Converting 50kW system from micro inverters to 8x SMA inverters

[pclausen]

Turns out there is an integration already developed for SMA in Home Assistant. I added integrations to the 4 SBs I have online so far and made a very crude dashboard:



Since all the sensors are now there and data is updated every few seconds, I can do something like what I have for my Davis weather station, which looks like this:



Or I can use Grafana to do something like this:



Or setup a table like view similar to what I have for my mining rigs: (that was the catalyst for going solar in the first place)



But first I want to get the other 4 inverters online, then tinker with collecting stats and monitoring.

[pclausen]

Man it sure is hot and humid here in VA today under mostly sunny skies. Played around with the layout a little:



Still trying to figure out how I want to group and label the individual DC strings.

I do have some basic graphing in place. Here's one of the 15 panel strings:



Not sure what is causing the spikes, but maybe that's when the sun pops out from behind a cloud?

I wonder what the graph will look like on cold clear days?

[nerdralph]

So with that finally out of the way, I completed wiring the #6 L1/L2 to each inverter, along with #10 Neutral and GND. I also did Ethernet homeruns to each inverter. Yes I know you can daisy chain them all together, but I always homerun each wired device back to the nearest switch.

You don't need to wire up N, just L1, L2 & Gnd. You should be able to find 8/2 for about 20% cheaper than 8/3. It used to be hard finding 8/2 local electrical wholesalers (they had 8/3), but now most of them carry it for the solar installers.

[pclausen]

Ah good to know. I had N wires to all the Micro Inverter strings and just left the THHN #10 wires there. I'll go ahead and pull them out for a much cleaner look. Fortunately I already had stock on hand, so I didn't buy anything additional for this project, other than the 300 MCM and #10 PV wire for the exposed runs.

[bcroe]

You don't need to wire up N, just L1, L2 & Gnd. You should be able to find 8/2 for about 20% cheaper than 8/3. It used to be hard finding 8/2 local electrical wholesalers (they had 8/3), but now most of them carry it for the solar installers.

My string inverters connect to neutral, for the line voltage monitors. Your
results may vary. Much of my wire came from the internet, lots of choices.
Bruce Roe

[pclausen]

Good point. I'll just leave them in place then since they are already run. I got 2 more inverters online this morning. These are the arrays on the hillside where some panels have cracked glass. For now, I just wired each array as 2x12 strings.

This is the configuration:



So that array has one cracked panel in each string.

The other array is like this:



So string A has 2 cracked panels and string B has none.

Looking at the output of each of those strings:



It looks like I am taking a small hit, maybe. But given other variables, like dirt on the panels, there may be no performance hit at all. One string with a cracked panel is only 8 watts lower than the one with no cracked panels. So until I start seeing the strings with cracked panels perform worse that those without, I'm tempted to just leave well enough alone. All 4 panels that cracked happened at the same time about 2 years ago when I was using a stump grinder to do some trenching in front of the shop building. (I know, I know)

[pclausen]

Had a chance to play a little with InfluxDB and Grafana today in Home Assistant. Got a rough dashboard going that looks as follows:



The large graph is probably the most interesting one, especially the red line (Hillside #1). That's the array that gets partial shade from the Hillside #2 array in the am.

Needs a lot more work, but its a start. I can get a lot more out of this already than what the Sunny Portal offers. I completely gave up on it when I discovered it doesn't support more than 4 inverters per site.

Ultimately, I want to create a dashboard similar to this one:

[pclausen]

I ran out of wire when making the 52 3.5ft extensions I need when converting the shop roof from micro inverters to strings. Another roll should finally get here by next week.

When I installed the 56 panels on the shop roof, I divided them into 3 sections (4x5, 4x4 and 4x5) so that I wouldn't have any issues with expansion and contraction with temperature changes.

The mounting system Ubiquiti used was pretty unique:



And here's one of the separations:



My plan is to work on one section at a time, and remove the top 3 rows of panels from each section, and stack them on this pallet:



So I'll have 12 or 15 panels on the pallet, depending on what section I'm working on. I'll put each panel on the pallet face down so that I can remove the micro inverters as I go. With the top 3 rows of panels gone, I'll be able to get to the micro inverters on the bottom row of panels and remove them without having to remove or lift those panels at all.

The 4 AC stings currently come down through the roof like this:



And the individual strings are joined in this box:



I'll probably scrap that junction box and get another one just like it and drill 8 small holes and then use robber grommets for each PV wire, much like I did here for one of my ground arrays:



Fun times ahead!

[J.P.M.]

I ran out of wire when making the 52 3.5ft extensions I need when converting the shop roof from micro inverters to strings. Another roll should finally get here by next week.

When I installed the 56 panels on the shop roof, I divided them into 3 sections (4x5, 4x4 and 4x5) so that I wouldn't have any issues with expansion and contraction with temperature changes.

The mounting system Ubiquiti used was pretty unique:



And here's one of the separations:



My plan is to work on one section at a time, and remove the top 3 rows of panels from each section, and stack them on this pallet:



So I'll have 12 or 15 panels on the pallet, depending on what section I'm working on. I'll put each panel on the pallet face down so that I can remove the micro inverters as I go. With the top 3 rows of panels gone, I'll be able to get to the micro inverters on the bottom row of panels and remove them without having to remove or lift those panels at all.

The 4 AC stings currently come down through the roof like this:



And the individual strings are joined in this box:



I'll probably scrap that junction box and get another one just like it and drill 8 small holes and then use robber grommets for each PV wire, much like I did here for one of my ground arrays:



Fun times ahead!

On the 3d photo:
1.) That pallet looks a bit worn and battered to be able to take maybe a 500+ lbm. load.
2.) What is/will keep the wood blocks at the left side in place when the pallet is loaded ?

On then 6th photo:
1.) I don't know the answer to this question and maybe you've already addressed the situation, but when, if at all does code allow holes to be drilled in a junction box ? Sec. 314.15 seems to address it, but those are not drainage openings. In any case, it still looks like the AHJ must sign off on it field modifications. Just sayin'.
2.) As shown, what will happen to liquid that drips onto/around the grommeted holes, especially as the grommet material dries out/contracts/cracks ? Just my opinion, but that looks like a lot of trust to place in rubber/neoprene/whatever grommet.
Condensate will drip off the underside of panels to whatever is below. I'd suggest that makes the underside of panels a damp/wet location.

[pclausen]

All good points. The pallet looks worse in the pic than it actually is. Other than those 2 board that were not nailed on straight, the wood is sound. It is a couple of months old and it what supported 15 panels I picked up recently to add another row to my pole barn. I will screw a couple of 2x4 to the side of the 6x6 blocks to tie them to the pallet to keep them in place.

Agree that drilling holes in a junction box and using grommets is certainly not ideal. I searched quite a bit back in 2019 when I did that particular ground array and never did find anything I could use to transition PV wires from strings into a junction box and or directly to conduit.

I had the same issue in 2020 when I did the pole barn extension. This is what I ended up doing for that install:



Looks like something like this would be a better choice:

https://www.amazon.com/dp/B08TCF3S13/ref=sspa_dk_detail_4?pd_rd_i=B08TCDW489&pd_rd_w=gD2xx&content-id=amzn1.sym.999c0877-3704-4f0f-9726-eebf80846a35&pf_rd_p=999c0877-3704-4f0f-9726-eebf80846a35&pf_rd_r=B07F3RQPH780PTS4333V&pd_rd_wg=QM0Ui&pd_rd_r=45febf78-2a67-4134-84ed-01b194bc9160&s=hi&sp_csd=d2lkZ2V0TmFtZT1zcF9kZXRhaWw&spLa=ZW5jcnlwdGVkUXVhbGlmaWVyPUExNldRTTJUQlhXRUJCJmVuY3J5cHRlZElkPUEwODMzNTEzMzRLSzQ2U0ZMR0k3TSZlbmNyeXB0ZWRBZElkPUEwMjQwODYxRjNCTVFRQjg3NUMxJndpZGdldE5hbWU9c3BfZGV0YWlsJmFjdGlvbj1jbGlja1JlZGlyZWN0JmRvTm90TG9nQ2xpY2s9dHJ1ZQ&th=1

[Ampster]

As far as the grommets are concerned, let gravity be your friend, Put the holes in the bottom of the J box and use drip loops. The weather head you posted in another picture is a good example,

[pclausen]

Good suggestion. I'll definitely do that with the new J box on the roof.

Played around with my dashboard a bit more:



Sill need to work on my weekly and monthly graphs.

[bcroe]

I once had a broken ceramic insulator on a huge diode, but it still tested
good. Months later, reverse leakage had become unacceptible. I
concluded semi conductors must be sealed to last. I would take those
2 cracked panels out while the weather is nice, and swap them with a
convenient pair in the string that already has 2 cracked. So when trouble
comes, it will only affect one string and be easily serviceable.

I must note just how much more wiring is need by a micro inverter array,
than my string array. Higher losses too. Your 20 July readout shows
line voltage of 129.18 plus 130.19, near 260VAC. Some inverter voltage
monitors are programmed for shutdown at 264, you are very close and
subject to any line variations. That happened here, short term fix was
re program inverters, eventually got the utility to lower voltage. 5 years
later I added some much bigger wire to lower voltage and increase efficiency.

What is your snow experience? Bruce Roe

Sn4iE2.JPG

[J.P.M.]

All good points. The pallet looks worse in the pic than it actually is. Other than those 2 board that were not nailed on straight, the wood is sound. It is a couple of months old and it what supported 15 panels I picked up recently to add another row to my pole barn. I will screw a couple of 2x4 to the side of the 6x6 blocks to tie them to the pallet to keep them in place.

Agree that drilling holes in a junction box and using grommets is certainly not ideal. I searched quite a bit back in 2019 when I did that particular ground array and never did find anything I could use to transition PV wires from strings into a junction box and or directly to conduit.

I had the same issue in 2020 when I did the pole barn extension. This is what I ended up doing for that install:



Looks like something like this would be a better choice:

https://www.amazon.com/dp/B08TCF3S13...HJ1ZQ&th=1

On the pallet: it looks to me like about the only thing keeping it from sliding down the roof is the sort of notch in the beams at the peak. I appreciate that it's a temporary thing but so is wind.

I've put penetration's on the bottom side of things that needed penetrations, but never a junction box. NEMA 4 or 4X which is what I usually specified and was spec'd when I was engineering process equipment and their control systems.

[pclausen]

I measured my PV cables, and the OD is right around 1/4". So I went ahead and ordered those cable glands I linked to earlier. They are for cables 4-8mm (0.16-0.31inch) so they should be just about right for my wires. I'll be sure to drill the holes for the glands on the downward facing (South) side. I suppose I could look at NEMA 4X enclosures like this one:

https://www.amazon.com/VEVOR-Electri...NrPXRydWU&th=1

But that might be overkill for what I'm doing. Once the install is done, it will never be opened again, so a fancy lockable door is not really needed.

I did screw on some support 2x4's to the pallet:



If I was really paranoid, I could also strap it to a couple of a solar panel roof anchors on the other side of the ridge. That would for sure keep it in place I would think, unless some crazy storm comes through while I have panels on the pallet. I plan to start with the first section early Wednesday morning (assuming my PV cable gets here Tuesday as the UPS tracker is currently showing) and maybe get all 42 panels from all 3 sections done if I hustle that day. Might spill over into Thursday, which looks ok for the first part of the day. The rest of the week, not so much.



Looking back from when I initially installed the shop roof array, it looks like I had all the prep done on 10/31/2016:



And the first few panel mounted around 5pm:



And was about 40% done on 11/4/2016:



And down to the last few panels on 11/6/2016:


So getting it all done in one day by myself might be a stretch. But when I did it originally, I had to load one panel at a time on the tractor after installing the micro inverter and landscape cable, drive it into position, climb the latter, pull the panel off the tractor, and then mount it, then climb back down the latter and repeat the process for the next panel.

This go round, I'll be on the roof the whole time, so I anticipate it going a LOT faster. But we'll see. Some of the fasteners might not want to come off easily after 6 years.