First off grid system - Hi Voltage DC, Grounding Safety concerns - any suggestions for my setup ?

[OFFGRIDR]

Hi All,

I'm building a PV array onto the metal roof of a 40x8 Ft Conex shipping container: 4 panels placed widthwise (445W, 49Voc, Isc=12A) 8panels placed
lengthwise (200W, 20Voc, Isc=12A). The funky positioning is to navigate around the skylights and solar vents and maximize the available footprint area.

My #1 concern is SAFETY, troubleshooting and serviceability as this is my first time working with solar panels so I think it best
to keep the solar string VOCs never exceed 49VDC as I have not found any detailed information on how to physically install or service high voltage DC safely while working up in the air touching a metal roof. Also, there would be little room to walk around the panels and you'd be leaning against the containers probably on a ladder touching your chest. The containers are physically sitting on railroad
ties. I don't mind extra cost for more switches or heavier gauge wire.

DC SHUTOFF:
I plan to route separate (+) (-) pairs per EACH of the 445W (49Voc) panels and a (+) (-) pair for a series string of 2 200W (40.4VOC) panels to an outside wall of the container with 8 DPDT breakers. - OK ?

DC Combiner box
This will sit on the interior wall behind the DC Shutoff and I'll finish parallelling the 49V panels and 40.4V strings
for routing into the All in One Growatts.

GROUNDING:
I plan to place a copper earth ground rod directly beneath the container where the DC cutoff box is located and tie the metal container
to this. I also will run separate green wires up to the roofs to keep the ground path more direct.

Questions:
1. Any suggestions for robust DPDT DC switches? (49VOC, 13A Isc)
2. Any resources available for how an advanced designer would use high
voltage DC Strings on a metal roof such as this comfortably AND
be able to troubleshoot, walk around ect? How to safely disconnect without resorting to cardboard shading?
3. GROUNDING: Would it be better or overkill to run INDIVIDUAL
ground wires to EACH solar panel frame and not rely on the painted
container to provide earth ground? I presume you DO want
the containers to have a good continuous earth ground and not partially
float. Over time I could see corrosion causing islands of areas to 'float' above earth ground where mouting rails connect.

Thanks in advance !!

 

[FilterGuy]

DC SHUTOFF:
I plan to route separate (+) (-) pairs per EACH of the 445W (49Voc) panels and a (+) (-) pair for a series string of 2 200W (40.4VOC) panels to an outside wall of the container with 8 DPDT breakers. - OK ?

DC Combiner box
This will sit on the interior wall behind the DC Shutoff and I'll finish parallelling the 49V panels and 40.4V strings
for routing into the All in One Growatts.

The 40.4v string will not be able to contribute if parallel them to the 49V panels. They will need to be on a separate controller

 

[JoeHam]

Your system your choice but it is not difficult to safely use panel voltage up to 150v and beyond.

Covering the panels with a blanket or cardboard while working makes it easy to install with minimal concern about live power while on the container.

Higher voltage/Lower current means you can safely use smaller wires and lower current breakers/fuses.

Personally I prefer working with higher voltage lower current versus lower voltage high current stuff.

Now 450v or even 600v is becoming more common on all in one systems. My largest MPPT’s max out at 250v so no personal experience that high.

 

[OFFGRIDR]

The 40.4v string will not be able to contribute if parallel them to the 49V panels. They will need to be on a separate controller

Thank you. Yes, I planned to keep them separate and use 2 separate controllers. I was concerned primarily with the DC high side between
panels and the first set of isolator switches. It seems most people r

Your system your choice but it is not difficult to safely use panel voltage up to 150v and beyond.

Covering the panels with a blanket or cardboard while working makes it easy to install with minimal concern about live power while on the container.

Higher voltage/Lower current means you can safely use smaller wires and lower current breakers/fuses.

Personally I prefer working with higher voltage lower current versus lower voltage high current stuff.

Now 450v or even 600v is becoming more common on all in one systems. My largest MPPT’s max out at 250v so no personal experience that high.

Thank you for the feedback.
Would you place a 150VDC string in an outer jacket / conduit for a situation where you were routing it on top of a metal roof in the hot sun ?

 

[FilterGuy]

Would you place a 150VDC string in an outer jacket / conduit for a situation where you were routing it on top of a metal roof in the hot sun ?

I typically would, but things get complicated with conduit and roofs.

* If there are more than 3 conducting wires in the conduit there is a de-rating schedule for the wire (You must use larger wire) This is because of the heat generated by the wires means the amount of current the wires can safely handle goes down.

* If the conduit is in the sun, there is a derating schedule for the wire based on how far the conduit is off the roof. (The further off the roof, the less you have to de-rate the wire) (Again, this is due to heat)

* There is also wire de-rating based on what the temp rating of the breakers you use. (Breakers are typically rated at less than the wires and the system has to be calculated based on the lowest rated temp)

It is a rather convoluted set of calculations and every time I have to do it I have to re-learn the process. There is a youtube video on it that was done by @SolarQueen but I can't find it right now. If she gets an alert on this mention she might be able to point you to it.

I have to believe there is a web calculator out there someplace that could do it for you but i have never seen it.

Note: A lot of DIYers don't bother with the de-rating, but their systems are not to code.

 

[OFFGRIDR]

Thanks again for your insight- I'll go with 100VDC strings which will make the routing MUCH cleaner. I'll route all PV paired inputs along One Top
EDGE visible from the ground to the Isolators and NOT across the roof where they'd be blind. I'll post when I get that done which will be
hopefully next week. I'll derate by a healthy amount since the runs are short.

 

[JoeHam]

And sadly the Solar Queen was taken from us much too soon.

Remembering Amy

Amy Beaudet, our very own Solar Queen, has passed away. Amy Beaudet, affectionately known as ‘The Solar Queen’ and a pioneer in the field of renewable energy, passed away on Sunday, May 2, 2021 at Brigham and Women’s Hospital in Boston, Massachusetts. She was 55 years old. AltE has a notice...

diysolarforum.com

 

[FilterGuy]

And sadly the Solar Queen was taken from us much too soon.

Remembering Amy

Amy Beaudet, our very own Solar Queen, has passed away. Amy Beaudet, affectionately known as ‘The Solar Queen’ and a pioneer in the field of renewable energy, passed away on Sunday, May 2, 2021 at Brigham and Women’s Hospital in Boston, Massachusetts. She was 55 years old. AltE has a notice...

diysolarforum.com

oh! Wow, I did not know. So sad.