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  • Advice on a project

    Hi guys

    Looking for some advice for a school project. We're looking to see if we can design a solar system that could power sport field floodlights that have a draw of 19.4KwH.

    These floodlights would rarely be used during the summer, but during the winter could be three times a week for 3 hours at a time.

    During the winter we get around 6.5 hours of daylight.

    What size off grid solar system would we need to ensure we had enough power to run these floodlights, including batteries?

    The challenge we have is all calculators we have found say to find out the power requirements of something and then multiply it by the number of hours used per day and then by days in the week, but these floodlights would be the only draw on this power supply and are only used for 3 hours at a time, so if used Saturday then potentially no more power needed until Tuesday evening, so for 3 full days the batteries could recharge.

    The other information I have about the floodlights is: 16 floodlights with 1.2kW per fixture and around 3.3Amps assuming 3phase.

    Any advice, help?

  • #2
    Originally posted by Topper View Post
    Hi guys

    Looking for some advice for a school project. We're looking to see if we can design a solar system that could power sport field floodlights that have a draw of 19.4KwH.
    Do you mean that they draw 19.4kW or use 19.4kWh a month or year ?

    Originally posted by Topper View Post
    These floodlights would rarely be used during the summer, but during the winter could be three times a week for 3 hours at a time.

    During the winter we get around 6.5 hours of daylight.
    You need to find your sun hours daylight is meaningless in solar terms.


    Originally posted by Topper View Post
    What size off grid solar system would we need to ensure we had enough power to run these floodlights, including batteries?
    Why have batteries? what is the average annual consumption of these lights? are they on their own meter?
    do you have net metering?

    Originally posted by Topper View Post
    The challenge we have is all calculators we have found say to find out the power requirements of something and then multiply it by the number of hours used per day and then by days in the week, but these floodlights would be the only draw on this power supply and are only used for 3 hours at a time, so if used Saturday then potentially no more power needed until Tuesday evening, so for 3 full days the batteries could recharge.
    high draw infrequent use makes for a very poor choice for off grid. This load is so high and so infrequent that if there was some reason to go off grid you would be far better off with a generator than solar.

    Originally posted by Topper View Post
    The other information I have about the floodlights is: 16 floodlights with 1.2kW per fixture and around 3.3Amps assuming 3phase.

    Any advice, help?
    So that first number should be 19.4kW not 19.4kWh
    Every 3 hour game would put you at 58.2kWh of usage

    You need to find out if it is really 3 phase or not and if so what voltage.

    trying to do this off grid with batteries would be extremely costly with a higher maintenance cost than using the grid
    OutBack FP1 w/ CS6P-250P http://bit.ly/1Sg5VNH

    Comment


    • #3
      Originally posted by ButchDeal View Post

      Do you mean that they draw 19.4kW or use 19.4kWh a month or year ?

      You need to find your sun hours daylight is meaningless in solar terms.

      Why have batteries? what is the average annual consumption of these lights? are they on their own meter?
      do you have net metering?

      high draw infrequent use makes for a very poor choice for off grid. This load is so high and so infrequent that if there was some reason to go off grid you would be far better off with a generator than solar.

      So that first number should be 19.4kW not 19.4kWh
      Every 3 hour game would put you at 58.2kWh of usage

      You need to find out if it is really 3 phase or not and if so what voltage.

      trying to do this off grid with batteries would be extremely costly with a higher maintenance cost than using the grid
      The first line of the OP says this is for a school project, so I'm assuming he/she just needs to run the numbers and make a report.

      So to boil it down to the basics, you have 19.4kW of power for about 3 hours per game. That's 58.2kWh per game. So you would need at least that much storage potential, which is quite a lot of batteries. Plus you have to take into account you can only utilize about 50% or so of the total capacity of the batteries.

      Next you need to determine how many panels you need. PVWatts will be a good place to start. Put in a baseline of a 1kW system and see how much you get out of it during the winter. Then factor in what the shortest time between games is. Then multiply the 1kW by how much power you need to get to.

      Solar Power for Dummies is a good resource for the basics.

      Comment


      • #4
        Are these existing lights? If so have you priced LED lights?
        9 kW solar, 42kWh LFP storage. EV owner since 2012

        Comment


        • #5
          Originally posted by emartin00 View Post

          The first line of the OP says this is for a school project, so I'm assuming he/she just needs to run the numbers and make a report.

          Why assume it is not going to actually be built? Also why assume it HAS to be off grid? The report could show a better option of a grid tie system that will for less money offset more of the school load...

          Originally posted by emartin00 View Post
          So to boil it down to the basics, you have 19.4kW of power for about 3 hours per game. That's 58.2kWh per game. So you would need at least that much storage potential, which is quite a lot of batteries. Plus you have to take into account you can only utilize about 50% or so of the total capacity of the batteries.
          Personally I think the assumption of only using the lights for 3 hours at a time is comical. Schools usually have the lights on before the game and after the game.
          They also use them for practice.

          OutBack FP1 w/ CS6P-250P http://bit.ly/1Sg5VNH

          Comment


          • #6
            Originally posted by Ampster View Post
            Are these existing lights? If so have you priced LED lights?
            excellent point. More savings could easily be had for far less expense by changing the bulbs out to more modern lights.
            Find out what bulbs are used at the field, then find the lumens of the bulbs. They are likely in groups or arrays per pole, so find the lumens per pole and then find a compatible lumen LED arrangement. I am sure there are more on the commercial side but just looking around here is a 15k lumen set that uses just 129watts ( similar lumens to a 400W Metal Halide for nearly 70% reducing in consumption)
            https://www.1000bulbs.com/product/209084/LITH-0465.html

            reducing consumption is usually a cheaper solution and often the best first step. If the existing bulbs are Metal Halide it would reduce the wattage from 19.4kW to 6kW. And 3 hour game consumption from 58.2kWh to 18kWh. More if the existing bulbs are less efficient than metal halide.

            if there is a budget you could also propose a rooftop grid tie system in combination with the LED change out of the lights on the field that could reduce the schools total electric bill year round.

            Some states and local governments have incentives specific to public entities to reduce their usage that would cover both the LEDs and the solar.
            Last edited by ButchDeal; 05-10-2019, 10:08 AM.
            OutBack FP1 w/ CS6P-250P http://bit.ly/1Sg5VNH

            Comment


            • #7
              Assuming grid power is available, I'm wondering if the OP knows the costs both in time, effort and maint. in doing an off grid application such as this vs. simply using grid power.

              Comment


              • #8
                Originally posted by Topper View Post
                Hi guys

                Looking for some advice for a school project.
                Is this a hypothetical system to practice the calculations, or something you actually want to build?

                Comment


                • #9
                  Originally posted by sdold View Post
                  Is this a hypothetical system to practice the calculations, or something you actually want to build?
                  Either that, or another possibility, some one at the school has convinced the kids the lighting of the games is killing the plant, and so to save their world they must come up with an off grid solution for the lights.
                  285Wx9 / MNClassic 150 / CSW4024 / TrojanL16H-ACx4

                  Comment


                  • #10
                    Originally posted by Matrix View Post

                    Either that, or another possibility, some one at the school has convinced the kids the lighting of the games is killing the plant, and so to save their world they must come up with an off grid solution for the lights.
                    To save the world they should play in the sunlight and forget about using the lights.

                    Comment


                    • #11
                      Whatever the solution - if that's the right word to use, I bet if the OP or whoever had the idea of off grid lighting for this application has read this thread, they may now have some knowledge of how impractical throwing off grid PV at this application actually is compared to simply running grid power to it, or, as SunEagle elegantly observes, simply using the field during daylight hours.

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                      • #12
                        In any case, the OP never made a second post after the original a couple days ago. Bruce Roe

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                        • #13
                          Originally posted by bcroe View Post
                          In any case, the OP never made a second post after the original a couple days ago. Bruce Roe
                          I saw that too. Figured he may have blown us off after Butch & Martin's posts and tried his luck over at AZW&S.

                          Comment


                          • #14
                            Cant find it on AZW&S. lol.
                            285Wx9 / MNClassic 150 / CSW4024 / TrojanL16H-ACx4

                            Comment


                            • #15
                              It would be fun to figure this out as a thought experiment. I think the battery would be the easy part: 16 fixtures X 1.2 kW = 19.2 kW, X 3 hours = 57.6 kWh for a night's worth of lighting. At 25% discharge I get 230 kWh battery or 4800 AH at 48V. How does that sound? Finding the inverter might be harder. He didn't say what voltage he needs so I'll guess 480/277 with 277V lighting.

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