12x12 Cabin - New to Solar - Please help!

[Doug24]

I have a Kill-A-Watt meter and tested it on a box fan. About 90 watts on high and around 55 or so on low. I'm more inclined to stay with the 12-volt route, as you have done, since my cabin is so tiny and I just need some small lights and ventilation. I'm not expecting to grow beyond that as there really is no need since we prioritize staying outside most of the time.

So I guess I'm trying to get a handle on a simple system that will meet that need but feel like I'm getting more confused as we go!

[Brian53713]

LED lights and fans come in 12 volt DC versions. You wouldn't have to buy an inverter. And I do recommend free shipping on those awesome 100 watt panels you're considering. Unless you can get those bigger Obviously good deal ones to your location and Up on the Roof by yourself easily. And if a large DC fan is noisy, do the obvious get a mid-sized or some small ones. And you won't lose as much power in the conversion. And based on the simple items you have previously and originally selected, do an important thing get an mppt charger. It will have the ability to expand panels and way more efficient.

[Ho jo]

I agree with Brian 3 100 watt panels 2 6 volt golf cart batteries and a 30 amp mppt charge controller. runs 2 14" dc fans half a dozen led lights. And I didn't have to take out a loan!! keep it simple

[Sunking]

So I guess I'm trying to get a handle on a simple system that will meet that need but feel like I'm getting more confused as we go!

Nothing to get confused about. All you have to do is figure out your daily wat hour usage. Once you got that is simple 5th grade math. Makes no difference how large or small the system is.

The main issue with low voltage is distribution, number of circuits required, length of circuits, and gauge of wire. It can get quite expensive. Got a fan, needs a circuit. Need two fans requires 2 circuits. With low voltage you do not have any voltage to play with respect to voltage loss.

Example a 12 AWG conductor at 12 volts technically can handle up to 15 amps. Sound like a lot but is 180 watts. But there is a catch. If the one-way distance of that wire is more than 5 to 6 feet is going to require larger wire to keep losses to lower than 3%. Say you needed 30 feet at 15 amps on 12 volts requires 6 AWG for a single circuit that can only give you 150 watts.

On the other hand if you run 120 volts at 15 amps is 1500 watts and you can run several devices daisy chained on a single circuit up to 60 feet away 1-way distance. That is 10 times the power at 10 times the distance. That is why one circuit breaker in you house can supply power to many outlets. You cannot do that with low voltage.

[Ho jo]

A 12x12 cabin? 5 amps for 2 fans 1 amp for 6 lights. 7 amps 12 volts 18 feet on 12 awg less than 3%.

[Doug24]

Thanks guys. So let me see if I can summarize...

3x100w panels. Wired in parallel
2x6v batteries wired in series
From the MPPT controller, load runs off that. I can run 12AWG to my fans and lights all of that one circuit with switches for each?

[Ho jo]

Batteries in series Panels in series. I ran 2 12 awg runs 3 lights 1 fan on each. I used 6 foot of 8 awg between charge controller and battery. And 12 awg between panels and cc

[SunEagle]

Thanks guys. So let me see if I can summarize...

3x100w panels. Wired in parallel
2x6v batteries wired in series
From the MPPT controller, load runs off that. I can run 12AWG to my fans and lights all of that one circuit with switches for each?

If you have a true MPPT CC then you probably can wire those 3 x 100w panels in series. This will help you avoid the need for fuse protection for each panel and a combiner box.

[Ho jo]

And if you do decide to go bigger your 12 foot roof will hold 3 more panels with 2 more bateries in series for 24 volts a no larger than 600 watt inverter you could watch a 32 inch tv for 12 hrs

[Doug24]

This is really great information, thank you all for posting a reply.

Is there a down side with buying 2 batteries now and 2 later, or should I get them all at once?

This is the charge controller I am looking at:

EPever 40A MPPT Solar Charge Controller Tracer A 4210A + Remote Meter MT-50 Solar Charge With LCD Display for solar Battery Charging: https://www.amazon.com/dp/B01GMUPGZA...v_ov_lig_dp_it

So where would I need fuses in this whole setup?

Thanks!

[Ho jo]

Mixing old and new batteries is not a good idea. My first batteries didn't last a year. Not that the batteries were bad it was because I didn't no how to take care of them. If yours last longer than a year consider yourself lucky. You learn as you go with solar I'm still learning. A 40 amp controller doesn't go well with 100 watt panels. 40 amps at 12 volts 520 watts max.The 100 watt panels your looking at have an open circuit voltage of 22.5 x 5= 112.5 volts that charge controller has 100 volts max. So you could only use 4 panels. A epever 3210an 30 amp 400 watts at 12 volts 4 panels max. And it's only $115. Look for hqst panels in my opinion same as renogy different label $115. If you decide to go to 24 volts later this controller will work. If and when you decide to go 24 I'd wait until your first batteries take the plung. Then buy 4 at the same time.With a 12 foot wide roof you can only fit 6 panels. So you are limited to 600 watts. Look back at sunkings math about sizing he is very knowledgeable.

[Sunking]

So you are limited to 600 watts.

If 600 watts is the maximum panel wattage you can grow into, Get yourself a 45 amp MPPT controller if you intend to use 12 volt battery. Just keep in mind panel wattage has to be matched to battery capacity. On a part time use application keep charge current to around C/10.

Example if you start with 300 watts of panels, charge current = 300 watts / 13.3 volts = 22.5 amps so a pair of 225 AH 6-volt golf cart batteries would be a perfect match.

Be very careful with Prime Number of panels. 1 and 3 work, but you are in trouble with 5, 7, 11, 13..... as that only allows you to wire panels in parallel and that is the last thing you want.

[Doug24]

Thank you both for your input. So, I could go with the epever 3210an 30 amp mppt controller now? That would allow for up to 4 panels now @ 12v. In the future, when my first set of 6v batteries fail, I can then get 4 6v batteries to go to 24v and that will allow for addition of the remaining 2 panels for a total of 6. Is that correct using this same controller?

[Ho jo]

Yes you could use 400 watts now But look at the perfect example sunking just gave you.

[Sunking]

Thank you both for your input. So, I could go with the epever 3210an 30 amp mppt controller now? That would allow for up to 4 panels now @ 12v. In the future, when my first set of 6v batteries fail, I can then get 4 6v batteries to go to 24v and that will allow for addition of the remaining 2 panels for a total of 6. Is that correct using this same controller?

Maybe, maybe not. If everything you run is 12 volts, you are married to 12 volts. If you convert to 24 volt battery, then you have to change everything out to 24 volt or buy an expensive 24/12 volt converter.

So if you do with a 30 amp MPPT controller and operate at 12 volts, maximum panel wattage is 400 watts, and max battery capacity is 300 AH. So think before you pull any triggers. You cannot recall a bullet once you pull the trigger or say: "I Do" if you get married to 12 volts.