28 panel 10kWh system - roof mounting question

[SHTF Power Anyway]

We purchased a 10 kWh kit which includes 28 370 watt panels which are going to be fed to a 12kWh Sol-ark with eFlex batteries. The design document shows running 2 10 panels in parallel to MPPT1 and 1 8 panel section in series to MPPT2. My neighbor thinks we need to provide physical separation of the two 10 panels in parallel from the 8 panels in series. We have limited roof space on the roof chosen to hold the panels. We're putting all of this on a barn that just barely perfectly fits the entire array. We're then feeding the power to a shop next to the house where we are planning on powering refrigeration/freezers and our water pump as well as lights and power tools (as power provides). We could put the 8 panels on the shop roof but doing so would limit future expansion. The shop roof is higher and harder to maintain and has less space so hence my choice of putting this on our open sided barn with lower roof allowing easier maintenance and safer installation. I had planned on two rows of 14 panels installed in portrait on Tamarack rails. Do I need the physical separation between the two 10 panels in parallel from the 8 in series? If so, how much separation and should I make a "break" in the rails where the separation occurs? Any help would be greatly appreciated.

 

[DThames]

The frames of all panels should be grounded. Not clear on any thoughts about why they should have any spacing between them. A little airflow helps keep them cooler and a bit higher production but that is all I can think of.

Some panels in series and some panels in parallel seems odd. You might create some series strings and then connect those strings in parallel, but parallel panels mean larger wires to your inverter. Can you provide kit instructions related to the panel connections that you mentioned?

 

[SHTF Power Anyway]

Grounding seems to be done via the Tamarack racking with #6 bare copper wire. My understanding is that there must be separation due to the differences in power between the 10 panels and the 8. I'm working with people with lots of electrical experience but not in solar so I'm running interference.

I'm attaching the diagram received from the vendor. He was aware that we were installing 28 panels in two rows in portrait. We have one last day of dry weather to get installation started on the roof. Damn the Washington State fall weather! lol

 

[DThames]

Grounding seems to be done via the Tamarack racking with #6 bare copper wire. My understanding is that there must be separation due to the differences in power between the 10 panels and the 8. I'm working with people with lots of electrical experience but not in solar so I'm running interference.

I'm attaching the diagram received from the vendor. He was aware that we were installing 28 panels in two rows in portrait. We have one last day of dry weather to get installation started on the roof. Damn the Washington State fall weather! lol

The photo of the panels doesn't dictate the way that they have to be placed on the roof. The photo is to show wiring (clearly). The photo shows 2 series strings, of 10 in each string, connected in parallel to one charger input. Then 8 in series going to the second charger input.

With 2 rows of 14 each row, you could series 5 columns of 2 rows, then move over and series 5 columns of 2 rows, move over and series 4 columns of 2 rows. Or you could series 8 on one end, 4 columns of 2 rows, then do 10 in series on top row and 10 in series on bottom row of the total minus the first 8. You can wire them up in a zigzag if you really wanted to. The insulation on the PV wire provides "distance". Still not clear on why anyone would thing they need to be physically apart.

If you have any chance of any shading the way you wire the 2 row layout could matter. Shading will kill a series string so better if you have shade on one end for part of the day, to series that end as a string so you don't have shading on more than one string, if that can be managed.

 

[Wellbuilt]

I see no reason to keep them separate I know if they are separate you need 36” between them .

 

[Hedges]

Mounting my panels on rails (ground mount), I kept a slight space ~ 1/8" between them. My reason was that if rails flexed under wind pressure, I didn't want compression on the glass.

36" between them? I haven't seen such a rule. What I have seen is requirement for walkways allowing fireman access. This has changed with new versions of the code, but latest I saw was 36" walkway from street side of house to ridge, and 36" space at ridge (can be 18" each side of ridge) to hack vent holes. Some places, the walkway must be within walls, not counting roof extending beyond wall.

10s2p into one MPPT, 8s into another.
A single panel of one 10s being shaded probably won't cause undue power loss. Four panels shaded so (6s + 4dark) || 10s might deliver only power of 10, might deliver power of 6s2p. Preferable if shade reaches two panels of each string, so you get the power of 8s2p.
But sun keeps passing over different places, so location of shade varies. Over-paneling is good.

The design has 20 panels on one MPPT, 8 on the other.
All panels of a single string need same orientation.
If arrays were 9s2p and 10s, that would be a bit less wattage on first MPPT.
What are panel specs? (To see if 10s2p might be more than can be harvested by MPPT.)

 

[SHTF Power Anyway]

The photo of the panels doesn't dictate the way that they have to be placed on the roof. The photo is to show wiring (clearly). The photo shows 2 series strings, of 10 in each string, connected in parallel to one charger input. Then 8 in series going to the second charger input.

With 2 rows of 14 each row, you could series 5 columns of 2 rows, then move over and series 5 columns of 2 rows, move over and series 4 columns of 2 rows. Or you could series 8 on one end, 4 columns of 2 rows, then do 10 in series on top row and 10 in series on bottom row of the total minus the first 8. You can wire them up in a zigzag if you really wanted to. The insulation on the PV wire provides "distance". Still not clear on why anyone would thing they need to be physically apart.

If you have any chance of any shading the way you wire the 2 row layout could matter. Shading will kill a series string so better if you have shade on one end for part of the day, to series that end as a string so you don't have shading on more than one string, if that can be managed.

Thank you for your reply. We have no problems with shading on that roof. I don't know why my neighbor felt that way except for his concern about the different power loads. I'm not an electrician myself (he is) but I haven't seen other arrays with spacing like he was suggesting so I thought I'd better ask.

 

[Supervstech]

Ok...

KWh is a daily production...

You have 10.3KW of panel production, capable of 56,980KWh of daily production with 5.5h sun...

 

[740GLE]

My only thought would be to try and capture early morning and later afternoon production by having the two arrays pointing different directions, vs all panels in same orientation. But that’s tough for each roof layout.

 

[Scph9002]

needs spacing because the metal expand in heat. The middle panels would get crushed

 

[Supervstech]

needs spacing because the metal expand in heat. The middle panels would get crushed

I am unaware of metal expansion beyond a few microns. Where did you get this schedule?

 

[740GLE]

36” seems reasonable for heat expansion ?

Sarcasm travels slower on the inter webs

 

[Hedges]

Looks like aluminum rails would be 23 ppm per degree

Thermal Expansion Coefficient of Aluminium

Find linear thermal expansion coefficient (α) and volumetric coefficient for thermal expansion (β) at 20°C for Aluminium or for different material like brass, copper, concrete, lead, silver, water and more

www.webconversiononline.com

So a 1m panel over 50 degrees would be 1150 um or 1.15 mm

Glass is many different formulations. Have to find a figure for the glazing of PV panel.
But this says for borosilcate glass 3 to 6 ppm

Glass Thermal Properties and Their Role in Product Design

Glass thermal properties determine how they will perform in different operating conditions. This article reviews their thermal properties and explains their application and importance in component design.

www.koppglass.com

Another, 7 or 8 ppm/degree

https://nvlpubs.nist.gov/nistpubs/jres/52/jresv52n6p311_A1b.pdf

That leaves a delta of about 1mm across a 1m panel.

 

[SHTF Power Anyway]

Ok...

KWh is a daily production...

You have 10.3KW of panel production, capable of 56,980KWh of daily production with 5.5h sun...

That sounds like a wonderful amount of power.... except I live in the PNW. This time of year with the orientation and tilt I'm stuck with for a long list of reasons, it's just enough power to handle refrigeration and lights in my shop. Mind you, I have a LOT of refrigeration. lol

 

[SHTF Power Anyway]

The frames of all panels should be grounded. Not clear on any thoughts about why they should have any spacing between them. A little airflow helps keep them cooler and a bit higher production but that is all I can think of.

Some panels in series and some panels in parallel seems odd. You might create some series strings and then connect those strings in parallel, but parallel panels mean larger wires to your inverter. Can you provide kit instructions related to the panel connections that you mentioned?

So, my husband and his good friend (both plant electricians) managed to put up the first row of racking in a moronic fashion. It's not straight. I'm both angry and mortified because I'm pretty sure it needed to be straight. I don't know how bad it is without taking measurements and the weather is not going to cooperate this week. It's rain/wind for days to come. So I'm trying to be prepared for our first day of good weather.

We are putting this on an old barn with metal roofing using the S-5! Protea brackets. I'm wondering the best way to go about fixing this situation. Does the racking have to be perfectly straight? I know it can and must be level...

Removing the brackets and starting over will leave holes that, even with some kind of sealant, will always be a problem for leaks and also weakens the metal. The Protea brackets do not attach into wood. The 4 screws just go into the metal so if I've got a ton of holes in the wrong place, it seems to me I've weakened the strength of the roofing. I'm not sure if I should remove what's there and caulk it and order replacement brackets since we blew the adhesive when these were installed wrong... I would love some advice.

Some days I think to myself, "Self, you would have been better off spending that extra $30k to hire this done."

 

[DThames]

If the bracket is like the one in the image below, there is some amount of adjustment in those slots. The adjustment should allow for the L-bracket part to be in line so the rails will be straight, parallel with each other. If they are so far out of alignment that the slots can't adjust, you might need to move some of them. They really don't have to be perfect, just look better if they are straight..ish.

 

[SHTF Power Anyway]

If the bracket is like the one in the image below, there is some amount of adjustment in those slots. The adjustment should allow for the L-bracket part to be in line so the rails will be straight, parallel with each other. If they are so far out of alignment that the slots can't adjust, you might need to move some of them. They really don't have to be perfect, just look better if they are straight..ish.


View attachment 71294

Thank you so much for your reply. I honestly feel better. Those are indeed the brackets that were used.

 

[SHTF Power Anyway]

The frames of all panels should be grounded. Not clear on any thoughts about why they should have any spacing between them. A little airflow helps keep them cooler and a bit higher production but that is all I can think of.

Some panels in series and some panels in parallel seems odd. You might create some series strings and then connect those strings in parallel, but parallel panels mean larger wires to your inverter. Can you provide kit instructions related to the panel connections that you mentioned?

What product do I buy to get the wiring down through the roof into the J-boxes and conduit? I see different options for composite roofing but I haven't seen anything for metal roofing and I don't know how to search for it as I'm not sure what it's called. Help!

 

[DThames]

What product do I buy to get the wiring down through the roof into the J-boxes and conduit? I see different options for composite roofing but I haven't seen anything for metal roofing and I don't know how to search for it as I'm not sure what it's called. Help!

I know zero about this but I got some Google hits by searching for "metal roof cable entry"