The main function of the solar inverter is to convert the DC power generated by the solar panels into AC power used by home appliances. All the electricity generated by the solar panels must be processed by the inverter before it can be output externally.
For the functions, solar inverters can be divided into on grid inverters and off grid inverters. So what is the difference between on grid and off grid inverter? This article will compare the difference between on grid and off grid inverter and introduce their roles in photovoltaic systems.
Main content:
1. On grid vs off grid
Before getting to the comparison between on grid and off grid solar inverter, first of all, we need to know what on grid and off grid mean.
An off-grid photovoltaic power station store solar power in batteries and then convert it into household 220V voltage through an inverter. And on grid photovoltaic power station refers to a on grid photovoltaic power station that is connected to the mains. There is no electric energy storage device in the on grid photovoltaic power station. It is directly converted into the voltage requirements required by the national grid through an inverter and is given priority to households. The electricity that cannot be used by households can be sold to the state.
On grid means that it must be connected to the public power grid, that is, solar power generation, household power grids, and public power grids are connected together. This is a power generation system that must rely on the existing power grid to operate.
At present, many countries are vigorously supporting solar power generation and have relevant policy support. As long as a home solar power system generates electricity, they will receive state subsidies. However, grid connection usually requires applying to the local State Grid department first.
2. Pros and cons of on grid and off grid
On grid
- Advantages
On grid photovoltaic power systems are mainly composed of solar panels and inverters. The solar panels emit electricity that is directly converted into 220V AC by the inverter and supplies power to household appliances. When the solar power generation exceeds the power used by household appliances, the excess electricity is transmitted to the public power grid. When the solar power generation cannot meet the use of household appliances, it is automatically supplemented from the power grid. The entire process is intelligently controlled and does not require manual operation.
Since this kind of photovoltaic power generation system does not require the use of batteries, it greatly saves costs. Especially the national grid connection policy has clearly stated that home photovoltaic power stations can be connected to the grid for free, and excess electricity can be sold to power companies.
From the long-term perspective of investment, based on the 25-year service life of a home photovoltaic power station, the cost can be recovered in about 6-10 years, and the remaining ten years will be earned. Therefore, if you want to save electricity bills and have convenient power supply, choose a on grid solar power generation system, which is also the current mainstream method.
- Disadvantages
However, on gird solar power systems also have disadvantages, that is, when the public grid is out of power, the solar power generation cannot operate. However, if the on grid inverter is replaced with a smart microgrid inverter (a hybrid on grid and off-grid inverter), the power station can still operate normally during a power outage.
So, how can we store the electricity generated during the day and use it at night? This requires adding a controller and a battery. During the day, the controller stores the power generated by photovoltaics in the battery. At night, the controller releases the power stored in the battery for lighting.
Off grid
- Advantages
Off grid photovoltaic power systems, also called independent / standalone photovoltaic power systems, are power generation systems that operate independently without relying on the power grid. They are mainly composed of solar panels, energy storage batteries, charge and discharge controllers, inverters and other components. The electricity generated by the solar panels flows directly into the battery and is stored. When it is necessary to power electrical appliances, the DC current in the battery passes through the inverter and is converted into 220V AC power.
This is a repetitive cycle of charge and discharge process. This kind of power generation system is not restricted by geography and is widely used. It can be installed and used wherever there is sunlight. Therefore, it is very suitable for remote areas without power grids, isolated islands, fishing boats, outdoor breeding bases, etc. It can also be used in areas with frequent power outages or for emergency power generation equipment and mobile transport, for example, as an RV inverter.
- Disadvantages
One of the biggest difference between on grid and off grid inverter is that off grid inverter must be equipped with batteries and accounts for 30-50% of the cost of the power generation system. Moreover, the service life of batteries is generally 3-5 years, and they have to be replaced after that, which increases the cost of use. In terms of economy, it is difficult to be widely promoted and used, so it is not suitable for use in places where electricity is convenient.
But it is very practical for households in areas without power grid or areas with frequent power outages. Especially to solve the lighting problem during power outage, DC energy-saving lamps can be used. Therefore, off grid power generation systems are specifically designed for use in areas without power grids or areas with frequent power outages.
3. Difference between on grid and off grid inverter
On grid inverter
On grid inverters are generally divided into photovoltaic power generation on grid inverters, wind power generation on grid inverters, power equipment power generation on grid inverters and other power generation equipment power generation on grid inverters. The biggest feature of on grid inverters is the high system power and low cost.
On grid inverters are generally used in systems of large-scale photovoltaic power stations. Many parallel photovoltaic strings are connected to the DC input end of the same centralized inverter. Generally, three-phase inverter IGBT power modules with high power are used. The smaller application ares use field effect transistors, while using a DSP conversion controller to improve the quality of the generated power, making it very close to a sine wave current.
The biggest difference between on grid and off grid inverter is that on grid inverter does not use any battery storage. The DC power generated from the solar panels is directly converted into AC power through inverter and directly fed to the public power grid. However, there are certain thresholds, which is that it must comply with the relevant requirements of the local power grid. Otherwise, grid connection cannot be provided.
Off grid inverter
Off grid inverters, like 2000w inverter or 3000w inverter, are typically a complete system solution of modular components, consisting of a number of manageable parts: inverter, solar charge controller, automatic generator starting module, and system control board.
As the name suggests, an off grid inverter is a system that is disconnected from the public grid. It is a device that converts DC power output from solar panels into AC power. It is not connected to the power grid and supplies power to the load independently. It first stores the DC power generated by the solar panel in the battery, and then transmits it to the off-grid inverter for inversion.
The AC power generated can be directly used by the load or returned to the battery for storage. It is more suitable for remote areas without power network coverage or unstable power supply, such as deserts, plateaus, and deep forest areas, and can provide power needs anytime and anywhere.
4. How to choose between on grid and off grid inverter
The on grid inverter can be used directly as an off grid inverter. The on grid inverter sends energy directly to the grid, so it needs to track the frequency and phase of the grid, which is equivalent to a current source. Of course, some inverters now claim to have low-voltage ride-through capabilities and can perform PQ regulation.
The off grid inverter is like building an independent small power grid by itself. It mainly controls its own voltage and is a voltage source. On grid inverters do not require energy storage, but the energy cannot be controlled. The amount of photovoltaic power generated can be sent to the grid. However, off grid systems generally require energy storage and do not send energy to the grid, and the grid has no right to interfere.
Above we introduced the difference between on grid and off grid inverter, when choosing an inverter, you need to make a judgment based on actual needs and application scenarios. If you have high requirements for power supply stability or require independent power supply, you can choose a hybrid or off grid solar inverter. If you need a large-scale photovoltaic power generation system, you can choose a on grid solar inverter.
If you are still not sure, check the inverter buying guide for more reference!
With the continuous development of new energy technology and the expansion of application fields, inverter technology is also constantly innovating and improving. In the future, various types of inverters will better meet the needs of different scenarios and make greater contributions to the development of clean energy for mankind.
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