Grid tie solar PV systems can be built or retrofitted with battery storage that will keep your power on during an electrical grid outage. A grid-tie solar system with battery backup is most useful if you live in an area where the electrical grid is unreliable, repairs to the grid tend to take a long time, or extreme weather events are common. The typical ways to integrate battery storage into a grid-tied PV system are:
AC-coupled systems are the most common setup for grid tie solar systems with battery backup, mainly because of the added efficiency of not sending all your power through a charge controller before getting to the inverter (not to mention not needing to buy a charge controller in the first place). The video below does a great job of explaining and diagramming the differences between AC-coupled and DC-coupled systems.
Whichever coupling method you use, the other main piece of equipment that needs to be added is a secondary electrical panel connected to your designated "critical loads" that you want to stay on when the grid goes down (typically your refrigerator, well pump, HVAC system, home computer, etc.).
Rather than AC coupling or DC coupling, you can choose a standalone emergency battery backup power system like the ones below. Completely independent of your grid-tied solar system, this method of battery backup doesn't automatically activate; it's an emergency power source you can plug your critical appliances into during a power outage. While energy capacities are lower than you'd usually have with an AC/DC coupled solution, standalone systems like these are less expensive and portable - great for true emergencies.
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No! Grid-tie solar systems with battery backup are designed with exactly this in mind. In fact, adding battery storage to a grid-tied solar system is most useful for people who live in areas where either the grid is unreliable and goes down frequently or extreme weather events are common.
Yes! Battery storage can be retrofitted to an existing PV system. Usually in this case the AC Coupling method is used, and to achieve it, you will need a few new major system components — specifically a battery-based inverter (sometimes called a hybrid inverter), a battery bank for storage, and a second breaker box for your critical loads.
The video here does a great job of explaining visually the differences between the two, as well as the pros and cons of each.
Typically, battery backup capacity for a grid-tied system is limited to the number of kilowatt-hours (kWh) needed to power the critical loads you don't want to be without during a grid outage. Use our Solar Load Calculator - inputting only what you determine are your critical loads - to figure out how much battery storage you need (divide your total Watt-hours per day by 1000 to get kWh per day).
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Amy the "Solar Queen" explains the AC coupling (1:10 mark) and DC coupling (7:00 mark) methods for adding battery storage to a grid-tied solar PV system.