wiring fixed and deployed solar to one controller

cruxarche

Observer
Hi all,
I am looking to upgrade my solar on my trailer. I have been using a renogy 100w suitcase for a few years, but the viewstar controller just failed on me. 100 watts has been ok but limiting in some situations. I want to upgrade to a roof mounted panel and keep my 100w solar suitcase for when it is needed.

I purchased a fancy new Victron energy smart solar mppt controller and would like to use it for both the fixed and portable panels. My question is, how should I wire up the panels to the controller. I am used to the controller being with the panel, but now it needs to be mounted on the trailer. How would you recommend making the connections? I cannot seem to wrap my mind around how to set this up. Particularly I am not sure how to make it convenient to deploy the solar when needed.

Thanks for your suggestions.

Setup:
rooftop panel (yet to be purchased)
renogy 100w suitcase (no controller)
Victron Energy 100/30 Smart Solar
Victron Energy bmv712 battery monitor (mounted in trailer)
Battery: two trojan t 105 6v (in series)
 

dreadlocks

Well-known member
your better off using separate controllers for this task as your roof panels are unlikely to match spec of your portable ones..
 

dwh

Tail-End Charlie
Get panels with the same voltage specs (Voc, Vmp) as your portable panel. Renogy probably has the same 100w panels in a fixed mount type frame.

Rig all panels in parallel so the voltage doesn't change and confuse the MPPT whenever you plugin/unplug the portable panel.
 

cruxarche

Observer
Thanks dwh. Similar panels are definitely available. I’m trying to figure out how to wire it so that I can conveniently switch back and forth between the different panels as needed. The controller is not going to be in a very convenient location to be regularly accessing it.
 

dwh

Tail-End Charlie
You don't switch back and forth. The fixed panel stays connected and running full-time. You just add the portable when you need it.

At the solar input to the charge controller, "Y" out in parallel - one to the fixed panel and one to a connector for the portable.
 

dwh

Tail-End Charlie
Like this, but one panel has a connector so you can plug/unplug it as needed.



 

cruxarche

Observer
Dwh, thanks. It’s the “Y out” part I’m struggling with. If I put an actual Y at the solar input of the controller with one input into the controller and two sets of wires on the other side I could leave the roof mounted panel connected all the time, and just plug in the portable as needed. But would that result in parallel Configuration for the panels?

Or am I supposed to put a Anderson or some other connector between the portable panel and the junction of the controller and the panels(indicated by the box). Just leaving extra line tucked away until I need to plug in the panel?

Sorry I don’t have the technical expertise to describe this well.
 

dwh

Tail-End Charlie
Dwh, thanks. It’s the “Y out” part I’m struggling with. If I put an actual Y at the solar input of the controller with one input into the controller and two sets of wires on the other side I could leave the roof mounted panel connected all the time, and just plug in the portable as needed.
Yes.


But would that result in parallel Configuration for the panels?
Depends on how you wire it. A Y would have both the solar panel's "+" together, and both the "-" together. That would be parallel.

Think of two 12v batteries. Wired in parallel, the voltage stays the same (12v), but the amperage (actually, amp*hours) doubles. In series, the amps stays the same, but the voltage doubles (24v).

Well, the same thing happens with solar panels. In parallel, the voltage stays the same but the amps double. If you wired them in series, the voltage would double.

The MPPT circuit first identifies the operating "range" of the solar, then fine tunes a bit in that range. So say you have two 18v panels. In parallel the voltage would be 18v, but in series it would be 36v.

So say you have the panels in series. The MPPT sets itself to operate in the 36v range. Then you remove one panel, and the solar drops to 18v. Well now the MPPT isn't working properly. It's in the wrong range.

But if you rig the panels in parallel, adding or removing one panel makes no difference, the solar is at 18v either way.

Not to mention that wiring the panels in parallel is easy. Figuring out how to wire them in series and then be able to remove one would be a pain.



Or am I supposed to put a Anderson or some other connector between the portable panel and the junction of the controller and the panels(indicated by the box). Just leaving extra line tucked away until I need to plug in the panel?
Yup, that's exactly what you do.
 

dreadlocks

Well-known member
Renogy probably has the same 100w panels in a fixed mount type frame.
If he has a 100W briefcase he's got 2x50W solar panels, he could match those same panels but its usually better to fit less bigger panels than more little panels.. and with that MPPT he dont have to use 12v panels, most tend to perfer house type panels that run at ~36v so they can even provide a bit of absorption charge while shaded.. If I were running 4x50W 12v panels with that Victron I'd have em in a series for higher voltage, less current and lower losses.. which would make hooking up a briefcase a bit of a challenge wiring wise (a jumper cable would have to sit in place of stored portable panels).. or he could install 1 200W+ panel thats much simpler wiring and lighter and makes less holes in the roof.. and then wire up a 2nd, smaller controller like a Genasun GV10 near battery w/a quick disconnect for his portable panels.

He'll scavenge more power w/separate controllers too, the diodes will basically cut off his fixed panels when hes using the portable ones because the'll have higher voltage.. If his fixed panels are getting 1A, and his portable are getting 4A his controller will be outputting 4A, but two controllers could handle the two different voltage discrepancies and would output 5A combined.
 
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cruxarche

Observer
Dread,
Thanks for your input. I see the cc you are recommending is mppt. If I’m using the victron mppt for the rooftop does the other controller connected to the same battery need to be mppt as well?
Asking because that seems like a nicer cc than I would have picked up to replace the cheap viewstar cc.
 

dreadlocks

Well-known member
dont have to be no, but MPPT is alot better than PWM and worth the marginal cost difference.. every solar array SHOULD have its own controller and that SHOULD be MPPT, its not a MUST but its highly recommended.

Ive got a Genasun GV10 from my other trailer, worked very well but for me 100W panel was typically not adequate fixed but for extending base loads a few more days, most of the time it only got a few hours of direct sunlight in a forest.. On my new trailer I'm thinking of wiring it up and using it with a suitcase panel to hold me over til I can gather up and install a much larger roof top system (~$1500).. then later I'll have both at my disposal if I need it.. I used suit case panels before in a forest and your always chasing the sun, so I dont see that as a final solution either.. like setting it up in morning only to come back in evening and finding out it went into shade soon after you left, plus worry of someone stealing it.. I've got a LiPo now and they can take a charge very fast, so this time around im planning on oversized fixed solar that can recharge the thing in a few hours, hopefully wont need the portable except some fringe cases (dun wanna climb on roof to clean off snow)

If your old viewstar was a PWM and you put a MPPT controller on it, you should notice a significant performance improvement out of your existing panel.. you also want to put your portable controller inside near the battery, so the higher voltage side has the longest cable run, it will incur less losses and so the controller has a good idea the temp of the battery.
 
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dwh

Tail-End Charlie
If he has a 100W briefcase he's got 2x50W solar panels,
Aye.


he could match those same panels but its usually better to fit less bigger panels than more little panels..
There are a couple of problems with that statement.

First of all, he doesn't need to match those same panels.

Second, bigger panels offer some advantages, but smaller panels also offer some advantages, so really it just depends. Smaller panels offer redundancy in case of a panel failure, and often offer more bypass diodes. Larger panels offer more square inches of solar cells facing the sun per square foot, which can be important on small roofs where every square inch matters, and larger panels can save quite a lot on the expense of copper wire in large installations.

Also, if he did match those same panels, then he would have mounting flexibility that a larger panel couldn't give him. For instance, he could mount one 50w panel to the left of a roof vent, and the other to the right of the vent.


and with that MPPT he dont have to use 12v panels, most tend to perfer house type panels that run at ~36v so they can even provide a bit of absorption charge while shaded..
I run a 300w panel into a Victron 100/30. I do that because I got the panel cheap, and since it's 36v and I want to charge a 12v battery, I pretty much have to use MPPT or accept the losses from running a 36v Vmp panel at battery voltage instead of Vmp, which would happen with a PWM.

As for shading, my 300w panel has 6 bypass diodes (one per every 12 cells, 6v drop per bypass), so it can produce at 36v (no diode bypass), or 30v (one bypass), 24v (two bypasses), or 18v (three bypasses). If there is so much shade that it gets 4 bypasses and drops to 12v, then that's not enough to charge a 12v battery so it's essentially a 100% loss.

But I run what I brung. There is no reason to suppose that that is what I'd "prefer". I wouldn't. I would prefer 3 x 100w panels, which would give me greater redundancy and rigged in series would still give me the 6 bypass diodes for shade tolerance. The reason I'm not running what I'd prefer, is that I got a good deal on the 300w, so what the hell.


But you're wrong that he doesn't have to use 12v (12v nominal, which is normaly 16v-22v Vmp) panels. He does because he's already got one. So if he wanted to get a 36v panel, then he would have to run separate charge controllers. By sticking with 18v Vmp, he can use just one controller.



If I were running 4x50W 12v panels with that Victron I'd have em in a series for higher voltage, less current and lower losses.. which would make hooking up a briefcase a bit of a challenge wiring wise (a jumper cable would have to sit in place of stored portable panels).. or he could install 1 200W+ panel thats much simpler wiring and lighter and makes less holes in the roof.. and then wire up a 2nd, smaller controller like a Genasun GV10 near battery w/a quick disconnect for his portable panels.
You're missing the point. This happens a lot on ExPo. Someone asks a question about how to use *what they already have*, and some guys jump on that immediately telling the guy how *he should be doing things* instead.

I don't do that unless he's asking to do the impossible. I try to answer *the question the guy actually asked*.

So, the OP has a 100w Renogy briefcase, which he still wants to use, but the charge controller failed. He wants to add another 100w fixed mount to the roof.

Okay, fine. Let's walk it through by the numbers...

Renogy offers several 100w "Portable Solar Suitcase". I don't know which one the OP has. But it doesn't matter - they are all around 18v Vmp.
So what is 18v Vmp? That's 36 x .5v cells in series = 18v.
There are two ways to do that. 18 cells per 50w panel, and the two 50w panels wired in series, or 36 cells per 50w panel and the two panels wired in parallel.
The only one that shows a wiring diagram shows this:




18 cells per 50w panel, two 50w panels in series to equal 36 cells in series for 18v Vmp.

So he wants to add a 100w panel. No problem. Renogy offers a four different 100w non-folding panels.

One has a Vmp of 17.8v. https://www.renogy.com/renogy-100-watt-12-volt-polycrystalline-solar-panel/
One has a Vmp of 16v. https://www.renogy.com/renogy-100-watt-12-volt-monocrystalline-solar-panel-slim-design/
One has a Vmp of 18.9v. https://www.renogy.com/renogy-100-watt-12-volt-monocrystalline-solar-panel/
Once has a Vmp of 17.7v. https://www.renogy.com/renogy-eclipse-100-watt-12-volt-monocrystalline-solar-panel/

Except for that one at 16v, any of the other three would work just fine in parallel with the 18v suitcase panel(s).

A 100w panel is exactly the same electrically as two 50s in series. It's going to be 36 x .5v cells in series either way.
The only real difference is that with the suitcase, half the cells are in one frame and half in the other, and with the fixed panel, all the cells are in one frame.
But it's still just 36 cells in series. (Well...not that 16v panel, that's going to be 32 cells in series.)

Personally, I'd probably go with the 17.8v just because that's closest to the 18v of the suitcase. But it really doesn't matter, a slight mismatch in Vmp is no big deal. A 2v mismatch (18v/16v) would still work, but if you can get closer, you might as well.


Okay, so he's already stated in the OP that he's going with a Victron MPPT. Fine. Get a fixed 100w panel with a Vmp close to the suitcase Vmp. Install the fixed 100w panel, rig a parallel to be able to plug in the suitcase as needed and run the parallel into the Victron at 18v.

Easy. Done deal.



He'll scavenge more power w/separate controllers too, the diodes will basically cut off his fixed panels when hes using the portable ones because the'll have higher voltage.. If his fixed panels are getting 1A, and his portable are getting 4A his controller will be outputting 4A, but two controllers could handle the two different voltage discrepancies and would output 5A combined.
Sorry man, but that's BS. Exactly how will which diodes to do what to "cut off his fixed panels"? That's not how it works.

The diodes are internal to the panels, and they are bypass diodes. The diodes in one panel don't affect the diodes in the other panel at all. They sure as hell do not "cut out" the other panel. It the cells of one panel get shaded and a bypass diode kicks in, that is only going to reduce the voltage of that one panel - it won't do anything to the other panel.

If a panel has a Vmp of 18v and has say two bypass diodes, if one diode bypasses, then that panel will only be putting out 9v and it won't contribute anything to charging a 12v battery. With two of them rigged in parallel, the other will still be putting out 18v.

Two controllers won't change that. One panel on one controller will still be putting out only 9v and not contributing to battery charging, while the other is running at 18v.

You seem to be basing this erroneous BS on the assumption that he'll have panels with two wildly different Vmp ratings, like one 18v and one 36v.
 

cruxarche

Observer
1534903186564.jpeg
Here is a photo of the suitcase panel specs. Honestly I’m keeping it because I have it but damn is it heavy. I’m considering flexible options for the second panel because I need to limit weight on the trailer roof. So for me weight is a priority consideration. Even over efficiency.

Thanks for the replies and input.
 

dwh

Tail-End Charlie
No big deal. Renogy offers two flexible 100w panels. One with a Vmp of 18.9v, and one at 17.5v. Either one is close enough to work in parallel with your 18v suitcase into a single MPPT controller.

But if weight is the primary consideration, you could dump the suitcase and make your own out of two 50w flexible panels. Renogy offers two 50w flexibles, one at 18.5v Vmp and one at 17.7v. Again, close enough to parallel into a single controller. For max efficiency to squeeze out every watt, I'd probably go with the 18.9v 100w on the roof, and a couple of the 18.5v 50w to make a portable folding suitcase. Then they would all 3 be paralleled into the controller.
 

cruxarche

Observer
Dwh,
Thanks. I was Comtemplating something like that. For now I think I’ll get the flexible up top. Get the controller mounted somewhere (still figuring out where, it’s a pop up trailer), and use the suitcase I have.

Then I can research making my own lightweight suitcase.
 
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