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Looking for advice on unusual system that switches between battery bank and grid

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  • Looking for advice on unusual system that switches between battery bank and grid

    Hi, I'm an engineering student working on a project that requires solar panels and a battery bank to help power a system. They want it to be a relatively smart system, and I can handle that aspect but I need some help finding the parts since I don't really know the language for describing what I want. The requirements of the project are:

    1. An 1800W system capable of switching between the grid and battery power
    2. Capable of detecting battery charge and switching between the grid and the batteries
    3. The inverter for the battery system must produce its own sine wave so that it can operate independently of the grid
    4. Only needs to power 120V appliances


    Attached I have a diagram of how I think the system should be implemented

    The parts I already have:
    1. Solar Panels
    2. Batteries (both lead acid and LiFePo4)

    The parts that I need
    1. Charge controller that can send a signal when
    a) Batteries are fully charged
    b) Batteires need to be charged
    2. Automatic Transfer Switch capable of taking in these signals and making the appropriate decision

    I can find a pure sine inverter easily enough I think, so the two parts above are really the only ones that I need help finding. I'm not sure how to go about this and I don't know the proper vocabulary to google what I'm looking for. I'm open to suggestions for these parts and for anything else I missed! I cobbled together these parts from information I recently googled and I have no experience whatsoever putting together a system like this.
    Attached Files

  • #2
    Yu have made something extremely over complicated. It does not need alll that switching and all yu need is a bimodal inverter or even better something like the outback flexpower one fully integerated. Will do all is needed and will be more efficient not switching and cycling batteries quite as much doing grid zero.

    is there no net metering where this is going?
    Last edited by ButchDeal; 03-08-2018, 07:41 PM.
    OutBack FP1 w/ CS6P-250P http://bit.ly/1Sg5VNH

    Comment


    • #3
      What guidance are you getting from your instructors or other engineering faculty ?

      What technical sources do you have available besides Google ?

      How much of this project are you expected to complete on your own ?

      How much of this project do you expect others to do for you ?

      Comment


      • #4
        How much of a load in Watts, do you need to power? Motors or any gear with poor Power Factor ? I know you spec'd a 1800W inverter, but knowing the load is 300W or 937W is critical. Gooing for a full 1800W for 6 hours or more is going to get really expensive in battery costs

        How long does the battery have to power the load ? Minutes? Hours?
        Powerfab top of pole PV mount (2) | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
        || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
        || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

        solar: http://tinyurl.com/LMR-Solar
        gen: http://tinyurl.com/LMR-Lister

        Comment


        • #5
          Originally posted by PralineJim View Post
          Hi, I'm an engineering student working on a project that requires solar panels and a battery bank to help power a system. They want it to be a relatively smart system, and I can handle that aspect but I need some help finding the parts since I don't really know the language for describing what I want. The requirements of the project are:

          1. An 1800W system capable of switching between the grid and battery power
          2. Capable of detecting battery charge and switching between the grid and the batteries
          3. The inverter for the battery system must produce its own sine wave so that it can operate independently of the grid
          4. Only needs to power 120V appliances


          Attached I have a diagram of how I think the system should be implemented

          The parts I already have:
          1. Solar Panels
          2. Batteries (both lead acid and LiFePo4)

          The parts that I need
          1. Charge controller that can send a signal when
          a) Batteries are fully charged
          b) Batteires need to be charged
          2. Automatic Transfer Switch capable of taking in these signals and making the appropriate decision

          I can find a pure sine inverter easily enough I think, so the two parts above are really the only ones that I need help finding. I'm not sure how to go about this and I don't know the proper vocabulary to google what I'm looking for. I'm open to suggestions for these parts and for anything else I missed! I cobbled together these parts from information I recently googled and I have no experience whatsoever putting together a system like this.

          ---------------------------------------------------------------------------------------

          You need to eat your wheaties before you can do anything else. I think you may have some of the things you need, but not everything? Seems like there'a few missing pieces to your pie.
          We size these systems from the budget to the array (budget - loads - inverter - battery's - charge controller - array)
          Hybrid system sizing is really not much different than regular battery backup sizing. What if the grid goes down, even with the hybrid system? Just make sure your inverter is a little smaller than your pv array. Array STC kW rating should equal ~110 - 120% of inverter operation kW rating.

          Battery backup system sizing starts with: load analysis.
          Your load analysis will include total AC power in W, Total DC power in W. You take the chosen appliances power rating and multiply by the operating time (hrs per day) to get the daily energy consumption in Wh/day. This information gives you the total energy you need to meet per day. Multiply the daily Wh energy consumption by inverter efficiency to get your weighted operating time and average daily DC energy consumption. * Make sure your inverter is rated for the 'surge' or 'duty cycle' of the chosen appliances. Look for a transformer based inverter that way it will produce a modified AC sine wave or better (within 59.6 and 60.5hz) or somewhere around there.

          The next step is: Critical Design Analysis
          You need to find out how much energy (irradiation. insolation) you can get from the sun at any given month of the year (peak sun hours per day). Your critical design month is the one with the lowest PSH per day at the array Azimuth. You need to look for the worst month so that your PV array will be adequate enough to provide sun on that worst time of the year ( we cal lit the black hole of winter). This will tell you how much PV needed to power that daily Wh from above.

          Thirdly: Battery Bank Sizing

          Obviously the most tricky part of the entire shebang. See the attached sheet #3 - Battery Bank Sizing. Depending on system voltage and battery rated capacity, you'll select a battery bank that meets your operating tmie. Autonomy isn't really an issue with Hybrid systems, but you should at least go through the exercise. The charge controller will be able to meet the depth of discharge, discharge rate, total in/out ampacity.

          Finally: Array Sizing

          Choose an array that can provide the required Wh/day at the battery charging efficiency during the worst weather time of the year.

          Here's a few keywords to help you search.

          Hybrid PV system sizing
          Bimodal PV system sizing
          Multi mode PV system sizing
          Battery backup system sizing

          Resources:
          Solar ABC's (wealth of information)
          NREL Redbook
          NREL PV Watts (energy from the sun)
          Solar ABC's Solar Reference Map


          I hope this helped if only a little.
          God bless and have fun!

          Comment


          • #6
            Wheel has already been invented and you cannot improve on it. As Butch told you the wheel is called a Bimodal aka Hybrid Inverter. Nothing complicated. Do your own work, this is a DIY Forum, not professional.
            MSEE, PE

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