PV array install

Anawa · January 2015

I'm currently in the process of installing a complete off-grid installation and would like some advice on monitoring the PV array install. I am performing a self-install because of the lack of truly knowledge designers/installers in my area and reasonable pricing.

The array will be mounted on a south facing metal roof with an 8/12 slope. It consists of: 18 ea. Kyocera 255 watt wired in series of 3 in a 6 parallel configuration. I've traded with my metal roofing contractor to mount the brackets, secure the panels, connect the MC4 wiring at each series config, label and tie the pairs together, then lay each pair (+-) in a tray under the ridge cap. The roofing contractor is responsible to string the cable from panel config to drop down to the combiner box. The combiner box is mounted on the wall just above where the FP2 is located.

After studying many PV mounting options, I'm using the S5 corrugated roof bracket. Each bracket is mounted every 18" into a full 1" wood furring strip with 4 ea. SS screws. Each PV panel will be held in-place with a minimum of 6 of these brackets, mounted the long side of the panel. It seems to be a very clean and resonably priced system.

S5 link: http://m.s-5.com/exposedfastened/CorruBracket.cfm

My situation is this. I know a roofer is not a knowledgeable PV installer, but a 8/12 metal roof is no where for a inexperienced person to be ... bodily damage and roof destruction are not risks that I relish. I think I can monitor the bracket attachment and placing of the panels without getting completely on the roof, but what is a good way to test that each of the panel config' are correctly connected? I have a multimeter to test the voltage. What's the best way to use it in this instance? Weather permitting, I hope to start this operation next week.

Comments on this process are welcome.

Thanks
Anawa in Georgia

BB. · January 2015

Re: PV array install

Measure the sort circuit current of the panel/string. You can use a DC Current Clamp meter (a good enough low cost meter)--Easier/safer than using a standard DMM.

Note, do not make/break the MC4 connectors under load--The arcing will damage the pin and socket (they are very fine/small diameter parts). You could wire in a switch in a jumper cable so you don't have to cover the panels to turn them "on/off". You should measure around 50% to 100% of Isc in the middle of the day (depending on sun position/weather). If you have two or more parallel connections, the current between strings should be pretty well matched (if measurements are made very close in time to each other/no changes in sun or weather).

Simply measuring Voc will work OK--But will not show if you have low resistance connections.

-Bill

Anawa · January 2015

Re: PV array install

Thanks BB. I will need some more info to be sure I understand the process you're advising.

In order to use the clamp meter, the line must be under load? Does this mean I will need to snap the +/- connectors at the terminal end and place the panel in a short circuit?

Anawa

Anawa · January 2015

Re: PV array install

BB, I'm thinking that installing a switch to open the circuit on the pair of MC4's would be time consuming and tedious just for a temporary measurement. I'm not discounting the procedure, just wondering if another way can be as effective.

I think I understand the concern regarding low resistance at the connections. The only connections between the rooftop panel string to the location of the combiner box where I would like to measure the panels are with the MC4's. I've purchased cable long enough so that the max number of MC4 connectors on one of the pairs is only 2 (two) and on the other run, there will be only one (1). Given the type of connector and the quantity on each run, is the measurement for low resistance at connections a major cause for concern is this instance?

Anawa

BB. · January 2015

Re: PV array install

Anawa wrote: »

Thanks BB. I will need some more info to be sure I understand the process you're advising.

In order to use the clamp meter, the line must be under load? Does this mean I will need to snap the +/- connectors at the terminal end and place the panel in a short circuit?

Anawa

Yes--You need to pull current through the wiring. DMM (digital mutli meters) use very little current when measuring voltage (millions of Ohms of meter resistance)--So any connection, even a very poor connection, can read full voltage.

Solar panels (at least standard crystalline panels) are perfectly OK to short circuit and measure Isc (short circuit current). If you have good connections, you should measure the maximum current available from the solar panel (of course, output current is proportional to amount of sunlight... Cloudy day, off angle sun, etc. will reduce the available current).

Anawa wrote: »

BB, I'm thinking that installing a switch to open the circuit on the pair of MC4's would be time consuming and tedious just for a temporary measurement. I'm not discounting the procedure, just wondering if another way can be as effective.

MC4 Connectors are very reliable--And as long as the crimp is made OK--You may not need to measure the total current.

Plus, once the charge controller and battery bank are connected, you can use the clamp meter to measure the current in each string (especially if the total output current from teh array does not look right).

Note that just looking at the sky and the current on the array input to the charge controller--A little haze/overcast, hot temperatures, and not 11am-1pm sun, you can be looking at near 50% of Isc rating... If you can get a clamp meter on each solar string connection--Then you can measure string A to B to C to etc... If all is well, each string should be almost identical current (solar panels share current very well).

I think I understand the concern regarding low resistance at the connections. The only connections between the rooftop panel string to the location of the combiner box where I would like to measure the panels are with the MC4's. I've purchased cable long enough so that the max number of MC4 connectors on one of the pairs is only 2 (two) and on the other run, there will be only one (1). Given the type of connector and the quantity on each run, is the measurement for low resistance at connections a major cause for concern is this instance?

It is not a major problem for most people--If you make it easy to measure each string's current from the combiner box with a clamp meter--Or even use the circuit breakers to turn off one string at a time and read the charge controller's current--That is all you have to do.

-Bill

Anawa · January 2015

Re: PV array install

Thanks for the info. I will think on this some more and get my plan together.

Anawa

zoneblue · January 2015

Re: PV array install

America sadly has little sense when it comes to metal roofing. AU/NZ pioneered metal roofing in the colonial era and it still the most common roofing here. Here ist mounted over 75x50mm purlins not ply deck, and teh metal is reasonably thick and capable of spanning 800mm centers.

That bracket looks promising enough when you look at it, but looking closely its mounted in the troughs not the crests. Looks to me like it would work just as well mounted on the crests... might be worth a test. Crest penetrations are virtually leak proof, with only minimal sealing required.

Anawa · January 2015

Re: PV array install

ZB, I'll send some images of the roof framing on the structure, later. I used 4" x 6" purlins between the trusses with "net" spans of 26"-27" for the metal roof deck. This configuration is definitely not typical here in the US, but it was what I needed and was able to be squeaked by the inspectors. It's all good.

The S-5 corrugated bracket that mounts between the ribs has factory applied butyl seals on the bottom .... peel and stick. Then, the 4 SS screws attaching the bracket have butyl washers, and the roofer will dab each screw head with silicone caulk. I'm hoping this will take care of any leaks.

FWIW, S-5 has corrugated brackets designed for the AU NZ market. Check out this link: http://m.s-5.com/exposedfastened/TopFix-CorruBracket-AU-and-Mini.cfm (I could not use this bracket because the configuration of my roof panel and material gauge is different)

Anawa in Georgia

westbranch · January 2015

Re: PV array install

here is a picture of our roof structure just before the steel roof was applied. and after... strapping is 2x4 and on about 2 foot spacing

Anawa · January 2015

Re: PV array install

Love the pics! Thanks for sharing.

Anawa in Georgia

zoneblue · January 2015

Re: PV array install

Now that looks like a real kiwi steel roof... Go WB!

zoneblue · January 2015

Re: PV array install

Just to be clear we fix coruagated roofing down, through the crests as well. Americans for some reason tend to use the troughs, i think because the steel is thinner. Thinner because you have the US style ply deck to support the roof. So for PV we always mount through the crests aswell. This can be as simple as a peice of stainless angle, and a butyl washer.

You can try this to see the difference. Drill a hole in the crest of a shed roof, and leave it for a year and see what happens. Almost no water comes through. DO it the trough and it will flood in. Its just the way corrugated steel is.

BB. · January 2015

Re: PV array install

At least in decades past, we secured through the crest too in the US. We had "ripple board" that goes on the cross pieces under the corrugated roof.

I have also seen a large job (good size aircraft hanger) where they did not buy the board (as I recall) and bolted in the valleys. Best you could say--Kept the sun off and the rain fell straight down in the building.

-Bill

zoneblue · January 2015

Re: PV array install

Another benfefit of crest penetration is that the bolts have a 20mm of bend which allows expansion and contraction of the metal to occur in both horizontl and vertical directions.

westbranch · January 2015

Re: PV array install

When we did ours the manufacturers instructions were NOT to penetrate the crests. So far we have had no leaks over 3 winters, only problem was a leak around the chimney pipe where the 'boot' that seals it, could not close off where the steel was joined (folded), tiny gap that the water came through when we had rain going horizontal so the rain 'hat' was useless, all other storms were dry. 50 yr silicon sealant to the rescue...

Anawa · January 2015

Re: PV array install

ZB, depends on the gauge of the roof metal whether to mount on ridge or trough. Here in the US, we have 26 & 28 ga. ... pretty flimsy stuff, but that's what we have to deal with. Trough mount is best for most circumstances here in the US for strength, not necessarily for leaks. We have to take extra precautions to seal for the leaks, such as butyl washers and silicone caulk... and hope its works for 20 years. Yep, it sucks, but living off-grid has some offsetting benefits.

What gauge in NZ? Can you guys really mount to ridge of corrugated roofing and feel comfortable about leaks for the long term? Just wondering and curious. I do appreciate input from all you guys and find this forum informative.

Anawa in Georgia

newl · January 2015

Re: PV array install

Typical residential roofing in Australia is .43mm base metal thickness which is ~27 gauge. Commercial is .48mm BMT on average which is ~26 gauge.

zoneblue · January 2015

Re: PV array install

NZ is 0.4mm for residential, 0.55mm for commerical. Comes in long run lengths up to 15m, so you never need to lap them.

The crest screws are not screwed tight, they dont need to be. Crest fixing is very very forgiving. The rubber washer and screw head acts more like an umbrella. Not that long ago the dominant form of fixing was a wide spring head nail, and no washer at all. They worked fine, but did tend to sometimes come off in hurricanes.

The pitch on this roof is only 5 degrees, and even at 800mm centers, you can walk on the roof without issue.

Attachment not found.

Surfpath · January 2015

Re: PV array install

Gotta love metal roofing for Solar installs.

Don't know this install (looks like standing seam, s-5 fastners & unistrut), but it looks pretty good. I don't think s-5 fasteners penetrate the roof.

softdown · January 2015

Re: PV array install

zoneblue wrote: »

America sadly has little sense when it comes to metal roofing. AU/NZ pioneered metal roofing in the colonial era and it still the most common roofing here. Here ist mounted over 75x50mm purlins not ply deck, and teh metal is reasonably thick and capable of spanning 800mm centers.

That bracket looks promising enough when you look at it, but looking closely its mounted in the troughs not the crests. Looks to me like it would work just as well mounted on the crests... might be worth a test. Crest penetrations are virtually leak proof, with only minimal sealing required.

I live in a valley where metal roofing is the norm rather than the exception. You call for 32" spans - we generally call for 24" spans on purlins....though 30" is rarely a problem. I think most people here use purlins rather than plywood. Purlins are faster, cheaper, and I would not be surprised if they are also stronger in many ways.

However I did use plywood on the last roof. Reason? America is a country riddled with criminals. It is simply too easy to open up a purlin style roof and hop in. If we didn't have so many guns, the crime epidemic would be even worse. It has gotten to the point that I am suspicious of almost everybody.

PV array install

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