Need advise

[kenr047]

I would like to install a 4k solar system with grid interactive inverter. Facts on inverters are not clear, I will use 99% grid tie but would like a battery back up for outages. Which inverter will allow me to operate on grid only with or without battery's? Also I would like to be able to switch off the system and not see any difference in powering the house from the grid. So far I have been looking at Outback and Xantrex, Xantrex looks like the one I need but I'm not clear on how they both operate.
Thanks

[Cariboocoot]

Welcome to the forum.

"Grid Interactive" can mean a lot of things, so let's look at the three basic inverters and how they can interact with the grid.

1). straight grid-tie: solar panels go directly to the inverter which then backfeeds the household/utility with whatever power it can muster from the panels. No back-up ability; grid goes down, you have no power.

2). off-grid used for back-up: utility and/or panels keep batteries charged. Utility feeds loads when available, inverter feeds loads when the grid goes down. No selling of surplus power to the grid.

3). hybrid system: panels keep batteries charged, surplus power production is sold to the utility. If the grid goes down inverter supplies back-up power from the batteries.

All those will utilize grid power for the loads primarily, with the exception that if you have surplus power it will either be sold back to the utility or lost.

Both the Outback Radian or Xantrex XW systems are of the hybrid variety. They can supply power from the batteries when the grid goes down, or sell surplus panel production when it is up.

I also have to mention that if your goal is back-up power for occasional, short outages you are better off buying a generator. Solar power systems, especially battery-based, are expensive. As back-up power it is usually not a good choice unless the outages are frequent, long-lasting, or involve critical loads that must be maintained.

[kenr047]

So far the information I see is that the outback inverter won't run w/o batteries, the Xantrex will. This has to be a system that anyone can operate, like my wife if I was not home. My ultimate goal is to sell power and be a little more self reliant. The battery backup makes sense to add at the beginning.
Looks like Outback runs thru the battery's all the time. If I lost one battery out of 4 (48v) then my transferred loads would all go down. Xantrex looks like it will run on its own w/o the battery's. Is there a better inverter that I haven't researched? I to new at this to risk tons of money and find out that I missed something.

[solarix]

The hybrid inverters need to have batteries all the time. They just don't need so many of them as a straight off-grid system does. Plus, any loads you want to be battery backed, run on the inverter all the time meaning you can't switch off the inverter system and just be on the grid without rewiring these loads. Most setups do have a bypass switch for doing this however. My advice is to do a straight grid-tied system as it is more efficient, way more reliable and more cost effective - and just get a generator for those infrequent outages. Of course if you have lots of money to spend, give me a call.

[ggunn]

I would like to install a 4k solar system with grid interactive inverter. Facts on inverters are not clear, I will use 99% grid tie but would like a battery back up for outages. Which inverter will allow me to operate on grid only with or without battery's? Also I would like to be able to switch off the system and not see any difference in powering the house from the grid. So far I have been looking at Outback and Xantrex, Xantrex looks like the one I need but I'm not clear on how they both operate.
Thanks

You cannot run AC loads off grid without batteries no matter what inverter you buy, if that is what you are asking.

[Cariboocoot]

So far the information I see is that the outback inverter won't run w/o batteries, the Xantrex will. This has to be a system that anyone can operate, like my wife if I was not home. My ultimate goal is to sell power and be a little more self reliant. The battery backup makes sense to add at the beginning.
Looks like Outback runs thru the battery's all the time. If I lost one battery out of 4 (48v) then my transferred loads would all go down. Xantrex looks like it will run on its own w/o the battery's. Is there a better inverter that I haven't researched? I to new at this to risk tons of money and find out that I missed something.

No: the Outback Radian and Xantrex XW inverters (as well as any other hybrid inverter such as the SMA Sunny Island) need batteries all the time or else they do not work.

I bring up the SMA because they also make straight grid-tie inverters (Sunny Boy) which can be coupled to the Sunny Island in a very manageable way. You could install a Sunny Boy GT system now and add the Sunny Island later for battery-based back-up.

But as has been pointed out, no batteries = no back-up power.

[mtdoc]

The Outback GVFX3648 is a "grid interactive" inverter that is large enough to support most normal households and would work well with a 4kw array. It's much less expensive than the Outback Radian inverters, Xantrex XW series, or SMA Sunny Island.

Unlike those however, when used alone - one GVFX will not supply 240 VAC loads without the use of an autotransformer. So - as always - it depends on what loads you are trying to supply/back up.

It does, of course require batteries!

[kenr047]

I'm not asking the right questions based on the answers i"m getting.
Will Xantrex still feed the grid (only the grid) with out batteries? Will any hybrid inverter?

[stephendv]

I'm not asking the right questions based on the answers i"m getting.
Will Xantrex still feed the grid (only the grid) with out batteries? Will any hybrid inverter?

No hybrid inverter will work without batteries.
The only inverter that will work without batteries is a Grid Tied Inverter.

EDIT: You can connect a Grid Tied inverter to some battery based inverters like the Xantrex XW or SMA sunny Island.

[BB.]

Xantrex has Grid Tied, Hybrid, and Off Grid inverters... So, it can get a bit confusing. It is the Xantrex XW Hybrid inverter that we are discussing here (and other brands).

Hybrid inverters are really using the Grid/Utility power as a "dump load". When the batteries are "full", any excess power is sent out to the grid.

You can setup a GT inverter to "back feed" some TSW type off grid inverters and actually recharge the battery bank (some Off Grid inverters are actually bi-directional regarding AC/DC power... The GT inverter can push current back through an Off Grid inverter and recharge the battery bank. The issue is how to control the charging of the battery bank. Normal Off Grid Inverters (when "back fed" power from a GT Inverter) do not have any way of stopping the recharging of the battery bank--so you either have to setup a dump load and/or controller to turn off the GT inverter when the battery bank is full.

The Xantrex XW, and (I think) some Magnum inverters can shift the 60 Hz frequency to (for example) 62Hz when the battery is full. That will "knock" the GT inverter off line until the frequency is restored back to 60Hz.

SMA's Sunny Island series is designed to vary/throttle the GT inverter the farther it gets from 60 Hz (it is actually quite smart and will not mess up your AC powered clocks as it keep track of how far the frequency has drifted).

There is no "cheap way" of doing this. Basically, you are removing the standard MPPT type battery charger and replacing it with a GT Inverter. There are a few advantages (GT inverters are less expansive and can send high voltage power longer distances than the "standard" MPPT type battery chargers).

-Bill