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  • small system in log cabin

    [h=2][B][SIZE=14px][FONT=arial]I am absolute newbie. In a log cabin, I would like to put together a 100 W panel (outside), Solar Charge Controller (like Sunix 20A 12V/24V) and a battery (e.g. 12 V 17 AH). This is to have some light (1 LED light) at night, to recharge phones and maybe later also to hook up a car (12V) microfridge (I see some tiny ones that are listed 42 W or 57W).[/FONT][/SIZE][/B][/h]
    [B][SIZE=14px][FONT=arial]Does that configuration make sense? Advice?

    Can I leave that system alone for months, or is there a fire risk with controller and battery being inside a log cabin?[/FONT][/SIZE][/B]

  • #2
    I would not leave any battery for months at a time. Take it with you when you go. That little battery will probably power the LED light and charge a phone (not enough info to know for certain) but it will not power the micro fridge long enough to be useful.

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    • #3
      Thanks! How big would the battery need to be for the tiny fridge?

      What is a good book to learn these basics, especially the electrical stuff? How about "Mobile Solar Power Made Easy! Mobile 12 volt off grid solar system design and installation."?

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      • #4
        You need more battery capacity and more solar panels. How much depends on a lot of unknown information. i.e. Where in the world is the cabin? How many hours of unobstructed sunlight will the panels get (at what time of year / average weather)? How many hours do you expect to run the micro fridge a day? I am unfamiliar with the book you mentioned. There is a lot of information in this forum. I suggest you spend a lot of time reading before you buy anything. When you are ready to buy, start with a Kill-a-Watt so you can determine how much power you will actually need. I am a junior member here. There are many who know a great deal more than I do. I suspect they would be more willing to help if you put some effort into educating yourself first.

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        • #5
          Originally posted by rbrilla View Post
          [h=2][B][SIZE=14px][FONT=arial]I am absolute newbie. In a log cabin, I would like to put together a 100 W panel (outside), Solar Charge Controller (like Sunix 20A 12V/24V) and a battery (e.g. 12 V 17 AH). This is to have some light (1 LED light) at night, to recharge phones and maybe later also to hook up a car (12V) microfridge (I see some tiny ones that are listed 42 W or 57W).[/FONT][/SIZE][/B][/h]
          [B][SIZE=14px][FONT=arial]Does that configuration make sense? Advice?

          Can I leave that system alone for months, or is there a fire risk with controller and battery being inside a log cabin?[/FONT][/SIZE][/B]
          No. That 17ah battery can safely deliver only about 50 watt hours a day.

          Instead of just guessing, you need to determine the number of watt hours you need to use each day. From there we can help you determine the battery size and pv panel wattage.

          Oh by the way. Just because something is "tiny" doesn't mean it will use a tiny amount of watt hours to run.

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          • #6
            Thank you, very helpful! I did not have any electricity there so far and therefore no "needs", rather possible upgrades, so I can experiment a little as the equipment is not pricey, and charging cellphones and some LED light should not be the issue (and I will not try a fridge there for now).
            Yes, I really need to brush up on my physics - I was confused that the technical detail sheets on amazon for such microfridges (see my post) lists "watts" and not watt hours - isn't that the unit for energy consumption? Does "42 W" stand for 42 W/day?

            And the other question is whether the intact system could be left alone without a device consuming electricity, of course the controller would charge but stop doing so once the battery is full. Where does the (solar) energy go then? I read that there is some heat development at the back of these controller units. Could this overheat?

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            • #7

              Example:

              When you turn on a 120 watt light bulb it will consume 120 watts.

              It draws 1 Amo of current operating on 120 volts. Power = Current x Voltage.

              if you run that light bulb for 10 hours it will have consumed 1200 watt/hours or 1.2kwh.

              Does that answer your question?

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              • #8
                Originally posted by PNW_Steve View Post
                if you run that light bulb for 10 hours it will have consumed 1200 watt/hours or 1.2kwh.
                If you run it for 10 hours .... it will consume 1200wh over 10 hours not 1200w/h (w/h should be wh)
                OutBack FP1 w/ CS6P-250P http://bit.ly/1Sg5VNH

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                • #9
                  Originally posted by SunEagle View Post

                  No. That 17ah battery can safely deliver only about 50 watt hours a day.
                  Yes, Steve and SunEagle, very helpful. I see now how underpowered that battery is considering that even that very small fridge constantly draws power like a 40+ Watt bulb. As I said, I think I will be fine charging cell phones and running one LED ceiling light with that configuration, that is definitely worth the 100+ Euros.

                  Any ideas about the other (heat/fire hazard) issue?

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                  • #10
                    rbrilla,

                    I am using a Grape Solar GS-5 referigerator which is 12/24 volt and the manufacturers recommended minimum power is 100 watt panel and 100 a.h. Battery at a minimum. I can confirm that it will run on that and it uses an average of 200-250 watt hours a day. It's rated power is 46 watts. My solar system is much larger than that. Hope that this information is of use for your planning.

                    Please note that the Grape Solar referigerator is a true compressor based referigerator so these values are true for compressor based referigerator, not to be confused to a peliter junction "chiller"

                    By comparison my Coleman 48 quart "chiller" which is peliter junction uses 12 volts at 4.0 amps , 48 watts, and does not cycle on and off....it's a steady 4.0 amps regardless of temperature. That's 48 watts times 24 hours is 1152 watt/hours a day......vs 200-240 watt hours a day for the true compressor referigerator.......big difference

                    Grape Solar has exited the referigerator business and these are no longer available but there are other manufacturers of this kind of referigerators, they are used in long haul trucking in the extended cab sleeper trucks as well as off gridders
                    Last edited by Tecnodave; 06-25-2019, 06:24 PM. Reason: A bit more information

                    Comment


                    • #11
                      Originally posted by Tecnodave View Post
                      rbrilla,

                      Please note that the Grape Solar referigerator is a true compressor based referigerator so these values are true for compressor based referigerator, not to be confused to a peliter junction "chiller"

                      By comparison my Coleman 48 quart "chiller" which is peliter junction uses 12 volts at 4.0 amps , 48 watts, and does not cycle on and off....it's a steady 4.0 amps regardless of temperature. That's 48 watts times 24 hours is 1152 watt/hours a day......vs 200-240 watt hours a day for the true compressor referigerator.......big difference
                      Thank you so much Tecnodave, this is super important and I had no idea, thinking "fridge is fridge". Looking at the German amazon (this is all meant for a hut in the austrian alps), it looks like the chillers are very small, you cannot adjust the temperature and apparently they can serve as warmers as well, correct? The "real" fridges have the compression cycle that we all know (humming fridge) and a thermostat. So I thought a tiny chiller is fine and economical but I ought to go with the most efficient real fridge.

                      Comment


                      • #12
                        Just my 2 cents, but I'd highly suggest getting a much larger solar panel, as you'll get a lot more for the money, which will leave you room for expansion (ceiling fan, laptop, etc.) Keep in mind that you'll only get the full 100W at full sun; if it's cloudy, expect more like 10W of output power (yes, 1/10 the rated power. Clouds are a real killer. Ditto for shade.)
                        At the very least, check the price per watt ($$ of the panel / the output wattage); depending on where you are, you might be able to procure 250-300W panels at 50 cents/watt (i.e. 250 * 0.5 = $125). Oftentimes, the tiny panels (100W and under) are sold on eBay for $1/watt or higher. The infamous Harbor Freight solar panels are one such example: they currently sell a 100W kit for $190, which is at least $1.50/W of generation capacity. In Columbus, Ohio, I can purchase a 310W solar panel brand new for $176 ($0.57/watt); overstock panels can be had for 50 cents/watt. According to eBay, overstock panels can be had for less than 25 cents/watt out in Arizona. You might also check Craigslist.

                        One caveat: with a larger panel, it will likely have a higher voltage, and I'd recommend an MPPT charger to get the most out of it (=a little more $$). But you won't be kicking yourself in three months thinking, "If only I had more power" .

                        And the other question is whether the intact system could be left alone without a device consuming electricity, of course the controller would charge but stop doing so once the battery is full. Where does the (solar) energy go then? I read that there is some heat development at the back of these controller units. Could this overheat?
                        I would say yes, you could leave the intact system alone with no issues, as long as it's set up safely and properly configured. Yes, the controller will stop charging once the battery is full. And once the battery is full, the power from the panel simply isn't used. TBH I really don't know where all that power "goes"--if it's not used, it basically doesn't exist!
                        A charge controller may get warm/hot, but only if power is being used out of it (i.e. charging the battery, running your micro fridge + your friend's cooler ). If there is no load, it should stay cold.

                        Comment


                        • #13
                          Originally posted by Tecnodave View Post
                          rbrilla,

                          I am using a Grape Solar GS-5 referigerator which is 12/24 volt and the manufacturers recommended minimum power is 100 watt panel and 100 a.h. Battery at a minimum. I can confirm that it will run on that and it uses an average of 200-250 watt hours a day. It's rated power is 46 watts. My solar system is much larger than that. Hope that this information is of use for your planning.

                          Please note that the Grape Solar referigerator is a true compressor based referigerator so these values are true for compressor based referigerator, not to be confused to a peliter junction "chiller"

                          By comparison my Coleman 48 quart "chiller" which is peliter junction uses 12 volts at 4.0 amps , 48 watts, and does not cycle on and off....it's a steady 4.0 amps regardless of temperature. That's 48 watts times 24 hours is 1152 watt/hours a day......vs 200-240 watt hours a day for the true compressor referigerator.......big difference

                          Grape Solar has exited the referigerator business and these are no longer available but there are other manufacturers of this kind of referigerators, they are used in long haul trucking in the extended cab sleeper trucks as well as off gridders
                          FWIW, Peltier, or thermoelectric cooling is a very inefficient way to cool things for most any common residential refrigeration application. Its advantages are it runs quiet, and requires little/no service. The big disadvantage is its absolutely crappy efficiency, usually and up to about an order of magnitude less efficient than modern and available equipment.

                          Peltier food refrigeration and off grid PV, or any PV for that matter, are incompatible.

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                          • #14
                            If it chills and heats it is a thermoelectric peliter junction unit. These are horribly inefficient.

                            Danfoss patented the DC permenant magnet compressor in the DC referigerators, this has been cloned by the Chinese company Colku. These are the only units suitable for small off grid use.

                            Danfoss is in Holland or maybe Denmark, but they only make the compressor part but I'm sure that this technology is available, I'm pretty sure that modern RV referigerator are using this technology by now. I'm on the other side of the globe so I do not know what is available there, I'm in Santa Cruz California

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                            • #15
                              Originally posted by Tecnodave View Post
                              If it chills and heats it is a thermoelectric peliter junction unit.
                              Well, that's not entirely correct. An ordinary heat pump running on a vapor compression cycle will also heat and cool.

                              There are some cooling units running on the thermoelectric cycle made for portable uses like camping, taking advantage of a feature I left out for thermoelectric coolers: They often weigh less, giving them a likely advantage for portable applications like camping.

                              I think we can all agree however that their poor efficiency usually knocks them out of the box for anything more than very small or specialized applications and for all common applications, and for that reason Peltier coolers are incompatible with most PV powered applications.

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