Choosing a Battery-Based Inverter

Intermediate

Inside this Article

Magnum Energy’s off-grid inverter
Magnum Energy’s off-grid inverters have optional remote metering and now carry a standard three-year warranty. A standard five-year warranty is offered, but only if the inverter is wired and mounted on Magnum BOS systems.
The inverter is wired and mounted on Magnum BOS systems.
Magnum Energy’s off-grid inverters have optional remote metering and now carry a standard three-year warranty. A standard five-year warranty is offered, but only if the inverter is wired and mounted on Magnum BOS systems.
The OutBack Power off-grid FX series inverter
The OutBack Power off-grid FX series inverters come in vented (shown) and sealed models. The sealed model is recommended for harsh environmental conditions (high humidity and corrosive salt air). The vented model supports high AC output power in hot environments.
OutBack Power’s new Radian series inverter
OutBack Power’s new Radian series inverter can be installed in off-grid or grid-tied systems. It has an 8,000-watt output rating, and offers split-phase 120/240 VAC output and dual AC inputs.
OutBack Power’s line of GT inverters
OutBack Power’s line of GT inverters are built strictly for grid-interactive usage and are not designed to be used with a generator. Like the off-grid series, the GT models are offered in sealed and vented models.
The OutBack Flexware 1000 system integration hardware supports up to four inverters and accommodates the charge controllers.
Inverters can be stacked for higher voltage, more current, or for multiple phases. This OutBack Flexware 1000 system integration hardware supports up to four inverters and accommodates the charge controllers and all required AC and DC balance-of-system components.
SMA America’s Sunny Island inverter
SMA America’s Sunny Island inverters can be used in both offgrid and on-grid systems, and support AC coupling to Sunny Boy batteryless grid-tied inverters. (Note: Two Sunny Island inverters are required for 240 VAC output to AC-couple to Sunny Boy inverters with 240 VAC output.)
The Schneider Electric XW series inverter
The Schneider Electric XW series inverter also can be used in either off-grid or grid-tied systems. It has 120/240 VAC split-phase output and dual AC inputs. The complete XW system shown here includes AC and DC balance-of-system equipment on the power distribution panel.
Exeltech MX inverter
Exeltech MX inverters can be configured in 1 kW increments up to 20 kW at 120V; in 2 kW to 40 kW at 240 V; and in 3 kW to 60 kW at 208 V three-phase. Up to 5 kW will fit into a “cage” at 120 V. Two cages are required for 240 V (one cage for each phase), which are bolted together as a single unit. Three cages are used for 208 V three-phase.
The Apollo TSW inverter
The Apollo TSW inverters offer 120/240 VAC split-phase output/input.
Magnum Energy’s off-grid inverter
The inverter is wired and mounted on Magnum BOS systems.
The OutBack Power off-grid FX series inverter
OutBack Power’s new Radian series inverter
OutBack Power’s line of GT inverters
The OutBack Flexware 1000 system integration hardware supports up to four inverters and accommodates the charge controllers.
SMA America’s Sunny Island inverter
The Schneider Electric XW series inverter
Exeltech MX inverter
The Apollo TSW inverter

A residential battery-based inverter has a primary task of accepting DC electricity and changing it into standard, household AC electricity. This seems simple enough, but wading through the inverter specifications can be overwhelming if you don’t understand what they mean and how they pertain to your system.

Your system may have other requirements (such as battery charging from an engine generator or the grid), and figuring out which features will be advantageous often depends on the system type and specifics. With no access to utility power, an off-grid system has to supply all of the electricity at all times. A grid-tied battery backup system has access to utility power, can use the inverter to export excess electricity back to the grid, and usually supplies electricity only to specific “critical” loads during a utility outage. These are some of the differences that make certain inverter features desirable in one system type but not necessarily in the other. As you go through the specification descriptions, you will see how these differences influence the inverter selection process.

This guide includes a specifications table for available battery-based, sine-wave inverters that are listed to the Underwriters Laboratories 1741 standard and commonly used in residential applications (2 to 8 kW). The compiled data is from manufacturers and their specifications sheets.

The Specs

Off-Grid, Grid-Tied, or Both tells us what system type(s) this inverter is built for.

Rated Continuous Output Power represents the inverter’s capacity. For example, a 2,000 W inverter is rated to supply 2 kW of AC power continuously. In an off-grid system, this value determines the total wattage limit of AC loads that can be run simultaneously. You must specify an inverter with an output power rating large enough to handle all of your simultaneous AC loads.

Let’s say we want to power the following at the same time:

  • a 1,400 W microwave
  • six 15 W lights
  • a 100 W refrigerator 
  • a 120 W TV 

In this case, an inverter with a continuous output power rating exceeding 1,710 W would suffice (1,400 + 90 + 100 + 120). Surge ratings are discussed separately.

For grid-tied battery-based inverters, the power rating is examined under two scenarios—when the grid is available and when there is an outage. When the grid is up, the inverter’s job is to convert all available DC power from the renewable energy system to AC, which is used in the home. If the array output exceeds household demand, the excess is sent to the utility. The inverter capacity must be large enough to accommodate the RE system size. For instance, an inverter for a 4,000 W PV array will generally be sized at that same power rating. (However, because climate factors such as warm temperatures will limit PV array output, the array-to-inverter ratio may vary.)

When the utility is down, the inverter’s job is to supply power to all the AC loads connected to it. Most of these systems include a “critical load subpanel” so that not all of a home’s loads have to be energized, which keeps battery and system costs down. The inverter capacity must be large enough to meet the total requirement of all connected AC loads that might be run simultaneously, and large enough to handle the RE output. (See “Sizing a Battery-Based Inverter” in the Circuit: Methods in this issue.)

Comments (4)

martin sattler_2's picture

Is this article from a HOME POWER print Issue? The date or Issue Number is not given. I have all back issues and would like a cross reference. Thanks, Martin

Scott Russell's picture

Looks like June/July 2012, Martin. Issue #149.

Justine Sanchez's picture

Hi George, yes they will need to invest in a battery-based inverter, and will need to separate out the loads they want to be backed up into a critical load sub panel, that will be powered from the battery-based inverter (that also has the ability to pull from the utility when present). I encourage you to check out some of our previous articles on GT systems with battery backup, such as this one from Flint Richter:
http://www.homepower.com/articles/g...
Cheers,
Justine
Home Power Magazine

George Wear's picture

Hi Justine, I have a grid-tied client in Hondurus where outages are common and power is expensive, but the grid will not accept any excess power generated. They want to start small with a backup system to power a critical load panel. Will they need a special inverter or special wiring in order for this?
thanks, George

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