Question about our new small system

[AndrewS]

Hi all, new here
We just tore down and rebuilt a new 2100sq.ft cabin, the old was running copper lines for propane lighting, the new we want to switch to a 12v solar system to run LED lights and 12v ceiling fans, with minimal phone charging. This is hunt camp with 11 other members and some members put the cart before the horse and started buying pieces of the system without much understanding of our needs/sizing.

What we have so far:
2 - 100w panels, one flexible, one rigid.
2 - 12v EV12A-A AGM batteries.
20a PWM controller - i need to check but I believe it can handle 12v/24v

The roof mounting location is free of shade cover at all times throughout the day and south facing.
What is our best method of connecting the panels (from what I understand parallel would be best for our 12v needs, controller type and can handle the input amps, and good if one panel goes down)
What is our best method of connecting the two batteries (from what I understand, again parallel for our 12v system).
The panels are roughly 15ft from the controller running 10 gage wire, and the controller is 2-ish feet from the batteries. IF we were to add another panel, would it then be easiest to add the third in series?

Thanks!

[NochiLife]

2100 square feet...if you're planning to do the whole thing with DC lighting, I would HIGHLY suggest running a 24vDC system. The major difficulty with running low DC voltage (especially for long runs) are twofold:
- the lower the voltage, the more current (amps) required to do the same work (watts)
- the higher the current, the greater the voltage loss in the wiring.
You could easily end up with 8v at the end of a long run if there's enough load on it (=hypothetical 34% voltage loss, down 4vDC due to line losses). However, if you're running 24v, the losses will much less: the loads will use half as much power to start with, resulting in 22v at the end of the line (down 2vDC)--which out of 24v is only a 17% loss.

As you can see it's a rather vicious cycle--the more current drawn, the more the voltage loss, which requires more current...and everything balances out running kind of weak.
It is relatively easy to find devices that run up to 30vDC; it's hard to find stuff much beyond that. Many 12v devices can also run on 24v--and if not, converters are relatively cheap and easy to install.

That all being said, you might be fine with 12v...just as long as you're aware of the possible issues with long runs of lower voltage systems.

IF you go with 12v, then your questions:
- yes, batteries would go in parallel. Make sure you don't cross the wires--that will be one unforgettable (and dangerous) moment!)
- Best method of connecting the panels: it would be best if they were perfectly matched. As long as they're the same voltage (Voc, Vmp), you should be fine putting them in parallel. For a PWM controller, you'll want to try to get the solar panel voltage close to the range of the battery voltage for best results.
- If you added a third panel, assuming it's the same voltage, you would add it in parallel. Trying to wire mismatched panels together can get very murky.

One more possibility, if you put all the lighting on a separate "circuit", you could get a booster to run the lights at 24vDC (again, minimizing losses), keeping the system at 12v.

IF you went with 24v, you could do that with your existing parts:
- both panels in SERIES
- both batteries in SERIES
- configure the PWM charger for 24v, etc.
- if you added additional panels, you would have to add two more panels at a time in a series-parallel configuration (panels in blocks of two connected in series, and each "block" connected in parallel.)

[bcroe]

With anything but the lightest LED load, your 100W panels will not be enough. Far more economical
might be some 250W grid tie panels. However, you might feel a need to take them with you when the
cabin is vacant.

Check the actual drain of your 12V fan. You need to calculate the watts of it and every load, then
multiply each by the daily hours of operation to get kilowatt hours, add up the daily total. With that
information you can start designing a system capable of the load, without soon destroying your
batteries.

If the 12V fan is your heaviest load, you should be able to get by on 12V by keeping the batteries
not too far from the fan. Very light loads can be farther away using wire much heavier than the
minimum size for the small currents. Panels may be operated efficiently at somewhat higher
voltage using an MPPT controller. Take your cues from the RV crowd. Bruce Roe

[AndrewS]

Thanks for the advise guys!
Let me summarize to ensure I am on the same page, and also ask some followup.
Also let's assume we proceed with 24v DC output starting at the top.

1. 2 - 100w panels connected in series (double the voltage, current stays the same)
2. PWM controller set for 24v input from panels
3. 2 - EV12A-A batteries connected in series = 24v output... are these batteries safe to be connected in series to output 24v?

We don't need an inverter (since we are staying DC), and we don't need a 12 to 24v converter (since the batteries output 24v)?

The LED fixtures are 6w, and the fans are 15w.
15 LED fixtures = 90W, 2 fans = 30w, 120w total. Absolute worst case scenario we need 5hrs with everything on, but more likely half that since all lights won't always be on.
So that's 600 watt hours, and 25amp hours at 24v, or 50amp hours at 12v?


IF our pre-purchased LED fixtures and fans are not rated for 24v, and we stick with 12v (connecting batteries in parallel), and we run thicker gage wire to that furthest fixtures, will this pose any damage to the batteries?

Thanks again

[NochiLife]

Thanks for the advise guys!
Let me summarize to ensure I am on the same page, and also ask some followup.
Also let's assume we proceed with 24v DC output starting at the top.

1. 2 - 100w panels connected in series (double the voltage, current stays the same)
2. PWM controller set for 24v input from panels
3. 2 - EV12A-A batteries connected in series = 24v output... are these batteries safe to be connected in series to output 24v?

Batteries don't care; you'll be just fine connecting them in series. Correct on the panels (double voltage, same current).

We don't need an inverter (since we are staying DC), and we don't need a 12 to 24v converter (since the batteries output 24v)?

Correct. Yay, score one!

The LED fixtures are 6w, and the fans are 15w.
15 LED fixtures = 90W, 2 fans = 30w, 120w total. Absolute worst case scenario we need 5hrs with everything on, but more likely half that since all lights won't always be on.
So that's 600 watt hours, and 25amp hours at 24v, or 50amp hours at 12v?

600 watt hours...you'll should be able to get that with full sunshine. However, let's put a hypothetical for cloudy weather: your 200W-rated panels will likely be producing in the order of 20W in heavy cloud cover. (Shocking, I know.) That shouldn't be much of a problem if the cabin is only used for a day or two at a time (as the batteries can recharge SLOWLY over the following cloudy days)--but if it's used for a week straight, your batteries might get a little low. (Of course, a good couple sunny days should recharge the batteries.)

That being said, you'll probably be just fine. . Light loads and solar go together like a hand in a (well fitted) glove.

IF our pre-purchased LED fixtures and fans are not rated for 24v, and we stick with 12v (connecting batteries in parallel), and we run thicker gage wire to that furthest fixtures, will this pose any damage to the batteries?

Thanks again

No, it won't cause damage to anything, unless you accidentally short anything out! (I will note right here: I HIGHLY recommend...no...REQUIRE DC-rated breakers between your batteries and anything connected to them. After accidentally shorting out a 48vDC lead acid battery bank with a meter I thought was in the voltage scale, I treat any sizable battery with frightened respect! As an aside, if something goes wrong, you can fix it and just reset the breaker, no fuses to buy. In addition, it's very easy to just shut something off to work on it.)

Keep in mind that running several "circuits" will spread the load across multiple wires, reducing the loss on any particular circuit. You'll probably be just fine even at 12v.
Mathematically, assuming one circuit, let's calculate the worst case scenario (just so we're surprised when it works better!):
- 12vDC into the lines
- 14AWG wire (regular cords are 18AWG, "low voltage lighting" often smaller, e.g. 22 AWG)
- 10A worst-case load
-> voltage at end of line: 9.104v, 29W power lost in the wire (calculated with ElectroDroid, a free Android app. Yes, that's a plug )

If 10AWG (NOT cheap, especially over long runs!), you'll have 10.8v at the end of the string, losing 11.45W in the wire (incidentally, about the same loss as 24v w/ 16AWG wire). Obviously, the less the load, the smaller the voltage drop and loss in the wire runs. And the more wire runs, the less loss in any individual run.

Have fun

[bcroe]

Thicker wires will never hurt your batteries. There are different ways to drive LEDs,
check what happens to watts when the voltage varies. The most efficient ones will
use the same energy at 24V as 12V, but make the most radio interference. Bruce Roe

[AndrewS]

Turns out the lights that were already purchased are only rated at 12-18v

https://www.amazon.ca/dp/B06XCDZWGB?ref_=pe_1139640_122623040_dpLink

If we still run a 24v circuit, and wire at least two lights in series per circuit, we should be ok? I think we will install 12-24v toggle switches in the wall (like automotive LED light bar auxiliary switches) so we aren't manually flipping the built in switch on the first light in series for each circuit to turn the rest in that circuit on.

[Mike90250]

those ceiling lights you linked to, appear to have driver circuitry. They may not play well wired in series like an incandescent bulb would. Ok to try it, but you may need a backup plan for a 24-12v DC-DC downconverter.

[NochiLife]

Running 2 lights in series...if you want to experiment, try it with lights you can afford to lose, and use a multimeter to measure the voltage across them. In my experience, they might balance out PROVIDING they don't have any internal oscillations or PWM dimming. (That resulted in a haywire of pulsing lights; fortunately, they were all rated for the voltage. Still burned out later for no reason at all--there's a good bit of garbage from China!)

Another option, if you're handy with a soldering iron and a little bit of work: you can buy 10 little DC-DC converters for less than $1/apiece. These are low power units, and would be good for one or two lights apiece. Trying to run all of the lights off a bigger unit would work, but you'd have the potential for dimmer lights at the farthest reaches.
I'd go with these: https://www.ebay.com/itm/10PCS-3V-40...r/293069838586
There are slightly cheaper options out there, but the maximum input voltage of the MP1584 converters is only 28v; in wintertime, a lead-acid bank could easily reach that. <poof>