DC Coupling VS. AC Coupling, How to Choose the Right ...

A PV energy storage system includes solar modules, controllers, inverters, batteries, loads, and other equipment. Today there are various technical routes, but whatever it is, the energy needs to be collected at a certain point. There are mainly two topologies in the market: DC coupling and AC coupling. Then you might ask: which configuration should be more preferred, AC or DC coupling? Today we are going to reveal the pros and cons of both.

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DC Coupling

As shown in the figure below, the DC power generated by the PV module is stored in the battery pack through the controller, and the grid can also charge the battery through the bidirectional DC-AC battery inverter. The gathering point of energy is at the DC battery end.

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 electrical appliance load, the battery will release the power, and the current is determined by the load. The energy storage system is connected to the grid. If the load capacity is small and the battery is fully charged, 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 PV power generation and load power consumption are not stable, it is necessary to rely on the battery to balance the energy of the system.

 AC Coupling

 

As shown in the figure below, the direct current generated by the PV modules is converted into alternating current through the inverter and is directly fed to the load or sent to the grid. The grid can also charge the battery through a bidirectional DC-AC inverter. The gathering point of energy is at the AC end.

The working principle of AC coupling: It includes a PV power supply system and a battery power supply system. The PV system consists of PV arrays and grid-connected inverters; the battery system consists of battery packs and bidirectional inverters. 

These two systems can either operate independently without interfering with each other or can be separated from the large power grid to form a micro-grid system.

 

Applicability Comparison of DC Coupling and AC Coupling

 

In a DC coupling system, the equipment is connected in series, with a close connection and respectively poor flexibility. While The AC coupling system is connected in parallel, with less contact and better flexibility. As a matter of fact, AC coupling is more suitable to apply to the situation where grid-connected inverters have already been installed and users want to upgrade to the energy storage system, and DC coupling is more for building a new system.

 Application of DC Coupling in the HPS System

 Our HPS is a hybrid inverter, which integrates a PV controller and a battery bidirectional inverter. The electricity generated by PV modules can be used to charge the battery through the MPPT controller, and can also be converted into AC for load use. When the PV power generation is not enough to support the load, the battery discharges to make up for the insufficient energy. The HPS can also be connected to the grid as needed, and the grid can be used to charge the battery or supply the load. In the HPS system, the gathering point of energy is the battery. Our HPS has the function of on-grid and off-grid auto-switching. It can meet the needs of most users. Limited by hardware, the PV controller of HPS can only connect PV panels with a certain capacity.

 

Application of AC Coupling in the HPS System

 

Due to historical reasons, many customers used to install grid-connected inverters. As we all know, the operation of grid-connected inverters must have a reference voltage. Once the power grid fails, the grid-connected inverter will stop running. And our HPS can run off-grid. Therefore, many customers ask, since HPS can run off-grid, if there is a solution to let the grid-connected inverter refer to the output voltage information of HPS to generate power. In this way, the original PV power generation system can be utilized to reduce investment costs. The answer is yes. This requires the aforementioned AC coupling. The specific method is to connect the grid-connected inverter to the load end of the HPS, and after the grid-connected inverter matches the communication protocol of the HPS, it will adjust the power generation of the grid-connected inverter according to the instructions of the HPS. In this way, the idea that grid-connected inverters can also be used in off-grid conditions is realized.

 Application of DC Coupling in the PCS System

 

The application of DC coupling in the PCS system is obvious. As shown in the figure, the power generated by the PV module is charged to the battery through the PV controller PBD, and can also be converted into AC power through the PCS to supply power to the load or to the grid. Different from HPS, in the DC coupling system of PCS, the PV controller PBD and the bidirectional inverter CS are separated, and the user can configure the appropriate number of PV controllers PBD and batteries according to the needs in order to obtain the maximum economic benefits.

Application of AC Coupling in the PCS System

 

Regarding the application of AC coupling in the PCS system, we have already taken it into consideration when designing the product. There is a PV inverter interface on the bypass cabinet, which is specially used to connect to the grid-connected inverter. Similarly, the grid-connected inverter needs to match our inverter communication protocol. At present, the inverters that can communicate directly with our inverters are limited to some of the brands that are members of SUNSPEC.

From above we can see that ATESS products can be used for both DC coupling and AC coupling, and the right solution is project specific. ATESS mainly focuses on DC coupling systems and has accumulated rich experience in this field. But also, we can provide AC coupling solutions as per customer demand.

 

Recommended article:
Guide to designing off-grid and hybrid solar systems
AC vs. DC Coupling Energy Storage Systems
Malaysia Battery Market Size & Share Analysis

For more information, please visit High surge capacity grid connected inverter.

Through this article, you must have gained a clear understanding of these two coupling methods, if you still have questions when designing your system, please keep in mind that ATESS is always here to help.

 

 

  

 

 

 

With the advent of microinverters, people are on the lookout for hybrid solar systems that can work with batteries. In fact, there are companies that have already launched microinverter battery backup systems into the market. So if you are wondering if microinverters can team up with batteries, the short answer is yes! 

However, the process is a bit complicated and technical. Let’s find out how the two work with each other!

Are Microinverters and Batteries Compatible?

Microinverters can definitely work with battery backups. You just have to employ a method known as “AC Coupling,” in which an AC battery inverter is used to link the batteries straight to the switchboard’s 240V AC.

The ability to divide the power flow between the grid and the backup system with microinverters is one benefit of employing the AC-coupled system. The size of the storage capacity can be adjusted with the use of microinverters.

For example, certain branch circuits can only connect to the main panel, while others can link to the sub-panel that the battery inverter supplies. The complete array is qualified for net metering credits even when parts of the microinverters are linked to the battery. However, because they are segregated from the essential loads’ panel, which is powered by the battery inverter, the microinverters attached to the main panel will stop producing if the grid goes down.

The battery inverter must be sized for the maximum AC output from the PV system that is connected to the essential loads’ panel. You need to ensure that the battery inverter system can handle the entire array’s AC output. Remember to choose a number of microinverters for these systems that are equal to or less than the kW capacity of the battery inverter. Then, place the remaining microinverters on the main panel.

How Do Microinverters and Batteries Work With Each Other? 

To understand the working of AC coupling, let’s first understand some fundamentals. 

The primary difference between Grid Connected and Off-Grid solar power systems is that off-grid systems need to store the energy in batteries. 

Historically, a regulator was the main tool used to control overcharging. It absorbs DC power from the energy source, analyzes how the battery is responding, and makes necessary adjustments. 

If the system has a 240V AC energy source, a battery charger is often used, which serves the same purpose but in a slightly different method. 

When the batteries are fully charged in either scenario, the regulator or charger will stop providing energy.

If you have Direct Current (DC) equipment, you can use the energy once it is stored in the batteries. However, in most situations, an inverter transforms the DC power to 240V AC, just like the main power.

Inverter manufacturers realized many years ago that it made sense to combine these into a single unit and created the off-grid inverter. These were often made to accept a range of inputs and outputs, including AC input from generators, DC input from batteries, etc. Generally, a regulator was still used to link the batteries to solar panels and other equipment.

Although it took some time, manufacturers discovered that they could use grid-tied inverters to convert the solar input to AC, which led to the creation of AC Coupling to simplify things.

Management, monitoring, and efficiency were optimized by mounting everything on an AC Bus, excluding the battery. Transmission losses were minimized, cable sizes were lowered, and flexibility was increased despite an increase in electronics cost.

So, what is the actual working process of this type of system?

In this kind of system, branch circuits are merged at a gateway combiner box while microinverters are connected to the modules. They are then supplied to a panel for important loads that is also wired to a battery inverter. This battery inverter is in charge of controlling the energy flow to the batteries and, in the event of a failure, simulating the grid’s frequency to maintain PV production. 

In order to isolate the essential loads’ panel from the grid and to separate from the grid input when the grid goes down, the battery inverter uses an internal contactor.

You can set up the system to include an external ATS on the grid side of the MSP to directly power the main service panel. 

From a safety standpoint, grid-connect inverters constantly look for a 240V AC reference source and are built to shut down if it’s not available. Thus, in a non-mains connected AC coupled system, a reference point must be established in order to deceive the Grid Connect inverters into thinking that the current is real. 

The inverter charger can accomplish this by generating 240V AC from the battery or by using additional sources (such as a generator) if they are available. In any case, as you could expect, this requires some rather complex controls to be done securely and consistently.

If the inverter and battery are large enough to carry all the loads and surge loads on the MSP, it may be unnecessary to use a separate critical loads panel. When a customer wants to power the main service panel, an external ATS is necessary; however, this comes at an additional cost and with more complexity.

Therefore, logically speaking, these kinds of systems can be connected with microinverters that offer solar as an AC source. All of your AC solar panels only require a simple solar panel and grid tie inverter swap. You won’t be left in the dark if you get a microinverter-based system because all you’ll need is an AC-linked system if you decide to add batteries in the future. 

Conclusion 

Microinverters can team up with batteries using AC coupling technology. If you are seeking a reliable and trustworthy company to get bulk microinverters, you should contact Beny today! They will help you get the best solutions for your business.

The company is the world’s best Compact single phase string inverter supplier. We are your one-stop shop for all needs. Our staff are highly-specialized and will help you find the product you need.