Need a Panel Suggestion between Serivice and main panel for solar

[dcg9381]

This is a little complicated. I've got a setup with 320A service. Shop got finished first (priorities, right?). I have a residence going up that is going to have a whole-house backup generator controlled by an ATS (Auto Transfer Switch).

This is all fine and good, but I want to be able to add a ground mounted solar array in the future. Generators and solar do not play nice together and I'm unwilling to get into a situation with relays or fancy controls. So I'd like to install a panel for future solar in front of the ATS.

I basically need a panel in front of my ATS that can pass 200A through to my main... It also needs to have 2-4 open slots so I can add a breaker for solar in the future...

In particular, I'm looking for a pretty specific suggestion (brand/model) and recommendations on how I should pass that 200A through to the main (breaker?).

 

[wyliesdiesels]

The panel youre labeling “main breaker panel” in the house is NOT a main breaker panel. It is a subpanel.

The problem you may run into here is most ATSs are setup as main service panels to go in between the meter and the first breaker panel on the service.

Are you using an ATS that switches the neutral and does not have a bonded neutral?

 

[dcg9381]

Yes, you're correct on that. I'm calling it the "main" in that's the primary panel for the residence, but you are absolutely right that it's a sub.

Ahh.. I get it, due to the bonding differences between a main and sub panel - you think an ATS might not work there. The ATS has not been purchased yet. Let me dig into a few manuals.

 

[dcg9381]

I *believe* both cases are supported - service rated entrance and non-service rated entrance.

Service rated:
It appears that neutral does not get switched. In the service rated case, neutral is connected to ground, and ground to a ground rod. (I assume this is the case where the ATS is essentially the "main" immediately off the service entrance)

Non-service rated:
Neutral not switched, but is isolated from ground. (I'd be using it this way, as it's a sub-panel)

Attached diagrams.

 

[wyliesdiesels]

Yes, you're correct on that. I'm calling it the "main" in that's the primary panel for the residence, but you are absolutely right that it's a sub.

Ahh.. I get it, due to the bonding differences between a main and sub panel - you think an ATS might not work there. The ATS has not been purchased yet. Let me dig into a few manuals.

yes need to make sure the ATS can function as a subpanel and NOT a main.

I *believe* both cases are supported - service rated entrance and non-service rated entrance.

Service rated:
It appears that neutral does not get switched. In the service rated case, neutral is connected to ground, and ground to a ground rod. (I assume this is the case where the ATS is essentially the "main" immediately off the service entrance)

Non-service rated:
Neutral not switched, but is isolated from ground. (I'd be using it this way, as it's a sub-panel)

Attached diagrams.

neutral and ground are typically on the same bar, so the GEC from the rods goes to the neutral bar.

 

[dcg9381]

yes need to make sure the ATS can function as a subpanel and NOT a main.

I believe this is the case - seems to be noted as "service entrance" and "non-service entrance" (sub-panel) in attachments above. Let me know if you agree.

I've never done an ATS. Electrician didn't blink an eye when I said I was adding one - he's aware of the power feed situation on this residence... I just like to understand what's going on.

Do you have a recommendation for a panel upstream of the ATS? I need something that can pass 200A and take a feed (solar) breaker.

 

[wyliesdiesels]

The hard part about adding the solar is that depending on loads and solar output, you may need to reduce the main breaker rating in this panel you want to add in.

so you need to do some calcs first before just picking out a panel.

 

[dcg9381]

Assume 6KW or less solar. Not a huge array. 20 panels. Typically 30A peak.

 

[wyliesdiesels]

well you will need to do a load calc...

 

[dcg9381]

Running load will be less than 20KW peak.. (I sized a generator). House is propane (dryer stove, tank less water heaters) foam insulated - so relatively low HVAC loads. Our normal running loads during high ambient temp, I'd actually bet 6-10KW.

I'd like a panel capable of 200A. There will literally be 2 breakers in that panels - a 200A breaker (from a 200A feed), yes 30A of solar ties in, but we'll never use all the power from a 200A main.. Solar just drops the pull from the main - I don't see why we'd need more than a 200A capable panel.

Is there a reasonably sized exterior rated panel, capable for handling a 200A pass-thru, with 2-4 additional slots?

It seems the "odd case" here is that I need 200A pass thru. That's the part that seems to require some electrical experience.... Suggestions?

 

[wyliesdiesels]

as i said, you should do a load calc as there is quite a bit to calculate here to make sure the buss of the panel is rated for everything you want here.

there are specific calcs for the solar being in the mix.

the main breaker may need to be reduced.

 

[dcg9381]

Again, I've done a load calc related to sizing the generator. Multiple upstream over-protections anyway at 200A. I'm unwilling to reduce the main (unless absolutely necessary).

As I understand it, the rule for busbar and solar is (690.64(B)(2), or 705.12(D)(2)):
(Busbar Rating (A) x 1.2) - Main Breaker Rating (A) = Max PV (A)

<200A busbar * 1.2> - 200A main breaker rating = Max PV

240 - 200 = 40A Max PV.

We'd be limited to (future) solar of 9.6KW, which is fine.


Can you recommend a 200A (or better) busbar rated panel that can do a 200A breaker and has at least 2-4 additional slots? It's the 200A breaker that is giving me grief.

 

[ezzzzzzz]

I have a generator and solar arrays. There may be work arounds but my solar is tied to the main grid through a net meter. The generator is fed through a ATS to a dedicated breaker panel which dictates which circuits get back up power. When the generator is running the show the solar arrays and grid are not part of the equation.

 

[dcg9381]

In the case here, adding a net meter for solar incurs a monthly fee, so it's non-ideal. The existing meter is already setup for solar (net).

I can do what you are suggesting, but need put the solar "upstream" of the residence, which is what I'm trying to do via adding the panel. The house is more ideally located than the service entrance (which has a panel on it) in terms of solar.

 

[ezzzzzzz]

I'm assuming you're part of a co-op? If so, have you asked them for assistance? I pay about $20@month for my meter regardless of solar or not. I've got three meters on the farm which I pay $20@month each but only one is a net meter. Anyhow, besides the offset to my electrical bill I'm also selling my energy credits through an SREC. My small 7.5k system gets me around $3000 a year which does a good job offsetting my energy costs.

 

[theoldwizard1]

Is your solar going to be "grid tie" so as to minimize your bill, or do you plan on going "off grid" (batteries and inverter). I either case, your ATS may be a problem.

If you are going grid tie, your ATS will prevent any power from the solar panels from entering your house. If you "cut the cord" to the PoCo. the ATS will be starting the generator anytime the batteries/inverter do not meet the demand. It will take extra wiring to charge the battery bank when the generator is running.

 

[dcg9381]

I'm assuming you're part of a co-op? If so, have you asked them for assistance? I pay about $20@month for my meter regardless of solar or not. I've got three meters on the farm which I pay $20@month each but only one is a net meter. Anyhow, besides the offset to my electrical bill I'm also selling my energy credits through an SREC. My small 7.5k system gets me around $3000 a year which does a good job offsetting my energy costs.

You power must cost a LOT more than mine. You're producing $250/mo+ in power from 7.5kw? I pay .107 per kWh.

I do have a co-op. They are not very "new technology" helpful. Great specs on the way they've been doing things, but their support of solar is very rudimentary. It's great because I've done a bunch of installs with them and I've never been red-tagged, but it's not great because they don't respect new technology - even if approved in the recent NEC... IE - they still require physical disconnects when new systems have rapid (automatic) shut-downs that are compliant with NEC.


Adding a new meter costs me $20 month - so I'd like to avoid that. It also would require a few thousand in additional work - concrete, meter pad, meter box, etc.

Basically, I get dollar for dollar credit on energy production versus use, as long as my net monthly is more than 0 kWh.

If I over produce, the co-op pays me "wholesale rates" - which is a fraction of what I have to pay them for power... As such, over-producing isn't a particularly good deal here. The best you can do is produce as much as you consume a month - that's the sweet spot. If I add a new meter for this, then I owe them $20 in energy just to break even.

Is your solar going to be "grid tie" so as to minimize your bill, or do you plan on going "off grid" (batteries and inverter). I either case, your ATS may be a problem..

I don't do off grid. The grid is my "battery" - at least in terms of dollar for dollar use credits - that's the only way that solar can be made to pay-back here in a reasonable amount of time.

The ATS is the "disaster" solution. If power fails - the generator comes on. It's highly unusual to lose power here for more than a few hours, but we'll be able to do a few weeks on propane.

I'm aware that I can't use solar with the generator on the house - but do appreciate you calling that out. The only way to get that to work is to do batteries, set circuits aside for being powered by the inverter, etc. I do get the "advantage" here, but the goal is to pay for solar and have the ATS/generator handle the power outage scenario.

 

[dcg9381]

Looks like this is one of those figure-it-out-yourself posts, so here's the follow up.
Helped that I asked me actual electrician.
He said "any panel with feed through lugs"
Course, I didn't know that panels came in lug categories, so here's what I learned..

Looks like all of the Siemens "P" panel series can accept feed-through lugs as an option. Lug kit for 200A AL wire: MLKA1A