AC Coupled Battery Storage System

AC DC solar battery options

When a home has an existing solar system, an AC Coupled storage system is often the most economical. Solar systems produce DC power. The inverter — whether a string inverter, like SMA or SolarEdge, or microinverters like Enphase — change that to AC power, match our utility grid. 

An AC Coupled battery system, like a Tesla PowerWall or Enphase Encharge, take that AC power after the inverter, and change it back to DC electricity via a built in inverter (or microinverters in the case of Enphase) to store it on a DC battery. Then when the energy is needed, it is again, changed back to AC. Each time we change energy from AC to DC to AC we call that a round trip. The typical round trip loses about 10% of the stored energy. While that is not the most efficient way to do it, it costs the least. Changing an existing solar system to support a DC coupled battery requires replacing many components with extra cost.

If possible, go with a DC coupled storage system

One other disadvantage of an AC coupled system is that the battery cannot control the output of the solar system (it can only turn it on and off). If during a grid outage, the solar system is producing 5,000 watts. If the battery is full, and the home only needs 2,000 watts of power in real time. There is no place for the extra 3,000 watts to go. The AC coupled battery, shuts off the solar system and the energy is instead taking from the battery.

This is a less than ideal scenario where solar power is lost. DC coupled systems do not have this limitation. Also, Enphase’s Ensemble system, while AC coupled, doesn’t have this limitation when installed with their microinverters. 

Discover more reasons to install solar with a DC battery storage system.