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  • off grid cabin

    The place I hunt is owned by a friend and it has a 10x20 storage building we use as a cabin. There is no electricity to the building (not an option) and we discussed adding solar power. It sits empty 5 days a week. We only want a couple of lights, charge a cell phone maybe and power for a portable DVD player for entertainment at night. Lights would only used an hour or so in the morning and maybe 3-4 hours a night at most 2 nights a week. The DVD probably 3 hours for a movie. We are good with not using an inverter and 12V power only. Two lights at 5W each for five hours a day I figured about 50W/Hours a day allowing for system losses. I don't have any idea how much power a cell phone charger or the DVD player take. I have read many of the sticky posts trying to figure out how much capacity we would need. I understand some of the formulas but don't quiet get all of it especially not knowing about the cell phone charger and DVD. Any recommendations on components, panel brand/size, battery size/type, etc? Of course cost is a consideration also.

  • #2
    Before you jump off into this I suggest you consider a few things. A solar panel in the middle of no where is going to attract attention, and if my friends hunt the same woods as you do would be their's upon sighting. Your power needs are minimal. So you might just consider buying a quality FLA or AGM battery with an AC charger. Charge the battery up at home and take it to camp with you. Bring it home to recharge.

    This might help. You said th ecabin is empty 5 days a week right. Leaving gin use for 2 days a week? Minimum battery size for a solar system is sized 3 to 5 day capacity. The reason for this is to maximize battery life and CYA for cloudy days. Regardless if you have a expensive panel and controller o rnot, the battery is going to be the same size and does not need to be recharged on site unless you leave it there for my friends to find. Save your money for something else.
    MSEE, PE

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    • #3
      I agree with Sunking. Get a battery and charge it before you go to the cabin and then recharge it when you get back home. Instead of spending anything on solar panels, charge controller and racking I would get a small inverter type generator and have that as a backup if the battery gets too low. It will also provide more power if you find you want to use another electrical device.

      Unless that cabin was secure and with little chance of anyone finding the solar panels where they can damage or steal them I would say it is not worth the risk of losing that investment.

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      • #4
        Thank you for your replies. That is what we have done in the past but were looking for another option. He comes up with ideas and I have to make them work or try to make him understand why it's not going too. We watched these videos of people with their 45w thunderjunk systems and multiple batteries and I didn't think they would work but he saw it on the internet so it had to be true. I've learned a lot from the posts I've read here. Being an auto tech I do understand some of the principles but some of the other stuff I had no idea about. It has sparked my curiosity to learn more about solar.

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        • #5
          I still suggest just getting a good battery first and try it before dumping a lot of money on something you do not likely need. Like I said the battery needs to be sized for at least 3 or 4 days either way. You can save a big chunk of cash just buying an AC charger then charge at home. If you were staying at the cabin for a week would be different,
          MSEE, PE

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          • #6
            Originally posted by RC3291 View Post
            Thank you for your replies. That is what we have done in the past but were looking for another option. He comes up with ideas and I have to make them work or try to make him understand why it's not going too. We watched these videos of people with their 45w thunderjunk systems and multiple batteries and I didn't think they would work but he saw it on the internet so it had to be true. I've learned a lot from the posts I've read here. Being an auto tech I do understand some of the principles but some of the other stuff I had no idea about. It has sparked my curiosity to learn more about solar.
            A word of caution when it comes to the Internet, YouTube and other video productions found on the WEB. Most are not really true and will mislead people into thinking they can do just about anything the poster says his system does. About 95% of what you see is entertainment or a hoax so please don't believe everything you see.

            A solar pv battery system does work for small or controlled loads. Some LED lights, computer charging and DVD player are relatively small watt hour users which can keep the battery and panel wattage to a manageable size. The size of your system also depends on what Latitude you are in and if you can get an unobstructed (no shadows) view of the Sun. Less usable sunlight means more panel wattage.

            What gets expensive is if you try to power up a small AC unit, refrigerator or coffee maker like some people want to do. Then the battery and panel system gets crazy expensive and big.

            Now a solar pv system in a remote area will work but unless you can protect it you may want to think about installing one. It can also get expensive if you undersize it based on an estimated daily watt hour loads and find out you need a bigger system. Off grid battery systems don't "grow" well. You have to size the up properly in the beginning or maybe start all over again.

            A less expensive path would be to just use that battery and charge it at home or from that small generator.

            We are just trying to give you a heads up on what to expect when going off grid.

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            • #7
              One thing to point out with the U-tube videos is that people like to post there accomplishments but not there failures. So many of the videos you see are of someone that just setup there system. Of course it works great as t's all new and everything is running off the oversized batteries. So the video gets posted.

              Then after a couple weeks the problems start popping up from them using more power then the system produces. They don't replace the video to show how bad it failed.

              That said, I do have a small system on a weekend cabin. I tried to size the batteries so that they would be discharged about 50% after a full weekends useage with no sun. Then I undersized the array a little by using 5 days of charging to replace that. It seems to be working OK. I do have problems with the batteries wanting to sulfcate if I don't do an equalize charge on them every couple months.

              Yes the way my system is setup it is abusing the batteries and shortining there life. But with a weekend sysm I figure 52 cycles at 50% discharge they will still last about 5 years. Actual end up being about 35% discharge with no sun and onlt about 25% discharge on a sunny winter weekend.

              I figured my usage a 1KW for the weekend. Used2 T-105 batteries as they would handle that by my calculations. They are actually larger then I needed but were cheaper then ordering in custom sized batteries.

              The array is 2 - 51 watt 12V panels wired in parrallel with a 10 amp charge controller. Winter low for isolaton in my area is about 1.5 hours. So in the winter it does no quite charge my batteries in the 5 days but we seldom make it up there every weekend then.

              Equalizing charge is done every 2 to 3 months with a 45 amp automotive charger running on my 3500w genny for 1 to 2 hours. While others will say that the charger doesn't reach a high enough voltage to equalize it does seem to be working. I'm on my second set of batteries and have had the system for about 10 years now. First set was replaced after 7 years but they propably should have been replaced after 5.

              My usage includes running a radio for 6 to 8 hours a day. My weakness as I need my tunes. That, I think, would be about the same as your DVD player.

              WWW

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              • #8
                Personally I'm good with charging the battery at home. Talking him into it might be another thing. I'll let him know the options, price and risks and let him decide. It's his money.

                The area the system would be located is at 32.7 degrees latitude and not shaded at all except for a short while very early morning and slightly relocating the panel might could overcome that. You would have to be right on top of it to see the panels because of an old barn and wood fences around a corral by the barn. I guess my question boils down to how much solar panel and controller would be needed to keep a deep cycle/marine battery charged given our limited usage? or would there be a better affordable battery type to use? I understand we may not get optimal life from the battery also.

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                • #9
                  Originally posted by RC3291 View Post
                  Personally I'm good with charging the battery at home. Talking him into it might be another thing. I'll let him know the options, price and risks and let him decide. It's his money.

                  The area the system would be located is at 32.7 degrees latitude and not shaded at all except for a short while very early morning and slightly relocating the panel might could overcome that. You would have to be right on top of it to see the panels because of an old barn and wood fences around a corral by the barn. I guess my question boils down to how much solar panel and controller would be needed to keep a deep cycle/marine battery charged given our limited usage? or would there be a better affordable battery type to use? I understand we may not get optimal life from the battery also.
                  I understand. So lets say that 50 watt hour daily usage is a low estimate. Instead we will use 150 watt hours (which is not really that much)

                  A system like that can be made from a 100 watt panel, 10 amp charge controller and a 12volt 50 AH AGM deep cycle battery. If you decide to run something that uses 120volt AC use an inverter no larger than 100 watts.

                  Now if that 150 watt hour a day estimate is low then you can double the panel and battery size and go with a 15amp charge controller. Unfortunately if you start out with the first and find out it is not enough the only thing you can re-use in the larger system would be that 100 watt panel. That 10amp CC is too small and you should never add a new battery to an old one. And while that 100 watt panel is still good adding a second one to get 200 watts will end up costing you twice as much then if you had purchased a 200 watt panel in the beginning. (100watt - 150watt panels cost ~ $2/watt, 200watt and larger cost ~$1/watt)

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                  • #10
                    Thank you all. Now I have enough information to either deter him from setting a solar system or build one that will work.

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