In distributed photovoltaic power generation systems, different expressions such as grid connected, off grid, and microgrid are often seen. What are their own characteristics? What are the differences? In fact, they represent several power generation systems related to distributed photovoltaic power generation. In this article, we not only introduce the main characteristics of grid connected power generation systems, grid connected power generation systems, off grid energy storage power generation systems, and microgrids, but also compare them in terms of their connection with the power grid, energy storage equipment requirements, application scenarios, and other aspects in a table for easy reference.
Grid connected power generation system
Grid connected photovoltaic system refers to a photovoltaic system directly connected to the public power grid. The core components of this system include photovoltaic modules, grid connected inverters, bidirectional meters, and the power grid itself. The function of grid connected inverters is to convert the direct current generated by photovoltaic modules into alternating current, which is then supplied to local loads. Excess electricity is sold back to the grid through bidirectional meters.
The grid connected power generation system relies on the external power grid and adopts a working mode of "spontaneous self use, surplus electricity grid connection" or "full grid connection". In the event of a power outage, the system does not operate to prevent the backflow of electricity into the grid, which could pose a safety hazard.
Off grid power generation system
Off grid power generation systems operate independently of the power grid and are not connected to it. It consists of photovoltaic modules, off grid inverters, batteries, and loads. This system is completely independent and does not rely on grid power supply, suitable for remote areas without grid coverage or areas with frequent power outages. Off grid systems must be equipped with energy storage devices, usually batteries, for use at night or in low light conditions.
Off grid power generation systems do not rely on the power grid, relying on the working mode of "storing while using" or "storing before using", and are not affected by power outages. This system has superior flexibility and maneuverability, and must be equipped with energy storage devices such as batteries to store the electricity generated during the day for use at night or in the absence of light.
Hybrid energy storage and generation system
Hybrid energy storage power generation systems are widely used in places where there are frequent power outages, or where photovoltaic self use cannot generate surplus electricity for grid connection, where self use electricity prices are much higher than grid connection prices, and where peak electricity prices are much higher than valley electricity prices.
The system consists of photovoltaic modules, solar hybrid integrated machines, batteries, loads, etc. The photovoltaic array converts solar energy into electrical energy under illumination, and supplies power to the load and charges the battery through a solar controlled inverter integrated machine; When there is no light, the battery supplies power to the solar controlled inverter integrated machine, and then supplies power to the AC load.
Compared to grid connected power generation systems, this system adds a charge and discharge controller and a battery. In the event of a power outage, the photovoltaic system can continue to operate, and the inverter can switch to off grid mode to supply power to the load.
Microgrid
A microgrid is a distribution network consisting of distributed power sources (such as photovoltaics and wind power), loads, energy storage systems, and control devices. Compared to the wide area integration of power generation, transmission, distribution, and use in the large power grid, microgrids mainly achieve on-site consumption of distributed renewable energy and energy exchange with the large power grid.
Microgrids can operate as independent power grids or be connected to the main power grid to exchange electrical energy. Microgrid systems have the characteristics of flexibility and efficiency, which can promote the large-scale integration of distributed power sources and renewable energy.
In microgrids, collaborative control between the main grid, distributed power sources, and energy storage systems is achieved through energy management systems to smooth out fluctuations in distributed energy.
Comparison Table of Various Systems
| Comparison items | Grid connected power generation system | Off grid power generation system | Hybrid energy storage and generation system | Microgrid system |
| Connection relationship with the power grid | Directly connecting to the public power grid can transmit excess electricity to the grid or obtain electricity from the grid. | Completely independent of the power grid operation, not dependent on external power grid supply, suitable for areas without power grid coverage. | It can be connected to the power grid or operate independently during power outages, with two working modes: grid connected and off grid. | It can be connected to the external power grid and operated independently when needed, achieving energy self-sufficiency in the region. |
| The demand for energy storage devices | Usually, energy storage devices are not needed because excess electricity can be directly transmitted to the grid. | Energy storage devices (such as batteries) must be equipped to store the electricity generated during the day for use at night or in the absence of light. | Energy storage devices are also required to achieve independent operation in the absence of a power grid. | May include energy storage devices to balance power supply and demand within the region and improve energy efficiency. |
| Application scenarios | Suitable for residential and commercial buildings in urban and suburban areas, as well as large-scale solar power plants. | Suitable for remote areas and areas without power grid coverage, such as mountainous areas and islands. | Suitable for areas with frequent power outages or users who wish to increase their energy self-sufficiency rate. | Suitable for small areas such as industrial parks and university campuses, it can achieve self-management and optimization of energy. |
| System complexity and cost | The structure is relatively simple and the cost is low because no energy storage equipment is required. | The structure is complex and the cost is high, requiring energy storage equipment and independent control systems. | The structure is complex and the cost is high, requiring inverters and energy storage devices that operate in both grid connected and off grid modes. | The structure is the most complex and costly, requiring the integration of multiple energy sources, energy storage systems, and complex energy management systems. |
| Stability and reliability of power supply | The power supply depends on the stability of the power grid, and the system will also stop working during power outages. | The power supply is completely independent and not affected by the power grid, but is limited by weather and energy storage capacity. | Combining the advantages of grid connection and off grid, it can continue to supply power during power outages, improving the stability and reliability of power supply | It can achieve a balance between power supply and demand within the region, improving the stability and reliability of power supply. |
Through this table, we can visually see the differences in the connection relationship with the grid, energy storage equipment requirements, application scenarios, system complexity and cost, as well as the stability and reliability of power supply for each photovoltaic power generation system. This helps us choose the appropriate system type based on specific application requirements and conditions.