Solar Power Rocks logo

Solar Power Rocks - Clear info on home solar power rebates, tax credits, and other benefits

Is a DC or AC battery right for your solar home?

Avatar for Ben Zientara
Published on 04/07/2020 in
Updated 04/07/2020
A DC-coupled battery system

Solar batteries come in two flavors, DC and AC coupled, which differ in how efficient they are and how they connect to your solar panels and the grid. If you’re adding a battery to an existing solar installation, it’s almost always more cost-effective to choose an AC-coupled battery. If you’re getting a new solar+battery installation, DC coupled solar batteries are almost always more efficient and simpler to operate.

But what’s the difference between AC and DC coupling, and which one is best for you? Let’s find out:

How Solar Homes Use AC and DC Electricity

Direct current (DC) electricity means electrons flowing in one direction to provide power to a circuit. Alternating current (AC) electricity means electrons flowing in two directions, switching rapidly. The reason we have AC electricity is it’s cheaper and safer to transmit over long distances, and therefore many of your home’s appliances were built to use it.

Solar panels create DC electricity, which in a home solar system flows into a box called a solar inverter, which changes the DC electricity to AC electricity your home’s wires carry to outlets and appliances. Batteries also store and transmit direct current (DC) electricity, and they also need to be connected to an inverter, too.

Solar battery banks can add flexibility and peace of mind for homeowners. You can use them to back up your whole home in the case of a power outage, or choose just enough batteries to keep critical loads up and running.

DC-Coupled Solar Batteries

When a battery is installed alongside a home solar system, the solar installer can install special equipment that first connects the solar panels to a charge controller, then to a battery bank, then a solar inverter, and finally to the home’s main electrical panel. This is called DC-coupled battery backup, because the battery is charged and discharged using DC electricity.

Some batteries commonly used in DC-Coupled systems include the 400V LG Chem Resu Lithium ion battery, SimpliPhi’s Lithium Ferrous Phosphate batteries and Trojan’s Flooded Lead Acid batteries.

Here’s a diagram of a DC-coupled solar battery system:

Diagram of a DC-coupled solar battery backup system, showing how the solar panels send DC electricity through the charge controller to the batteries.

Advantages of DC-Coupled Batteries

  • More efficient, because there is no conversion of DC to AC until after the batteries charge.
  • Makes it easy to charge the batteries from solar panels, even when the grid is down.
  • Many popular DC-coupled batteries can be installed as AC-coupled systems by adding a battery-based inverter between the main panel and the battery.

Disadvantages of DC-Coupled Batteries

  • DC Coupling is not available for pv systems that use microinverters
  • If the inverter fails, both the batteries and solar panels won’t work
  • DC-coupled batteries are more difficult to add to an existing solar installation

AC-Coupled Solar Batteries

For a long time, DC-coupled batteries were the only kind available, but more recently, people who already have solar panels needed an easy way to add battery backup in case of power outages and mandatory shut-offs.

For people who already have solar attached to a grid tie inverter or microinverters, a DC-coupled battery doesn’t usually make sense. Why install expensive new equipment that replaces what’s already working? Instead, current solar owners can add AC-coupled battery storage to an existing solar system.

Unlike a DC-Coupled system, an AC-coupled battery has its own inverter, which means it produces AC output that goes directly to your home’s main panel. Special wiring allows the battery to charge from the grid or your solar panels, and also maintain backup power if the grid goes down.

Popular AC Batteries include the Tesla Powerwall II, Panasonic EverVolt AC, and the Sonnen Eco.

Here’s how an AC battery system all connects together:

Diagram of an AC-coupled solar system, showing a separate battery attached on the AC side of the main panel

Advantages of AC-Coupled Batteries

  • Relatively easy to add to a home because they come with all the hardware necessary
  • Can be added to a home with or without solar panels
  • If something goes wrong with your solar panels or inverter, the batteries can keep working, and if something goes wrong with your batteries, the solar panels can keep working

Disadvantages of AC-Coupled Batteries

  • Less efficient than DC systems, because the electricity needs to be converted from AC to DC for charging, then back to AC for use in the home.
  • Additional hardware means more parts that can fail and cause problems

There’s a lot more to learn, and if you want to see if a solar battery is right for your house, get the process started with our new solar panel calculator today!

Last modified: April 7, 2020

2 thoughts on “Is a DC or AC battery right for your solar home?

  1. Dear Ben the point of disadvantages that DC Coupling is not available for pv systems that use microinverters. Is not correct we have demonstrated that with DC microconverters it’s easy to do this.
    see https://dc.systems/applications/building/8-main/133-circl-pavilion-of-abn-amro-bank by using 535x DC microconverters connected to a 350V bus. On that bus we have installed 3 active front ends of 50kW with a 100kWh battery bank connected to the same DC link of 350V

    1. Avatar for Ben Zientara Ben Zientara says:

      Thanks for the info, Harry. Looking forward to following your progress!

Have anything to add?

Your email address will not be published.


Subscribe to get solar news

The Federal Solar Tax Credit Has Stepped Down. It Steps Down Again In:

Days
2
2
1
Hours
0
0
Minutes
5
7
Seconds
5
9
Learn more about the Federal Solar Tax Credit before it goes away.

Solar Power Rocks is a Wave Solar company

Wave Solar Logo