Energy storage technology refers to the process of storing energy through a medium or device and releasing it when needed; photovoltaic + energy storage is the combination of solar photovoltaic power generation and energy storage technology to store the electricity generated by the photovoltaic system in order to ensure a stable power supply when needed. Currently, the system solutions for photovoltaic + energy storage on the market mainly include DC coupling and AC coupling . So what are the differences between these two solutions?

The difference between DC coupling and AC coupling

DC coupling means that the energy storage battery and photovoltaic modules are connected to the DC side of the photovoltaic storage machine, the photovoltaic storage machine is directly connected to the photovoltaic modules, and the energy collection point is on the DC side; AC coupling means that the energy storage system and the photovoltaic system are connected on the AC side, the energy storage system (battery, energy storage inverter) and the photovoltaic system (photovoltaic modules, photovoltaic inverter) work independently of each other, and the energy collection point is on the AC side. However, due to the differences in line structure, electrical equipment, etc., there are also significant differences in working principles, flexibility, efficiency, etc.

Differences in working principles

DC coupling: In this solution, the photovoltaic inverter and the bidirectional converter are integrated into a photovoltaic storage machine, which is directly connected to the photovoltaic modules, the power grid, the battery, etc. to form a whole. When the photovoltaic system is running, the generated electricity can be used to charge the battery through the photovoltaic storage machine, and can also be used to power the load or be input into the power grid.

AC coupling: This solution includes two parts: photovoltaic system and energy storage system. The photovoltaic system consists of photovoltaic array and photovoltaic inverter; the energy storage system consists of energy storage inverter and battery. The two systems can operate independently without interfering with each other, or they can be disconnected from the grid to form a microgrid system. When the photovoltaic system is running, the generated electricity can be used to power the load or input into the grid through the photovoltaic inverter, and can also be used to charge the battery through the energy storage inverter.

2. Difference in flexibility

DC coupling: In this solution, PV panels, integrated photovoltaic storage devices and batteries are in serial state and are closely connected to each other. The addition and removal of equipment is relatively complex and the flexibility is average.

It is mainly used in new PV markets, such as newly installed photovoltaic storage systems. PV panels, integrated photovoltaic storage devices and batteries need to be designed according to the user's load power and power consumption.

AC coupling: In this solution, the photovoltaic inverter, energy storage inverter and battery are in parallel state, with flexible connection and more convenient equipment addition and subtraction. It can be applied to the photovoltaic stock and new markets. If a new energy storage system is added to the original photovoltaic system, it can be directly integrated into the equipment without additional system design adjustments. In principle, the design of the energy storage system has no direct relationship with the photovoltaic system and can be determined according to demand.

3. Differences in photovoltaic utilization
From the perspective of photovoltaic utilization efficiency, the two solutions have their own characteristics: in the DC coupling system , the photovoltaic modules store electrical energy in the battery through the controller, with an efficiency of more than 95%, and can store electrical energy for use at night. This solution is more suitable for situations where daytime electricity consumption is less than nighttime electricity consumption; while in the AC coupling system , the photovoltaic modules directly supply power to the load through the photovoltaic inverter, with an efficiency of more than 96%, and this solution is more suitable for situations where daytime electricity consumption is greater than nighttime electricity consumption.

2. Lucas-tech AC coupling solution
As a professional provider of photovoltaic storage solutions, Lucas-tech provides AC-coupled household photovoltaic storage system solutions , including energy storage inverters and batteries. The power generated by the inverter photovoltaic system can be used by household loads, and the excess can be used to charge the battery; the energy storage system can discharge from the battery for household loads. At the same time, the photovoltaic storage system also provides an off-grid function, which can continue to supply power to the load when the power grid is out of power. Lucas-tech's household photovoltaic storage system is safe, efficient and flexible.

Lucas-tech household energy storage inverters are compatible with low-voltage batteries and can be used with existing inverters to form an AC coupling system, which can avoid the risk of DC high voltage on the battery side and the photovoltaic side, ensuring the ultimate safety of the system. The product adopts an original design to increase the inverter efficiency of low-voltage batteries by up to 96.5%; it is suitable for existing photovoltaic stocks and new markets; it also supports parallel connection, which can easily expand and transform the capacity, and improve the flexibility of system configuration and installation.

In summary, the characteristics and selection of DC coupling and AC coupling are not absolute, and more considerations need to be made in combination with actual application needs. Lucas-tech has been deeply involved in the field of photovoltaic storage for many years, and has achieved innovative layout of products such as energy storage inverters, providing AC coupling system technical solutions with ultra-low voltage operation, high-efficiency inversion, high flexibility and other characteristics, which can realize the wide application of products in photovoltaic stock and new markets , and promote the high-quality coordinated development of photovoltaic + energy storage.