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Solar offgrid system without genset - need reviews

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  • Solar offgrid system without genset - need reviews

    I was designing up an off-grid solar system for a village(no genset involved).
    Peak load is about 10.3 kW
    Daily consumption is 79 kWh/day (about 250 households)


    Considering DOD of 60%(and 90% discharging eff.) and rest all efficiency, battery size was estimated at 140kWh.
    Inverter chosen was 48VDC-230VAC ( 3 inverters of about 4.5kw).
    So batteries were put in series to have 48V bus. Two strings were chosen for reliability. So per string Ah = (140*1000)/48 = 1500Ah.

    only 2v batteries have such large capacities . So a total of 48 2V (2strings of 48V) batteries were chosen.

    Considering everything PV wattage =25kW.
    So i might need about 4-5 80A charge controller depending upon my array voltage.

    System Layout
    PV(25kW) - Controller(80A*4) - Battery(2v 2 strings 24bat/string) - Inverter(48V-230AC 3*4.5kW) - LOAD

    Does it look like a realistic system??

  • #2
    Without knowing where this will be located I can't say
    But a daily discharge of 60% and no generator is a recipe for being in the dark and short lived batteries.
    NABCEP certified Technical Sales Professional

    [URL="http://www.solarpaneltalk.com/showthread.php?5334-Solar-Off-Grid-Battery-Design"]http://www.solarpaneltalk.com/showth...Battery-Design[/URL]

    [URL]http://www.calculator.net/voltage-drop-calculator.html[/URL] (Voltage drop Calculator among others)

    [URL="http://www.gaisma.com"]www.gaisma.com[/URL]

    Comment


    • #3
      the village is based in kenya(at equator). Avg peak sunshine hours are around 5.78..
      still find it not good?

      Comment


      • #4
        Originally posted by snoopy View Post
        the village is based in kenya(at equator). Avg peak sunshine hours are around 5.78..
        still find it not good?
        IMO you are gambling that you will always have enough sunshine to recharge the battery bank before they are drained or discharged to the point of shortening their life.

        That's fine if you can live without power for a day or two. Having a generator set doesn't mean you have to use it a lot. It is a form of insurance that not only covers you for a string of "no sunshine" it is also a necessary "tool" to maintain a battery bank by being able to charge them at a higher voltage to EQ them. Keeps them healthy and will get you a longer life.

        So the cost of installing a gen set and fuel tank to be used every once in a while is probably a lot cheaper then replacing that very large battery bank every couple of years instead of every 5 years.

        Comment


        • #5
          You have a recipe for disaster. You must have a genny and no more than 35% daily DOD. Failure to do that will result in huge monetary losses. You will destroy your batteries in short order.
          MSEE, PE

          Comment


          • #6
            @sunking

            Batteries like hoppecke power vl (http://www.hoppecke.com/content/down...ower_VL_en.pdf) claim a life of about 1500 cycle at 80% DOD and 2000cycles at 60%. I am keeping my DOD already at 60%. Dont you think it is more than enough?

            Solar batteries are made to last longer even at deeper discharge level.

            Comment


            • #7
              Originally posted by snoopy View Post
              @sunking

              Batteries like hoppecke power vl (http://www.hoppecke.com/content/down...ower_VL_en.pdf) claim a life of about 1500 cycle at 80% DOD and 2000cycles at 60%. I am keeping my DOD already at 60%. Dont you think it is more than enough?

              Solar batteries are made to last longer even at deeper discharge level.
              Even if those batteries can go to 60% DOD with 2000 cycles why take the chance of not having a few days of spare capacity in case you get bad weather.

              Going below 50% SOC may or may not hurt a battery but it sure can leave you short of power when you need it.

              Comment


              • #8
                As long as you are willing to accept occasional days without power to prevent overdischarge of the battery bank, that is your (and the community's) decision. You will need to have a hard cutoff voltage to protect the battery bank, and not make it easy to override.
                SunnyBoy 3000 US, 18 BP Solar 175B panels.

                Comment


                • #9
                  Wonder how much of a problem generator fuel would be and at what cost?

                  Do the Life Cycle projections figure on batteries that are rarely,
                  if ever brought up to a full charge.
                  Just dogged all the time.

                  Is there any money available to go to an additional Level with the system
                  which may or may not involve a generator.
                  Just a generator type function of extended charge time and power.
                  As in power to the people.
                  After midnite.

                  Bill Blake

                  Comment


                  • #10
                    Originally posted by snoopy View Post
                    @sunking

                    Batteries like hoppecke power vl (http://www.hoppecke.com/content/down...ower_VL_en.pdf) claim a life of about 1500 cycle at 80% DOD and 2000cycles at 60%. I am keeping my DOD already at 60%. Dont you think it is more than enough?

                    Solar batteries are made to last longer even at deeper discharge level.
                    That is assuming they are fully recharged after each discharge, Equalized regularly. Without a generator they will never be fully recharged or ever Equalized. One cloudy day and it will take two days top recover while in the dark. You will be lucky to make it one year.
                    MSEE, PE

                    Comment


                    • #11
                      Originally posted by SunEagle View Post
                      IMO you are gambling that you will always have enough sunshine to recharge the battery bank before they are drained or discharged to the point of shortening their life.

                      That's fine if you can live without power for a day or two.
                      To amplify what SunEagle said: are you willing to live without power -- without any power -- during each cloudy day and every day thereafter until the battery is fully charged?
                      Even if people order you to turn the damn power on?
                      Then you might be able to get away without a genset.

                      Comment


                      • #12
                        Originally posted by inetdog View Post
                        As long as you are willing to accept occasional days without power to prevent overdischarge of the battery bank, that is your (and the community's) decision. You will need to have a hard cutoff voltage to protect the battery bank, and not make it easy to override.
                        ^^^This is what you will have to do.

                        How do you know the power consumption? Are they on diesel?

                        Comment


                        • #13
                          Originally posted by Sundetective View Post
                          Wonder how much of a problem generator fuel would be and at what cost?

                          Do the Life Cycle projections figure on batteries that are rarely,
                          if ever brought up to a full charge.
                          Just dogged all the time.

                          Is there any money available to go to an additional Level with the system
                          which may or may not involve a generator.
                          Just a generator type function of extended charge time and power.
                          As in power to the people.
                          After midnite.

                          Bill Blake
                          The 800 pound gorilla is not just life cycles but cycles at what
                          percentage of original capacity.

                          Then just how many hours worth of charge does it really take
                          'to make it right' when you have so many houses sucking
                          so deeply on those battery banks, like they are delicious cocktails.

                          Even if you increased the size of the solar arrays tremendously
                          how much could the batteries take and what is the cost for
                          whipping the badboys so hard most days - in Longevity.

                          What percentage of all this solar power would just be rejected,
                          flat out, if the batteries ever did make it to say 90% SOC (or so).

                          Sandia National Labs, Changhong Batteries and others
                          have run studies on these matters for us.

                          Some day, some place they are going to say,
                          over the mid to long
                          run were killin our selves.
                          Old Bill was right.

                          We have to 'timeshift the sunlight'.
                          At least a tad of it.

                          Bill Blake

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