8400w Grid Tie System - Kit or piece it together?

[DanS26]

I'd question the POCO rep again about no change to your meter setup. In your neck of the woods it is highly unlikely that you have a solar ready meter.

[foo1bar]

With that said, these inverters have a peak output of 5kw @ 240v which means 20.8amps. With the SB7.7, I was going to need a single 40a breaker (32a potential).

Most likely the inverters have documentation that specifies what size breaker to use.
(And I would expect for a 5kW inverter for that to be a 30A breaker.)

You may want to do a breaker box that combines the two inverter's outputs - a pair of 30A connected to the inverters, connected to a 60A in your current shed's subpanel.
60A subpanels are pretty cheap at the HD/Lowes/Menards/Farm&Fleet/etc.

anything over 40A (~ 7.6kw ) usually requires a lineside tap

Possibly not in this case.

"The panel only has 1 220v 20a circuit (welder), 2 110v 20a circuits (outlets on north/south walls), and 1 110v 15a circuit (lighting). No plans to add any more. Wouldn't I still be fine?"

Assuming the pair of 20A circuits for outlets are on opposite legs, he currently has 40A on one side, 55A on the other.
So don't have to worry much about downgrading the supplying breaker and tripping it.
If he has a 125A busbar, he could downgrade the breaker feeding the busbar to a 90A breaker and have a 60A solar supply breaker at the opposite end of the busbar and meet the 120% rule.
If he doesn't have a 125A busbar, it might be possible to downgrade even more and fit it in, but I'd probably just spend 3-6 hours and $200, and replace the subpanel. (or if it's not an end-feed bus bar, then I'd definitely replace the subpanel.)
I think with a 125A busbar he might be able to not worry about opposite-end-feed and 120% rule - 60A + 55A = 115A, so would already be under the 125A rating.
But that means no additional breakers added to the panel in the future - or at most a 20A on the leg that currently only has 40A.

He probably also has to look at how his main panel is setup (I'm assuming he has a main panel next to his meter, feeding the shed's subpanel)

(disclaimer - I'm not an electrician - anyone reading this should use this just as information for starting point for their own research into code requirements and figuring out how to be code compliant)

[Mr4btTahoe]

I'd question the POCO rep again about no change to your meter setup. In your neck of the woods it is highly unlikely that you have a solar ready meter.

Someone had mentioned something about an additional meter previously. They do have to change the standard meter to a "net metering" meter. Someone had said that an additional meter may be required on the solar side of the system. They don't require anything of the sort.

As far as the roof, my contractor friend took a look at it today and I hadn't paid much attention but my purlins are ran on edge instead of on flat and the span between trusses is just under 8'. I think I'll be going with the XR100 setup rails.

After some thinking and looking at the specs on the SB7.7 (still only a 32a max output), the 7.7 suggests an array size just over 9kw. My planned array will be just over 8kw so for the sake of simplicity and cost, I'll go with the single SB7.7 for the time being. If need ever arises to expand, we'll upsize the panel/wiring to the shop and add an additional inverter.. but I don't see that being an issue.

As far as the panel in the shop, I'll go out and verify what it is. I know it is top feed and I'm almost certain its a square d homeline panel.. but I'll double check and update. Staying with the 7.7, I should be good with that panel... shouldn't I? I'd bottom feed the panel with a 40a solar breaker. I'll check it out here in just a minute.

[Mr4btTahoe]

Cant ID the bus bar rating so far. The only labels on the panel interior indicate "accessories" to use which one of them is the main lugs which are 125a rated... but from my understanding, that could be just a general cabinet sticker and not actually indicate the bus rating.

What is the best way to ID bus rating when it isn't labeled?

I was misunderstanding the 120% rule. I was under the impression that it was the load that needed to be under 120%... not the supply. So.. 100a main and a 40a feed... I'd be fine if it has a 125a bus. If I cant figure it out, I'll either change the panel or go line side (which would be simple considering I've got a main disconnect at the meter).

[Mr4btTahoe]

Ok. I THINK I have my components sorted out. Going to list everything out... if you can think of any major components or hardware that I'm missing, please point it out.

I'll be ordering everything from Renvu. From what I've researched, they seem to be a solid vendor. Prices also look to be good compared to most places I've seen.

Anyways.. The List...

24 - Risen Energy 340w Panels

1 - SMA SB-7.7 Inverter

250' - Titan 10awg PV cable

100' - #6 Ground Wire

30 each - Male / Female MC4 connectors (everything will be wired in series.. 2 strings of 12 panels)

MC4 Crimping tool

NEC Label Package

12 - 14' IronRidge XR100 Rails (3 sections per main rail.. 4 rails total 42' long)
8 - XR100 Bonded Rail Splice
13 - UFO Clamps (4 per package)
10 - L-Foot Mount (4 per package) (Being installed on corrugated metal pole barn roof)
10 - Rail Bolts (4 per package)
2 - Stopper Sleeve (4 per package)
1 - Low Profile Ground Lug (2 per package)

I'm sure I'll have a few other odds and ends.. but I think that's it on major components. I'll still need to get the components for the AC side which shouldn't add up to much. Price shipped to my work is just over $8100 which puts me well under budget so I've got some wiggle room if things come up.

Thoughts?

[foo1bar]

100' - #6 Ground Wire

30 each - Male / Female MC4 connectors (everything will be wired in series.. 2 strings of 12 panels)

I'd check the price on #6 (or #4) wire at the local big box store and the local electrical supply house. They may be cheaper.

30 ea of MC4 is a lot for what you've described..
I would guess you'll need more like 5 - maybe 10 to give you a chance to screw them up.
You'll need one pair (M/F) for each end of each string, so that's 2.
If you have two spots where you can't just connect one panel to the next - that'd be another 2.
Plan on screwing up one or two (ex. crimp a male on the wire when you needed female or forget to put the covering onto the wire before you crimp and can't get it on)
That's a lot less than 30.

I'd look at "S5!" clamps - if you're working on a standing seam roof, I've seen them recommended by others (haven't ever used them myself)
I'd really look into the best methods for attaching to your kind of roof - you don't want to deal with roof leaks in 5 years.

[Mr4btTahoe]

I'd check the price on #6 (or #4) wire at the local big box store and the local electrical supply house. They may be cheaper.

30 ea of MC4 is a lot for what you've described..
I would guess you'll need more like 5 - maybe 10 to give you a chance to screw them up.
You'll need one pair (M/F) for each end of each string, so that's 2.
If you have two spots where you can't just connect one panel to the next - that'd be another 2.
Plan on screwing up one or two (ex. crimp a male on the wire when you needed female or forget to put the covering onto the wire before you crimp and can't get it on)
That's a lot less than 30.

I'd look at "S5!" clamps - if you're working on a standing seam roof, I've seen them recommended by others (haven't ever used them myself)
I'd really look into the best methods for attaching to your kind of roof - you don't want to deal with roof leaks in 5 years.

I was thinking that the cables on the panels themselves wouldn't be long enough to go panel to panel... so that makes sense.

I'll check prices local on ground cable.

I'll also take a look at the clamps you suggest. I've been looking for more information on attaching to a metal roof like mine but so far, haven't found much information on products geared specifically for that.

My plan for the L Foot was to only attach to the flats between the ribs and anchor directly to the purlins/trusses. Non-Silicone based sealant under the foot and seals on the bolts to prevent leaks. If I can come up with a better option that is cost effective, I'll go for it.

Thanks for the input!

[Mr4btTahoe]

Just got an email from our local building commission. From what they say, their requirements are just the $30 utility permit and a basic electrical inspection. Haven't heard directly from the inspector yet but it sounds like as long as I do a clean install on the electrical, that is all they care about.

Hoping to start ordering components by the end of the month/early next month.

[ButchDeal]

Just got an email from our local building commission. From what they say, their requirements are just the $30 utility permit and a basic electrical inspection. Haven't heard directly from the inspector yet but it sounds like as long as I do a clean install on the electrical, that is all they care about.

Hoping to start ordering components by the end of the month/early next month.

That is pretty much all that is usually required. It is the electrical inspection that is checking for code compliance.

[Mr4btTahoe]

That is pretty much all that is usually required. It is the electrical inspection that is checking for code compliance.

Considering I cant seem to get a hold of the actual inspector to give me some details.. let me run this by you and see what you think.

Panels will all be wired in series (2 strings). Would you suggest fusing between the panels and inverter? I'd think it would be a good idea.

Array grounded using proper ground lugs and #6 ground wire

All wiring between the panels and inverter will be using MC4 connectors and 10awg PV cable (fairly short run).

For AC power... Line side tap using IDEAL GP-500C insulated taps to a 40a subpanel. Wiring of proper size all in conduit. No external meters or disconnects required by the POCO. Any way to find out what my county may require other then talking to the inspector?

Cant really think of anything else other then the labeling. Sounds pretty straight forward...

[ButchDeal]

Considering I cant seem to get a hold of the actual inspector to give me some details.. let me run this by you and see what you think.

Panels will all be wired in series (2 strings). Would you suggest fusing between the panels and inverter? I'd think it would be a good idea.

As long as you only have two strings you do not need fuses and there should be a DC disconnect on the inverter. I would just land both on it directly unless the wire run is very long then combine them on the roof with single wire set down.

Array grounded using proper ground lugs and #6 ground wire

sounds good.

All wiring between the panels and inverter will be using MC4 connectors and 10awg PV cable (fairly short run).

need wire clips (not cable ties) to support the wires on the rails. If you combine it you don't need to continue MC4.
should be in conduit once you leave the array. Did you determine if you need rapid shutdown? that will increase costs a bit.

For AC power... Line side tap using IDEAL GP-500C insulated taps to a 40a subpanel. Wiring of proper size all in conduit. No external meters or disconnects required by the POCO. Any way to find out what my county may require other then talking to the inspector?

Not really a line side tap since it is after the disconnect but similar. you might be able to tie into the lugs at the disconnect easily.
Most counties list code requirements and standards. Since you only have the one inverter you could go with a 40A fused disconnect box instead of a sub panel.

Cant really think of anything else other then the labeling. Sounds pretty straight forward...

Labeling can be very specific in some place and you likely will need one at the meter itself explaining the solar is at a remote location and how to find it...

[Mr4btTahoe]

Thanks bud! Greatly appreciate the input.

I apparently spoke to soon.. Just got off the phone with the inspector. Seems like a great guy... Said he has no requirements as far as engineered drawings and such.. that his main concern will be electrical and basically, as long as I use some common sense, I shouldn't have any issues. County doesn't require anything more then what the POCO requires. No rapid shut down devices or additional disconnects/meters.

I'll add proper wire clips to my list and the disconnect box.

As far as wire runs.. the longest run will be ~55' (from the far end of the array back to the inverter. I'll be sure to run everything in conduit post array.

I'll also look up labeling requirements. That will probably be the most time consuming thing...

Thanks again!

[Mr4btTahoe]

Last question for a bit....

The SMA SB-7.7 inverter specs say...

Max DC Voltage - 600v

Rated MPP Voltage - 195-480v

MPPT Operating Range - 150-550v


Now the panels.

Open voltage rating is 46.8 (which would be 561.6v per string)

Max Power Voltage is 38.2 (which would be 458.4v per string)

Am I going to be OK wiring 12 panels in series with these specs? I would say yes.. but I'd like to know for sure as I'm not 100% certain which ratings really matter.

Thanks!

[ButchDeal]

Last question for a bit....

The SMA SB-7.7 inverter specs say...

Max DC Voltage - 600v

Rated MPP Voltage - 195-480v

MPPT Operating Range - 150-550v


Now the panels.

Open voltage rating is 46.8 (which would be 561.6v per string)

Max Power Voltage is 38.2 (which would be 458.4v per string)

Am I going to be OK wiring 12 panels in series with these specs? I would say yes.. but I'd like to know for sure as I'm not 100% certain which ratings really matter.

Thanks!

you need to derate those voltages for local weather cold temps will increase.
You want the strings as high as possible without getting close to the 600V peak.

a simpler solution is to use SolarEdge SE7600 and optimizers as you will not have to worry much about strings.

other wise you can go to SolarDesigntool.com and get a free month trial to do your design work. They can also get you a permit pack for a fee but you likely can make your own from the design it spits out.

[Mr4btTahoe]

you need to derate those voltages for local weather cold temps will increase.
You want the strings as high as possible without getting close to the 600V peak.

a simpler solution is to use SolarEdge SE7600 and optimizers as you will not have to worry much about strings.

other wise you can go to SolarDesigntool.com and get a free month trial to do your design work. They can also get you a permit pack for a fee but you likely can make your own from the design it spits out.

Looks like I'll be over voltage in the cold months. The inverter I want to go with has the ability to run 3 strings... so I could just wire them up as 3 strings of 8 couldn't I?

Would make wire routing on the rack a bit more complicated, but would keep me within specs.

After toying with solardesigntool.com the SB7.0 seems to be a better fit when using 3 strings of 8 panels which would save me a bit of cost... and give me the potential to add an SB3.0 down the road if I need more juice... and still be within the 10k and under regulations.