Choosing an Inverter: Page 3 of 4

Intermediate

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Aurora Power One grid-tied inverter
With maximum power point tracking (MPPT) for two separate series strings, the Aurora Power One grid-tied inverter can accommodate two subarrays with different orientations or nominal voltages.
Fronius IG+ 11.4
The Fronius IG+ 11.4 is one of the largest residential grid-tied inverters.
SMA America Sunny Boy 700
The SMA America Sunny Boy 700 is the smallest of the available grid-tied string inverters.
Advanced Energy’s PV Powered inverter
Advanced Energy’s PV Powered inverter has integrated AC and DC disconnects.
SMA America’s Sunny Beam remote monitor.
SMA America’s Sunny Beam remote monitor.
Kaco online monitoring screen capture.
Kaco offers online monitoring.
Enphase Microinverter
This microinverter from Enphase can send monitoring information to a smartphone.
SolarBridge Microinverter
This SolarBridge microinverter attaches to the back of a PV module.
Enecsys Microinverter
An Enecsys microinverter.
Exeltech AC Module
This Exeltech AC module has a microinverter permanently attached (as shown in the background photo; it is not available as a stand-alone inverter).
SMA America’s transformerless inverter.
SMA America’s transformerless inverter.
MagnaSine off-grid inverter.
Magnum Energy’s MagnaSine off-grid inverter.
Apollo Solar off-grid inverter.
Apollo Solar’s off-grid inverter.
Schneider Electric’s Xantrex XW battery-based inverter.
Schneider Electric’s Xantrex XW battery-based inverter.
OutBack Power’s off-grid inverter.
OutBack Power’s off-grid inverter.
Xantrex Monitor
A Xantrex monitor.
OutBack Power’s MATE3
OutBack Power’s MATE3 monitor.
Magnum Energy Monitor
A Magnum Energy monitor.
Aurora Power One grid-tied inverter
Fronius IG+ 11.4
SMA America Sunny Boy 700
Advanced Energy’s PV Powered inverter
SMA America’s Sunny Beam remote monitor.
Kaco online monitoring screen capture.
Enphase Microinverter
SolarBridge Microinverter
Enecsys Microinverter
Exeltech AC Module
SMA America’s transformerless inverter.
MagnaSine off-grid inverter.
Apollo Solar off-grid inverter.
Schneider Electric’s Xantrex XW battery-based inverter.
OutBack Power’s off-grid inverter.
Xantrex Monitor
OutBack Power’s MATE3
Magnum Energy Monitor

Efficiency Ratings. Manufacturers have their own efficiency ratings, but for accurate production projections, it’s wise to obtain them from an independent source, such as the Go Solar California Initiative (gosolarcalifornia.org). Manufacturers’ efficiency ratings (often labeled “Maximum Efficiency” on spec sheets) could be based on testing at lower ambient temperatures and under other conditions that do not reflect realistic field operation, but optimize inverter performance. The Go Solar California Initiative ratings (labeled “CEC Efficiency” on spec sheets) will be slightly lower (generally around 1%).  

Choosing an Off-Grid Inverter

An off-grid inverter is sized differently than a grid-tied inverter—the latter has grid power available to supplement PV production. An off-grid inverter must have enough AC output power to cover any AC loads that might run simultaneously. For example, if you have 2,850 W of AC loads, then you might choose an inverter with 3,000 W of continuous output power. Any surge requirements (common with compressors and motors, such as in refrigerators, well pumps, etc.) need to be checked against inverter “surge” or “overload” specs (see “Sizing a Battery Based Inverter” in HP149).

Since the inverter draws from a battery bank instead of the PV array, the DC voltage input needs to match the nominal battery bank voltage (generally 12, 24, or 48 V). Inverter model numbers usually reflect both the AC power output and the DC battery voltage. For example, the OutBack VFX 3648 can produce up to 3,600 AC watts continuously and works on a 48 VDC battery bank.

Most quality stand-alone inverters produce a pure sine wave. The AC electricity from the utility is a fairly clean sine wave form, and higher-end inverters match or beat this quality. Modified square-wave inverters tend to be less expensive, but the power quality is not as good. Many appliances actually run fine on a modified square wave, but some loads, including thermostats, clocks, fans, and power tool battery chargers, might not function properly. Sine wave inverters are highly preferred, as they will run motors more efficiently, and consumer electronics with less noise and electrical interference. 

AC Output Voltage. Some off-grid inverters have a 120 VAC output, requiring “stacking” two inverters to make 240 V, or need a 120/240 step-up transformer. Other inverters have single-phase 120/240 V AC output. Since most larger generators are also 120/240 V, they should be connected to an inverter that accepts a 240 V AC input, or run through a transformer to step it down to 120 V. Using only one 120 V leg of a 240 V generator can increase generator run time. Three-phase AC loads can also be run with some inverters. Each manufacturer will specify if this is possible and how it is done.

Other Options. Off-grid inverters have many helpful features and programming options. Most have built-in chargers to charge batteries from an AC power source. They should also have a programmable low-voltage disconnect (LVD) to keep batteries from being overdischarged. Other options may include automatic generator starting, battery monitoring, remote displays, a Web interface, and auxiliary relays (for various functions such as operating a battery box fan).

Grid-Tied with Battery Backup

A grid-tied with battery backup (GTBB) inverter has to work both as a grid-tied inverter and a stand-alone inverter to energize loads when the grid is down. Choosing is fairly simple, since there aren’t very many available models (see “Choosing a Battery-Based Inverter” in HP149).

GTBB inverters must have a large enough AC power rating to pass through the full PV array output (like a grid-tied inverter) and to power the backed-up AC loads subpanel (like an off-grid inverter). For example, a 4 kW PV array with 2.5 kW of loads on the backed-up subpanel necessitates using a 4 kW inverter to meet the PV array requirement even though the load power needs are less (surge load sizing applies, as well). The battery bank voltage must match the inverter, as in off-grid systems, and the AC output voltage must also match the utility voltage, as in grid-tied systems.

Comments (2)

ideas2014's picture

dear Lena
i have question may leads us to debate i hop any one with good understanding & experience in solar power can give me good productive answer ,,
we all know that the new interactive BB grid tie inverter has 2 AC input , one usually used for gird and the second one used for Diesel generator as standbye power supply ...in case no wind or no grid .
here i want suggest new option , which i hop we can share opinions and solutions ...
i want use the main AC input relaying on my solar power which generates 230 AC 10 KW and will use the other AC input for the grid ,,incase my solar power supply fails for any reason i can relay on the grid immediatly
thru this way i will avoid the losses from the power generation source from the solar power cells thru charge controler , charging batteries and then inverter ,,or even using DC from my solar to feed the battery

i think this model can work with outback power and SMA ..i wish to know this wrong , possible or not ,,,better or not

what or how u see guys this suggestion ? am i crazy or stupid ,,,thanx for sharing
thanx

Michael Welch's picture

Hi Ideas2014. You have a lot of questions and unresolved issues in this installation you are considering. While our articles and authors can be quite informative, you will find much more satisfaction in finding a local experienced, reputable professional who you can work with directly.

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