Solar panel wiring

[HABBERDABBER]

No luck with a quick search on the forum, so here's my question.


I have two 100W portable panels. If I wanted to use both, would I wire in series or parallel? Why do some people wire in series for 24V? Is one wiring scheme better, more efficient or desirable?


Panels would be connected to a charge controller and feed twp 6V batteries interconnected in series.


Any advice, anyone?

[Jim Bennett]

Your panels are most likely about 18V, so your option with two panels is to wire in parralel for 18V output, or series for a 36V outlet.

The advantage of using twice the voltage is that you use half the amperage. This allows for less resistance in a smaller sized cable. You do need to use an MPPT solar controller to make the 36V work. I have four panels on my trailer wired with two in series, and the two sets in parallel. I also wired my portable panels in series as you need the voltages to be as close together as possible to minimize any loss.

This said, if I was to do it again I would not do series. The runs in reality are very short so any losses would be minimal. I need to replace my stolen portable setup and may just keep it to 18V, which would require some wiring changed in the existing roof panels, but that is not a tough thing.

So, my vote is keeping them in parallel.

[fudge_brownie]

One issue with parallel wiring will be: since they are portable you could have a long wiring run, you would need to use a heavy gauge wire in such a situation, ie 10. I would recommend 50 feet of wire and the best I have found is speaker wire. I like a brand called KnuKonceptz https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1, it coils and transports very nice, also can be used underfoot but not driven on.

I assume the two panels are identical? They really have to be in a parallel install.

[Vermilye]

Originally Posted by fudge_brownie

One issue with parallel wiring will be: since they are portable you could have a long wiring run, you would need to use a heavy gauge wire in such a situation, ie 10. I would recommend 50 feet of wire and the best I have found is speaker wire. I like a brand called KnuKonceptz https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1, it coils and transports very nice, also can be used underfoot but not driven on.

I assume the two panels are identical? They really have to be in a parallel install.

Another possibility for very flexible #10 wire is GS PowerFlex. About the same $, and also from Amazon, no shipping if you have prime or can wait.

[MyronL]

What I done.

[Semievolved]

it really is important to know your panel specifications to advise on this. plus, your choice of a controller will be dictated at some level by panel output. if the panels can be configured such that the max V output is not much above the battery V, then you may be just as well off using a PWM controller, save quite a few bucks from a MPPT and more reliable as well. If they're nominal 18V panels though, max V will likely be around 24V and you'll benefit from a MPPT. If max output is more like 18V, you could hook them in parallel and use a PWM and not lose much relative to a MPPT. As others have pointed out, the length of your runs should also be considered, i.e. the longer the run the more important it is to drop the current as low as possible (series preferred) but then you have the higher V to contend with almost certainly requiring MPPT controller.

[HABBERDABBER]

I composed a lengthy response to all the suggestions and between my ISP or the forum, it's gone, baby, gone, before posting.


So, tomorrow I'll recompose, but for now I'd like to thank all for their advice and suggestions. I'll likely go with parallel connection, but I have more questions.



Until mañana,

[mtnest]

I feel your pain, Tom. To lose something while in the process of writing is frustrating. When I remember to do so I copy myself as I write, just to be on the safe side. I'm looking for forward to the continuation of this thread.

[AKCamper]

Originally Posted by HABBERDABBER

No luck with a quick search on the forum, so here's my question.


I have two 100W portable panels. If I wanted to use both, would I wire in series or parallel? Why do some people wire in series for 24V? Is one wiring scheme better, more efficient or desirable?


Panels would be connected to a charge controller and feed twp 6V batteries interconnected in series.


Any advice, anyone?

We have the same trailer as you. The Renogy website has a good wire size calculator under their learning tab. I set my charge controller up like Myron in our storage box. The best wire I have found is made or at least sold by polar wire products in Anchorage Alaska. They sell an extremely flexible silicone duplex wire in almost any gauge you want. At the present time I am setting up a dual 100 watt tiltable panel setup for our truck canopy. I also have a 100 watt portable panel as well. All panels are Renogy. Of course I use a 20 amp PWM controller since the panels are wired in parallel

[John in Santa Cruz]

Originally Posted by fudge_brownie

One issue with parallel wiring will be: since they are portable you could have a long wiring run, you would need to use a heavy gauge wire in such a situation, ie 10. I would recommend 50 feet of wire and the best I have found is speaker wire. I like a brand called KnuKonceptz https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1, it coils and transports very nice, also can be used underfoot but not driven on.

I assume the two panels are identical? They really have to be in a parallel install.

another choice for 10 gauge wire is Marine 10/2. very high quality wire, fully tinned pure copper, with an outer jacket similar to Romex.

re; identical, they need to be similar voltage, they can be different sizes/current outputs. When you hook things in parallel, the voltage stays the same, and the current output is added together.

[alanmalk]

Originally Posted by John in Santa Cruz

...
re; identical, they need to be similar voltage, they can be different sizes/current outputs. When you hook things in parallel, the voltage stays the same, and the current output is added together.

If someone gave me a free 24 V (commercial - house size) panel that I wanted to use as a portable, I would make sure that there was a diode in the roof-mounted Escape panel and use them in parallel. But first, I would confirm that my original non-MPPT controller could work with the maximum voltage that the 24 V panel could produce - which might be in the neighborhood of 36 V unloaded.

There is no harm in using mixed voltages when the panels are isolated by diodes, but without a MPPT controller there is harm to the pocketbook. (Or - a lot of power going to waste. Note the free in the first paragraph.) If you want to try this experiment, I see 20 Amp Schottky diodes selling for less than 1 USD at Mouser.
--
Alan

[NEWYORKHILLBILLY]

for wire I like the 10-2 tray cable as it has a shield. I have a roll i bought for my install then the neighbor came over and give me some 8 Ga stuff so i used that

[John in Santa Cruz]

if you use diodes to isolate dissimilar voltage panels, only the higher voltage panel will supply any current, the lower voltage panel might as well be disconnected.

[John in Santa Cruz]

Originally Posted by NEWYORKHILLBILLY

for wire I like the 10-2 tray cable as it has a shield. I have a roll i bought for my install then the neighbor came over and give me some 8 Ga stuff so i used that

check out marine 10/2, its got much finer stranding, so its more flexible, and its fully tinned. its probably more expensive than tray cable, however. the sheathing is generally white, and it can be had with black+red or yellow+red conductors. it also comes in 8/2 for real high current installs or longer runs.

[AKCamper]

Originally Posted by NEWYORKHILLBILLY

for wire I like the 10-2 tray cable as it has a shield. I have a roll i bought for my install then the neighbor came over and give me some 8 Ga stuff so i used that

I really like the silicone artic superflex blue sold by polar wire in Anchorage, AK. 8 gauge duplex is $1.77 / ft. And 6 gauge duplex is $2.42 / ft.

[Semievolved]

In case it helps anybody, I've had great results working with this company for all the wire:


https://www.wireandcableyourway.com/


as good prices I have found anywhere and fast shipping, great customer service.

[Jim Bennett]

I have had great luck with buying good materials, along with getting some great advice, from a local solar supply company. Folks could check in their neighbourhood for one.

[alanmalk]

Originally Posted by John in Santa Cruz

if you use diodes to isolate dissimilar voltage panels, only the higher voltage panel will supply any current, the lower voltage panel might as well be disconnected.

That is true - until the higher voltage panel can not supply the full current required by the load. That is the critical parameter.

An extreme example: Picture a pair of 9V transistor radio batteries (the little guys) hooked in series to make a 18V battery. Put it in parallel with a 12V car battery protected by a diode. 18V is available when there is no load. Now connect a moderate load like a 12V car headlamp (10 amps more or less). The lower voltage 12V battery is supplying all the power since the 18V battery is worthless with this type of load.

Another extreme example: Mix two panels of different voltages and connect an amp meter into a short circuit. You will see the combined max amperage of both panels. Clearly both are producing their rated amperage.

Bottom line: Every panel is helpful when charging the typical Escape trailer battery that was used overnight - say 40% down by sunrise. Plus it reasonable to assume that the average solar user will have panels in the 15V to 19V range as a practical matter. Yes, perhaps someone might toss in a big 24V "industrial" panel - but unlikely. But the point is, once that big 250Watt monster panel hits its max output, its voltage begins to drop and eventually the lower voltage panels contribute useful power.

I personally conducted similar tests using small 6V and 9V panels and can verify the output amperage to be greater than the rated output of the higher voltage panel. (I was using a DC-DC boost converter to charge a small 12V AGM battery for a portable ham radio. I will also say that home made panels are ultra-fragile!)

But, and there is always a but: A modern MPPT controller may current limit to keep the voltage high, in which case, yes, the lower panel may contribute nothing. But the standard Escape controller is not "smart". It functions more like an On-Off switch (but a fast one). The "On" cycle connects the source directly into the battery and will pull down the panel(s) voltage to close to the average battery voltage. When the battery is nearly charged the lower voltage panel stops contributing - but at that point it's not needed.

Finally, if anyone is getting a headache from reading this - remember, none of the above is needed for a good camping trip. This is just a paper exercise.
--
Alan

[John in Santa Cruz]

yeah, that happens because the higher voltage source is dragged down to the lower voltage by the excessive current demands.

[HABBERDABBER]

My situation: 2 Lensun 100W panels through separate charge controllers is my question.


I have two 6V stock batteries. I have a good quality, but dated ASC (automatic sequencing charger) solar controller, rated for 8 amps.


If I ran both 100W panels through this controller, I'd be over the 8 A max.


One Lensun came with it's own charge controller.



Can I attach each 100W panel (identical units) separately and directly to my batteries, via & through the 2 different charge controllers?


Do the tandem lead acid batteries really care if they're receiving possibly slightly different charge voltages from 2 sources? I wouldn't.


I know I can buy some gee-whiz device, but I am an infrequent solar user, not interested in top tech capability, just wanting to get the job done with what I have.


Any speculations, advice or direction is appreciated. Please provide.



bon voyage,