The grid connection of solar energy storage batteries is a key technology to realize the large-scale application of solar energy, which connects the solar energy storage system to the public power grid, realizing the two-way flow of electricity between the system and the grid. This technology not only solves the problem of intermittent and volatile solar power generation but also improves the stability and reliability of the grid, promotes the integration of renewable energy, and provides a new way for energy supply. A grid-connected solar energy storage system mainly consists of solar panels, energy storage batteries, inverters, and grid connection devices. The inverter is the core component of grid connection, which converts the direct current (DC) generated by solar panels and stored in batteries into alternating current (AC) that matches the grid’s voltage, frequency, and phase, ensuring that the electricity can be smoothly fed into the grid or used by users.

There are two main types of grid connection modes for solar energy storage batteries: grid-tied mode and off-grid mode with grid connection function. The grid-tied mode is the most common mode, where the solar energy storage system is connected in parallel with the public power grid. When the solar radiation is sufficient, the solar panels generate electricity, part of which is used by the user, and the surplus is stored in the battery or fed into the grid; when the solar radiation is insufficient or the user’s electricity demand exceeds the solar generation, the battery releases stored electricity, and if the battery capacity is insufficient, the grid supplements the power. This mode can effectively improve the utilization rate of solar energy, reduce the user’s reliance on the grid, and allow users to obtain economic benefits by feeding surplus electricity back to the grid. For example, in many countries and regions, there are feed-in tariff policies, where users can sell the surplus electricity generated by their solar energy storage systems to the grid at a certain price, increasing their income.

The off-grid mode with grid connection function is mainly used in areas with unstable grid power supply or no grid coverage. In normal times, the system operates in off-grid mode, providing power for users through solar energy and energy storage batteries; when the battery capacity is insufficient or there is an emergency, the system can be connected to the grid to obtain supplementary power, ensuring the continuous and stable power supply for users. This mode is particularly suitable for remote areas, islands, and rural areas, solving the problem of energy supply in these areas. In addition, the grid connection of solar energy storage batteries also involves battery-to-grid (B2G) technology, which allows the energy storage battery to feed surplus electricity back to the grid, realizing the two-way interaction between the battery and the grid. This technology can not only improve the utilization rate of the battery but also provide peak shaving, valley filling, and frequency regulation services for the grid, reducing the pressure on grid operation.

The grid connection of solar energy storage batteries also faces some technical and policy challenges. Technically, the grid connection needs to solve the problems of voltage stability, frequency regulation, and harmonic pollution, ensuring that the electricity fed into the grid meets the grid standards. Inverters play a key role in this process, as they need to quickly adjust the output voltage and frequency to match the grid, and suppress harmonic pollution. Policy-wise, the lack of uniform grid connection standards and policies in some regions has restricted the development of grid-connected solar energy storage systems. For example, 50 U.S. states have 50 different storage policies, which increases the difficulty of grid connection for enterprises and users. However, with the continuous advancement of technology and the improvement of relevant policies, the grid connection technology of solar energy storage batteries is becoming more and more mature. Many countries and regions are formulating and improving grid connection standards and policies, encouraging the development of grid-connected solar energy storage systems, and promoting the large-scale integration of solar energy into the grid.