Help with panel count and wiring configuration

[Stepandwolf]

There are two sets of connectors for two arrays of 3S3P (18 panels total).

Each set of connectors can convert three parallel 3S strings to a single pair, so the two sets take up to 3 parallel strings each and convert them to a single pair.

What I linked would allow for TWO of these:

View attachment 187331

that drawing would be a 18 panel total, right? If we were doing 6 panels on each string, then wouldn't it be a 2>1 vs. 3>1?

 

[sunshine_eggo]

Yep

3S2P x 2:

https://www.amazon.com/BougeRV-Solar-Branch-Connectors-Parallel/dp/B0788J7PNH

 

[Nobodybusiness]

Max PV Array Open Circuit Voltage 145Vdc
PV Array MPPT Voltage Range 60~115Vdc

Wow that’s low.
Didn’t realize they were that low..

 

[sunshine_eggo]

Wow that’s low.
Didn’t realize they were that low..

This model is from the prior generation of Voltronics-type AiO where 145-150Voc was the norm with an occasional 250V unit. The 450-500V models weren't readily available at that time.

 

[wheisenburg]

I found the max volts values, but don't see where you got the max power values from?

I got the max power from the data sheets on the inverter. They say the Max DC input is 8000 watts divided into 2 MPPT inputs. So each MPPT can handle 4000 watts. Since the whole purpose of an MPPT controller is to vary the Voltage / Amperage to achieve the best power production based on conditions, you are at best going to just be able to estimate the volts and current. The say max power is achieved by the panels at 8.13 amps. So that would be the best estimate of the working current.

So if you run a 3S2P array into one MPPT you will only be running 16 amps. I seem to recall that if you are only running 2 strings per MPPT you don't need to use a combiner. The purpose of the combiner is in part to individually fuse the circuits. Since the combined current of two strings is only 16 amps and the wires will handle that, you don't really need this. If you put 4 parallel strings on a single MPPT circuit the the array could output 32 amps. You would then need to fuse each circuit so that 32 amps couldn't back feed into wires that are not sized to handle that much current.

So your simplest option would be to build two 3S2P arrays and then to feed each array into a single MPPT.

8 gage wire specified by the manual should be fine for this inverter. The reason is that the 8000 watts is going to be split into 2 separate 4000 watt MPPT controllers. With a 3S5P array your Max current into each MPPT will only be 40 amps. The total current with two of these array is 80 amps, but there are two separate wires carrying the current so it will be fine.


fyi, MPPT stands for Maximum Power Point Tracker. The amps and voltage produced by a solar panel is going to depend on various conditions like the temperature, the strength of the sun and the angle that the sun is hitting the panel. The MPPT controller will periodically sweep the voltage and measure current at each point in the voltage sweep. Then it will calculate Volts * Amps = Watts for each point in the curve. Then it will pick the voltage the produces the most watts. So basically the circuit will optimize for the voltage that allows the panel to produce the most power. It will do this continuously throughout the day as conditions change.

 

[Stepandwolf]

I got the max power from the data sheets on the inverter. They say the Max DC input is 8000 watts divided into 2 MPPT inputs. So each MPPT can handle 4000 watts. Since the whole purpose of an MPPT controller is to vary the Voltage / Amperage to achieve the best power production based on conditions, you are at best going to just be able to estimate the volts and current. The say max power is achieved by the panels at 8.13 amps. So that would be the best estimate of the working current.

So if you run a 3S2P array into one MPPT you will only be running 16 amps. I seem to recall that if you are only running 2 strings per MPPT you don't need to use a combiner. The purpose of the combiner is in part to individually fuse the circuits. Since the combined current of two strings is only 16 amps and the wires will handle that, you don't really need this. If you put 4 parallel strings on a single MPPT circuit the the array could output 32 amps. You would then need to fuse each circuit so that 32 amps couldn't back feed into wires that are not sized to handle that much current.

So your simplest option would be to build two 3S2P arrays and then to feed each array into a single MPPT.

8 gage wire specified by the manual should be fine for this inverter. The reason is that the 8000 watts is going to be split into 2 separate 4000 watt MPPT controllers. With a 3S5P array your Max current into each MPPT will only be 40 amps. The total current with two of these array is 80 amps, but there are two separate wires carrying the current so it will be fine.


fyi, MPPT stands for Maximum Power Point Tracker. The amps and voltage produced by a solar panel is going to depend on various conditions like the temperature, the strength of the sun and the angle that the sun is hitting the panel. The MPPT controller will periodically sweep the voltage and measure current at each point in the voltage sweep. Then it will calculate Volts * Amps = Watts for each point in the curve. Then it will pick the voltage the produces the most watts. So basically the circuit will optimize for the voltage that allows the panel to produce the most power. It will do this continuously throughout the day as conditions change.

Hi guys....I have been Lost In Space for the past couple months and wanted to touch base...Thanks for the great, detailed explanation.

I figured to optimize the space, on top of a 40' container, I can go 7 panels wide, and put in two rows for a total of 14 panels. If I am mounting them on unistruts I could theoretically go 3 rows of 7, but I suspect they would lift the CONEX off the ground.

Based on 14 panels, how would you suggest I configure the LV6048?

As a side note, I mentioned Unistruts. My thought was to attach strap hinges screwed or welded to the CONEX frame rail, and then connected to a 10' Unistrut. I would attach another row of hinges and Unistruts across the other side of the CONEX, and then could tip them together for various angles. Seems it is not that much in materials to do it with hinges than just bolting everything together otherwise? Would 12ga Unistruts handle the windload? Was thinking 6" HD strap hinges.

Side benefit, water collection system

 

[OffGridForGood]

standard strut is not very stiff, they make double strut (two pcs welded together) that is stiffer - you can do a search and get load tables online.
The other option is to attach a plate or angle to the strut to increase it's stiffness.
be sure to pick or build hinges or pivots that will take to full load of the panels/frame and the applied loads snow/wind. Most hinges are not very strong really, I prefer to pin plates together to create a strong pivot point. Pairs of angle on each side of a box section works well as one option.

 

[Stepandwolf]

standard strut is not very stiff, they make double strut (two pcs welded together) that is stiffer - you can do a search and get load tables online.
The other option is to attach a plate or angle to the strut to increase it's stiffness.
be sure to pick or build hinges or pivots that will take to full load of the panels/frame and the applied loads snow/wind. Most hinges are not very strong really, I prefer to pin plates together to create a strong pivot point. Pairs of angle on each side of a box section works well as one option.

I am ignorant on constructing one of these frames so I don't know how you would attach a plate to the strut? Are you just suggesting that behind where the hinge mounts, you have a piece of steel, i.e. wedging the strut between the hinge and the plate? I don't know how to pin plates together. By pairs of angle, are you referring to slotted angle iron? an 8' 1-1/2 angle iron is $60 vs. $35 for a unistrut. I was considering an angle iron across the struts, or perhaps two rows of angle iron, just to give the whole frame more rigidity.

I didn't think of a strap hinge as being particularly weak I just checked....they run in the 60-100# range...the panels aren't that heavy, but the wind load would exceed that....interested in hearing more about a hinge solution, or perhaps it is best to skip the hinge as a weak point?

 

[OffGridForGood]

if you deal with snow, the pivot is a good idea - ask me how I know!
There are many ways to connect a plate or angle to the strut - bolting with unistrut-brackets, welding, bolt plates to the sides of the strut etc.

The easiest way for you may be to pick a small box section say 4" x 2" for example, the box may only need to be 5-6 feet long attached the back of the strut and centred - so the 10-foot strut has 2 feet of projection longer than the box section at each end.
You can drill through the strut into the box section, and tap for bolts. Some guys like to use self-drilling-self-taping screws but I feel these are a bit small for this application.
Then to make your pivots, put a 4" x 4" angle on each side of the box section - lift the box enough relative to the angle that it can pivot without binding - drill through the angle - the box section - the other angle - install decent sized bolts - 1/2" diameter bolts work well for this in my experience.

 

[Stepandwolf]

if you deal with snow, the pivot is a good idea - ask me how I know!
There are many ways to connect a plate or angle to the strut - bolting with unistrut-brackets, welding, bolt plates to the sides of the strut etc.

The easiest way for you may be to pick a small box section say 4" x 2" for example, the box may only need to be 5-6 feet long attached the back of the strut and centred - so the 10-foot strut has 2 feet of projection longer than the box section at each end.
You can drill through the strut into the box section, and tap for bolts. Some guys like to use self-drilling-self-taping screws but I feel these are a bit small for this application.
Then to make your pivots, put a 4" x 4" angle on each side of the box section - lift the box enough relative to the angle that it can pivot without binding - drill through the angle - the box section - the other angle - install decent sized bolts - 1/2" diameter bolts work well for this in my experience.

You mentioned snow first, which actually isn't an issue, although 6" yesterday. I did some YTing and the first video I found was Red Poppy Farm or something like that. He was using unistruts to mount panels to the roof of his house. He used a horizontal strut attached to the roof and then used hinges to attach unistruts going vertically that he put the panels on. In his case 3 panels, and wide enough that he needed to extend the 10' struts. Then on the back, he had struts going back down to the roof with another set of hinges. He also put a couple struts at an angle at the ends to provide support.
He is in Idaho, and gets 100" of snow so he added an additional brace mid-way as an after thought.

He used a much better hinge than the strap hinges I found, and I wrote him to ask the source of the hinges.

Another big difference, is I was going to put the verticals and the end of the horizontal panels, i.e. 8 total for the row of 7 panels. Instead, he mounted the panels on the long side and had two struts per "column" of 3 panels, doubling the number of struts, but going three rows over 10' in height.

Even during his install of a couple arrays, he said they had strong wind, i.e. 50+...my area has very high winds...

thanks

 

[OffGridForGood]

I tilt my panels because of snow, and the side benefit is the extra bit of solar during crappy winter low light, so a win win.
I am not trying to tell you there is only one way to build a tilt array, there are lots of ways. I work with strut daily in my work, and know it's limitations in my environment. You need to assess what will work in your environment and plan for that. Wind loads can be higher than snow loads in exposed areas, and wind speeds can be a lot more than 50mph, plan carefully your panels have 25 years of weather to deal with. It is the worst day, not the average day you need to be ready for.

 

[Stepandwolf]

I appreciate your real world strut experience and where my land is located, there is a tremendous amount of wind, but not so much snow. That is why I was joking that a third row of panels would probably launch my CONEX. From a design standpoint, debating if I need one strut per panel, i.e. between the panels, or two per column of panels like he did. Likewise, I am wondering if a regular steel right angle might be better than a Unistrut with all the holes cut in it, possibly weakening the whole thing. I looked at the double Unistrut which also doubles the price which makes me wonder if a right angle would be best, or like he did, just a Unistrut, but perhaps two per column vs. 1.
Thanks

BTW, since you are in Ontario, did you know that Toronto is south of Minneapolis

 

[OffGridForGood]

YUP! but I live 1000 miles from Toronto, thank-goodness!
Fun Fact the southern border of Ontario is the same latitude as the Northern border of California !
(and the Northern most point of Ontario is 350 miles further North than the Southernmost tip of Alaska!!)

 

[Stepandwolf]

YUP! but I live 1000 miles from Toronto, thank-goodness!
Fun Fact the southern border of Ontario is the same latitude as the Northern border of California !
(and the Northern most point of Ontario is 350 miles further North than the Southernmost tip of Alaska!!)

And the tip of MN is further north than Maine.

 

[MarkSolar]

... where my land is located, there is a tremendous amount of wind, but not so much snow.

When I put in my ground mount I used a few wind numbers to do rough calculations just as a sanity check. A 60mph wind generates 10 psf and a 100mph wind generates 25psf. A flat wall has a drag coefficient of about 2 and a sphere has a coefficient of about 0.5. So I assume a tilted solar mount has a horizontal and vertical drag of about 1 to make things easy. So in a 60mph wind, if your array is as long as the 40' trailer and tilted so it appears to be 5' high, that's 200sf times 10psf gives 2000# of force horizontally and the same vertically. For a 100mph wind it's 2.5 times that much so 5000# horizontally and vertically. The force on the side of the CONEX itself would be 40x8x25 = 8000# and by coincidence a 40' CONEX weighs about 8000#, so you'd be close to tipping the thing over in a 100mph wind. A container blowing over seems impossible until you watch some videos of 40' semis tipping over in the wind on the interstate. The problem with wind is the dynamic loading. If it starts gusting at the right frequency, those numbers go up a lot. That's why the IronRidge stuff all looks like it could survive a nuclear blast.

 

[Stepandwolf]

When I put in my ground mount I used a few wind numbers to do rough calculations just as a sanity check. A 60mph wind generates 10 psf and a 100mph wind generates 25psf. A flat wall has a drag coefficient of about 2 and a sphere has a coefficient of about 0.5. So I assume a tilted solar mount has a horizontal and vertical drag of about 1 to make things easy. So in a 60mph wind, if your array is as long as the 40' trailer and tilted so it appears to be 5' high, that's 200sf times 10psf gives 2000# of force horizontally and the same vertically. For a 100mph wind it's 2.5 times that much so 5000# horizontally and vertically. The force on the side of the CONEX itself would be 40x8x25 = 8000# and by coincidence a 40' CONEX weighs about 8000#, so you'd be close to tipping the thing over in a 100mph wind. A container blowing over seems impossible until you watch some videos of 40' semis tipping over in the wind on the interstate. The problem with wind is the dynamic loading. If it starts gusting at the right frequency, those numbers go up a lot. That's why the IronRidge stuff all looks like it could survive a nuclear blast.

I was half kidding about tipping over...aside from shelving, the batteries,etc., there will typically be a 6-7,000# tractor and an ATV in the container so I doubt any amount of wind could actually tip it over. The concern is the strength of the hinges and the struts themselves. I mentioned the Idaho guy who used two struts per column of 3 panels that were wider than mine as he had to extend the10' Unistruts quite a bit to go 3 panels tall. He did a pair of struts per column whereas I was only going to put a strut between pair of columns,i.e. 8 struts in the row vs. 14. He had each strut braced by another strut and then for snow load, another interim brace. Snow won't be an issue. Debatingif the 8 struts is enough or if I should go 2 per column like he did. Likewise, if a Unistrut has the strength of a 1.5" or 2"steel right angle. A U-channel would theoretically be stronger, but with all the slots cut, that would weaken it.

Thanks so much!