Whole House Generator with Grid Tied Solar System

[paul65k]

Sooooooooooooooooo, I know we've covered this before but just wanted to solicit some opinions here on both the feasibility as well as any potential code issues. Let me start by outlining my system:

First of all the grid tied electrical panel is fed through a main sub-panel which is separated from the main utility pedestal/meter which has only the main breaker installed there. The circuits are distributed through this subpanel and is also where my solar system feeds back into the grid through 2 separate circuits (220V). The solar system is a 4.4KW system installed which utilizes 2 strings of Enphase MicroInverters each feeding into the aforementioned main distribution panel.

On the Generator side I currently have a manual transfer switch installed between the pedestal/meter and the subpanel. I have been using a large portable generator to power the house during outages managing the load by turning off first the solar feed into the system and other circuits as needed, then powering up the generator. This works well and isolates the solar system so no opportunity for energizing the panels and of course backfeeding to the grid as a result of the transfer switch.

I'm now looking to upgrade the generator to an automatic system and I need to isolate the solar system from the distribution panel to eliminate the opportunity to 1) energize the panels and 2) damage the generator with likely potential backfeed.

Sooooooooooooooooooooo, here's what I am thinking: Rewire the solar circuits all the way back to the service pedestal bus with it's own disconnect breaker(s) which would isolate the solar from the rest of the circuits and then replace the manual transfer switch with the automatic transfer switch which would have more power (not to mention convenience of being automatic) powering the main distribution panel with no need for manual power management even though it would still be an option if desired.

It would seem that this would isolate the solar system from the generator power when energized and then re-energized (5 minutes) after the utility power is restored and after the generator shuts itself off automatically.


What say you guys about this idea? Is there a better or safer way to do this......would tying the system to the main bus at the pedestal with it's own disconnect (in addition to the existing AC disconnect that is in the system) work? I realize I'll have to resubmit to the utility and I already have the permit side covered.......are there some hidden issues here that I am missing???

Thanks in advance!

[gmanInPA]

I wonder (meaning - I'm not sure it's possible) if the easiest and least expensive route might be to just install a hybrid inverter? Why you ask.....? Because you could leave almost all your circuits as-is and the inverter would use it's own internal automatic transfer switch to prevent back-feeding the 'grid' (the grid being your main panel), but would potentially allow you to power your sub-panel via solar even in a grid outage. You might need a minimally-sized battery for such (some inverters would require such). You would wire up your new generator input into your hybrid inverter's generator input (you'll need an AGS module in most cases), and you can setup the inverter to trigger on based on a number of events such as battery state of charge, inverter load, etc. I know this is not what you were originally thinking... but it is an option that would not only be safe, but perhaps the least disruptive to what you have.

[jflorey2]

I wonder (meaning - I'm not sure it's possible) if the easiest and least expensive route might be to just install a hybrid inverter? Why you ask.....? Because you could leave almost all your circuits as-is and the inverter would use it's own internal automatic transfer switch to prevent back-feeding the 'grid' (the grid being your main panel), but would potentially allow you to power your sub-panel via solar even in a grid outage.

There is little difference between what you proposed and what he proposed. Both systems have an automatic transfer switch to switch between protected loads and "standard" loads. Since this is a microinverter installation there is no ability to run "off grid" during outages (without AC coupling, which sounds difficult in this case.)

[gmanInPA]

Well, I was hoping that it was indeed similar, otherwise it would not accomplish what he was wanting to do, right? I was just trying to suggest something that would require less re-wiring of his existing panels/circuits. I have zero knowledge of microinverters and that they can or cannot do. If it doesn't work, so be it.

[Sunking]

Gaman using a hybrid requires moving circuits and a new panel. Hybrid Inverters have a Built-In Transfer Switch. Th eproblem is the size of the Switch is typically 60-Amps. Code requires you to limit capacity when on Emergency. They will not allow whole house to run off a Hybrid. It has to be limited to Emergency Circuits. Only way to do that is by Installing an Emergency Breaker Panel fed from the Hybrid Inverter ATS. No way around it.

With a pad mounted Generator, it is installed between the Meter and Service Disconnect, just behind where the Solar is tapped in. There is no rewiring of the house as the generator can run everything. What the code will require is the generator be sized properly either by load calculations or test measurements.

[gmanInPA]

Gaman using a hybrid requires moving circuits and a new panel. Hybrid Inverters have a Built-In Transfer Switch. Th eproblem is the size of the Switch is typically 60-Amps. Code requires you to limit capacity when on Emergency. They will not allow whole house to run off a Hybrid. It has to be limited to Emergency Circuits. Only way to do that is by Installing an Emergency Breaker Panel fed from the Hybrid Inverter ATS. No way around it.

With a pad mounted Generator, it is installed between the Meter and Service Disconnect, just behind where the Solar is tapped in. There is no rewiring of the house as the generator can run everything. What the code will require is the generator be sized properly either by load calculations or test measurements.

It sounded to me as though the OP already had his generator-fed loads in the same sub-panel off of the main, with a DPDT switch of some kinds between the main and the sub panel. I assumed these were the critical loads and thus, already wired separately. I'm operating under the assumption that between the generator only feeding the sub-panel (though it appears that it could feed the main as well?) and a 4kW system, this isn't a whole-house operation. This seems like a very unusual grid-tied setup to begin with.

[sensij]

It sounds like the OP wants to essentially do a line side tap, and the whole house is fed from the same panel in which the PV is currently brought in as a load side connection. As long as the AHJ is good with that, no reason to complicate this with a hybrid system.

[paul65k]

It sounds like the OP wants to essentially do a line side tap, and the whole house is fed from the same panel in which the PV is currently brought in as a load side connection. As long as the AHJ is good with that, no reason to complicate this with a hybrid system.

Gentlemen,
Thanks for the thoughtful replies

This is exactly how it is set up today. After thinking about this a little I think I will simply remove the Side feed solar Breakers from the main distribution panel (where they are today and were signed off. I will add a small sub panel on the utility side of the transfer switch and re-route the 2 Solar Circuits (15A/220 each) into this new sub panel and then they will only energize/produce when the Grid is hot.

This way I can feed the whole house with the standby generator with no human intervention and it will turn itself on/off when power is off/restored from the POCO all teh while the solar system will be completely isolated.

While micro-inverter systems are a different animal; as it is today an installation with a 2 way meter here in SoCal it is OK to "Side Feed" into the main distribution panel as long as there is an accessible disconnect for the solar system which is clearly marked/placarded to SCE's specs.

Hopefully this will be a relatively simple change/installation.

[Sunking]

It sounds like the OP wants to essentially do a line side tap, and the whole house is fed from the same panel in which the PV is currently brought in as a load side connection. As long as the AHJ is good with that, no reason to complicate this with a hybrid system.

That is how I understood it. I agree.

[solar pete]

Code requires you to limit capacity when on Emergency. They will not allow whole house to run off a Hybrid. It has to be limited to Emergency Circuits.

WHY? is this a whole of USA thing? or just limited to the OP's location? Seems totally whack to me

Anyway this hybrid runs however it damn likes....pilgrims

[Sunking]

WHY? is this a whole of USA thing? or just limited to the OP's location? :[/FONT]

National and local electrical codes. It may seem whacky at first, or if you do not understand electrical safety. Think of it this way. Imagine doing this.




I think that should make the point.

[solar pete]

But seriously folks, why is it then we can have a whole house hybrid system operating safely to code here in OZ but you cant in the States, perhaps we are confusing some terminology? As I understand it this is how Andys works. 30kW Solar PV system (panels) bloody great bank of batteries and the gird. House will run off solar when available, then batteries until they hit their pre-set limits and if required the grid, we have the system set not to charge from the grid, but can do if required. Why cant this be achieved in the States?

[Mike90250]

You cannot run a standard 200A service house, off a 60A transfer relay (inside a hybrid inverter) But a 20KW generator with a 300A transfer switch is no problem.

So to solve the issue of the hybrid inverter only being able to pass 60A, you have it feed a load designed to limit at 60A (your emergency load panel)

[ButchDeal]

But seriously folks, why is it then we can have a whole house hybrid system operating safely to code here in OZ but you cant in the States, perhaps we are confusing some terminology? As I understand it this is how Andys works. 30kW Solar PV system (panels) bloody great bank of batteries and the gird. House will run off solar when available, then batteries until they hit their pre-set limits and if required the grid, we have the system set not to charge from the grid, but can do if required. Why cant this be achieved in the States?

you can run a whole house off of a bimodal system in the US. You just have to have enough inverter to handle it. You just stack a few Outback or Xantrex inverters till you have enough power. Simple. If Andy has a 30kw array then he likely has quite a few 8kw bimodal inverters teamed.
It is the same configuration except the emergency panel has the whole house on it, and the MSP (grid side) has nothing but all the inverters and grid.

Two can be stacked more easily:

http://www.outbackpower.com/downloads/documents/wiring_diagram/Radian_Grid_Interactive_Two_Stack_Oneline_Rev_4.pdf

Four is a bit more complicated like this:
http://www.outbackpower.com/download...line_Rev-4.pdf

[solar pete]

Thanks Butch, yep he has 6 inverters and 3 Seltronics SP-Pro series I think they were 7.5kW I thought they were a charge controller, so is it more likely they are bimodal inverters? or are they essentially a CC on steroids?

[ButchDeal]

It is hard to tell but they don't seem to sell charge controllers. They have bimodal inverters and seem to pair with third party CC or do AC coupling. So it sounds like either an AC coupled configuration with grid tie inverters and 3 bimodal inverters. Or more likely 6 CC and 3 bimodal inverters.