DC or AC Coupled Battery Storage? How Should You Decide?

Views: 1597     Author: Site Editor     Publish Time: 2022-02-15      Origin: Site


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With the growing demand for home energy storage batteries, the choice of solar energy storage system has become the biggest headache. If you want to retrofit and upgrade your existing solar power system, which is the good solution, AC coupled battery storage system or DC coupled battery storage system?

Before answering this question, we need to take you to understand what is AC coupled battery storage system, what is DC coupled battery storage system, and what is the essential difference between them?

Usually what we call DC, means direct current, electrons flow straight, moving from positive to negative; AC stands for alternating current, different from DC, its direction changes with time, AC can transmit power more efficiently, so it is applicable to our daily life in household appliances. The electricity produced through photovoltaic solar panels is basically DC, and the energy is also stored in the form of DC in the solar energy storage system.

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What is AC Coupled Battery Storage System?

We now know that photovoltaic systems produce DC electricity, but we need to convert it to AC electricity for commercial and home appliances, and this is where AC coupled battery systems are important. If you use an AC-coupled system, then you need to add a new hybrid inverter system between the solar battery system and the solar panels. The hybrid inverter system can support the conversion of DC and AC power from the solar batteries, so the solar panels do not have to be connected directly to the storage batteries, but first contact the inverter connected to the batteries.

AC-Coupled system

How Does An AC-coupled Battery Storage System Work?

AC coupling works: It contains a PV power supply system and a battery power supply system. The photovoltaic system consists of a photovoltaic array and a grid-connected inverter; the solar energy storage system consists of a battery bank and a bi-directional inverter. These two systems can either operate independently without interfering with each other or can be separated from the grid to form a micro-grid system.

In an AC-coupled system, DC solar energy flows from the solar panels to the solar inverter, which converts it to AC power. The AC power can then flow to your home appliances, or to another inverter that converts it back to DC power for storage in the battery system. With an AC-coupled system, any electricity stored in the battery needs to be reversed three separate times to be used in your home - once from the panel to the inverter, again from the inverter to the storage battery, and finally from the storage battery to your home appliances.

What are the Cons and Pros of AC-coupled Battery Storage Systems?

Cons: Low energy conversion efficiency. Compared to DC-coupled batteries, the process of getting energy from the PV panel to your home appliance involves three conversion processes, so a lot of energy is lost in the process.

Pros: Simplicity, if you already have a solar power system, then AC coupled batteries are easier to install into an existing system, you don't have to make any changes, and they have higher compatibility, you can use solar panels to charge solar batteries as well as the grid, which means you can still get power backup from the grid when your solar panels are not generating power.

What is A DC-coupled Battery Storage System?

Unlike AC-side storage systems, DC storage systems combine solar power and a battery inverter. The solar batteries can be connected directly to the PV panels, and the energy from the storage battery system is then transferred to individual home appliances via a hybrid inverter, eliminating the need for additional equipment between the solar panels and the storage batteries.

DC-Coupled system

How Does A DC-coupled Battery Storage System Work?

The working principle of DC coupling: when the PV system is running, the MPPT controller is used to charge the battery; when there is a demand from the appliance load, the home energy storage battery will release power, and the size of the current is determined by the load. The energy storage system is connected to the grid, if the load is small and the storage battery is full, the PV system can supply power to the grid. When the load power is greater than the PV power, the grid and PV can supply power to the load at the same time. Because both PV power and load power are not stable, they rely on the battery to balance the system energy.

In a DC-coupled storage system, DC solar energy flows directly from the PV panel to the home storage battery system, which then converts the DC power to AC power for home appliances through a hybrid solar inverter. In contrast, DC-coupled solar batteries require only one power conversion instead of three. It uses the DC power from the solar panel to charge the battery.

What Are the Cons and Pros of DC-coupled Battery Storage Systems?

Cons: DC-coupled batteries are more difficult to install, especially for retrofitting existing solar power systems, and you your purchased storage battery and inverter systems need to communicate correctly to ensure they charge and discharge at the multiplier rates they strive for.

Pros: The system has higher conversion efficiency, with only one DC and AC conversion process throughout, and lower energy loss. And it is more suitable for newly installed solar systems. DC-coupled systems require fewer solar modules and fit into more compact installation spaces.

AC Coupled vs DC Coupled Battery Storage, How to Choose?

Both DC coupling and AC coupling are currently mature programs, each with its own advantages and disadvantages, according to different applications, choose the most appropriate program, the following is a comparison of the two programs.

1、Cost comparison

DC coupling includes controller, two-way inverter and switching switch, AC coupling includes grid-connected inverter, two-way inverter and distribution cabinet, from the cost point of view, the controller is cheaper than the grid-connected inverter, switching switch is also cheaper than the distribution cabinet, DC coupling program can also be made into an integrated control inverter, equipment costs and installation costs can be saved, so the DC coupling program than the AC coupling program The cost is a little lower than the AC coupling program.

2、Applicability comparison

DC coupling system, the controller, battery and inverter are serial, the connection is tighter, but less flexible. In AC coupled system, the grid-connected inverter, battery and bi-directional converter are in parallel, and the connection is not tight, but the flexibility is better. If in an installed PV system, it is necessary to add an energy storage system, it is better to use AC coupling, as long as the battery and bi-directional converter are added, it does not affect the original PV system, and the design of the energy storage system is in principle not directly related to the PV system, it can be determined according to the demand. If it is a newly installed off-grid system, PV, battery, inverter are designed according to the user's load power and power consumption, with DC coupling system is more suitable. But DC coupling system power are relatively small, generally below 500kW, and then the larger system with AC coupling is better control.

3、Efficiency comparison

From the PV utilization efficiency, the two programs have their own characteristics, if the user daytime load is more, less at night, with AC coupling is better, PV modules through the grid-connected inverter directly to the load power supply, the efficiency can reach more than 96%. If the user has less load during the day and more at night, the PV power needs to be stored during the day and used at night, it is better to use DC coupling, the PV module stores the electricity to the battery through the controller, the efficiency can reach more than 95%, if it is AC coupling, the PV first has to be turned into AC power through the inverter, and then into DC power through the two-way converter, the efficiency will drop to about 90%.

battery bank backup for home

To summarize whether a DC or AC battery storage system is better for you depends on several factors, such as

  ● Is it a newly planned system or a storage retrofit?

  ● Are the proper connections left open when installing an existing system?

  ● How large/powerful is your system, or how large do you want it to be?

  ● Do you want to maintain flexibility and be able to run the system without a solar batteries storage system?

Use Home Solar Batteries to Increase Self-use

Both solar battery system configurations can be used as backup power and off-grid systems, but you will need an inverter designed for stand-alone operation. Whether you choose a DC battery storage system or an AC battery storage system, you can increase your PV self-consumption. With a home solar battery system, you can use the solar energy already backed up in the system even if there is no sunlight, which means you not only have more flexibility in the timing of your electricity consumption, but also less dependence on the public grid and rising market prices. As a result, you can reduce your electricity bill by increasing your percentage of self-consumption.

Are you also considering a solar system with lithium-ion battery storage? Get a free consultation today. At BSLBATT LITHIUM, we focus more on quality and therefore use only high-quality modules from top LiFePo4 battery manufacturers such as BYD or CATL. As a manufacturer of home batteries, we will find the ideal solution for your AC or DC battery storage system.