on grid, but want off grid capability?

[Ampster]

The key to AC coupling is frequency.

[mudhole]

just so i understand, there is no special signal or frequency that comes from the grid, just a 240 ac power source to trip the GT inverter?

[Ampster]

so i did a little reading on AC coupling, see if my understanding is correct, basically your grid tie is disconnected and by using a battery bank and inverter, you change your grid tie to that new power source, mimicking the grid, which actuates your full system?

Yes that is the concept. I don't use the terms mimick or trick because it is more complicated than those terms imply. It often requires some rewiring as part of the hybrid install and the hybrid needs to be capable of AC coupling. I have been doing it for the past four years. Most of the time when the grid is up there is no difference depending how the hybrid is configured. Only when the grid goes down does the coupling take place and the hybrid grid forming inverter controls the GT grid dependent inverter by changing frequency if there is not enough load to use all the power which the GT inverter will try to put out.

[mudhole]

so i did a little reading on AC coupling, see if my understanding is correct, basically your grid tie is disconnected and by using a battery bank and an inverter, you change your grid tie to that new power source, mimicking the grid, which actuates your full system?

[Ampster]

I agree with your description. I was trying to be brief concerning mudhole's question about a hybrid inverter if the grid is down and wouldn't back feed it.

No worries. If you don't know anything about AC coupling it is better to be brief. The question in the title was about wanting off grid capability when the OP has a GT inverter. There are a number of ways to do that. AC coupling is only one solution.

[SunEagle]

Most hybrid inverters manufactured today are much more versatile than that. In addition to charging their batteries, they can provide AC to serve the loads and most importantly they can AC couple to a GT grid dependent inverter to leverage the GT inverter solar panels without having to reconfigure them. It literally is a hybrid of an GT inverter and an Off Grid inverter with batteries. When the grid is up a hybrid inverter CAN back feed the grid but when the grid is down it can operate like an Off Grid inverter with all the protections mentioned earlier .In this context I am using the term back feed to mean export.

I agree with your description. I was trying to be brief concerning mudhole's question about a hybrid inverter if the grid is down and wouldn't back feed it.

[Ampster]

A hybrid inverter should only charge a local battery system and not back feed the grid.

Most hybrid inverters manufactured today are much more versatile than that. In addition to charging their batteries, they can provide AC to serve the loads and most importantly they can AC couple to a GT grid dependent inverter to leverage the GT inverter solar panels without having to reconfigure them. It literally is a hybrid of an GT inverter and an Off Grid inverter with batteries. When the grid is up a hybrid inverter CAN back feed the grid but when the grid is down it can operate like an Off Grid inverter with all the protections mentioned earlier .In this context I am using the term back feed to mean export.

[Ampster]

so, the hybrid inverter will still run when the grid goes down? if so, how does that work without the danger of linesmen getting electrocuted?

The typical hybrid inverter has a automatic transfer switch to protect linesmen. That is a code requirement of any gird interactive inverter.

Also as I mentioned earlier it can act as a grid forming inverter to AC couple your GT grid dependent inverter so that those solar panels can be used to charge your batteries and serve your loads. AC coupling is a great way to leverage a GT inverter in order to to use it when the grid is down. It is what a Tesla Powerwall does to essentially add batteries to a GT inverter. Some people do not like the term "trick a GT inverter" and shy away from anything that would be similar. I agree AC coupling is more complicated than that. but it is commonly used in circumstances like yours. I do the same with an Outback Skybox that AC couples to my Enphase inverters. AC coupling is much more effective than trying to use a UPS and have all those conversions. A UPS also cannot leverage your existing GT inverter so you can get the benefit of your solar panels in your GT inverter.

[peakbagger]

A hybrid inverter will have an automated transfer switch built into it to separate the house loads from the grid. It will also have UL1741 SA protection circuitry built into it to ensure that the ATS opens to the grid if the grid goes down.

[SunEagle]

so, the hybrid inverter will still run when the grid goes down? if so, how does that work without the danger of linesmen getting electrocuted?

A hybrid inverter should only charge a local battery system and not back feed the grid.

[mudhole]

so, the hybrid inverter will still run when the grid goes down? if so, how does that work without the danger of linesmen getting electrocuted?

[littleharbor2]

You can go with a separate hybrid inverter or another option is using a Sunny Island inverter in conjunction with your Sunny Boy GTI. This combination may require only certain models of Sunny Boy inverters. so maybe or maybe not an option for you.

[Mike90250]

thanks mike90250, so 1. when you say 100ah per Kw, did you mean per Kw-h? or whatever my peak Kw is?, 2. my thought was to just have a completely different inverter, just for off grid.

For every KW of power the inverter produces, there needs to be about 100ah of battery ( @ 48V. or 200ah battery @ 24V) to "buffer" the 120Hz surges the inverter draws. too small of battery and the inverter starts distorting it's output and generating excess internal heat. If you have 2kw of loads, you need 200ah of battery to keep the inverter safe. ( all in the fine print of the manual)
This is totally different than the amount of battery required to sustain a load for a set amount of hours.

[SunEagle]

this just seems so clumsy, DC to AC to DC to AC

They do make water pumps that run directly from a solar panel and actually have a float switch to turn it off if the tank gets full.

[mudhole]

this just seems so clumsy, DC to AC to DC to AC