Three manufacturers dominate the grid-tied, battery-backup inverter market: OutBack Power Systems, Schneider Electric (formerly Xantrex), and SMA America. Each company offers an inverter—some with different AC outputs or in different configurations—that is listed to UL Standard 1741 for grid interconnection and has battery-based capabilities.
OutBack Power Systems
OutBack Power experienced early adoption in the off-grid market because its equipment had features and operations not yet filled by other inverter manufacturers. It soon became a player in the grid-tied with battery backup market niche with its GTFX, GVFX, and, more recently, SmartRE products.
The GT stands for grid-tie; the GV is the higher-powered, vented model—both are variations of the rugged off-grid FX inverter. The sealed GT versions are available in 24 V, 2.5 kW and 48 V, 3 kW models. The vented versions come in 24 V, 3.5 kW and 48 V, 3.6 kW models.
All versions have single-phase 120 V output. Two G-series inverters can be “stacked” for 120/240-volt split-phase output. OutBack also produces AC and DC FLEXware panels that hold all BOS components, overcurrent devices, shunts, and bypass breakers. There are many versions of OutBack-inverter-based power panels that are pre-assembled, and tested to save labor costs and on-site assembly. At least one third-party manufacturer makes power panels that integrate with the FX series of inverters.
OutBack’s newest product—the SmartRE—provides easy installation with a quality battery backup grid-tied system. The SmartRE incarnation of the GTFX includes two AC inputs—much like the Xantrex XW. The combination of grid and backup engine generator inputs make this a very flexible unit. All four of the SmartRE models are 48 V with 2.5 or 3 kW and either 120 V or 120/240 V versions.
The company has a long history of reliable products that were the foundation of battery-based RE equipment. Its grid-tied with battery backup inverter is the XW, replacing the old workhorse SW, which was one of the first grid-tied with battery backup inverters.
The XW is a sine-wave inverter that offers split-phase (120/240 AC) voltage output and a 200% surge capacity for 10 seconds. The company offers 24 V, 4 kW; 48 V, 4.5 kW; and 48 V, 6 kW models. Any of these models can be stacked with one or two other inverters of the same type to double or triple the output capabilities. All models can accept two AC inputs—the first AC input will typically be the grid; the second may be a backup engine generator. Adding a generator can minimize battery and PV costs, since you can design for fewer days of autonomy and a smaller charging source.
The XW can be purchased with a complete integrated AC/DC power distribution panel for up to three parallel inverters and four XW MPPT 60-150 PV charge controllers.
SMA America’s Sunny Island is an off-grid inverter that can function as a battery backup grid-tied inverter—but that’s not all. It can be installed with the company’s Sunny Boy batteryless grid-tied inverter, allowing the Sunny Boy to continue to produce power even while the grid is down.
One of the Sunny Island’s outputs is wired into the same subpanel containing the grid-tied inverter’s output and all of the backed-up loads. The other Sunny Island output backfeeds a breaker in the main load center. When the grid is present, the Sunny Island can charge the batteries while the grid-tied inverter “sells” power to the grid. If the grid goes down, the Sunny Island disconnects from the main load center and starts to invert battery power to the backup panel. The grid-tied inverter sees the AC, and the Sunny Boy acts as if the grid is still present, continuing to produce power. The Sunny Island prioritizes powering the backed-up loads with the grid-tied inverter’s output first and will then supplement with inverted battery power if needed.
The Sunny Island output is 120 V, so if your backed-up loads need 240 V or the output of your Sunny Boy inverter is 240 V, you will need two Sunny Islands or an 120 to 240 V autotransformer between the Sunny Island and backed-up subpanel.
The Sunny Island system may not be the most cost-effective way to install a battery-backup grid-tied system—but it is the only product that is engineered to allow an existing grid-tied batteryless inverter system to add battery backup.