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Sizing a solar system ?

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    Sizing a solar system ?

    Living here in Fl I was thinking about getting a solar system that would be big enough to just run my ac system . That is probably my biggest load due to being on most all the time . I just would like to be able to run the ac but have the solar available to then use for well pump and misc in the house should lose power for days due to a Hurricane . Being solar is not my background any information on how to do this would be appreciated .

    #2
    I won't claim to know a lot about PV systems, but I do know that it is typical for systems that are interconnected to grid that you must have grid power or you get no power from the PV system. This I believe is mostly so they won't backfeed into the grid. That effects your want to use it for standby when there is no grid power. There may be ways around this but just a FYI thing you need to be aware of.
    I live for today, I'm just a day behind.

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      #3
      Originally posted by Davebones View Post
      Living here in Fl I was thinking about getting a solar system that would be big enough to just run my ac system . That is probably my biggest load due to being on most all the time . I just would like to be able to run the ac but have the solar available to then use for well pump and misc in the house should lose power for days due to a Hurricane . Being solar is not my background any information on how to do this would be appreciated .
      For power during a grid outage you'll need to have batteries and a battery inverter along with solar, and if you want to use it to run HVAC equipment for an extended period of time you'll need a lot of battery capacity. You cannot run your HVAC (or anything else, practically speaking) directly off a grid tied PV system with no grid connection.

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        #4
        I figured I would need to have a battery system . I'm just trying to educate myself on how to go about doing this .

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          #5
          I think, that after you run the numbers, you will find that a gas generator makes more sense. But the goal of your question is education, not advice

          Step 1 is to figure out your daily _energy_ use, in terms of kWh.

          Step 2 is to figure out how much solar capacity is required to reliably produce that many kWh. The key here is reliably. You have sunny days and cloudy day; the length of the day and the weather impact production. On a hot, humid, cloudy day you will need to have enough production to cover your usage.

          Step 3 is to figure out the energy storage capacity needed. You always need some capacity because well, night But if you can use energy from one day to the next perhaps you can get away with less solar production capacity at the cost of more energy storage capacity.

          Step 4 is to figure out your peak power demand. Your inverters have to be able to provide enough _power_ for things like starting your well pump or HVAC load.

          The reason that grid tied systems are so popular is that you don't need the energy storage, and also you don't need the surge capacity to start loads. The grid is treated as your battery and your surge source.

          You can do some horse trading. For example you can use a VFD driven well pump or HVAC system to eliminate the starting surges. More expensive loads but lower inverter capacity needed.

          Others will give you a more detailed response, but this should help you get started thinking about things.

          -Jon

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            #6
            Originally posted by Davebones View Post
            I figured I would need to have a battery system . I'm just trying to educate myself on how to go about doing this .
            Generally, you start with all the loads you want to keep alive during a power outage (e.g., your refrigerator draws (X Watts) times (Y hours/day it runs) = (Z kilowatt hours/day)) and total them up. Then you decide how many days you want them to stay alive if there is no appreciable sunlight (days of autonomy). Multiply those numbers together and you get how much available battery capacity you'll need. Then you design the amount of PV you'll need to have to keep the batteries charged.

            As winnie pointed out, you also need to consider your peak demand and make sure that the battery inverter(s) will deliver the instantaneous power it will take to service it.

            As you may see, for a large home that you expect to keep sustainably fully functional, this can be an arduous design task resulting in a very expensive system. My advice is to familiarize yourself with the concepts but to go to someone who does this stuff for a living to do the actual design.

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              #7
              There's gonna hafta be a whole lotta batteries!
              Master Electrician
              Electrical Contractor
              Richmond, VA

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                #8
                There is another configuration to consider for completness, namely battery power with generator support. You can use a PV charged battery bank and inverter designed to also work like a grid tied unit but with a generator.
                The battery can handle low loads without having to run the generator as long as PV can keep the batteries charged.
                For bad weather or heavy loads the generator kicks in. And for really heavy loads the inverter can supplement the generator. A limited subset of the hybrid inverter systems offer generator support mode.

                Sent from my XT1585 using Tapatalk

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                  #9
                  I appreciate the information I am getting . I will go to someone who does this for a living when I get ready . Thanks again to all who are replying .

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