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  • First solar powered system. But I still have a few questions.

    Hi, First timer here.

    I’m trying to put together my very first solar powered system. I’ve done a lot of research but still have a few doubts I hope you can help me to solve them.

    First, here are my off-grid system specs:
    • 1 12v 100W solar panel.
      • Voc 22.5 | Vmp 18.9 | Imp 5.29 | Isc 5.75
    • 20A MPPT charge controller from EPSolar.
      • Max.PV open circuit voltage:100VDC
      • Max.PV input power:12V 260W; 24V 520W
    • 1 12v 100Ah AGM deep cycle battery.

    I’m starting small to only power a few LED bulbs and a small 12v pump for 30 min/day.

    At some point, I hope to have 4 100W in a 24v series-parallel array to get the most of my CC and get a DC to AC power inverter.


    Here are my questions:
    • I plan to get a 20ft 10 AWG wire for the panel/cc, would it work?
    • I read on another thread that no fuse is needed from the array to the CC unless I have 3 or more strings in parallel, so even if I had 2 strings of 200W, would I be good without a fuse ?
    • The 12v DC LED bulbs and pump I want to power up at night, do I need to wire them directly to the 12v battery?, or to the DC Load terminal on my charge controller ?, or how does it work if I have some 12v appliances?
    • Even if at some point I have a 24v array of 2 strings of 200W, would it be ok to keep my battery bank at 12v? or would I be wasting power?

    These are some of the question I have stumbled upon. I’m sure once I keep going some others will pop up.

    Thanks in advance for any help / advices.

    Regards,
    Abraham

  • #2
    that looks like a nice charge controller. 20' of 10AWG is fine but higher panel voltage reduces line loss due to resistance=heat, I love fuses and breakers especially on battery terminals. good rule where ever you have a concern. Even though this look like a nice CC, you can only draw 10 amps through the load terminals of the CC, however unless you can adjust the Low volt disconnect, from 11.1 way too low, I would change to 11.9 to 12.1 for the longest battery life. If the pump draws more than 100 watts you will want to power directly from battery, preferably through a stand alone LVD with user selectable cut out set points.

    Comment


    • Logan5
      Logan5 commented
      Editing a comment
      A good quality MPPT controller should handle 12 volt with a high solar array input, but you will be better served by the 24 volt system.

  • #3
    Your biggest mistake is using low voltage, low power, expensive Battery panels. You want to use 200 watt or higher grid tied panels. GT panels cost half of Battery panels per watt. If you use GT panels you must use MPPT controller. By using Battery Panels wiht MPPT you just defeat a lot of the advantages of MPPT.

    Your second mistake is using too small of a controller if you plan to grow. At 20 Amps max input power @ 12 volt battery is 200 watts, and for 24 volts is 400 watts.

    Lastly is why are you using AGM? A 12 volt 100 AH AGM cost twice as much as a 12 volt 100 AH FLA and the AGM only last half as long as FLA. You are paying up 400% for AGM. What is your justification to use AGM?
    MSEE, PE

    Comment


    • #4
      Thank you all for your input


      @Logan5

      Originally posted by Logan5 View Post
      20' of 10AWG is fine but higher panel voltage reduces line loss due to resistance=heat.
      I'll probably can place them a bit closer, around 15ft. Hopefully that helps to reduce the loss.

      Originally posted by Logan5 View Post
      I love fuses and breakers especially on battery terminals. good rule where ever you have a concern.
      I was planning to set a 20A fuse between the CC and the battery. If I grow my battery bank with let's say a total of 4 100 Ah batteries in parallel, should I place 1 fuse for each battery, I'm still a bit confused when and where to place fuse.

      Originally posted by Logan5 View Post
      If the pump draws more than 100 watts you will want to power directly from battery, preferably through a stand alone LVD with user selectable cut out set points.
      The pump is labeled as 36W. It's a really small pump for an irrigation system.



      @sunking

      You want to use 200 watt or higher grid tied panels
      I'm on the country, there is no electricity around.

      Your second mistake is using too small of a controller if you plan to grow.
      I only expect to power this small pump, a few LED bulbs right now, and later probably a small tv and laptop for a few hours and only for the weekends.

      What is your justification to use AGM
      I don't really have one other than I believe they are low maintenance and they will be inside a small cabin. I did not know if it was safe to keep FLA batteries inside during the week with limited ventilation.
      Should I consider expanding the battery bank with FLA batteries later on ?

      Comment


      • #5
        Originally posted by avrahamvr View Post
        @sunking


        I'm on the country, there is no electricity around.
        OK but what does that have to do with what size panel you use? You want the most from your investment money, the most efficient, and safest system you can build. The low voltage 100 watt panels you bought cost you 2 to 3 times more than buying a higher voltage Grid Tied Panel. You could have bought a 200 to 300 watt GT panel for what you paid for a 100 watt battery panel. Only catch is if you use GT panels, you must use a MPPT Controller, Guess what? You have a MPPT Controller.

        So what does not having electricity have to do with what kind of panel you buy? You have chosen the most Expensive, most Inefficient, and higher risk path you could have chosen.


        Originally posted by avrahamvr View Post
        I only expect to power this small pump, a few LED bulbs right now, and later probably a small tv and laptop for a few hours and only for the weekends.
        OK compounded from above, for the same money you spent now with a 100 watt, you could have already been at maximum growth of 300 watts. Since you went with low voltage panels, you are stuck using them for growth. That means to grow, you trash the 100 watt panel, and go buy a 300 watt panel. It would be foolish to grow with your panels.

        When you want to grow the system, take your 100 watt panel and sell it. Then buy a 200, 250, or 300 watt panel. Lot less expensive buying 2 more 100 watt battery panels.


        Originally posted by avrahamvr View Post
        I don't really have one other than I believe they are low maintenance and they will be inside a small cabin. I did not know if it was safe to keep FLA batteries inside during the week with limited ventilation.
        Should I consider expanding the battery bank with FLA batteries later on ?
        You might have a valid reason to use AGM as they do have Solar and RE applications. Before deciding I would want to justify the roughly 400% higher cost of AGM. Is that true for you too?

        I think I know the answer to that question. So how do you qualify AGM. Well you should consider using AGM if you answer yes to any of the following Statements

        1. Confined, tight, enclosed space where hydrogen gas can build up to unsafe levels? Example UPS cabinets
        2. Where charge/discharge rates exceed C/6.
        3. Spills are unacceptable. Examples air/space craft, 4-wheel drive ATV, or unusual installation orientation like on their side.
        4. Extreme cold environments. Talking -40F
        5. Minimize weight.

        So #1 might apply to you, but I have doubts.
        MSEE, PE

        Comment


        • #6
          for safety you should place a fuse or breaker directly on the terminal many say on both poz and neg. the CC is it's own fuse. you should also have a fused load panel for your pump and other loads. If you only use cabin weekends a properly charged AGM will last some time. but if you over discharge and take days to a week to recover, will have to be carried out for replace sooner than later. 36 watts is a small pump is this to run a misting system? When working with low voltage the short run is best. If I were you, I would work with what you have for now, or until AGM battery fails or you need a larger system. Then buy a 24 volt deep cycle FLA battery system and a grid tie panel. FLA battery can be inside cabinet with vent. or attached shed outside with vent. could also be in battery box under cabin, if flood free zone. You will need to keep distilled water on hand. and inspect each visit. if you run a 24 volt battery bank and 2 grid tie type panels in series, would send around 70 volts over your AWG10 @ 20 feet with almost no loss. Your quality MPPT CC will convert it to 24 volts and charge your batteries. this can also work at 12 volts although much less efficient. you can not expand your battery bank, the one you have is fixed, you replace a battery bank, not some, all of the batteries have to go, or be used in another application. USED BATTERIES MIXED WITH NEW, DAMAGE THE NEW BATTERIES. Parallel batteries are difficult to maintain and end up damaging the batteries.

          Comment


          • #7
            Grid tie panels do the same thing as 12 volt battery panels, just at higher voltage, perfect for off gird applications and hella cheaper with MPPT controller. "Grid tie panels do not have to be grid tied"

            Comment


            • #8
              Originally posted by Sunking View Post

              You want the most from your investment money, the most efficient, and safest system you can build. The low voltage 100 watt panels you bought cost you 2 to 3 times more than buying a higher voltage Grid Tied Panel. You could have bought a 200 to 300 watt GT panel for what you paid for a 100 watt battery panel.
              Ohhhhhh! Linky (like, an eBay auction link)? I don't really comprehend everything that you're saying...but I'm all for getting 300 watts for the price of 100 watts. Where can I find myself one of these panels??

              Thanks in advance!!!

              Comment


              • #9
                Thanks again,

                @sunking,

                You could have bought a 200 to 300 watt GT panel for what you paid for a 100 watt battery panel.
                Aight, I did know I could use grid tied panels without a grid, that's good to know. Do you have any link or model so I can look for it on the internet?

                You have chosen the most Expensive, most Inefficient, and higher risk path you could have chosen.
                Risky in what way?. I've not installed anything yet, that's why I'm consulting the experts.

                Since you went with low voltage panels, you are stuck using them for growth.
                What could be considered a high voltage panel? . A 24v panel ?

                So #1 might apply to you, but I have doubts.
                I have my doubts too. But I didn't wanto to take a risk.



                @Logan5,
                Thanks for the advices about the fuses. Also, thanks for explaining I could use grid tied panels without a grid

                36 watts is a small pump is this to run a misting system?
                Yes.

                Parallel batteries are difficult to maintain and end up damaging the batteries.
                If I have 4 100Ah batteries, would you recommend to wire them in series instead of parallel, and then get an 48v DC to AC inverter?

                Comment


                • #10
                  yes, a 12 volt inverter is mostly a toy. 24 to 48 volts is better suited for off grid applications. If your cabin is small don't use an inverter at all. keep all your loads 12 or 24 volts and a 24 to 48 volt battery bank will serve you well. misting system also includes a fan? if so you must calculate this into your load estimations. If you are using an inverter just to run a fan, I highly recommend looking at the Fantastic/endless breeze 12 volt fan. you can save some energy on the misting system by getting a hand pump type, you can pump it up and last over an hour. 36 watts is a lot for vapor mist. the less power you need the less you spend on batteries.

                  Comment

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