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12x12 Cabin - New to Solar - Please help!

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  • 12x12 Cabin - New to Solar - Please help!

    Hello all. First post here! I've been reading the forums and also looking at solar equipment but, quite frankly, I figured it may be much easier to just solicit input from you all about a potential solar build.

    I have a 12x12 cabin/bunk house on a piece of wooded property in central Illinois. Fortunately, to the immediate south, there are no trees and the cabin has equal 45 degree gambrel roof pitch, so I have ample opportunity for sun. I'm not looking for much here...a basic system that would allow me to run a few lights (LED so low wattage ~15-20 watts) and a couple of fans (less than 100 watts each), that's about it. I would like the power to last overnight so I don't cook if the fans die out when the batteries run low. I've done some digging through Amazon looking at equipment and this is what I have come up with so far.

    Charge controller - psc=0&ref_=lv_ov_lig_dp_it
    Solar Panel -
    Inverter -
    Extension Cables -
    Mounting Hardware -

    Now the questions -

    Will this setup suffice for a basic entry level system? If not, what would you recommend?
    Is one panel enough, or do I need more?
    What battery(s) should I consider getting?

    This is very much a part time cabin for me, one night at a time as weather permits. I want something that will work, but budget minded as well as I cut my teeth on solar.

    I greatly appreciate any and all input you good folks could provide. If this whole setup screams failure and you have other ideas, please share!

    Thank you.

  • #2
    Hi Doug, welcome to Solar Panel Talk, it might take a day or two for the admins to approve your account for additional posts, but I've approved this one in the meantime to get you started. I'll delete the other one. Looking forward to hearing about your project.


    • #3
      Short answer, I would recommend at least one more panel, A 300 watt pure sine wave inverter and a couple 6 volt golf cart batteries. This would get you through overnighter once a week or so. There's upgrades I could suggest to the charge controller but it will cost you more. You could save some money by using a larger format panel which would help to make up for the better charge controller.
      2.2kw Suntech mono, Classic 200, NEW Trace SW4024


      • #4
        Thanks, Steve, appreciate the help and will certainly keep the group posted as I move forward!

        LittleHarbor - I'm up for whatever suggestions you may have. As mentioned, I have no background in solar so I'm just going by what I *think* may work. Please feel free to share what you would do in my situation. If you could post links to the equipment you recommend, that would be very helpful as well.

        Thanks all for the help!


        • #5
          The proper approach would be to calculate your loads and design from there. Others here are much better at doing the math and explaining it in a coherent way in text. I would guess that your needs would expand knowing you are making your own power from solar and have the availability to charge devices run stereo and electronics and even refrigerate food and beverages. That being said I think designing on your minimal loads listed may be a mistake.

          As to suggestions for controllers there are hundreds of MPPT charge controllers available, some good, some not so good. If you stick to the name brands there are Morningstar, Midnite solar, Magnum, Xantrex you cant go wrong. There are some decent brands from overseas mfg. EP Ever makes a wide variety of controllers, Renogy is another. MPPT controllers allow you to use much cheaper grid tie type panels by taking the higher voltage output and stepping it down to charge your lower voltage battery. They can harvest more of the panels power output by using all the voltage and current instead of just passing the panels current along at the batteries voltage, costing you a percentage of power lost.

          Budget usually restricts what you ultimately end up buying so I won't suggest any one brand. I would suggest a higher end brand and model if I did.

          If you aren't already committed to any voltage I would recommend you not even consider 12 volts and start with a 24 volt system. Once you commit to 12 volts you are stuck with a severely limited system which you would need to replace components to step up. A waste of money in my mind. Of course you would be able to sell off these parts but I think it's a losing proposition and an unnecessary hassle.
          2.2kw Suntech mono, Classic 200, NEW Trace SW4024


          • #6
            Thanks again, LH. I'm certainly not set on 12v, it's just what I gravitated towards given my lack of knowledge of solar in general.

            I would estimate the max load at any given time to be less than 300 watts. That figures 100 watts for each fan and then some low wattage LED bulbs. If/when I build my next/bigger cabin, then expand-ability certainly comes into play, but for right now, just looking for a basic setup that will get me through a night or two.

            What all is entailed with going to 24v? Is that just wiring some 12v batteries in a specific configuration to get to that point? Are different solar panels needed?

            Sorry for all the newbie questions, just trying to wrap my head around all this.
            Last edited by Doug24; 06-14-2018, 11:21 AM.


            • #7
              Your biggest expense will be new inverter and new batteries. You don't want to just add more batteries to an older bank.

              Inverters are one voltage only. There is a market for used equipment if you care to sell it. Nearly all charge controllers will do 12 or 24 volts,
              so you may not need to replace it

              the better ones do higher voltages too

              You can add more panels relatively easily but finding panels to match the output of original panels sometimes can be challenging. As far as wiring up panels and batteries, series wiring is easier and uses less wire and connections. When it comes to batteries you should avoid wiring your battery bank in anything but a single series string. Stay away from 12 volt deep cycle batteries. They will cause you to have to parallel wire your batteries in all but the smallest battery banks.

              You need to properly fuse your battery bank on all load and charging source connections. These Blue Seas fuses are some of the best and easiest to use. Blue Sea terminal fuse..jpgBlue Sea dual terminal fuse.jpg
              Last edited by littleharbor; 06-14-2018, 12:10 PM.
              2.2kw Suntech mono, Classic 200, NEW Trace SW4024


              • #8
                You may want to look at a premade kit by a good solar retailer. An example might be like this:

                It appears to have quality components, and has mounting and battery options.

                Other online retailers also make different kits based on needs and budget.


                • #9
                  You might want to look into getting a few 12V computer fans and putting them into a box. I've built a couple and they work nice at my camp for sleeping. Common AC fans are very inefficient. If you are smart, you can get the loads down quite low. You always screw things up when you start. Something to consider is getting yourself a new car battery and trying the old one at camp. I have an almost totally dead battery from my boat that only has about 10AH capacity. Not much more than a SLA and that supplies my needs at night saving my ONE good battery to run my fridge. Just adjust your life. I gag when I read about these massive battery systems. Buy more panels and do things during the day.


                  • #10
                    Thank you both Citabria and PNPmacnab. To your point PNP, I did look at just doing "camper" lights and get a couple of 12v radiator fans (maybe with a speed control to limit noise) that I could mount into a "box" and put in front of the window. In that regard, there would be no need for an inverter.


                    • #11
                      In regards to the 24v setup, please see attached picture I found online. Based on that, here is what I am proposing:

                      1 - Connect (2) 100W solar panels in series to get 24 Volts
                      2 - Connect to MPPT charging controller
                      3 - Connect (2) 12v batteries in series for 24v.

                      I'm assuming that will get me to the 24v vs 12v system as recommended above, correct? Questions:

                      1. Will 2 panels get me by or so I need 4?
                      2. Will the MPPT controller's load connection step down the voltage to run 12v items or do I need an inverter?
                      3. Will the 2 batteries do for a night or two of light usage such as low wattage LED lights and a fan or two, or will I need more?
                      4. During winter months, or if it's cloudy, how does one hook up a generator to charge up the batteries? Do you just have a shut off to the charge controller and put a charger on them?

                      Thank you again!
                      Attached Files
                      Last edited by Doug24; 06-15-2018, 02:45 PM.


                      • #12
                        Doug you really need to get a handle on your 24 hour daily usage. By that I mean Watt Hours.

                        Watt Hours = Watts x Hours.

                        So look at the wattage of each device and how long in hours each will run and add then all up. I seriously doubt you need a 1000 watt, 24 volt system. That would add up to 2 Kwh per day and that will cost you several thousand dollars with a $1500 battery every few years. So here is a how you build a part time system that is not used every day.

                        1. Determine your daily Watt Hours.

                        2. Based on daily watt hours you determine battery voltage.

                        a. 100 to 1000 watt hours = 12 volts
                        b. 1000 to 2000 watt hours = 24 volts
                        c. 2000 to 4000 wat hours = 48 volts

                        3. Find Battery Size in Amp Hours = Daily Watt Hours x 3 / Battery Voltage from above. Examples:

                        a. 1000 wh x 3 / 12 volts = 250 AH
                        b. 2000 wh x 3 / 24 volts = 250 AH
                        c. 4000 wh x 3 / 48 volts = 250 AH

                        4. Determine MPPT Controller minimum Amperage = Battery AH / 10. Example; 250 AH / 10 = 25 amps.

                        Find Panel Wattage = Battery AH / 10 x Battery Voltage. Examples;

                        250 AH / 10 x 12 volts = 300 watts
                        250 AH / 10 x 24 volts = 600 watts
                        250 AH / 10 x 48 volts = 1200 watts

                        Rest is up to you and be careful what you ask for as it gets expensive. There is absolutely no reason to use a battery larger than 250 AH or more than 1200 watts panels.

                        If you use an Inverter it SHALL NOT BE LARGER THAN PANEL WATTAGE.

                        Last comment unless your battery AH is 100 AH @ 12 volts or less (400 watt hours per day), you will not be using 12 volt batteries. You will be using 6-Volt golf cart batteries. So DO NOT GET TRAPPED IN A 12 VOLT TOY BOX. Batteries are not 12 volts.
                        Last edited by Sunking; 06-15-2018, 03:51 PM.
                        MSEE, PE


                        • #13
                          Thanks, Sunking, I appreciate the thorough response you typed out, as well as your patience.

                          Before I get too elaborate with my response and more questions, am I just better off sticking with 12v items (e.g. large computer case fans) and camper lights? A standard box fan on high is around 100 watts so that quickly jumps up my numbers if I were to run it 8-10 hours over a 24 hour period. By contrast, it seems that a computer case fan is running somewhere near 5W. So, is 12v that much more efficient or am I missing something in the conversion? I know I would need multiple case fans, but that still seems more reasonable than going with an inverter and the larger draw of a box fan. I could also use 12 volt camper lights as well since the cabin is quiet small.

                          The batteries I was looking at were 100 AH @ 12v fwiw. So I'm assuming that would recommend 2 6v if its a 12v system and 4 6v if 24, is that accurate?

                          Thank you again.


                          • #14
                            Originally posted by Doug24 View Post
                            Before I get too elaborate with my response and more questions, am I just better off sticking with 12v items (e.g. large computer case fans) and camper lights?
                            Depends on your daily watt hours.

                            Originally posted by Doug24 View Post
                            A standard box fan on high is around 100 watts so that quickly jumps up my numbers if I were to run it 8-10 hours over a 24 hour period. By contrast, it seems that a computer case fan is running somewhere near 5W. So, is 12v that much more efficient or am I missing something in the conversion?
                            Yep you are missing something, cfm/watt. FWIW cfm = cubic feet per minute. The lower the voltage, the less efficient. A 5 watt 12 volt computer fan moves roughly 100 cfm and that is 20 cfm/watt. A modern 120 VAC using induction motor runs around 30 cfm/watt or 50% more efficient. So a 100 watt fan, around 16-iches with 100 watt motor will move 3000 cfm. Or you can use 20 x 5 watt computer fans consuming the same 100 watts only moves 2000 cfm.

                            To run those 20 x 12 volt fans would take a lot more and larger wire means a lot more money and energy loss. Think of it like gasoline mpg. Which goes further on 1 gallon of gasoline. 20 mpg or 30 mpg? No free ride.
                            Last edited by Sunking; 06-15-2018, 05:48 PM.
                            MSEE, PE


                            • #15
                              In general a large fan will be more efficient than several small fans, and quieter too. Bruce Roe