AC Coupling Vs. DC Coupling: What's the Difference?

Homeowners and businesses are going solar as electricity prices rise. Today, you also have the solution for the excessive energy produced by solar panels - a battery storage system. It is pocket-friendly, reduces carbon footprint, and offers consistent energy.

There are two popular options for coupling storage setup: AC and DC coupling. While most believe a DC-coupled system is better in efficiency, oversizing, and affordability, this is not always true. In cases where you want ease and flexibility, AC coupling might be better.

So, AC-coupled or DC-coupled storage solutions; which is better? If you are confused about choosing the right storage setup for your specific energy needs, don't worry and keep reading.

What is AC coupling?

An AC-coupled solar battery is an energy storage solution in which the battery is connected to the grid using an AC (alternating current) connection. In this process, the power is inverted three times in one cycle.

Let's understand this in simple terms. In an AC-coupled system, your solar panel directs DC electricity into an inverter. This inverter converts the DC power into AC electricity to run your home appliances.

However, if the energy is not needed, it flows directly into another inverter. The second inverter converts the AC into DC power so the battery can store it. Later, when the energy is required, the system again inverts it into AC electricity so the appliances receive safe power.

AC batteries usually have a lithium battery module, which includes a battery management system and an inverter. Hence, they are compact and easy to install. That said, AC-coupled solutions are relatively new and not widely used due to energy losses during repeated conversions.

What is DC coupling?

A DC coupling storage solution involves storing energy directly from your solar panel to the battery without any conversion. Unlike an AC-coupled setup, it only transforms the DC power into AC once to power the appliances.

Let's simplify it. In a DC-coupled solar battery system, the DC energy produced by your solar panel directly flows into the charge controller. This controller feeds the power into your solar battery without any conversion.

Once done, the inverter next to your battery converts the energy into AC power. This means all the energy from the solar panel is being used to power your home appliances.

As the power is only once inverted, there are minimal power losses, and DC-coupled battery systems offer more efficiency. Moreover, such systems provide off-grid backup solutions in cases of emergencies.

AC vs. DC coupling: Key differences explained

Let's get this straight before diving into the AC vs. DC coupling. Solar panels produce energy in DC form, whereas our house appliances run on AC power. Hence, an inverter is used in solar installations to convert DC energy into usable AC power.

This is where our most obvious difference lies when it comes to AC-coupled vs. DC-coupled storage systems - the number of inverters and energy conversions. An AC-coupled setup requires two inverters: one to convert the solar panel energy (DC) to power for home appliances (AC) and the second to charge the batteries, one time each. Hence, AC coupling involves inverting powers three times before use.

In comparison, DC-coupled systems do not require converting the DC power from the solar panel, as it directly feeds it into the battery. Hence, only a single inverter is needed to convert the DC power into AC, which runs the appliances. Similarly, unlike AC coupling, the system undergoes only one conversion.

Another key distinction when comparing AC coupling vs. DC coupling systems is the need for a charge controller. This controller limits the electricity entering the battery, which protects it from damage and overcharging. As the DC-coupled system produces surplus energy, using a charge controller is a must, which is not the same in AC batteries.

It may sound tricky, but both systems have advantages and disadvantages, making them less or more suited to different applications. So, let's look at each setup's main pros and cons so you can determine which is best for you.

Pros and cons of AC-coupled systems

Pros of AC-coupled battery systems

• Ease of Installation:AC-coupled battery setups are easy to install, especially when retrofitting storage into an existing system. They are also simple to integrate with your house's existing wiring, which means less labor and a low installation cost.
• Flexibility: AC batteries are also more flexible when deciding the installation location. You can choose to place the inverters farther from the batteries.
• Versatility: In an AC-coupled system, the battery can be charged using both the grid and solar panels. So, even if the solar panels are not generating enough power, the grid can directly refill the battery.
• Reliability: Considering that an AC-coupled setup can incorporate multiple inverters and batteries in several locations helps you recover in cases of a power outage. All the inverters provide more combined power and do not influence energy generation.

Cons of AC-coupled battery systems

• Low efficiency: The energy in the AC-coupled systems is inverted three times. Each conversion results in power losses and ultimately makes them less efficient.
• Affordability: Despite low installation costs, AC battery solar storage is costly due to the equipment investment.
• Power supply limitation: The AC systems do not have a transformer and are not used off-grid. Hence, they are inefficient at managing surplus load from several appliances.

Pros and cons of DC-coupled systems

Pros of DC-coupled systems

• Cost-effective: DC-coupled solar storage setups are cheaper than their counterparts, as they demand a single inverter and less equipment.
• Greater efficiency: Unlike AC battery coupling, DC-coupled systems convert power once during each cycle. This reduces energy losses and makes them more efficient.
• Oversizing: DC batteries let the solar panels generate more electricity than their inverter ratings. The produced energy can power the EV charger, battery, etc.
• Backup power during outages: AC and DC coupling setups both offer backup power. This allows you to use excess energy to meet your power needs during emergencies.

Cons of DC-coupled systems

• Lacks flexibility: In a DC-coupled setup, the inverter must be close to the battery. Therefore, you are left with a few installation options. Expanding a DC system is also challenging, as the components demand compatibility with the existing structure.
• Less resilient: DC storage systems use a single inverter. So, if the inverter fails, you will lose both the battery capacity and the solar panel energy.

Which coupling system is right for you?

Though both AC and DC-coupled battery storage solutions are great for residential users, there are a few things to consider.

• AC systems are easily integrated with existing solar panel systems, whereas DC coupling demands specific components compatible with the existing structure.
• DC-coupled systems offer high efficiency due to minimal energy losses. Compared, AC coupling is characterized by prominent power losses due to conversion.
• AC battery storage is complex and involves more equipment than a DC alternative.
• You can easily expand and upgrade an AC battery storage setup by adding more solar panels and batteries. Due to compatibility issues, the same is not possible for DC batteries.
• Homeowners who want to improve their solar setups might prefer AC coupling. However, DC coupling is a better option if you prioritize efficiency and planning for off-grid living.

AC vs. DC coupling: Common cases

Now that we know what to consider when choosing the right coupling storage, let's put this into practice. Below are two situations where homeowners benefit from each of the coupling storage solutions.

In the first scenario, we have a California homeowner who already has an existing grid solar system. He/ she can best benefit from AC coupling. It will be cheaper and quicker to install. Here, adding an inverter to manage your battery will avoid the complex rewiring.

A compact and efficient inverter charger like the Renogy 3000W Pure Sine Wave Inverter Charger might help in this situation. It can deliver up to 9000W in the grid. Plus, you can connect this inverter to both the grid and the battery bank as you like. Pairing this with the Renogy LiFePO4 battery can help you improve energy storage safety and efficiency.

 

Now, for the second situation, we have a person considering setting up an off-grid cabin in Colorado. Here, a DC-coupled system would work better, as there is no existing grid structure and you would need maximum efficiency. The DC coupling will ensure minimal energy loss and you will have a reliable power supply, regardless of the limited resources.

This situation calls for a few components, like the Renogy 48V solar inverter charger. It is compatible with most batteries and has a power-saving mode for convenience. The good part is that it offers continuous energy even if other charging methods fail. Pair this with the Renogy 48V LiFePO4 battery and MPPT charge controller to get an uninterrupted power supply.

Conclusion

So, AC coupling vs. DC coupling: which is better? If you are still asking yourself this, know there is no right answer. The correct decision lies in your needs and preferences.

For instance, if your house already has solar panels installed and you just want to add a storage facility, AC coupling is the solution. In contrast, a DC-coupled system will work if you plan an entirely new solar system installation and want a storage facility.

Stay calm and make a checklist of your requirements to reach the right conclusion.