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Old 07-08-14, 06:27 AM   #1
stevehull
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Default grid tie issue with generator

I am in the engineering phase of putting up ~ 10kW of solar PV. However, I do need an answer to an situation we have here.

Power outages are not uncommon and I require generator backup for watering livestock, keeping freezers going and other essentials.

I understand that the proposed Enphase microinvertors system cuts off PV AC power output when grid connection is lost. But what if I turn on the generator?

The system I have is a manual transfer switch and I use a power take off generator attached to my tractor.

This generator power would "trick" the microinvertors to think that grid AC is available.

In the case of a power outage, do I manually turn off solar PV. How is this done?


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Old 07-08-14, 07:55 AM   #2
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Warning: I am not an electrician and am not fluent in the NEC.

My grid tie system goes through its own utilty meter and is tied into the grid on the utility pole side of my original meter. They pay me based on the PV system meter and bill me based on the original meter.

That said, I thought the transfer switch for a generator was supposed to be wired so that the loads could be carried while at the same time the grid can't be fed by the generator. In other words, the transfer switch makes a physical break in the connection from the grid and makes the connection to the generator powered circuits. If your area is like that, then your Enphase {or whatever inverter you go with} array will be offline for the duration of the outage. The best way I know to keep your PV making power during a grid outage is to go with a Sunny Island inverter and a battery bank. I promise that going the Sunny Island route is a lot of upfront cost. Done right though and it would be a very nice system.
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Old 07-08-14, 10:34 AM   #3
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You might consider AC coupling
http://enphase.com/global/files/Enph...ed-Systems.pdf

Letting the generator simulate the grid will void the 25 year warranty. I wanted to do the exact same thing when I was doing my solar.

With the warranty issue stated you have a large PV system and if the generator and the solar made more than you could use that power needs to go somewhere. The microinvertes would just keep increasing the voltage back to the generator. They would end shutting them self’s down if there was nowhere for the power to go.


Here is a post on this subject
https://community.enphaseenergy.com/...lter_by%5D=all

Solar mike can maybe post some good solutions that he has used in the field.
I have been reading about AC coupling but have no real world experience with it.

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Old 07-08-14, 01:03 PM   #4
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PB
Excellent post about Enphase. I realize that I must have some sort of "dump load", but did not know the very tight 60 Hz frequency range that the Enphase microinvertors require to operate.

Dump loads are not difficult (50 gallon electric resistance water heaters are great), but the control system to switch them in and out looks daunting.

Yes, I could do batteries, but that would be a lot of money for infrequent outages.

I think that I will just have to manually disconnect the PV panel and go with my generator when we are out of power. Is that what you do?


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Old 07-08-14, 01:19 PM   #5
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Quote:
Originally Posted by stevehull View Post
PB

I think that I will just have to manually disconnect the PV panel and go with my generator when we are out of power. Is that what you do?


Steve
Yes that is exactly what I do. It is the most cost effective and I like to have short payback on projects if possible.

My utility requires a manual lockable physical disconnect switch to remove the PV system. This is a perfect place to disconnect to array when the power goes off.




I do hope the recycled EV car batteries will become a way to do this much more reasonable priced in the future. When they are done in the cars they are still have lots of life left in them for other applications.
Solar power will be a great place for them to still be very useful.
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Old 07-10-14, 11:30 AM   #6
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If you go with micros or grid tie only system you are going to want to make sure you disconnect them before starting up a generator as they will likely try to back feed power to the generator and fry it.
You could go with a hybrid bymodal system like those from Outback which have some batteries and will disconnect an emergency panel from the main grid keeping it alive. The Outback systems are bydirectional inverters and support generators so you would have a better time of it.
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Old 07-10-14, 11:35 AM   #7
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Quote:
Originally Posted by stevehull View Post
Yes, I could do batteries, but that would be a lot of money for infrequent outages.
actually not too bad. Since you have decent generator you could go with the minimum battery bank size. Since the batteries are mostly in float and discharge only during outages, and you could insure (with the generator) that they do not discharge very much, lead acid would last quite a long time (10-12 years).
You would probably be looking at about $2k or so for the battery bank. Added bonus is that you would not need the generator running ALL the time but still have power, allowing a savings in wear / fuel.
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Old 07-10-14, 07:42 PM   #8
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Which manual transfer system are you using, and where do you intend to drop your 10kw grid tie PV in?

In my enphase system, I have two trunk cables with 10 inverters per string. Those two strings drop into a separate panel to be combined (and to protect the 12awg trunk cable)before going into my service entrance panel (outside). My entire house runs off a second panel (inside) down stream of my service entrance panel.

If you could drop your 10kw of PV into a panel located between your grid meter and the panel where your manual transfer is disconnecting the world downstream, then everything down stream of your manual transfer would be running off the generator and the PV would be isolated on the outside just like the grid.
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Old 07-10-14, 07:56 PM   #9
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Check out Builditsolar.com. He has already worked the bugs out and can reconnect to batteries for power outages. Designing and Installing a Grid-Tie PV System
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Old 07-13-14, 11:02 AM   #10
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Have you looked at inverters that can operate either grid tie or off grid?

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