Grid Tie System with Standby Generator

[Technoyogi]

My house has a standby generator with an automatic transfer switch (it's fairly rural so we get frequent power outages). When the utility power fails, the switch automatically powers up the generator and then switches power over (the utility service is isolated). I am interested in a 7kW grid tie system. As long as we are on the grid, things are fine. But in the case of an outage, I am worried about feeding power back into the generator. If the panels are producing 7kW and the house is only consuming 2kW, then it trying to feed 5kW back into the generator. I don't think the generator can handle this. How is this situation normally handled? I could just automatically shut off the solar during an outage, but that sees like a waste.

Regards, Technoyogi

[Sunking]

Real simple, if you loose commercial power, the solar PV turns off, the automatic transfer switch (ATS) operates to isolate you from the grid as designed and to electrical codes, and the generator picks up the load in the house.

The PV system will not reconnect until commercial power has been restored for about 5 minute without interruption. Once commercial power is restored, the generator turns off, the ATS re-connects you back to commercial power, and then the PV system will turn on when all is clear

[Technoyogi]

Thanks, I guess this is putting the grid tie inverter feed in between the utility meter and the ATS. Is there any way to put it on the other side of the ATS?

Are there codes saying where the PV should be placed in the system?

Regards, Stephen

[russ]

@ Technoyogi - Welcome to Solar Panel Talk!

You found the right guy - Sunking knows this stuff very well!

Again, Welcome!
Russ

[Sunking]

Thanks, I guess this is putting the grid tie inverter feed in between the utility meter and the ATS. Is there any way to put it on the other side of the ATS?

No Sir electrical codes prevent it. Grid tie inverters can only run when you have commercial power available in your configuration.

[Vandergraaff]

Has anyone developed a method or "black box" which would reconfigure a system during a power outage, to essentially change a grid tie system into an off grid system?

[Sunking]

Has anyone developed a method or "black box" which would reconfigure a system during a power outage, to essentially change a grid tie system into an off grid system?

Will not work, a GTI is a current source and will only operate with a very low impedance of the grid. Every bit of current has to be used, otherwise it will go into over voltage and shut itself down as designed.

[Mike90250]

That is a whole different type of inverter, a hybrid off-grid/Grid tie. Sunny Boy makes one ( sunny island), and Xantrex makes a line (the XW series)

[stumpy40]

Sunking, I have same exact situation. I have a gen that I want to use to power entire house during storms. I have installed a GT 16kw system. How would the ATS be located? I have a 400A main with 2 200A subs in the house. The solar subpanel is a 125A and is line side tapped. Would this method of install pose any problems?

[Sunking]

Sunking, I have same exact situation. I have a gen that I want to use to power entire house during storms. I have installed a GT 16kw system. How would the ATS be located?

The only place it is allowed to go, immediately after the meter disconnect.

[stumpy40]

Gotcha....so if I installed the solar subpanel line side tap...could I still make it work?

[ahec2222]

How do You isolate the solar panel's breaker from the Backup Generator?

How do You isolate the solar panel's breaker from the Backup Generator? If the solar starts producing power ,won't it will feed into the generator and short something out?? In other words , wouldn't I have to turn the Breaker off that feeds the solar panel inverter to prevent accidental back feed??

[inetdog]

How do You isolate the solar panel's breaker from the Backup Generator? If the solar starts producing power ,won't it will feed into the generator and short something out?? In other words , wouldn't I have to turn the Breaker off that feeds the solar panel inverter to prevent accidental back feed??

If you have an automatic or manual transfer switch between the POCO service connection and your building main panel, and you feed your generator into the other input of the transfer switch, then if you legally connect your grid tie inverter output to the POCO side of the transfer switch there is no way that it can end up connected to the generator.

If instead of a transfer switch you use an interlock between the main breaker and the generator breaker, the again you connect the PV on the POCO side of the main breaker (with its own service rated disconnect). Then when you open the main breaker before closing the generator breaker you cannot end up with the PV connected to the generator.

If, on the other hand, you feed the PV into the main panel through a load side breaker, just as the generator is fed in, you need to come up with a mechanical interlock that requires BOTH the main and PV breakers to be open before you can close the generator breaker.

Piece of cake until you try to get it inspected and approved.

[jainsushant]

Hi

Though I am asking this question in another thread also, but I wish to know if I am certain that my consumption will be much more than what my PV panels can generate and there will be then no chance of PV current reaching generators, then will it not be better for me to connect the GTI on the common output of Mains and DG? i.e. when Mains fail, the GTI will consider DG output as grid and keep producing electricity and save me fuel?

Regards

Sushant

[jainsushant]

Hi Technoyogi

While my knowledge is very limited in solar, but I strongly feel that you should use a battery system than a Grid Tie. As you mentioned that the grid supply is very erratic, it will mean that your GTI will not be doing any work most of the time. And if you are from India (Like me), the main power cuts are normally during the peak afternoons only which means production may be near zero only. A battery system will be more expensive, but still will be worth it.

Regards

Sushant