Let's get technical!
In electrical terminology, a solar inverter “inverts” DC power to AC power.
DC power is “direct-current”, which is the power stored in batteries. AC power is an “alternating current”, which cannot be stored in batteries. We should note: Some companies market “AC Batteries”, however, this is a marketing term and is not technically accurate.
Your solar panels on the roof produce DC power, which is then “inverted” to AC power. AC power is what the utility company sells, and therefore what homes use.
If you’re designing from scratch, we prefer DC-Coupled equipment when designing your system. There is some loss when inverting DC to AC (or AC to DC), so we attempt to minimize this loss in our design process. Also, it eliminates unnecessary expenses.
AC-Coupling is when an inverter can take AC power from another inverter and pass it through to the grid (sell back to utility), power your house in the event of a power outage, and charge the batteries by “converting” AC to DC power. Changing AC to DC requires a “converter”, while DC to AC requires an “inverter”.
Why is this important to you?
1. If you are starting from scratch, make sure your inverter has the ability to AC Couple. This will allow you to add more solar in the future using micro-inverters (such as Enphase) or a central inverter (such as SMA). For instance, you may only want to add (5) panels, in which case micro-inverters would make the most sense.
2. If you already have solar, AC Coupling is a benefit because you can use your existing technology and simply add an "off-grid" capable inverter to utilize your solar system. We have done this many times with various systems, including Solar Edge, SMA, Enphase, and others. Generac PWRcell and Sol-Ark work great in these situations.
Solar terminology can be confusing, so hopefully, this helps define AC-Coupling for our existing and future clients. Contact us if you’d like to receive a free 1st draft design and proposal!