Need to Reduce solar voltage!!

[timselectric]

Will shorting the diode make the battery’s drain when there’s no sun on panels? Or will the controller block that from happening?

Nope

 

[javiercartwright]

To reduce the solar voltage on your temporary system, you can try a few things. One option is to use a voltage regulator or a buck converter to lower the voltage before it reaches the controller. Another is to shade the panels partially to decrease their output.

 

[timselectric]

So are you doing 2s3p now?

Currently going for 2 2/3s2p.

 

[vashkoproimage]

Nope

All glued inside boxes.

 

[timselectric]

All glued inside boxes.

That's a shame.
I mean, it's a good thing. Just not for what you want to do.

 

[timselectric]

I mean, it's a good thing.

For longevity. But not for servicing.

 

[vashkoproimage]

That's a shame.
I mean, it's a good thing. Just not for what you want to do.

What if I shade 1/3 area with reflective shield? Would that cause issues with diode overheating or causing issues long term over winter if done this way? I’m not particularly sure how the diode works and bypasses that section if shaded. Not sure if heating will occur.

 

[timselectric]

Would that cause issues with diode overheating or causing issues long term over winter if done this way?

That would be my concern.
Especially now, since it's not easily accessible.

 

[Hedges]

True. Diodes can overheat with full Isc forced through them, resulting in plastic melting and glass breaking.
Best that diodes activate only with shadows when sun is off-angle, like 45 degrees.

We've encountered the idea of reducing Voc many times. No good ideas except shorting out a section or an entire panel.
There is very little margin in many SCC before they get killed.

Midnight Classic they got clever, realized that FETs only see full Voc if the buck converter switches. When Vpv is too high, they simply don't switch transistors, and the have Voc - Vbatt across them. When panels warm up and voltage drops, if low enough, they begin switching.

Best thing you can do is wire the panels 2s, not 3s. If your panels are placed in groups of 3, you may not be able to do 2s3p unless you run wires between the groups. 2s2p would protect the equipment from damage.

https://diysolarforum.com/attachments/img_2719-jpeg.179292/

 

[SamDeleted]

Best thing you can do is wire the panels 2s, not 3s. If your panels are placed in groups of 3, you may not be able to do 2s3p unless you run wires between the groups. 2s2p would protect the equipment from damage.

Covered, post #2 ?

 

[pollenface]

Vash , from the beginning this has been a confusing thread, (I think for everyone?)

I agree, i had to go over it a few times and I'm still confused.

 

[Ampster]

Best thing you can do is wire the panels 2s

That was my thought as well. The OP said it would not work because of voltage drop. However I never got an answer why voltage drop was an issue if it was above startup voltage? With voltage off solar panels who cares if the voltage drops more than 3% unless it drops below start up or the cost of new wire is less than the revenue from the higher voltage.
EDIT: I checked the SCC and the startup voltage is 60 volts so 2S would not be an issue.

 

[Hedges]

Exactly. 3% is a recommendation for AC wires, matters for motors which draw 5x at startup so 15% droop. Matters less for resistive loads.

For PV, nothing wrong with designing for 5%, 10%, 25%, even 50% voltage droop in some extreme cases with long wires (hundreds to thousands of feet). Max droop only happens at peak power.

For short wires, ampacity of wires and temperature rise is the limiting factor.

If voltage droops to bottom of MPPT range, then PV panels operate above Vmp, reducing power harvesting. To be avoided, but if only at full current, can probably live with it. When panels put out 1/4 as much during off season and clouds, voltage drop is 1/4 as much so most of the produced power is delivered.

 

[Ampster]

Covered, post #2

I read post #2 and it did not describe why @vashkoproimage could not wire them as three sets of 2 panels in series other than rewiring the panels. In another post the OP said he was concerned about voltage drop and presumably the expense or difficulty of increasing wire size for the run from the panels to the inverter. Why is voltage drop an issue unless it drops below the start up voltage of the SCC?
EDIT: Just before this post @Hedges raised the same issue in more detail and explained why voltage drop in this situation might not be an issue. As far as I can tell @vashkoproimage has not responded to that question? It seems that would be a lot simpler than some of the other solutions that would reduce output more than some small voltage drop. I also reread the thread and another valid concern is that three sets of panels could produce 39 Amps which is above what the wire is rated at and that may be a valid concern, However, I think the SCC is limited to 3500 Watts and at 100 volts that would only be 35 Amps which is right at the limit for 10 AWG wire and only at peak output for part of the day.

 

[SamDeleted]

I read post #2 and it did not describe why @vashkoproimage could not wire them as three sets of 2 panels in series other than rewiring the panels. In another post the OP said he was concerned about voltage drop and presumably the expense or difficulty of increasing wire size for the run from the panels to the inverter. Why is voltage drop an issue unless it drops below the start up voltage of the SCC?
EDIT: Just before this post @Hedges raised the same issue in more detail and explained why voltage drop in this situation might not be an issue. As far as I can tell @vashkoproimage has not responded to that question? It seems that would be a lot simpler than some of the other solutions that would reduce output more than some small voltage drop.

That is a good question.


@Hedges definitely explained it all better and more in-depth than me ?

 

[vashkoproimage]

I read post #2 and it did not describe why @vashkoproimage could not wire them as three sets of 2 panels in series other than rewiring the panels. In another post the OP said he was concerned about voltage drop and presumably the expense or difficulty of increasing wire size for the run from the panels to the inverter. Why is voltage drop an issue unless it drops below the start up voltage of the SCC?

Not possible to do 2 panels in series. 3 panels are on one array and the 2nd array of 3 panels are about 150 feet about from first. They are secured to the concrete and are fully tiltable from summer and winter setup. If I had a nice level spot I would have put all of them together from the start. But it’s not the case. By the time I finish building our house, I will clear some trees and make a nice array for a permanent situation.

 

[vashkoproimage]

That is a good question.


@Hedges definitely explained it all better and more in-depth than me ?

Please read post from the start. Clearly stated running 3 sets of 2 panels not possible. Why keep pushing that idea when I already thought of that option?

 

[Ampster]

Not possible to do 2 panels in series. 3 panels are on one array and the 2nd array of 3 panels are about 150 feet about from first

That is a completely different issue from voltage drop and makes sense. It would have been more helpful if you had repeated that explanation rather than expecting us to read your mind or interpret what you meant when you said it would not work because of voltage drop. When you redo the system you can evaluate the cost of bigger wire versus a SCC with a higher voltage limit. In the meantime I think you have several temporary options. I know you think it was perfectly clear but for clarity for future readers you might want to add the physical limitations in the posts where you said voltage drop was the issue.

 

[Ampster]

Please read post from the start.

It is a confusing thread and as others have said, it would have been more clear if the OP had edited his initial post to clarify all the constraints. I was confused by the voltage drop statement when in fact it was the physical location of the panels that apparently was the operative issue. And as it turns out this is only a temporary situation until the house is completed and more area is cleared so the panels can be combined in one spot or a new SCC with greater capacity is acquired.

 

[vashkoproimage]

That is a completely different issue from voltage drop and makes sense. When you redo the system you can evaluate the cost of bigger wire versus a SCC with a higher voltage limit. In the meantime I think you have several temporary options.

If I was to somehow manage connecting all six panels to my first array, 3 sets of 2 panels. With my 10 gauge wire running 160 feet. 98.84 Voc and 40.47 amps running to my controller. I will need to run 6 gauge wire that distance to make it 3% voltage drop, because of the high amps and lower voltage. 2 awg wire if I want to be under the 1.5% voltage drop.

 

[vashkoproimage]

It is a confusing thread and as others have said, it would have been more clear if the OP had edited his initial post to clarify all the constraints. I was confused by the voltage drop statement when in fact it was the physical location of the panels that apparently was the operative issue. And as it turns out this is only a temporary situation until the house is completed and more area is cleared so the panels can be combined in one spot or a new SCC with greater capacity is acquired.

Nothing confusing. Very Simple. Need to drop voltage on current setup of 2 arrays of 3 panels. Talking about wiring and moving panels is not an option. I have considered this already. Don’t you think? Lol

 

[Ampster]

I will need to run 6 gauge wire that distance to make it 3% voltage drop

I understand the physical limitations. I do not understand your concern about voltage drop from a bunch of solar panels as long as the current carrying capacity of the wire is not exceeded. I do understand with the physical limitations and with three panels in series why you would want to drop voltage on certain days to not fry your SCC.

 

[Ampster]

I have considered this already. Don’t you think?

Dont I think?
I can't read your mind and as others have said the thread is confusing because presumably others cannot read your mind either. I also think most of the posts in this thread are genuinly trying to be helpful.
That is what I think.

 

[vashkoproimage]

I understand the physical limitations. I do not understand your concern about voltage drop from a bunch of solar panels as long as the current carrying capacity of the wire is not exceeded.

It was never a concern about the wiring I have set up. Concern was about lowering voltage from current setup without rearranging current setup.

 

[vashkoproimage]

Dont I think?
I can't read your mind and as others have said the thread is confusing because presumably others cannot read your mind either. I also think most of the posts in this thread are genuinly trying to be helpful.
That is what I think.

You don’t have to read my mind. Lol. I clearly mention 3 sets of 2 panels was not an option on current setup.