small solar setup

[OhYou_]

I just picked up ~10kw of panels (36x315w) and I need to start mounting them up soonish.
My goal is 6s6p, I have 2ga THHN 600v rated copper to run between the controller and the array (6-8M run)
That's about as far as I've got.
Charge controller is 128V 180A rated and I forgot how much VoC but more than enough for 6s at 42v each
All the power side equipment is in place and running off of 1.2kw of panels I mounted earlier to test before I got the 36.

NEC rules dont apply here so I dont need AFCI, dont need rapid shutdown, and knowing this risk, I instead want to mitigate it by basically making sure everything is done well so that there instead isnt a failure. I might implement GFCI, though it will be diy.
My plan is to get the wire out to some kind of box where I break out into 6x inputs, one for each panel string.
Does anyone have recommendations for basically everything? I'm probably underthinking it.

Atm I'm thinking I just run EMT out to a metal enclosure under the roof, pull the 2ga through it, hook it up to some splitters, run some pv wire out under the roof and pop it through to connect to the panels using some kind of roof jacks. Should the 6x PV wire also be in conduit?
Should I worry about conduit on the roof itself? it is a flat metal roof with wood below the metal roughly every 4ft, I can just screw brackets into those to mount the panels or something or if I really need strength, there is W beam directly under the wood, I can bolt it down instead.

No idea on panel mounts, the 4 are up there with 2x4 and a cheap set of panel mount brackets that wouldnt be very cheap at 36x

 

[robbob2112]

You broke the first rule already - spend nothing without a plan

Post in thread 'Robbob2112 Answer thread'

Jan 14, 2025

Standard Blurb

Don't spend any money, until you have planned out the entire system. An eraser is cheap, but returns can be costly.

Planning

1. Energy Audit - what do you have to power?
2. Size the inverter for your maximum instantaneous demand (including surges).
3. Size the battery for how long you want power, when the sun isn't shining.
4. Size the PV to cover the loads and recharge the battery, when the sun is shining for your area - most in the US use 4hrs or 5 hours a day of sun
5. Trying to use old equipment you already have usually costs more in design compromises than just...

• robbob2112

• 

If you are putting the panels on the roof the RSD serves the purpose for shutdown in case a fireman needs access... but assuming you don't care about that the RSD also lets you push a button and turn off all the panels in case you are outside and see smoke rising from the roof area.... Say from a faulty MC4 or a critter chewing a wire and letting it short to the frames.. ... The only way I would skip RSD is if it is on a barn or building nobody lives in.. Now on a metal roof it might not matter so much --- you decide if there is a fire up there will it burn through... if so and you care then RSD.

Do put an IMO disconnect on the wall of the house just before it enters -- this lets you turn off current going inside and gives you a convenient place to do your EMT conduit to and from.

In or on a dwelling the PV wires should be inside metal conduit and there should be an EGC run along with them to tie to the panel frames... The PV wires should be 156% of the max current expected out of the panels...

In the link at the top - the ASCE tool will let you look at wind and snow loads for your area so you know how beefy the racking needs to be and how close together you need to put the brackets that bolt to the roof.

You are talking about a combiner box -- bring the panel wires down to the combiner and put an IMO switch inside it along with fuses for the PV wires and a breaker to connect the wire to go inside .... Better to stick with metal for the combiner verse the cheap plastic ones they sell that just burn away if there is an issue inside... You can buy ready built or you can make your own depending on budget... Vevor sells NEMA boxes in a lot of sizes so you can have plenty of room. Bigger is better than little IMO

Once you are done combining that pair of wires runs inside to the inverter in EMT conduit ,. the EGC connects to the main electrical panel ground system and every other metal box you can touch...

Your metal roof will need to be connected to the EGC and to the building ground systems -- they make special clamps for that to bite into the metal for the roof and the racking ...

That should get you started with topic to research .. there are many complete systems posted in show-n-tell ....

note - most of the above advice follows the NEC because it just make sense for safety ---connecting everything together to keep from getting a shock... and the rest...

 

[OhYou_]

You broke the first rule already - spend nothing without a plan

...

Sorry I should have clarified it isnt for a house, the structure with the metal roof is a 40x56 steel pole barn with a metal roof, it has no walls and under it is a few tractors. lining the north and south sides are shipping containers. One of which holds the rest of the components. No one lives in the structure except one container will be equipped with a bit of a living space as an office. This was my key decision to forgo RSD/AFCI requirements since ehh.
The site is rural, the only fire fighters that would show up would be wildfire teams. That being said I can add a safety disconnect sure, I hadn't thought about an external one.

Unfortunately, IMO doesnt seem to offer a dc rated disconnect for ~100A of load, so I'm not sure what you would suggest I put on the wall just outside the entry point into the container.
What would you suggest in this case since also I'm not spending $1500 on a safety switch, so my best effort would either be a 100A circuit breaker outside in a box you have to open to access it to shut off the load, or I suppose I could bring all 6 strings down to the entrypoint and combine them there with 2-3 multi-pole disconnects for safety cutoff. I can run each in a separate EMT to reduce risk of them melting together in a fault.
it doesnt seem anyone makes a 6 string shutoff switch, only at most 4.

also for your quote, the plan is:
1: a workshop
2: 9kw total(7.5 HV, 1.5 LV), iirc ~13kw surge
3: 12.8kw HV (100a rated cells, 300a capable bms), 3.5kw LV, sizes are plenty.
4: ~11kw PV (prob 10kw now because used)
5: too late for that but I'm well under still.

I have a 128v hv battery which powers the main 7.5kw inverter and takes in the power from the charger/PV, and a small DC-DC to fill a 12.8v 280ah battery to run small stuff and the office space, it has it's own 1500w inverter, but a lot of the load is just 12v dc there.

 

[OhYou_]

My plan for GFCI was the following.
6x contactors, https://www.digikey.com/en/products/detail/altran-magnetics-llc/ASEV30-B/14120027
one for the negative leg of each string. all go in the combiner box.
Microcontroller that literally just monitors for ground faults in either positive to ground or negative to ground and simply shuts off the contactors.
this would function as whole HV GFCI since it would also tell the BMS to shut down.
I can just follow that 156% rule and ground strap everything together for it to work properly.

it can also function as somewhat of a RSD I suppose. one contactor for each leg 12 total is more ideal but lol $400

 

[robbob2112]

I understand now... pole barn and metal roof - no rsd needed or required. I would want a means of disconnect, but this time in the form of a dc rated outdoor knife switch... the usual method is to bring the string lines down off the roof and combine them at a level you can reach it.

IMO makes multiposition units and naked switches.... I switch per string or pair of strings and you can turn them off a few at a time. This way you could check or work on the strings in the daytime.

I would be tempted to use a bunch of these and just a switch --- they are used pulls, so order a few extra... I have about 20 and 2 came with the contacts burned from use... they work but have 300milliohms verse 3milliohms contact resistance... and the bad ones vary in resistance each time they close.

Batteryhookup has other models as well.

TE Connectivity EV200AAANA 500a 0-900vdc Tyco 12/24v

These were recovered from EV battery modules. These are VERY EXPENSIVE online. If you have any project that needs a high current relay this is your chance to save some money. Make a cheap 30a BMS into a 500a BMS. This will work for batteries in the 9-36v range so perfect for Lifepo4 and Lithium...

batteryhookup.com

 

[OhYou_]

I understand now... pole barn and metal roof - no rsd needed or required. I would want a means of disconnect, but this time in the form of a dc rated outdoor knife switch... the usual method is to bring the string lines down off the roof and combine them at a level you can reach it.

IMO makes multiposition units and naked switches.... I switch per string or pair of strings and you can turn them off a few at a time. This way you could check or work on the strings in the daytime.

I would be tempted to use a bunch of these and just a switch --- they are used pulls, so order a few extra... I have about 20 and 2 came with the contacts burned from use... they work but have 300milliohms verse 3milliohms contact resistance... and the bad ones vary in resistance each time they close.

Batteryhookup has other models as well.

TE Connectivity EV200AAANA 500a 0-900vdc Tyco 12/24v

These were recovered from EV battery modules. These are VERY EXPENSIVE online. If you have any project that needs a high current relay this is your chance to save some money. Make a cheap 30a BMS into a 500a BMS. This will work for batteries in the 9-36v range so perfect for Lifepo4 and Lithium...

batteryhookup.com

I keep forgetting that place exists, even though ive bought stuff from them before hah.
Yeah that should work.
a question on the combiner, I was thinking about making my own because the quality of cheaper ones looks concerning.
Should I do two pole breakers for each string? most seem to have a single pole breaker on the positive feeds, and all the negatives just hit a bus bar and go.

 

[robbob2112]

I like to disconnect both lines -- if there is a short up there the negative could have voltage on it as well.

If it were a mobile install single pole would be the answer.

 

[robbob2112]

I have found these pre-made combiners use a metal case and are good quality - they are a bit on the expensive side for just the components - but they come pre-wired and ready to go--- If I factor in the time, wire, crimp, rails, and everything else it is only about 10% difference than just buying a Vevor box and all components to assemble... Seems worth it to me

I have one of them and the only thing I would replace is the SPD set that is in there --- it seems to be no-name junk -- I will remove them and add a midnite solar SPD in their place.

The DIN rail mounting is super handy

PV Combiner Boxes Select 4-1 to 8-4 – Watts247 Affordable DIY Solar Power

watts247.com