There are two ways that home battery backup can work with solar. It can either be AC or DC coupled. Before explaining how the systems work, it’s important to know that AC (Alternating Current) is usable in your home, while DC (Direct Current) is what your solar system will produce.
AC coupled battery systems store energy as AC. Your solar system will produce DC and convert to AC on the roof. The AC will be converted back to DC to be stored in the battery. When it’s time to be used, it will be converted once again to AC so you can use it in your home. The advantages to an AC coupled battery system are that they are easy to retrofit to existing solar systems and expand upon if you’d like to increase your battery storage. Enphase is generally regarded the best option for AC coupled battery on the market today.
DC coupled battery systems store energy as DC. The DC your system produces is sent and stored as DC in your battery. When you need to use your stored energy, the battery converts it to AC so you can use it in your home. The advantages to a DC coupled battery system are that they only require 1 conversion to be used in your home and are generally better when it comes to storing energy during the day and using it during peak demand time from the utility. Tesla’s Powerwall with the SolarEdge inverter is anticipated to be the best option as far as DC batteries go, but it has yet to hit the market.