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  • Battery and Solar panel size

    Hey folks, new to this forum so not sure where to ask this but there seems to be many intelligent people on here so any help would be appreciated.

    I own a creek hut with its main source of power being a petrol fuelled 2kva genorator. I have whipped up some calculations and would just like advice on how to optimise my system.

    I wish to run a 700w appliance for 20 hrs each day 240v. That will use 14kw over a 20 hr period. Here in North qld we get around 4-5 hrs solid daylight and 2-3 low intensity however it varies between summer and winter. I plan to use a 12v battery system with a 12v-240v 1000w inverter.

    14kwh / 4 hours sunlight = 3.5kw system
    80% efficiency so a 4.5kw system is needed.

    10x 150aH 12v deep cycle AGM batteries = 18kwh of battery

    Will i need to include a 50% discharge on this so x20 batteries? or will the constant draw of power allow maybe for 60-80% discharge?

    Is it correct to assume 700w ac will draw about 70amps dc?

    How many solar panels can be connected parralel? Will it be dependant on my charge controller amperage capacity?

    Are there any reccomendations or items I must add?


    Thanks all😊😊😊

  • #2
    Hello buono97 and welcome to Solar Panel Talk

    Unfortunately your calculations are way off.

    A battery system needs to be sized about 4 to 5 times what you will use daily. So if you plan to use 14kWh a day then the battery needs to have a rating somewhere between 56 an 70 kWh. That would be a huge system and very impractical at 12volt. More likely very expensive even at 48volt.

    Also your solar pv wattage needs to be able to deliver about 120% of what you use because of losses. It should also be sized based on the shortest solar insolation day which is probably much less than that 4-5 hours. I would estimate you are looking at around 10kw of solar panels.

    As much as I would like to say using solar to power your appliances is a great way to save money, it sometimes is not when they are big ones that have a 700 watt rating.

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    • #3
      Originally posted by SunEagle View Post
      Hello buono97 and welcome to Solar Panel Talk

      Unfortunately your calculations are way off.

      A battery system needs to be sized about 4 to 5 times what you will use daily. So if you plan to use 14kWh a day then the battery needs to have a rating somewhere between 56 an 70 kWh. That would be a huge system and very impractical at 12volt. More likely very expensive even at 48volt.

      Also your solar pv wattage needs to be able to deliver about 120% of what you use because of losses. It should also be sized based on the shortest solar insolation day which is probably much less than that 4-5 hours. I would estimate you are looking at around 10kw of solar panels.

      As much as I would like to say using solar to power your appliances is a great way to save money, it sometimes is not when they are big ones that have a 700 watt rating.
      SunEagle thank you for confirming the feasibility of my request.

      ​I am now beginning to understand the limitations of battery storage. Would cost approx. $2000 a year for fuel vs $30,000 for battery storage and panels and probably more for the rest. Maybe one day...

      Comment


      • #4
        Originally posted by buono97 View Post

        SunEagle thank you for confirming the feasibility of my request.

        ​I am now beginning to understand the limitations of battery storage. Would cost approx. $2000 a year for fuel vs $30,000 for battery storage and panels and probably more for the rest. Maybe one day...
        I agree that some day batteries prices will come down and become financially a good decision for a lot more people. But for now only the rich can afford them.

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        • #5
          Originally posted by buono97 View Post

          SunEagle thank you for confirming the feasibility of my request.

          ​I am now beginning to understand the limitations of battery storage. Would cost approx. $2000 a year for fuel vs $30,000 for battery storage and panels and probably more for the rest. Maybe one day...
          You can still look into a much smaller battery bank charged by the generator to provide power for your smaller convenience loads like lighting and music without out having to start up the generator or run it continuously. That could easily make sense. The fuel costs to run your generator will be much higher per watt used when the generator is lightly loaded.
          SunnyBoy 3000 US, 18 BP Solar 175B panels.

          Comment


          • #6
            Originally posted by inetdog View Post
            You can still look into a much smaller battery bank charged by the generator to provide power for your smaller convenience loads like lighting and music without out having to start up the generator or run it continuously. That could easily make sense. The fuel costs to run your generator will be much higher per watt used when the generator is lightly loaded.
            Thanks! I will definitely be looking into this, thought running some fans and TV's wouldn't require so much capacity. Maybe replacing the fixtures in the hut with newer (hopefully more efficient) models could be a massive step in the right direction. Lighting and music wouldn't need as much either as they're rarely used.




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