Grid Tie System with Standby Generator

[jflorey2]

My electrician is under the impression that my system, as I described it above, is safe and will work. He doesn't think the inverter will try to feed power onto the system if the generator is supplying power.

It will certainly try. If the voltage and frequency are stable enough it will succeed. It depends on the inverter and generator.

If you can recommend a "fix" for my system, I'd love to hear it.

Simplest way is to move the barn branch circuit to a place upstream of the transfer switch.

[GlennT]

You are not going to get an answer because it does not meet any code requirements and will not pass inspection. That means it is NOT SAFE.

Well, I have been forthcoming on my system and asked for recommendations on how to fix it. Will I have to run another set of wires from my AC disconnect in the barn to tie into the system on the "grid side" of the transfer switch at the house? It's already passed inspection. I just want to make it safe. Please help?

[Sunking]

Ok, but are you speaking from experience, or conjecture? I would like to have someone chime in who's actually had an installation like mine and see what they discovered. Thanks for your input.

You are not going to get an answer because it does not meet any code requirements and will not pass inspection. That means it is NOT SAFE.

[GlennT]

Many things go into a "system schematic" and few installs are the same. So, if you can be more specific, are you looking simple grid tie? Grid tie with transfer relay and generator backup? Grid tie with transfer relay and hybrid inverter & generator backup?

When you decide, I'll move your question to it's own thread, and not hijack this one.

Thanks. I'll tell you what I've got here. Right next to the new Net Meter just installed by the utility is the Transfer Switch for the 20 kW Generac. When power fails, the switch connects the generator to my main panel in the house. On that panel is a 40 amp DP CB that feeds a 110 ft underground wire (#8AWG) to 100 amp subpanel in my barn. (The solar panels are mounted on my barn because it had a better roof with no shading issues.) On this subpanel is a 35 amp DP CB which connects the AC output of the SolarEdge 6000 GT inverter.

I'm not familiar with "transfer relay", or understand what that does.

My electrician is under the impression that my system, as I described it above, is safe and will work. He doesn't think the inverter will try to feed power onto the system if the generator is supplying power.

If you can recommend a "fix" for my system, I'd love to hear it.

[Mike90250]

I would like to get my hands on an electrical diagram which shows all the elements in their proper positions. Are there diagrams available on this forum from anyone?

Thanks, Glenn

Many things go into a "system schematic" and few installs are the same. So, if you can be more specific, are you looking simple grid tie? Grid tie with transfer relay and generator backup? Grid tie with transfer relay and hybrid inverter & generator backup?

When you decide, I'll move your question to it's own thread, and not hijack this one.

[GlennT]

I would like to get my hands on an electrical diagram which shows all the elements in their proper positions. Are there diagrams available on this forum from anyone?

Thanks, Glenn

[Naptown]

I would hope that no one has an installation like yours as it is not the recommended way to install. Grid tie inverters should always be upstream of any transfer switch. Bimodal systems are a different story altogether.

Furthermore why would you want to risk it?
Tying into the poco side of a transfer switch is fail safe.

Any change in load will cause a generator ( well most not including inverter type) to change frequency.
This in theory should shut the inverter down but still not worth the risk.

[ButchDeal]

Ok, but are you speaking from experience, or conjecture? I would like to have someone chime in who's actually had an installation like mine and see what they discovered. Thanks for your input.

I would hope that no one has an installation like yours as it is not the recommended way to install. Grid tie inverters should always be upstream of any transfer switch. Bimodal systems are a different story altogether.

[GlennT]

If the Generator happens to put out good clean current for long enough the SolarEdge will think that the grid is back and turn itself on, and try to dump lots of power into the generator, thus causing smoke and blown generator.

Ok, but are you speaking from experience, or conjecture? I would like to have someone chime in who's actually had an installation like mine and see what they discovered. Thanks for your input.

[ButchDeal]

That's the way it seems to me also, but sunking says it's just not a problem because apparently, the GT inverter knows the difference between generator power and grid power, and won't try to parallel with the generator.

You say you get a lot of smoke....but wouldn't the GT inverter (SolarEdge) recognize some type of fault condition and shut itself off, or open a OCPD?

No it is a gamble. Sunking was mostly talking about bimodal inverters not straight GTI inverters like the SolarEdge. Your best bet is to move the interconnect to the other side of your transfer switch. If the Generator happens to put out good clean current for long enough the SolarEdge will think that the grid is back and turn itself on, and try to dump lots of power into the generator, thus causing smoke and blown generator.

[GlennT]

If you connect a generator and a GT inverter together, on a sunny day, you are only safe for as long as your house loads exceed your solar power.

That's the way it seems to me also, but sunking says it's just not a problem because apparently, the GT inverter knows the difference between generator power and grid power, and won't try to parallel with the generator.

You say you get a lot of smoke....but wouldn't the GT inverter (SolarEdge) recognize some type of fault condition and shut itself off, or open a OCPD?

[Mike90250]

But my GT inverter is not connected on the grid side of the transfer switch. It's on the house side. I think in this case, the generator would again provide AC power to the GT inverter and it may attempt to parallel with the generator. I'm just not sure what it will do.

If you connect a generator and a GT inverter together, on a sunny day, you are only safe for as long as your house loads exceed your solar power. If the spa heater cuts off, and the GTI attempts to push power into the genset, you get a lot of smoke, that is expensive. Yes, it may work for a short while, but most homes have less than 1Kw base loads.

[inetdog]

This is an old message I found while researching my situation, and I wanted to see if you still maintain it works this way. I've found conflicting information on how this may play out. How does the PV inverter differentiate between grid power and generator power? I've been told that my Generac power is "grid quality".

Thanks.

One way is that the inverter/charger has two AC inputs, one for grid power and one for generator power. The grid power input, AC1, has a transfer switch to disconnect the grid when it goes down and the inverter goes to standalone mode.
If generator power is available on AC2 the unit can be programmed to operate in grid-tie mode with the generator as the source. Since the unit is measuring current (and power) flow from the generator, the GTI output can be throttled back to prevent back feeding the generator. And any remaining solar power can go to the batteries.

Search the forum for "generator support" and you will find some very good threads on configuring this mode.
Not all hybrid inverters have this capability. Some Outback and some Xantrex/Schneider models do.

Just to clarify, there is a transfer switch on AC1 only, but the AC2 input would not be connected to the house lines (including the GT function) unless the AC1 transfer switch is open.
The difference is that when AC1 input goes away the inverter will work with or without an input on AC2, it will just work in a different control mode with it than without it.

[GlennT]

[QUOTE=Mike90250;177964]It Depends. Different brands have differences.
Grid Tie, the GT inverter just shuts off when the grid fails. The transfer switch isolates the house from the GT and the Grid, so the generator can power just the house (not the GT inverter)"

But my GT inverter is not connected on the grid side of the transfer switch. It's on the house side. I think in this case, the generator would again provide AC power to the GT inverter and it may attempt to parallel with the generator. I'm just not sure what it will do.

[Mike90250]

This is an old message I found while researching my situation, and I wanted to see if you still maintain it works this way. I've found conflicting information on how this may play out. How does the PV inverter differentiate between grid power and generator power? I've been told that my Generac power is "grid quality".

Thanks.

It Depends. Different brands have differences.
Grid Tie, the GT inverter just shuts off when the grid fails. The transfer switch isolates the house from the GT and the Grid, so the generator can power just the house (not the GT inverter)


For off grid:
My XW has a wider range of acceptance for AC2 (generator) than it does for AC1 (grid).