing self-consumption surplus power is the most ideal mode, so that you can not only get a higher price of spontaneous self-consumption, but also sell electricity to the grid when it cannot be used.
However, there are many obstacles in the actual operation process, due to the asymmetry of information between photovoltaic practitioners and local power grid companies, and lack of understanding of each other's professional knowledge, which is why this model has become the most incomprehensible part.
The biggest disadvantage of this operating model is that its revenue model cannot be fixed. The proportion of spontaneous self-consumption and the proportion of surplus electricity on the Internet are always changing.
● Fully on-grid electricity selling mode
In the past ten years of the great development of pv power generation, direct on-grid electricity sales have always been the mainstream of photovoltaic applications. This grid-connected form is not only suitable for future distributed fixed electricity price projects.
5. Application fields of photovoltaic power generation system
The photovoltaic power generation system can be used widely and provide convenience for people to satisfy their daily use.
- User solar power
- Photovoltaic water pump
- Solve the problem of drinking and irrigation of deep water wells in areas without electricity.
- Solar water purifier to solve the problem of drinking water and purify water quality in areas without electricity.
- Transportation field
- Communication field
- Photovoltaic power station
- Independent photovoltaic power station, wind-solar complementary power station, etc.
- Compatible with automobiles Solar cars, battery charging equipment, etc.
6. ConclusionPhotovoltaic power generation is a technology that uses the photovoltaic effect of the semiconductor interface to directly convert light energy into electrical energy. It is mainly composed of three parts: the solar panel, controller, and inverter, and the main components are composed of electronic components. After the solar cells are packaged and protected in series, a large area solar cell module can be formed, and then combined with the power controller and other components to form a pv power generation device.