DIY Junction Box or Solar Combiner Box

GA, excellent advice, I received additional advice, this morning and It appears that an empty box does have to be UL listed even though it is Gov't spec airtight already.

Thank you for your opinion.

Im wondering if it would be possible to use a large junction box and add the connection rail, Junction boxs are 1/4 of the price of solar combiner boxes, what do you think?

Well, at least as far as the enclosure, that should be no problem.

You'd have to make sure that what you put in the enclosure also meets all appropriate standards (like ratings of breakers, size of busbar for the load, ...)

I don't know if this would be acceptable, but what about using indoors UL rated boxes - ie designed to be used in a roof space - and then having an inexpensice but durable weatherproof enclosure over them to provide the 'indoors' environment....

Just a thought

Maybe, GA, I'll ask around, unless someone here knows the answer.

DIY solar combiner box

AC breakers. Here in Australia, most domestic AC breakers can be used in a DC circuit. Thermal and magnetic overload detection, are usually the 2 defined ways for protection.

A de-rating factor of 80% is a common nominal correction.

Up to a DC Voltage of about 50VDC.

But..........Check the particular specifications for the Brand of breaker........!

Cheers

Mark N.

Mark, I do not understand your reply to this thread, I thought this was about enclosures not circuit breakers.

This is a decent solution, the expensive part is the connections. any breakers end up being disconnects, since individual solar panel, won't be putting out enough power trip a breaker like these

all the wires should come in from the sides or bottom. you can't really make panels water proof, better to accept that there will be water & direct it away from the connections

It depends on how many connections you need to make, how often you will need to access them, if you need to be able to isolate individual panels

here's a different way to goSafety Switch

you might be better off with a traditional enclosure

I can help you figure this out here or by email

GA, Garthh,

I guess you know my story, the utility companies are not really paying enough to make solar work commercially. Everyone says it's all working, but the truth is the solar developers made all these proposals based on prices comming down. Most of these farms will get built and be found to be unprofitable. Mine is the cheapest I have seen and it is currently only projected to make investors 10% and they all want 15% ROI.

Thanks for you advice, you rock!

I'll be in touch.

Spacecannon

Code compliance is one aspect of your project. There is also a technical side. Military ammo boxes and NEMA enclosures are not vapor tight. This means that water vapor can permeate through the organic seals and raise the dew point of the internal space. All it then takes is for ambient temperature to fall below the internal dew point, and water will condense on the coolest parts. So, the longevity of your boxes will depend on the outside environment. The better way involves either hermetic sealing with dry gas inside the seals, or continuous purging with a dry gas.

Just a note to confirm that because you are building on a farm, you may be able to adjust some building inspection requirements and equipment, but if you are going to grid tie, your system will need to comply with NEC, at least where we build PV systems.

GA, Yah your right, When i say farm I mean a 1.1Mw PV, Grid tied, commercial solar farm, in the desert.

Yes, they are ridiculously expensive. I build my own using positive and negative copper bus bars mounted on insulators then the bus bars are drilled and have screw down terminals bolted at even spacing for each solar panel set. You then cable a single heavier guage wire from each bus bar down to your controller. Naturally you can only combine as many panels for each group as your controller can accept. In my small system I only needed 1 combiner.

As far as codes go I don't know because I live in the Dominican Republic where codes are few and far between but for high voltage arrays above 24V you should fuse each positive down feeder for your own protection.

John

I am involved with some advanced thinking in PV technology. One of the concepts involves putting DC/DC converters at each panel so the output voltage will be considerably higher and the power bus losses much lower. This will require reliable weather proof converters, but the economics are promising.

Is DC-DC conversion more economically feasable than simply using series strings which work at high voltages (400-600VDC)? It would seem to me that the DC-DC conversion is unnecessary and would add losses?? Correct me if I'm wrong.

John

John, I'm far from an expert in these matters but as I understand, it has to do with reliability. If you series up a bunch of PV panels and one of them fails, you have real urgent problems. In parallel, you have more flexibility

I've had a fair amount of exposure to whats going on, but won't claim to be an expert. In large thin film arrays where each panel has a Voc of 135VDC you only have to put a few in series before you have a high enough voltage for modern grid tie inverters. So you would have dozens of groups in series/parallel. Using good construction techniques failures are not very common and even in the event you would only lose a small group. The person asking the question says he's doing a MegaWatt array which is huge and most likely thin film unless he has space restrictions. So he needs to do a whole lot of combining with that many panels and custom combiner panels may be a cost saving issue for him.

I've also looked at panels which each have a tiny inverter on them and the AC outputs are all combined and synchronized for grid tie. This saves all the DC wiring and expenses incurred. He may want to consider this also.

John

I like the idea of the tiny inverter but my people tell me that reliability issues have prevented that method from being widely accepted to date. To be practical you are going to need small electronic assemblies that can operate reliably in all kinds of environments for long periods of time. I believe it can be done, but it's not a trivial task.

GA, yes, thin film, ground mount.

Good suggestion on the small inverters, and I looked into it, it's not as financially feasible. It increases the cost per watt and the number of parts that can go wrong.

I don't want to put words in your mouth but I think you agree that a reliable, low cost inverter would solve your problem.

It's a tough thread, but to boil it down, OP wants to build what he is calling small PV farm using home made combiner boxes. Turns out he is talking 1.1 megawatts. While it has been interesting, it's pretty sketchy.

DC/DC converter?

still limited NEC 600 VDC on residential,

if you are talking commercial, and go to 1000 VDC (pretty much PV panel limit), then converting higher, then inverting AC lower, that would be a rare solution. (As in losses from upconverting being less than reduced transmission losses)

Are you talking miles?

I would love to be running a solar panel and battery system but the wife says they are ugly and doesn't want to spend $65,000! There are many solar sites and companies out there. Most States require a State approved system as do many local utilities that offer power buyback and incentives. State and the local utility incentives in Texas are quite friendly.

Solar Panels Georgia

Yes, wish I were living in Texas.