Choosing a Battery-Based Inverter: Page 2 of 3

Intermediate

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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

Nominal Battery Voltage dictates the battery bank configuration. Only a few inverters (such as those from Exeltech) can accommodate multiple battery bank voltages. Most household-sized inverters require either 24 or 48 V battery banks. There are a few 12 V inverters on our list, but these are usually for smaller systems (think cabin-sized) that serve only a few AC loads.

AC Output Voltage has been limited to 120 VAC for a single inverter until the last few years. Now, several inverters have split-phase 120/240 VAC to power both standard 120 VAC loads and 240 VAC loads (such as a well pump). These inverters also have battery chargers to charge the battery bank using both legs of a 240 VAC generator. This saves generator run time and avoids having to include a 120/240 step-up/down autotransformer. Split-phase inverters also negate problems with wiring a single inverter to a load center that has multi-wire branch circuits, since this can possibly overload the neutral conductor. Additionally, several inverters on our list can also be connected in groups of three to supply three-phase 208 VAC output, commonly used in small commercial systems. (To see which models have this functionality, see the “Stackability” column in the table and look for “3Ph.”)

Peak Surge ratings reflect the inverter’s capability to supply significantly more than its continuous power rating for short periods of time. Certain appliances (i.e., those that have motors, like washing machines, refrigerators, and well pumps) will briefly draw more power upon initial startup. To find the surge requirement for a particular appliance, check the appliance spec sheet for the “start amps,” or contact the appliance manufacturer. Alternatively, you can measure it with a recording clamp-on ammeter.

Stackability is the capability to connect multiple inverters together to create 120/240 VAC output (series stacking) or increase output current (parallel stacking). Historically, the ability to series stack was handy for systems that needed to power 240 VAC loads, using inverters with 120 VAC-only output. Now that more split-phase inverters are available, stacking is usually done to increase inverter output capacity (amps). Stacked inverters can be programmed to activate only if needed so that when there is low power demand, standby losses are reduced (see “No-Load Draw”).

Peak Efficiency is the ratio of AC power out of the inverter to power in from the DC power source. The higher the efficiency, the less energy that is wasted in the inversion. Actual operating efficiency will vary depending on how much power is being pulled through the inverter, so inverter efficiency curves can be more helpful than the peak efficiency specification, and are often available in inverter manuals. On-grid systems spend most of their time processing RE-generated power to send to the home/grid, so high efficiency at the RE system’s power output rating is best. Since off-grid systems can spend much of their time requiring significantly lower power (when only a few loads are running), consider an inverter that has high efficiency at lower power output.

No-Load Draw (aka “Idle,” “Standby,” or “Tare” Loss) tells how many watts each inverter consumes simply by being “on.” This power needs to be accounted for when performing a load analysis for an off-grid system. Multiply the no-load draw by 24 hours to calculate the daily energy (watt-hours) consumed by the inverter.

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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