ReedN
I was wondering how this should be hooked up when I currently have a Sunnyboy SMA (Grid-Tie Inverter) currently connected to my electrical panel.

From what I have found there are two ways to hook this up.
1) Tied to the utility side of the ATS so that the inverter powers down when the utility side goes down. This is seen as the most conservative approach.
2) Tied to the generator side of the ATS so that the solar panels assist with the load. This has some potential issues:
A) If the generator doesn't produce a clean waveform the inverter will power off.
B) If the house doesn't consume all the power the solar is providing it will attempt to feed the power to the generator in the form of higher voltages, essentially what it would do trying to feed the grid with excess power. This will likely cause the generator to shut itself down if it detects the over-voltage (best case scenario) or possibility destroy the equipment (perhaps).

The above was based on a couple of web pages I was able to find, but honestly there wasn't much information. Curious if others on this forum can help add their insights?
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murphy
My solar panels are connected in the main disconnect for the house which is about 30 feet before the ATS. If the power company goes down the panels shut down and the generator starts. Your power company is very likely going to tell you what you can and can't do. Even though I am grid tied I have two meters provided by the power company. One measures power coming in and the other measures power going out. This was mandated, they didn't want any part of running a meter backwards. I also have a third meter, that belongs to me, that measures production from the panels.

You do not want to tie your inverter to the generator. My grid tied power does not go back to the power company. It is used by my neighbors and they get billed for it.
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Birken Vogt
If solar goes to the generator it will make it a motor and the engine will spin faster. (i.e. the frequency goes up.) When the frequency goes very far up the inverter will drop off line because it is out of spec, it knows it is not the power co. or the poco is unstable. This will happen around 61 or 62 Hz. Then after things settle down for 5 minutes or so the inverter will reconnect and the cycle will repeat indefinitely.

Not something you want to have happening. Make it so that the inverter and the generator never see each other.
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JayH
The forum software is acting wonky and about a week's worth of posts have gone missing.

You (or someone) suggested a proposal to put the solar inverters on a small breaker panel connected to the meter ahead of the transfer switch. If you do that, the new panel feeding the inverters would have to be service-rated and would become the service equipment as it's connected directly to the meter.

You might be better off leaving your existing service panel, inverters, and breakers in place as-is. Use an RTG-style ATS with built-in breaker panel behind your existing panel to feed the critical loads. You could leave non-critical loads such as range and dryer on the existing panel. This could save you some re-wiring and expense.
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ReedN
Strange, yeah a couple of my posts disappeared.

The two problems doing it with the RTG ATS behind my main panel is that I want the whole house backed up and leaving many unprotected defeats that purpose. Also there's a lot of moving of the critical circuits to the new panel which would be a lot of work vs. just running a new SER from panel to panel.
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Hutch
What I've seen done was a magnetic contactor between the inverter and the main panel. When the utility power goes down the contactor will drop out, and the inverter won't see the generator. Once the utility power comes back on you will need to physically turn contactor back on.
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murphy
The block diagram that was here and then disappeared is exactly the way my system is configured. When the power company fails the inverters automatically shut down.
Your power company may have a say in the configuration. Mine doesn't allow reversing a meter. They provided two meters and paid for the second meter box. One meter measures power coming from the power company and the other measures power flowing to the power company.

When I do a test with the house on the generator the feed from the power company and inverters is obviously cut. However the inverters are still connected to the power company and all generated power from the panels is fed to the power company during the test.
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Hutch
If the inverters are connected to the grid during an outage isn't that putting linemen in danger? How are you doing your test.
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murphy
Hutch;n60007 wrote:
If the inverters are connected to the grid during an outage isn't that putting linemen in danger? How are you doing your test.


No the inverters are required to immediately shut down when utility power is lost. I have microinverters. There is one under each PV panel. If they didn't have that capability the power company would not allow them to be used.

There are several ways to do the test. The most common, that I have seen on the forum, is to put a switch in the N1 line. Opening the switch simulates a power failure, the generator starts, and when it is stable the house load is connected to the generator which isolates the power company and the PV panels from the house.
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ReedN
Hutch;n60005 wrote:
What I've seen done was a magnetic contactor between the inverter and the main panel. When the utility power goes down the contactor will drop out, and the inverter won't see the generator. Once the utility power comes back on you will need to physically turn contactor back on.


My inverters are specifically grid-tie inverters which are designed to be directly connected to the utility power. In the event the utility power goes down the inverters shut themselves down as well.

So in essence I only need an empty breaker location for plugging them in. This was the main panel, but in the new configuration, because they would try to drive the backup generator, they'll need to be moved to a non-generator backed up location before the ATS so they power down in the event of the utility power going down.
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JayH
Hutch;n60007 wrote:
If the inverters are connected to the grid during an outage isn't that putting linemen in danger? How are you doing your test.


The inverters used for grid-tie have multiple design features to prevent exactly this. They require stable grid power at precisely 60 Hertz before they'll come on, along with a timed delay in the event of any interruption. Unless the grid is present at the inverter output, the inverter output won't be applied to the grid.
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