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  • Advice on building standalone solar panel

    I am hoping to build a standalone solar system to power farm gates which have 2x 90w 230v ac motors. As the gates are 1.5km from the mains supply I think solar would be the way to go. The gates would be operated about 10 times a day. I have a 260w 30.79vmp astronergy panel and a 20amp mppt controller that were from another system. My questions are what size inverter and battery bank would I need to comfortably get this up and running?
    I am located in Ireland.
    Your advise greatly appreciated.

    Thanks in advance

  • #2
    This is a fairly straight-forward calculation, but requires a few more facts and assumptions.

    The motors are 180 watts total and will be run 10 times per day. How long do they run? If we assume 60 seconds, then you need
    Energy = 180 watts * 10 times * 1/60 hour = 30 watt hours per day

    Do you get full sun every day? If so, you only need enough battery to run the gates one day, and then recharge. If you plan for 4 straight days of storm/clouds, then you need to plan for enough battery to run the gates 5 straight days between recharge.

    The most economical and practical batteries are old-fashioned wet lead-acid batteries, similar to car batteries. There are a few varities of these, but don't worry about that now. All lead-acid batteries love being fully charged and hate being deep discharged. For long life, it is best to use at most 40% of their charge.

    Based on all of the above assumptions, you need 30 watt hours * 5 days = 150 watt hours / 40% = 375 watt hours of battery.

    I don't know if your MPPT controller also charges batteries or if it puts out 230VAC. You need something capable of delivering 180 watts continuous at 230VAC from the batteries. The motors may have a starting current higher than 90 watts, so it is probably necessary to get at least 400 watts.

    Your panel puts out 260 watts. Assuming that you get at least 3 hours of bright sun a day, you can easily get 375 watt hours of energy from that panel to recharge the battery in one day after 5 days of use.

    I hope this gives you a good start. Please keep asking questions. You also want to find the specifications for your MPPT controller, then start looking for a charger/inverter in the 400 to 500 watt range.
    7kW Roof PV, APsystems QS1 micros, Nissan Leaf EV

    Comment


    • #3
      Thanks Bob for your detailed breakdown, as we are in Ireland we get alot of cloudy days so I know I'll have to take that into account when calculating the daylight hours of sun. The mppt controller is an epever 20amp which is 12/24v . If I connect a 12v 400/500 watt inverter will it still trip out when the controller starts to put over 14.5v into the batteries on a good day? Or how do I avoid overvoltage tripping out the inverter?

      I had a12v 1500w inverter and I connected it to a 180amp hr battery which I had charging from the panel. On a cloudy day it is OK but when the panel starts to increase its output and the controller goes above the inverters rated overvoltage of (from memory) around 14.5v the inverter trips out.
      Obviously I need to get this sized correctly before I build this on site.

      Many thanks

      Aleister

      Comment


      • #4
        Mr. Maxwell:

        With respect to your location's somewhat limited solar resource availability, if you're looking for some decent solar resource and sizing info for preliminary design, see something called "PVWatts" on the web. It's a solar modeling tool from the U.S. NREL and pretty user friendly.

        That limited availability is probably some of why Bob-n suggested 5X an estimated daily requirement. You may well have cloudy weather 80 % of the time or the clouds will only allow 20 % of the sun to get through, or some combination of both and other resource limiting factors.

        If you do take a snoop of the model, read all the help screens a couple of times before you get your array orientations reasonably close and make a few runs.

        Welcome to the neighborhood.

        Erie Go Brach.

        Comment


        • #5
          Originally posted by Aleister Maxwell View Post
          .......... If I connect a 12v 400/500 watt inverter will it still trip out when the controller starts to put over 14.5v into the batteries on a good day? Or how do I avoid overvoltage tripping out the inverter?

          I had a12v 1500w inverter and I connected it to a 180amp hr battery which I had charging from the panel. On a cloudy day it is OK but when the panel starts to increase its output and the controller goes above the inverters rated overvoltage of (from memory) around 14.5v the inverter trips out.
          .......
          Each inverter may have its own overvoltage trip point so it would be hard to predict. I am surprised that they are that sensitive. If you can adjust the charge controller that would be the simplest. There are some work arounds to lower the voltage that the inverter sees but I don't have enough detailed experience to give you more than the concept. If I had to figure it out I would do some Internet research. Diodes drop voltage and if you have a convenient electonics store they may be able to advise you.

          Comment


          • #6


            Thanks for that J. P. M, I will check out that Web link.

            Ampster

            Comment


            • #7
              Ampster, thanks

              I just need to get it configured correctly , I know there won't be much demand on it but I need to be sure that when I need it to work the inverter won't have tripped out resulting in no power when needed.

              Thanks

              A. M

              Comment


              • #8
                Originally posted by Ampster View Post
                Each inverter may have its own overvoltage trip point so it would be hard to predict. I am surprised that they are that sensitive. If you can adjust the charge controller that would be the simplest. There are some work arounds to lower the voltage that the inverter sees but I don't have enough detailed experience to give you more than the concept. If I had to figure it out I would do some Internet research. Diodes drop voltage and if you have a convenient electonics store they may be able to advise you.
                The concept to try to use add-on components to lower voltage to the inverter is flawed. It works on paper if you are sloppy, but never in the field.

                you will have to carefully design your system so the controller output is below the inverter overload. That means selecting a configurable charge controller, and a inverter designed to work from a solar charger, not a vehicle inverter.
                These parts are going to be "next tier" commodities, not the cheap stuff at auto parts stores.
                I will suggest some parts, but they are not cheap.

                First, you will need more solar panels, because of your weather conditions, you need to be able to charge quickly, and also charge in cloudy conditions.
                Your controller will need tight regulation to not trip the inverter I would suggest the Prostar 25A https://www.morningstarcorp.com/products/prostar-mppt/
                and for a inverter, the 230V version of the sure sine which has a 600w surge limit. Hopefuly that would run your gate motors. otherwise, you must use a larger inverter and pay for it's associated higher losses. https://www.morningstarcorp.com/products/suresine/
                I am not confident the suresine can handle the starting surge of your motors, so you need to research their surge.
                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


                • #9
                  Originally posted by Aleister Maxwell View Post
                  .....
                  I just need to get it configured correctly , I know there won't be much demand on it but I need to be sure that when I need it to work the inverter won't have tripped out resulting in no power when needed.
                  Yes, I see the inverter trip out as the biggest problem that needs a solution. That should be easy to test and/or find a work around. Adding battery or solar panel capacity should be easy if you have more demand than anticipated. I see lots of those gates in my part of the country and they don't look like they need large panels but I am in the sunny part of the California wine country. .

                  Comment


                  • #10
                    Thanks guys and for those Mike, I will look up those links now and get the sizing of everything right.

                    Ampster--glad to hear the setup works for others, albeit in a sunny climate

                    Comment


                    • #11
                      I have a gate operator that opens a 16' metal gate, and runs off a 12v DC system.
                      Uses a 20w panel, and a 12ah gel battery, going on 6 years now. Hmmm, maybe it's about time to change the battery.

                      I'll get a pic of it tomorrow. Major brand in the USA
                      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


                      • #12
                        Here's the gate information & pics
                        16' metal gate, apx 90lbs
                        Liftmaster RSW12V 12V 30W motor Electronic control panel w/radio remote, fire dept override
                        20W PV panel

                        20200815_064345.png


                        20200815_064354.png

                        20200815_064416.png

                        20200815_064407.png
                        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


                        • #13
                          1.5km is only 5000 feet.

                          Seems like you could do a direct burial 6/6/6 aluminium for ~$3400(USD) plus cost of renting a trenching tool.


                          Voltage would be ~223V if you started with 230V at the supply end and it was ~1A of current. (I'd expect that 220V vs. 230V the motors would still work)


                          Do you have any other needs for power at/near that location?
                          If so, it might be a better option (financially) than doing an off-grid solar setup.

                          Comment


                          • #14
                            Since that is a very long run of wire, using a pair of step up/step down transformers to put 480V on the long line would allow you to cut wire size by a factor of 4.
                            Also note, however, that the 10V drop during operation could be much larger while the motor is starting and may or may not be a problem.
                            The inverter in a standalone system has to be sized with surge capability to start the motor.
                            Last edited by inetdog; 08-17-2020, 05:12 PM.
                            SunnyBoy 3000 US, 18 BP Solar 175B panels.

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