Help with SOLAR electric system design...

Good morning fellas. I very much appreciate all this info. I spent several hours last night watching videos and searching the internet trying to educate myself on solar and the different methods of harnessing solar power.
I think I’ve come to the conclusion that it seems to make the most sense to take the equipment that I have (less the batteries) and stick it on Craigslist and/or EBay to see if I can sell it. Hopefully I can generate enough revenue to subsidize my off-grid cabin needs.
The inverters sell for around $1500 ea when new and the chargers sell for about $275 ea new. These units are about 3 years old. I guess I’ll look to get about .50 cents on the dollar for them. If I can get $1500 to $1800, that will give me a good start I think...

McGeiver - as you've indicated, the Midnite KID seems to be a logical fit at this point for my needs. In your opinion, what would be an appropriately sized solar array that could work to fully charge and maintain those 4 batteries via a Midnite KID? I assume a 24volt battery arrangement would be best with that controller? Based on charts/graphs I’ve seen, it looks like I get as low as 2.5 average hours of winter sun and as high as 5.5 to 6 hours of summer sun. At this point, I think my power “load” needs will be sufficient with this battery setup?
For the sake of discussion, let’s assume money is not a concern. Within reason...

WNY- assuming you’re off-grid, how do you maintain the temp of your batteries in cold weather.

I’m thinking a 2500 to 3000 watt inverter should adequate. Does that seem appropriate?
Any suggestions?

My brain is a little overwhelmed with all the internet research at this point. I think I may give it the afternoon off to process all I’ve learned and watch some NCAA tourney...

Thanks again guys!

Steve

Amount of panels Depends on how fast and output you need to use and recharge your system and how much capacity.
My 2 x 250watt panels only put out 7-8amps/ea ( in Series, voltage doubles but current stays same) and the controller takes the extra voltage and converts to current. so it can send almost 10-14amps to batteries, if they are down a ways from use, it might take all day to recharge depending on the sun and usage in the house. When I had 4 x 250 watt panels (lost 2 in a wind storm), it was perfect for charging and usage for us. more than enough power to run house and keep batteries charged.

It's just a summer house, don't live there except some summer weekends, as long the batteries stay charged, usually no problems in the winter, there is NO heat in the house (except wood stove). they've been running for over 4 years now (Lead acid), check them every few months for water levels. Uses about a gallon for 12 batteries. The Outback charger works good at maintaining them. Midnight Solar has a good charger also.

Inverter, depends on your load requirements. 2500w would be a good choice to start with. you can get charger/inverters also, if you have a generator and want to tie that in also to suppliment or charge if needed. ours are older ones, but I think 2000-2500watt, but work fine, we have no high loads when staying there, usually just radio, lighting, small refrigerator. etc...
water pump is only 12vdc DC runs directly off battery bank. storage tank. drain system for winter.

I think I have "solar" researched myself into a point of paralysis... LOL

Before I go any further, I want to clarify that any and all advice that is given to me from anyone on this forum regarding solar design and/or how to install electrical systems and/or appliances is strictly for the purpose of my understanding of electricity. I am using the cabin in this thread as a reference and an example only. If I do attempt any electrical work of any kind, it is at my own discretion and I am responsible for any failures or potential hazards, damages or injuries.

Based on different online calculators I have experimented with, I think I have come up with a plan to use one of the inverters I have, and have a go at a 12v off-grid system in the cabin.
I know that a 12v system is really small but the daily watt hour number I seem to come up with when we use the cabin is about 2200wh. With a 12 volt system, I can use one of the inverters I have and don't have to sell it for 50 cents on the dollar. I can also use a lot of RV type of accessories that are readily available (lighting, fans, etc.). Including an RV fridge that can run on propane, 12v, or 120v AC that I have.
Here is where I think I'm going at this point. Maybe one of you good folks can redirect me if necessary...

Inverter - Use the 12 volt Xantrex 3012 inverter to convert the DC for AC loads.

Storage - As you know, I have four 12v 225ah GEL batteries. I'm going to setup two parallel 12v battery banks.

For solar charging - The calculators tell me I need a minimum of three 250 watt solar panels. They also tell me I need a charge controller that can handle 63 amps. The Midnite Classic 150 SL MPPT is the direction I'm leaning. That looks to be a quality product with good reviews and gives me room for upgrading my system to 24v or 48v at some point down the road. This has a 96 amp rating so I can add on more solar panels if I want. Also, because we rarely use this place for more than 2 or 3 days at a time, as long as I don't deplete the batteries less than 50% (I'll probably try and keep it to 70%), the system can charge for days, if not weeks after we have left...

For AC charging - The Xantrex 3012 inverter has a built in battery charger. It senses AC power and will switch from inverter mode to charging mode automatically. It has a 3 stage charging system (bulk, absorption and float). When I'm at the cabin for several days in cloudy weather, I can always fire up a small generator and let it top everything off.

Wire size - (THIS IS AN AREA IN WHICH I'M STRUGGLING. I don't have confidence in my level of comprehension of the amperage produced by these panels to determine the appropriate fuse/breaker sizing and wire sizing to the charge controller)
So here is a solar panel that I was considering - Canadian Solar 305 Watt Mono. It's a 20v 305w panel. Estimated efficiency up to 18.63%. I assume that the solar panels will each come with some sort of cable that can connect the 3 panels in series to get to a junction box of some sort.
So, if volts x amps equal watts, if I take the 305 watt rating of the panels and divide them by the 20v rating I come up with 15.25 amps of DC per panel (305/20=15.25) or 45.75 amps for all three panels. But, if I put the panels in series, the volts will triple to 60 volts, correct? Then the amps will drop from 45.75 to 5.08 amps (305/60=5.08), correct? I believe 16 gauge wire is rated for 10 amps, I think??? If so, I could run two 16 gauge wires (+ and -) from a junction box at the solar panels for about 15' to 20' to the charge controller.
What size wire do I use from the charge controller to the battery bank to charge the batteries? Still 16ga? That seems small but I don't know what the factors are to calculate this...
I am going to mount the 12 volt inverter within a couple of feet (literally 2 feet) of the batteries to reduce the wire cable size needed to make that connection. That is how it was setup on the truck it came out of.
From the inverter to a small panel box, maybe a two circuit panel box with a main, I'll run some 10ga wire and put that on a 30 amp breaker to feed AC loads to the cabin.

My guess is that there are a multitude things in the scenario above that are either incorrect or that even could be done differently. But this is my jumping off point to see if I'm comprehending anything I have been researching...

Thank you in advance to anyone that is taking their time to read through this and give input. It is much appreciated!!!

Solar panels have factory installed + and - leads with special plug ends...type MC4. They keep the polarity right by fitting together only one way and have equal to 14 ga. wire.
No fuse needed for a single string of panels...2 strings or more, yes fuse each string from the other(s).
Fuse size is generally 15 amp and referenced to wire size and NOT to panel size.
No junction box likely needed simply use some MC4 plugs. And for your number of panels...just need to add extension cable set (recommend these be 10 ga.) with MC4 plugs on one end...other end can connect to fuse/breaker switch just before the Midnite Classic.

The lower the DC voltage the more that voltage has to overcome any voltage drop thru a wire and making shortest length comes first...then bigger wire size comes next to over come losses..

What McGiever said is correct. You can get MC4 extension cables (usually 10-12AWG (gauge) to run back to a junction box or to controller, depending on how many panels, length, etc..
I ran 25' MC4 10AWG extension cables from panels to a 3 circuit DC 15Amp each breaker box (Midnight Solar) mounted outside for up to 3 pair of panels (future expansion).
From there I ran 6 AWG 40' or so to the controller near the battery bank. I think I used a Heavy 2-4AWG from controller to batteries. as large as the Controller could handle in the output connection. I used max 60 amp rating of my controller. not that I'll ever see that. but thought I'd be safe using as large of wire as possible. Only running about 4 feet to the batteries.
all the batteries are interconnected with very heavy looking like weld cable, probably 0 AWG, i'm not sure, but it's large.

Now take all you learned and apply it here to test your understanding in the heart of it all...

Thanks fellas for the feedback!
McGeiver - thanks for those graphics. I’m a very visual person. Those help a lot. The three Rs of education were never my strong suit. I’m just a KY hillbilly that struggled through high school and was lucky to graduate... Image searches and YouTube university are a blessing for me...

Steve

Your very welcome Steve,
Place CC as close as possible to batteries to keep 12 VDC heavy cable short as possible...other side of partition wall works well for close but separate from any battery off-gassing hydrogen vapors...your AGMs have near none since they're sealed type, any F.L.A. are vented though with off-gassing when under heavy charge...hydrogen gas and electric spark are bad together.

From what I see many of the newer installations use micro -inverters

to reduce the IR lose due to wire size , you go right to 240v ac at the

panel and smaller wire is needed especially when the panels have a

long run to the control panel.

https://www.google.com/search?client=firefox-b-1- ... APt_jJ4S_w

https://www.wholesalesolar.com/brands/enphase-energy

BigBarrney

BigBarney wrote: ↑

Wed. Apr. 03, 2019 5:20 pm

From what I see many of the newer installations use micro -inverters

to reduce the IR lose due to wire size , you go right to 240v ac at the

panel and smaller wire is needed especially when the panels have a

long run to the control panel.

https://www.google.com/search?client=firefox-b-1- ... APt_jJ4S_w

https://www.wholesalesolar.com/brands/enphase-energy

BigBarrney

All well and fine, BB, but that doesn't align with the OP's desire to reuse what he already has in hand and is already paid for...

Hard to integrate old technology with old , some times you need to

move on having learned more on the way...

BigBarney

BigBarney wrote: ↑

Fri. Apr. 05, 2019 11:56 am

Hard to integrate old technology with old , some times you need to

move on having learned more on the way...

BigBarney

Yup, though he's in his very early learning curve still, not progressed near that far, let's not trip him up just because we know other ways...
BTW: There are no such micro-inverters, that you brought into this conversation, for his off-grid, just only for grid-tied...none going to ever be in his little cabin anyways.

You don't need to be connected to the grid to have 60 cy ac power...

You can tickle with a battery a inverter/charger to do the same thing.

Also a generator can do this with the proper equipment..

BigBarney

BigBarney wrote: ↑

Fri. Apr. 05, 2019 1:21 pm

You don't need to be connected to the grid to have 60 cy ac power...

You can tickle with a battery a inverter/charger to do the same thing.

Also a generator can do this with the proper equipment..

BigBarney

Hope you're not saying I'm mistaken about a micro-inverter working only on-grid...if so you are spreading false information due to your lack of knowledge in this matter.

Imagine IF you even were right, wouldn't be too clever at all to be required to running a portable generator so that your solar off-grid system could work...

Off Grid...
All DC...
No AC conversion losses...
Most Grid tied systems use an inverter coupled to the sine wave of the power co...