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 youâ€™re adding a battery to an existing solar installation, itâ€™s almost always more cost-effective to choose an AC-coupled battery. If youâ€™re getting a new solar+battery installation, DC coupled solar batteries are almost always more efficient and simpler to operate.
But whatâ€™s the difference between AC and DC coupling, and which one is best for you? Letâ€™s find out:
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 itâ€™s cheaper and safer to transmit over long distances, and therefore many of your homeâ€™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 homeâ€™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.
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 homeâ€™s main electrical panel. This is called DC-coupled battery backup, because the battery is charged and discharged using DC electricity.
Hereâ€™s a diagram of a DC-coupled solar battery system:
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 doesnâ€™t usually make sense. Why install expensive new equipment that replaces whatâ€™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 homeâ€™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.
Hereâ€™s how an AC battery system all connects together:
Thereâ€™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