The unfortunate truth is that the grid is reliable until it isn’t, and not having electricity is a modern inconvenience. You already have solar power, but you need power in the event of a blackout. Now what do we do?
What if we told you that you could add emergency backup batteries without throwing away your existing system? This process is called AC coupling.
Why can’t grid-connected solar systems provide power during power outages?
The main reason a grid-connected solar system doesn’t provide power when your utility goes out is for safety. Electrical codes require the inverter to shut down automatically when the power is cut off from the grid. It is important to turn off the inverter because it is not safe for the power generated by your panels to enter the grid while line crews try to restore utility power to your community. This means that if you want to get power during an outage, you will need backup power sources, such as generators or backup batteries, which cannot feed back into the grid.
What is AC coupling?
Ac coupling is a method of adding backup batteries to existing grid-connected solar power generation systems. Your existing system stays the same, except when your utility goes out, your grid-connected inverter is powered through an attached battery inverter that is connected to energy storage (battery). This new inverter uses electricity stored in a battery pack to power your home when there is no utility power.
How does AC coupling work?
Battery-based inverters connect to an electrical subpanel that contains the circuits for all the loads you think you must use during a utility outage. When the battery-based inverter detects a grid failure, it automatically cuts power from the grid and starts powering your base load from the battery.
What if the grid goes out during the day?
The transfer switch automatically cuts you off from the grid and connects to your baseload subpanel. Your battery-based inverter starts supplying power from your battery, and your grid-connected inverter perceives it as “utility” power, so it keeps running. When the sun comes out, your solar panels charge your battery, and your baseload is powered by your battery. Once grid power is restored, your battery inverter is shut down, and your grid-connected inverter is reconnected to the grid to provide normal power for your entire home.
What if the power goes out at night?
It’s like having no electricity during the day, except your solar panels can’t charge the battery. Instead, your baseload will use the electricity stored in the battery until the panels produce electricity again.
How big does my battery pack need to be?
The size of the battery pack depends on the base load you want to keep working during a power outage. Some base loads may include; Refrigerator/freezer, well pump, cell phone charger, CPAP machine, septic pump and some lights. Backing up all the load at home is hardly cost effective.
Ac coupling – Is it really that simple?
It is certainly possible to later integrate the battery into a grid-connected system, but unfortunately AC coupling has some drawbacks to consider. There are design limitations to integrating the size of a hybrid system into an existing array, and it is sometimes not possible to use an entire solar array for battery charging without significant and often prohibitive expense.
Conclusion
In short, it is not ideal to design “out of the gate” in this way, because under the road, you install a completely separate inverter and battery pack, and you may only be able to integrate a few solar arrays. If you know you’re going to use solar power as a backup battery, it’s always easiest and most economical to do these things at the same time. However, if you already have an array, AC coupling can provide you with all the comfort and convenience you want when your grid goes out.
