Generator with Grid tied Windmill

[tedge]

I'm looking at a generator install in a house which has a grid-tied windmill. The inverter is a Trace Gridtek 10 inverter. I'm wondering how a generator interacts with the inverter? I understand that the inverter output shuts off when the utility power is lost, to prevent backfeeding to the grid. But what happens when a standby generator comes on and the inverter sees incoming power? Do I need to install a relay so that the inverter output does not connect to the system unless there is utility power? Or maybe it doesn't matter and the windmill power synchs with the generator power?

If anyone knows how this all comes together, I'd appreciate some feedback.

Thanks.

 

[BillK-AZ]

Generator with Grid tied Windmill-

Generator with Grid tied Windmill-

Do not do this in any way that would allow the wind generator to backfeed the generator because the load is insufficient to use all the wind energy. Ithis condition will smoke something quickly. After the smoke they do not seem to work.

Get the manual on the Trace Gridtek 10 inverter, it may have a safe way of doing this. The related Trace SW-series inverters could grid-tie (and feed back excess energy legally) and they had separate inputs for a generator. Doing it otherwise will not meet code requirements.

 

[tedge]

So here's my thought...

If I can install a relay which pulls in with utility power present, and breaks the inverter output connection to the panel when the utility drops out, I should be covered correct?

Is the inverter sensing the utility power directly through the 60A line that connects it to the panel? Or is there some other control circuitry that it senses utility power through?

 

[BillK-AZ]

Gridtek 10 inverter

Gridtek 10 inverter

This is not a Trace product, it is a Bergey Windpower Co. product.

It is listed only to work with the grid. If you are missing the manual, you should be able to get one from Bergey. It is not listed on their web site.

The relay is tricky because while opening the relay contacts on loss of utility voltage, the contacts will close immediately on return of the utility and this may present out of phase voltage. Do you have to have this inspected? Do you want to maintain any insurance?

If you managed to get it working in parallel with a generator, it will try to feed any excess power back into the generator because it does not know it is a generator. This can destroy generators and perhaps the expensive Gridteck.

There is a product designed to do what you describe from SMA America, their WindyBoy inverter combined with their SunnyIsland. See http://www.sma-america.com/en_US/products/overview.html and http://www.sma-america.com/en_US/products/wind-power-inverters.html

 

[al hildenbrand]

Also, the PoCo itself, is likely to have a whole raft of regulation about what they require. Over here, the PoCo is real skittish about small power generators (sources, not the machine) that have any possibility of interacting with their grid. A lot of the PoCo employees understand that the PoCo is skittish, but very few actually understand their own rules and requirements. Just being sure that you are talking with the right person or authority is half of the game.

 

[brian john]

ASCO, GENERAC, ONAN, Russle Electric and Zenith for starters amke transfer switches for isolating sources.

 

[tedge]

I guess I don't see the difference between a relay pulling in when the utility power comes on or just a straight connection to the panel like it is now. Either way the inverter will see utility power as soon as it is re-connected. Also in either case, the inverter will be off as it won't be sensing AC power until the utility source comes back online.

I talked to a guy at Bergey the other day, and he told me the same thing that BillK-AZ said: do not connect them so that the generator and inverter run at the same time. He also said that the inverter senses the presence of AC through the inverter output line that is landed on a 2-pole 60A breaker in the panel. So I'll break that line with a relay which pulls in when the utility power is present, closing the 240v output circuit. When the generator fires up, that line will remain open.

I will be using a Generac auto-transfer switch for the generator, but it would be installed well ahead of where the 2-pole 60A inverter output breaker is. To me it's not an issue for the POCO because the whole system will be isolated from the grid by that switch.

Am I missing something here? Is it legal?

 

[BillK-AZ]

Generator with Grid tied Windmill

Two points:
1. Legal is using only listed devices according to their listings. How are you connecting the relay coil to the utility? Line side Tap? Read the rules for that.

2. Please consider the sequence when the utility power returns. The generator will likely be running and the transfer switch is in the generator position, connecting the electrical panel and ultimately, the inverter to the generator. Utility power returns, and your relay connects the inverter to the panel. The transfer switch will usually wait 30 seconds or so before transferring the panel to the utility. What happens if the inverter starts before transfer to the utility?

 

[tedge]

Good points

1) I would probably be picking up the utility power for the relay coil by tapping the utility side conductors in the transfer switch. The switch will be after the main service disconnect, so it wouldn't be a "line side" tap of the service conductors, it would be a feeder tap at that point.

2) Now I get what you were saying about the timing of the relay pulling in. I could use a time delay relay to avoid this, no? Let's say that I install a 5 min. delay relay (or whatever would be needed based on the transfer switch timing) so that it wouldn't close until the delay time has counted down.

Please understand that I'm not trying to argue about this. I'm just trying to figure out a solution to a convoluted problem.

 

[BillK-AZ]

Generator with Grid tied Windmill-

Generator with Grid tied Windmill-

Perhaps you can use an automatic transfer switch with auxiliary switch that closes when in the utility position?