Solar install turning out really bad - looking for some help/advice please.

[bcroe]

What's even more confusing though is that for the DC run from the combiner box to the inverter (50' run), they show 2AWG wire! Now that's a little nuts because the inverter won't even take that big of a wire, the largest it will allow is 6AWG which is what we used.

I am trying to figure out just what your DC voltage & current are. IF you had 4 strings of
10 panels (of 72 cells), they would nominally run about 360V and 8.61A peak per string,
or 34.4A total (but only if all panels could see best sun at the same time). A loop of 6
gauge 100' long would be about 0.04 ohms, giving worst case 1.38V drop. That is only
0.38% loss, and with varied panel orientations, even that number is too high.

HOWEVER, your optimizers change the numbers. I don't know how your strings are
arranged, and have yet to hear an exact explanation of the algorithm optimizers use
in operation. So I can't come up with accurate numbers. Perhaps checking the inverter
readout could show what the DC numbers really are? Bruce Roe

[sensij]

I am trying to figure out just what your DC voltage & current are. IF you had 4 strings of
10 panels (of 72 cells), they would nominally run about 360V and 8.61A peak per string,
or 34.4A total (but only if all panels could see best sun at the same time). A loop of 6
gauge 100' long would be about 0.04 ohms, giving worst case 1.38V drop. That is only
0.38% loss, and with varied panel orientations, even that number is too high.

HOWEVER, your optimizers change the numbers. I don't know how your strings are
arranged, and have yet to hear an exact explanation of the algorithm optimizers use
in operation. So I can't come up with accurate numbers. Perhaps checking the inverter
readout could show what the DC numbers really are? Bruce Roe

SolarEdge systems operate at about 350 Vdc. The optimizers are capable of converting the output of the panel as needed to maintain that voltage in the string. String size doesn't matter in the way it does for other string inverters or charge controllers. The voltage drop difference of 2 AWG or 6 AWG on the DC side is a couple tenths of a percent. Probably not enough to justify the higher cost of the larger wire.

More discussion of the AC wire size for this system is in this thread. The ground wire sizing is covered by different rules, and SolarEdge (with an ungrounded PV circuit) will have different requirements than the transformer based inverter.

Volusiano... your posts do not show a good understanding of the code involved. While I respect your enthusiasm and ability to logic your way through it, you should refrain from posting specific conductor or OCPD sizing unless you can justify it with a code citation.

[HX_Guy]

I am trying to figure out just what your DC voltage & current are. IF you had 4 strings of
10 panels (of 72 cells), they would nominally run about 360V and 8.61A peak per string,
or 34.4A total (but only if all panels could see best sun at the same time). A loop of 6
gauge 100' long would be about 0.04 ohms, giving worst case 1.38V drop. That is only
0.38% loss, and with varied panel orientations, even that number is too high.

HOWEVER, your optimizers change the numbers. I don't know how your strings are
arranged, and have yet to hear an exact explanation of the algorithm optimizers use
in operation. So I can't come up with accurate numbers. Perhaps checking the inverter
readout could show what the DC numbers really are? Bruce Roe

I believe the current fluctuates in order to keep the DC voltage around 350V or so (in reality it looks like it keeps it more around 370VDC looking at the inverter LCD display). Here is the spec sheet on the inverter, mine is the P400.

http://www.solaredge.com/files/pdfs/products/power-optimizers/p-series-us-application-note.pdf

Worst case it looks that it would output 15A, which is what the fuse in the combiner is too. I've got 3 strings wired in parallel (1 of 16 panels, 1 of 13 panels and 1 of 11 panels), so worst case scenario that would be 45A but I don't think that would ever happen...more realistically like you said, 8.61A x 3 strings = 25.83A.

The permit however was designed for 4 strings of 10 panels, or 60A total...which is maybe why it asked for 2AWG wire. After talking to SolarEdge however, I changed the strings down to 3 and they said 6AWG would be more than plenty, they actually said even 10AWG would be fine and I could go with 8AWG to be safe.

[Volusiano]

Volusiano... your posts do not show a good understanding of the code involved. While I respect your enthusiasm and ability to logic your way through it, you should refrain from posting specific conductor or OCPD sizing unless you can justify it with a code citation.

I'm not offended by what you said, and I admit I don't have expert understanding of the code, so I'd like you to educate me on what I said so far that's not in accordance to code for my own education.

I believe I said the inverter's max output current rating is 47.5A so the 60A breaker and 6 awg wiring should be good. This is not based on my direct knowledge of the code. This is based on my observation that my 60A breaker has 6 awg wire and it passed inspection so the assumption is that it passed codes. I think you agreed with this in one of your posts (you said "The SE11400A has a 47.5 A rating, and 125% of that is just under 60 A. Once the breaker is set at 60 A, the wire size follows.").

I believe the other thing I said without any code knowledge is that usually common practice for ground wire is to go 1 size lower (in this case 8 awg for ground if main wires are 6 awg). This is again not based on my knowledge of code but based on my observation of how my solar system wiring set up is, which passed code (8 awg for ground wire and 6 awg for main wires to 60A breaker in my setup).

My statement about guessing 10 awg for ground wire maybe OK (for 6 awg main wires) because the ground wire doesn't have to carry full continuous load before the breaker trips is neither based on my observation of my system nor based on code which I don't have expert knowledge of. It's just an educated guess on my part and that's why I only said "I think it's OK" and I didn't say "I'm sure it's OK".

I looked at the link you gave about "More discussion about AC wiring sizes for this system in this thread" but I didn't see any discussion about ac wiring sizes there. Did you give the wrong link? I'd be interested in seeing a link that discusses what the ground wiring size needs to be and what all the rules pertaining to it are.

If I made any other references to wiring sizes beside the 2 citations above, and did it so erroneously without an understanding of code, please point it out so I'm aware of it so I can retract it by editing my post(s) to take it out.

Again, I'm not offended by your comment. My response here is more in the interest of learning for clarification on what I said wrong (per code) for self education. Thanks.

[HX_Guy]

Some additional information on the maximum DC current, saw this label on the side of the inverter.

So knowing this information, what is the proper size wire for a 50' run from the combiner box to the inverter?

[bcroe]

Some additional information on the maximum DC current, saw this label on the side of the inverter.

So knowing this information, what is the proper size wire for a 50' run from the combiner box to the inverter?

OK, that is more good info. The inverter has a max 34.5 ADC. Just maybe, your
max is 3 times a panel Impp? What did it read out?

I'd worry that a string of 16 panels would have a Vmpp on the order of 576 VDC.
Do the Optimizers somehow avoid that issue for the 500 VDC max inverter? What
limits do Optimizers placed on number of panels?

A guess is, the more difference in the number of panels between strings, the
more difficult for the Optimizers to operate the strings in parallel.

Still trying to figure the algorithm Optimizers use. Practicality dictates that they
are used in series strings, so all the Optimizers in a string are putting out the same
current. How about, every panel tries to deliver its maximum current starting up?
The panels with less capability (shaded, etc) can't keep up, so they are bypassed,
zero output voltage? The Optimizer starts multiplying the panel output current (by
stepping down its panel voltage) till the current matches the current from the strongest
panels? This "current multiplication" is adjusted to keep the Optimizer's panel on
its present Vmpp? So each Optimizer puts out the same current, but since some
panels are shaded, they may have lower voltages? So the string total voltage
could go ANYWHERE depending on sun? But this doesn't allow parallel strings?
And certainly doesn't set any particular overall string voltage?

A problem with something like this, is you have a bunch of closed loop systems
trying to work together. They could start hunting for an operating point, or
oscillation. So how does it REALLY work?

The output voltage limits printed on your inverter look like the standard ones for
my Fronius, except mine are programmable. Should be OK unless your line
voltage is too high. Mine was 254 VAC, and pushing back inverter power
raised it even higher. Bruce Roe

[Volusiano]

Some additional information on the maximum DC current, saw this label on the side of the inverter.

So knowing this information, what is the proper size wire for a 50' run from the combiner box to the inverter?

This Wiki AWG link shows a resistance of 0.3951 milliOhm per ft for 6 awg copper. You have 50 feet so that's 0.3951*50=19.755 milliOhm. Your max input current is 34.5A DC. So the max dc voltage drop over your 50' 6 awg run would be 34.5*0.019755=0.68V dc. This is not even 1Vdc, a drop in a bucket. If the inverter is operating at minimum voltage of 270V dc, that's 0.68/270=0.2%. If the inverter is operating at max 500Vdc then it's 0.68/500=0.14%.

You can go through the same math for 4 awg and 8 awg and 10 awg if you want. But given how tiny the voltage drop seems to be even at max input dc current as seen above for your 6 awg 50' long wire run, is it even a concern anymore? Especially if your setup typically operates at 350Vdc like you said (if I remember what you said correctly), the less than 1V drop across your 6 awg wire is not going to take your inverter out of range (270Vdc min input) any time soon.

And the 6 awg wire should be able to handle the 34.5A dc current just fine. 34.5*1.25=43.125A and the 6 awg ampacity at 60C is 55A according to that AWG Wiki link. 8 awg might not have been sufficient if you go by 60C (40A<43.125A), but if you go by 75C then it might have been sufficient since 50A>43.125A. This is all based on that Wiki awg table from that link above.

And once again, disclaimer: I don't have any expert knowledge of code so I'm not citing code numbers here to support my finding of the wiring gauge discussion above. The opinion above is strictly mine based on the calculation I did above and AWG Wiki table I used as shown in the link. Anyone can check my work above in case I made any mistake. But it's pretty simple calculation I think. Listen to my opinion or not at your own risk and if you're not sure, you'd be best consult the codes to be sure.

[sdold]

You have 50 feet so that's 0.3951*50=19.755 milliOhm. Your max input current is 34.5A DC. So the max dc voltage drop over your 50' 6 awg run would be 34.5*0.019755=0.68V dc.

I think it's 1.36V, since the current has to make a round-trip (100').

[bcroe]

Hm, I don't think so because all you care about is the effect of the voltage drop at the inverter's input, so wherever the current goes after that is irrelevant.

And the current doesn't really make the round trip back (to where?), it just goes out to the grid and ends up wherever it ends up, right? Like maybe to your own loads or your neighbor's circuit panel through their loads to their ground.

HA HA HA HA HA HA HA HA HA HA (stopped to roll on the floor) HA HA HA.
thanks for making my night. Bruce Roe

[HX_Guy]

Worked on tidying up and fixing a couple things today...

First I took care of the ungrounded disconnect box, hopefully I did this properly. Used a 8AWG bare copper wire, scratched off a bit of the paint inside for a good bond, and used the same grounding lug. It looks good to me, but I have no experience with this.







Then I worked on running the CAT5 cable from about a 10' distance away from the inverter, to the inverter.
I got lucky here in the sense that the house already had a cable running to this location from the networking box inside the house, just had to crimp on a connector on this end and plug into the networking switch in the other end.









Cleaned up the rat's nest of conduit as best I could by moving the irrigation control box.





I'm definitely glad I insisted on the installer re-running the metal conduit down and under the fence instead of the crap he originally did, looks a lot cleaner.





Now just have to paint everything the color of the house and it's all done.

[HX_Guy]

OK, that is more good info. The inverter has a max 34.5 ADC. Just maybe, your
max is 3 times a panel Impp? What did it read out?

I'd worry that a string of 16 panels would have a Vmpp on the order of 576 VDC.
Do the Optimizers somehow avoid that issue for the 500 VDC max inverter? What
limits do Optimizers placed on number of panels?

You can actually have up to 25 panels per string, but no more than 5250W DC, which is why my string is 16 panels.
The way I understand it, if you have shading issues or different orientations, the more panels per string, the better.

Here is a long video on the SolarEdge Optimizers, but the explanation on how they work starts at 21:25.

http://youtu.be/QsGC3FA5ilk

[Volusiano]

Was it easy to feed the conduits under the fence in your case?

I allowed my installer to run the conduit over the fence because there were already other prior conduits under the fence and there was no more space for more conduits without some major drilling. Plus this is a 1" conduit so it'd be even harder to fit. But it didn't look too bad in the end after I painted everything the same color of the wall (well everything except the labels on the boxes and labels on the conduits and the inverters in case of warranty return). In the end it blends in pretty well with the wall after painted anyway.

[bcroe]

Did I say something wrong or funny? If I said something wrong, I'd like to know what. If I said something funny, it wasn't intended and I didn't mean to mock anybody. But glad I was able to entertain you and make your night, LOL!

I didn't know if that was a joke or not. But if you really think an electrical circuit doesn't
need to have a complete round CIRCUIT back to the beginning, you need to take a break
for basic electricity 101. Bruce

[HX_Guy]

Was it easy to feed the conduits under the fence in your case?

I allowed my installer to run the conduit over the fence because there were already other prior conduits under the fence and there was no more space for more conduits without some major drilling. Plus this is a 1" conduit so it'd be even harder to fit. But it didn't look too bad in the end after I painted everything the same color of the wall (well everything except the labels on the boxes and conduits and the inverters in case of warranty return). In the end it blends in pretty well with the wall after painted.

Yeah, there was plenty of space...the only other conduit already there was the one going to the pool. My installer used 3/4" EMT though, I don't think 1" would have fit. (Permit specified 1"...I'm curious how the inspection is going to go in regards to that.)

[Living Large]

Hm, I don't think so because all you care about is the effect of the voltage drop at the inverter's input, so wherever the current goes after that is irrelevant.

And the current doesn't really make the round trip back (to where?), it just goes out to the grid and ends up wherever it ends up, right? Like maybe to your own loads or your neighbor's circuit panel through their loads to their ground.

Hmmm. Well, let's look at this. From Array+ -----> Inverter+, you lose xV in the wire. From there, the current doesn't disappear or fall into the ground, but goes back to the panel over the same distance and voltage drop: Inverter- ------> Array-, and you drop another xV. So in fact you lose 2xV, not xV.

The suggestion that the current "doesn't really make the round trip back" and "wherever it goes after that is irrelevant" is quite interesting, since without a circuit there is no current through the array. Think of the cost savings in not running the return wire - if the current just flowed out the end.

And remember, the electrons are actually going in the opposite direction of the current. The Bizarro world!