Energy storage systems for solar are becoming more popular. People want to have back-up power during power outages and changes in net metering and time of use electric rates can give energy storage options a better payback. When going solar, many people feel pressured that they must make the decision about energy storage up front. But the truth is that adding energy storage to an existing grid-tied system is easy.
The best part is that you do not have to remove or change any of your existing grid-tie system when you add batteries. This surprises many people who understand traditional solar power systems with batteries, but it is all about DC coupling versus AC coupling. For many years, solar with energy storage was always set up as a DC coupled system. Solar panels were connected to a charge controller which managed the solar power going into the batteries and kept the batteries from being overcharged. The power from the solar panels and the batteries is all DC, hence the term DC coupling. Then a battery-based inverter was used to convert the DC power from the batteries to AC power to feed the loads. This technology is all still used for some systems, but it is no longer the only option.
This is great news for anyone who has grid-tied solar already installed and wants to add energy storage. Grid-tied systems have the solar panels connected to an inverter (or microinverters) that change that DC power from the solar to AC power from the loads. These grid-tied inverters do not work with batteries, and until the last decade, installing a battery system meant removing that grid-tied inverter and replacing it with a charge controller and battery-based inverter. But now there is a better way that is rapidly gaining popularity and it is called AC coupling.
In an AC coupled system, you connect the AC output of a battery-based inverter to the AC output of a grid-tied inverter. This will work with any grid-tied inverter or microinverters, but you must be careful in your choice of the battery-based inverter as it needs to have the right functionality. Inverters like the Outback GS Radian are specially designed with AC coupling in mind. Outback even packages it with batteries as a complete kit to make the choice easy.
If you have a grid-tied solar system, you probably already know that it does not work during a power outage. The reason for this is that grid-tied inverters will not make
AC power unless they have AC power coming to them from the grid. When you install the battery-based inverter, it creates AC power that is exactly the same the grid. The grid-tied inverter sees this AC power and syncs up with it.
But the real magic is what happens next. The battery-based inverter takes that AC power from the grid-tie inverter and uses it to charge the batteries. More importantly, the battery-based inverter must regulate the charge to the batteries so they don’t get overcharged. That is why a specially designed inverter like the Outback GS Radian is required.
One last thing that must be said is that when you add the energy storage to your grid-tied system, it must be designed so that power is not fed to the grid during a power outage. This is accomplished by simply making what we call a “backed-up load center”. You choose the loads that you want to have running during a power outage and put them on a separate subpanel. This backed-up load center must be isolated from the grid by the battery-based inverter. When the grid is on, these backed-up loads are powered by the grid and your solar just like all your other loads. When the grid goes down, these backed-up loads are powered by your solar and your battery-based inverter.
So relax, take the pressure off yourself, and feel free to install your solar without worrying about the energy storage option. Adding it later is as simple as buying the pre-packaged Outback solar kit whenever you decide the time is right.