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  • Solar panel efficency

    Hi, I have successfully installed a solar panel system to power my swimming pool pump but I wonder if it could be more efficient than I have it set up. It works well but just don't want to missing a trick. Here is what I have:

    The pool pump is 48V 500W

    I have 3 x 250W 24V solar panels. I have 2 of them wired in series to get my 48V and then the 3rd panel in parallel to boost my wattage.

    According to my charge controller the input is around 68V 8A 450W

    The charge controller can only handle max 15A and open voltage <100V

    Could I be doing anything more efficiently?

    Many thanks


  • #2
    I see 3 issues with your arrangement.

    The first is using an odd number of panels. That single 250w will bring down the voltage of the 2 x 250w and lower the charging voltage
    The second is you need something bigger than a 15A CC
    The third is that you did not mention any batteries in your system so your pool pump will end up either not working in low sunlight or run very slow.

    Get a 4th 250watt panel and wire them 2S2P.

    Get a 30amp MPPT type CC which will utilize more panel wattage then that 15A CC.

    Your battery system should be around 200Ah.

    Comment


    • #3
      Originally posted by virtualpete View Post
      Could I be doing anything more efficiently?
      Well, without particulars of location and pump use, it's hard to say. If your question is: Is there a more efficient way to use alternate energy to meet the duty ? maybe. But I'm wondering, again, depending on the application and location, including hours of pump operation, if it might have been more cost effective and less maint. and depending on existing pump age and pump particulars, to simply change out the pump to a more efficient model, and rely on grid power.

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      • #4
        Thanks Guys for the input, will disconnect the 3rd series panel and see if it makes much difference. I have limited useable roof space so will struggle with a 4th panel. The pool room is 35m away from the panels and very pleased that i am losing minimal voltage over that distance using 10 swg cable.

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        • #5
          3 panels only deliver with all in parallel or all in series. Get a different CC, put all 3 in series or
          get a 4th for a 2S2P panel setup.

          Your 10 gauge wire loop has a resistance of around 0.23 ohms, about 1.8V loss at 8A. Bruce Roe

          Comment


          • #6
            Thanks Bruce, excuse my ignorance as new to the solar world but [LEFT][COLOR=#252C2F][FONT=inherit]2S2P panel setup does that mean 2 panels in series and 2 panels in parallel? If i put all 3 in series that will give me 72V min but only 250w which may not be enough to run [/FONT][/COLOR][/LEFT][COLOR=#007670]the 48V 500w pump or maybe it will?? [/COLOR][LEFT][COLOR=#252C2F][FONT=inherit]Also not sure what CC to go for as i need 48v for[COLOR=#b01100] the pool pump? Pete[/COLOR][/FONT][/COLOR][/LEFT]

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            • #7
              Right 2 in series, in parallel with another 2 in series. I will throw out another idea, you might be
              able to parallel 3 or 4 which will then tend more toward a panel open circuit voltage, and run the
              pump direct at reduced speed. If that is not enough speed, you are back to one of the above
              solutions.

              A CC usually implies a battery to stabilize the system, but it risks destruction at night. Perhaps a
              big capacitor would work instead of a battery. Bruce Roe
              Last edited by bcroe; 05-23-2019, 11:28 PM.

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              • #8
                If the CC reads 68V at 8A, then the single nominal 24V panel in parallel is not contributing anything at all to the power output. At 68V, it is back biased and not delivering any current at all.
                All three in series should give you about 102V at 8A, which is too high a voltage for your CC, and all three in parallel 1. Would not charge a 48V battery bank or 2. power a 48V motor very well, since the voltage under load would be about 34V.
                It would really help if you can tell us the MPP Voltage and Current of your "24V" panels. It sounds like the 24 means intended for use with a 24V battery rather than having a Maximum Power Point voltage of 24.
                If you do not actually have batteries, then instead of a CC between panels and motor you would need what is called a Linear Current Booster. This will take the panel output and convert both voltage and current to whatever value combination will deliver the most power to the motor at any given time. It specifically allows for letting the output voltage go down if that will better match panels to motor instead of regulating the output voltage to a preset value.

                More importantly, whether you put panels in series or in parallel the available wattage simply adds as long as the voltage and current are compatible with the load they are driving. An LCB set for a maximum motor voltage of 48V would take the 68V and 16A available from 2S2P and deliver 48V at up to about 22A. What is the load current of the motor at 48V input and normal water circulation resistance?
                Last edited by inetdog; 05-23-2019, 07:16 PM.
                SunnyBoy 3000 US, 18 BP Solar 175B panels.

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                • #9
                  Thanks inetdog, very useful input. I will try and find out more about the panels as the information is a bit sparse. All I know from the label is that they are 250w 7.6A 24V. Pete

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                  • #10
                    Actually I realised I said something wrong but not sure if it makes a huge difference. I have 2 panels in parallel and 1 in series working on the bases that 2 in parallel will give me 500w 24v and the1 in series will bring me up to 48v. Sorry to muck you around

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                    • #11
                      Originally posted by virtualpete View Post
                      Actually I realised I said something wrong but not sure if it makes a huge difference. I have 2 panels in parallel and 1 in series working on the bases that 2 in parallel will give me 500w 24v and the1 in series will bring me up to 48v. Sorry to muck you around


                      That configuration will result in the output of two panels in series being that the current in a series string will be equal to the lowest current output of the individual components of the string. Basically the second parallel panel is doing nothing.
                      2.2kw Suntech mono, Classic 200, NEW Trace SW4024

                      Comment


                      • #12
                        Thanks littleharbor, but if I remove the 2nd panel in parallel I will end up with just 2 in series giving me 48v at 250w, would that be better? Presumably from what you are saying the Amps will increase and it will still work fine? It does work great at the moment just dont want to make it less so.

                        Comment


                        • #13
                          Originally posted by virtualpete View Post
                          Thanks littleharbor, but if I remove the 2nd panel in parallel I will end up with just 2 in series giving me 48v at 250w, would that be better? Presumably from what you are saying the Amps will increase and it will still work fine? It does work great at the moment just dont want to make it less so.
                          You are getting your values mixed up. 2 x 250watt panel in series will get you about 48v at 500Watts. By adding the third panel in parallel you actually drop the voltage to somewhere between 48v and 24v even though you have added another 250w for a total of 750watts.

                          Wattage will always add up. Voltage will only add in SERIES not in parallel. Amperage will only add in PARALLEL not in series.

                          If you want to charge a 48V battery system you will need more than 48V so that third panel in parallel will not help you.

                          If you want to use the third panel then find a Charge controller that will handle the voltage of 3 of those 250w panels wired in series.

                          Comment


                          • #14
                            Originally posted by SunEagle View Post

                            You are getting your values mixed up. 2 x 250watt panel in series will get you about 48v at 500Watts. By adding the third panel in parallel you actually drop the voltage to somewhere between 48v and 24v even though you have added another 250w for a total of 750watts.

                            Wattage will always add up. Voltage will only add in SERIES not in parallel. Amperage will only add in PARALLEL not in series.

                            If you want to charge a 48V battery system you will need more than 48V so that third panel in parallel will not help you.

                            If you want to use the third panel then find a Charge controller that will handle the voltage of 3 of those 250w panels wired in series.
                            +1 above.

                            The thing you're confused with is, in series the current stays the same. The wattage always adds, parallel or series. These are important facts to get right before you start making all these connections based on your assumptions. Larger amounts of power can be very dangerous or even deadly when making connections incorrectly.

                            Another thing you need to know. Those 250 watt panels aren't true 24 volt panels. Take my word on this. Two, in series isn't going to give you high enough voltage to properly charge a 48 volt battery bank. This issue is even more critical when trying to charge using an MPPT controller. Bottom line, you need a different controller that will handle all 3 panels in series. i.e. 150 Voc. max
                            2.2kw Suntech mono, Classic 200, NEW Trace SW4024

                            Comment


                            • #15
                              Thanks SunEagle, so to conclude from this I am running my pool pump directly from the PVs via the charge controller main reason being we have plenty of sun here in Southern Spain and i can get a good 8 hrs run from the pool pump which is ample for the size of the pool. Electricity here is the most expensive in Europe at Euros 0.18c per kwh and my previous pool pump 240v 1200w was near on 50% of the electricity bill hence the need for change, I opted for a DC pump 48v 500w which gave me enough flow rate and head pressure for my situation and it does work a treat running at around 3500 rpm. I am going to try just 2 panels in series to see if it helps the preformance as it would be interesting to see. Pete

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