AC Coupled vs. DC Coupled: The Great Solar Power Systems

FACTS CHECKED BY  Bob Smith

When planning your construction project, deciding between an AC-coupled vs. DC-coupled solar power system can significantly impact several things. Since it is so important, you may wonder: How do Direct Current and Alternative Current differ? We will discuss the differences between AC coupled vs. DC Coupled to help you make an educated choice for your project.

What is an AC Coupled System?

Inverter with manual switches

Inverter with manual switches

An AC-coupled system is the most common type of solar system. It uses a grid-tied inverter to convert DC power from the solar panels into AC power for use in the home. Solar panels generate DC power which they feed into an inverter, which converts it into an alternating current that powers appliances in your home. However, this system requires an additional inverter. 

AC Coupled vs. DC coupled: DC Coupled Systems.

As we’ve seen, the connection to the batteries is vital when comparing an AC-coupled vs. DC-coupled system. The DC Coupled solar power system is one in which the solar panels are directly connected to the battery bank. A DC cable connects the panel and battery bank, so all the energy the panels produce goes into charging the batteries. 

A DC Coupled system only requires one multimode inverter. It converts DC power from the batteries to AC power for home use. The inverter also supplies power to the utility grid when your batteries are fully charged.

AC Coupled vs. DC Coupled: What is the difference?

The main difference between AC Coupled vs. DC Coupled systems is the number of inverters. The AC coupled requires a PhotoVoltaic panel inverter and a battery inverter, while the DC only needs one modulated inverter.

Advantages of AC Coupled

Retrofitting – Scaling an AC-coupled battery system is relatively simple. This is because technicians connect the batteries to the end of the system. Therefore, you will not need to redesign your solar panel power system to increase your battery capacity.

Flexibility– The main advantage is that you can pair it with any photovoltaic panel and inverter, including microinverters. The only requirement is that the voltage is compatible with your home’s electrical system. 

Adaptability to power volatility– AC solar battery packs can recharge using power from the national grid. This happens in case your PV panels need to generate more power. 

Redundancy-This is the ability to continue operations using a secondary system when the primary system fails. The two inverters in an AC Coupled system allow it to automatically switch to power from the grid if one of the inverters fails. Combining inverters also increases the overall capacity of your system.

Solar batteries in a garage

Disadvantages of AC Coupled System

  • The three-fold power conversion in an AC Coupled circuit means you lose much power. Each conversion loses you a couple of percentage points which add up to a significant kW of power after some time.
  • AC-coupled circuit costs more than a DC-coupled system because it requires two inverters.

Advantages of DC Coupled System

  • Efficiency-  DC Coupled systems only convert power to AC once. Therefore, the DC-coupled system is relatively more efficient and loses less power during conversion. The efficiency of battery charging hits up to 99% in a DC Coupled system.
A DC Coupled System

A DC Coupled System

  • Simplicity- Because there is no need for AC/DC conversion, wiring is simpler and easier to install, which reduces costs and makes maintenance easier. Wiring also lasts longer since it does not have to withstand voltage fluctuation from the changeover from AC to DC back again.
  • A DC Coupled battery storage system works well even in an off-grid setup. 
  • If your DC Coupled setup produces less than 10kW of power, you are eligible for net metering. Therefore, you can get back as many power credits as you transfer to the electric grid.
  • DC Coupled systems are perfect for powering DC appliances. Home appliances convert AC power to DC, and switching to a DC circuit system will make you more energy efficient.
  • Ultimately, a DC Coupled system is cheaper to install as it only requires a single inverter. As a result, installing the solar panel power system requires less wiring and labor during installation.

Disadvantages of DC Coupled Circuit System

  • Adding batteries or solar panels to this setup is a complex process. Therefore, it is more expensive to retrofit.
  • The system requires a voltage controller. Some modern battery packs are not compatible with solar controllers, reducing the viability of DC Coupling in modern solar power systems.
  • This type of circuit is battery intensive. All the power in a DC Coupled system first goes through the batteries before powering your house with little grid support. Therefore, batteries have a shorter lifespan.

Which is best for you?

DC Coupled solar power systems are better for small home setups. They offer more value for money since they’re cheaper. This setup is also easy to install, with only a few complications when you want to scale up. Its efficiency also gives you more kWh than a similar AC Coupled setup.

Summary

Choosing between an AC-coupled vs. DC-coupled system boils down to your application demands and budget. Understanding which is better for your project is only half the battle, and you also have to know how and where to implement it in your system design. More importantly, whichever way you choose, make sure you use the correct type of inverter for whatever system you are trying to hook up to your panels.

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