Creative way to harness excess DC power in oversized system?

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  • coffeeshopdj
    Junior Member
    • Jul 2019
    • 1
    #1

    Creative way to harness excess DC power in oversized system?

    My SolarEdge SE5000 (c.2012) is oversized by almost 2x.
    System peaks at 5250 watts, at which time the excess power is clipped (audible buzzing from the inverter). It has been operating this way for over a year.
    Without re-configuring the panels, I want to be able to harvest the extra DC power before it is clipped by the inverter.
    Ideally - I would like to have some control over *when* I could take the excess (ie, only when the inverter is generating 5000+ watts), since, I would rather maximize the FIT payments than use all of the power myself.
    If I measure the DC voltage at the inverter terminals (or, look at the display) - I can see between 350V and 415V. I wonder if I could leverage the fact that the optimizers (P400's) are delivering 350V or higher in full-sun situations?

    The loads that I would like to power from the extra power are as follows:
    • Resistive DC element (to float in the swimming pool); or AC, or contained in an old hot-water tank inline with the plumbing returns; any suggestions on this - I guess it needs to operate at 350V and higher?
    • Continuous duty submersible waterfall pump; currently a 120V AC model (1/3HP, 3.4A); although, I could change this to a DC motor if it were necessary to do-so

    Perhaps for the resistive heating element, I could directly connect to the 350-415VDC terminals, and, the power drawn will be limited by the heating element itself (say a 3000 Watt element)? I think it should not matter if that element is AC or DC rated?

    Would something like this work: http://www.vicorpower.com/documents/...13D0yzz_ds.pdf combined with a pure-sinewave inverter from 12VDC to 120VAC for the pump? Any less expensive suggestions?

    Thanks!
    Tags: diy, dump load, pump, solaredge, water heating
    • ButchDeal
      Solar Fanatic
      • Apr 2014
      • 3802
      #2
      Originally posted by coffeeshopdj
      My SolarEdge SE5000 (c.2012) is oversized by almost 2x.
      System peaks at 5250 watts, at which time the excess power is clipped (audible buzzing from the inverter). It has been operating this way for over a year.
      If that is an SE5000A from 2012 then you are WAY over the allowed DC on that inverter and have voided the warranty.

      Originally posted by coffeeshopdj
      Without re-configuring the panels, I want to be able to harvest the extra DC power before it is clipped by the inverter.
      Ideally - I would like to have some control over *when* I could take the excess (ie, only when the inverter is generating 5000+ watts), since, I would rather maximize the FIT payments than use all of the power myself.
      If I measure the DC voltage at the inverter terminals (or, look at the display) - I can see between 350V and 415V. I wonder if I could leverage the fact that the optimizers (P400's) are delivering 350V or higher in full-sun situations?

      The loads that I would like to power from the extra power are as follows:
      • Resistive DC element (to float in the swimming pool); or AC, or contained in an old hot-water tank inline with the plumbing returns; any suggestions on this - I guess it needs to operate at 350V and higher?
      • Continuous duty submersible waterfall pump; currently a 120V AC model (1/3HP, 3.4A); although, I could change this to a DC motor if it were necessary to do-so

      Perhaps for the resistive heating element, I could directly connect to the 350-415VDC terminals, and, the power drawn will be limited by the heating element itself (say a 3000 Watt element)? I think it should not matter if that element is AC or DC rated?

      Would something like this work: http://www.vicorpower.com/documents/...13D0yzz_ds.pdf combined with a pure-sinewave inverter from 12VDC to 120VAC for the pump? Any less expensive suggestions?

      Thanks!
      It is not safe and way outside code to be playing around with DC above 50V like this. and it surely will effect the safety and the operation of the system having some odd load on the DC side interrupting the communication.

      Your best solution would be to add another inverter or replace your current inverter with a larger HDWave version.
      Is all of the PV in the same tile and azimuth? is there shading?
      OutBack FP1 w/ CS6P-250P http://bit.ly/1Sg5VNH

        Comment

        • bcroe
          Solar Fanatic
          • Jan 2012
          • 5203
          #3
          The only practical solution is increase the size of your inverter plant to avoid clipping. On a
          ground mount it would be possible to completely rearrange panel orientation to produce a
          much longer, lower level peak power such as I have done. Bruce Roe

          NScurJn17.jpg

            Comment

            • NochiLife
              Member
              • Jun 2019
              • 63
              #4
              Originally posted by coffeeshopdj
              My SolarEdge SE5000 (c.2012) is oversized by almost 2x.
              System peaks at 5250 watts, at which time the excess power is clipped (audible buzzing from the inverter). It has been operating this way for over a year.
              Without re-configuring the panels, I want to be able to harvest the extra DC power before it is clipped by the inverter.
              Ideally - I would like to have some control over *when* I could take the excess (ie, only when the inverter is generating 5000+ watts), since, I would rather maximize the FIT payments than use all of the power myself.
              If I measure the DC voltage at the inverter terminals (or, look at the display) - I can see between 350V and 415V. I wonder if I could leverage the fact that the optimizers (P400's) are delivering 350V or higher in full-sun situations?
              ONLY if you are VERY electrically literate. Proceed at your OWN risk only.
              Firstly, you will NEED a DC-rated breaker, at least 500vDC rated. (These can be found on eBay,) Please note that there is a BIG difference between an AC-rated breaker, and a DC-rated breaker; they are not interchangeable. Watch these YouTube videos BEFORE doing anything with that voltage:
              - What happens if an AC-rated breaker is used on a DC circuit: https://www.youtube.com/watch?v=csMQ9A-4Pws
              - What happens if a DC-rated breaker is connected backwards: https://www.youtube.com/watch?v=Cup5fMGaE2g


              The loads that I would like to power from the extra power are as follows:
              • Resistive DC element (to float in the swimming pool); or AC, or contained in an old hot-water tank inline with the plumbing returns; any suggestions on this - I guess it needs to operate at 350V and higher?
              • Continuous duty submersible waterfall pump; currently a 120V AC model (1/3HP, 3.4A); although, I could change this to a DC motor if it were necessary to do-so

              Perhaps for the resistive heating element, I could directly connect to the 350-415VDC terminals, and, the power drawn will be limited by the heating element itself (say a 3000 Watt element)? I think it should not matter if that element is AC or DC rated?
              - A resistive element is a standard choice for "dumping" excess power. A standard water heater element will work just fine on DC, though keep in mind that the "220vAC" rating on such elements is the RMS rating (yes, it peaks intermittently at 360v), but the equivalent DC rating would be 220vDC. (You could put two heating elements together to get 440vDC rating.) If you ran a 220vAC element on 400vDC, it'll use way more power than it's rated for, and likely burn out fairly quickly. Yes, you could connect it to the DC terminals WITH A PROPERLY DC-RATED BREAKER! 100vDC will easily throw a one-inch arc. 400vDC? I don't want to know.
              - A synchronous AC motor (capacitor start, etc.) will NOT run on DC. Actually, putting DC voltage on such motors will turn them into a very nice brake (though they will quickly burn out if run at such DC voltages.)

              - The difficulty with this voltage is that it exceeds 360vDC. Otherwise, you could run certain 220v appliances (with a switch-mode power supply, i.e. computer power supplies, inverter-based air conditioners, etc.) directly off of the DC supply.


              Would something like this work: http://www.vicorpower.com/documents/...13D0yzz_ds.pdf combined with a pure-sinewave inverter from 12VDC to 120VAC for the pump? Any less expensive suggestions?

              Thanks!
              The problem with that DC-DC converter is that I'm certain that the Voc (open circuit voltage) of your solar array is far higher than the converter's rated maximum of 415vDC. At high DC voltages (actually, for that matter, at 55vDC), flipping a breaker can easily cause a "surge" that will exceed that voltage, and blow the expensive converter out. (I'm having problems on my DIY hobbyist stuff with the LM3414HV, which is rated for 65vDC, but it readily blows out at 55v due to a power-up surge.)

              Probably the easiest way to use the excess power (though not the cheapest) would be a 600v-rated MPPT. Working with 48vDC is a lot safer, and easier (though you would need a small battery bank). NOTE that if you're on a grid-tie system, you might get into troubles pretty fast with the authorities with any modifications of the system.

                Comment

                • ButchDeal
                  Solar Fanatic
                  • Apr 2014
                  • 3802
                  #5
                  Originally posted by NochiLife
                  ONLY if you are VERY electrically literate. Proceed at your OWN risk only.
                  Firstly, you will NEED a DC-rated breaker, at least 500vDC rated.

                  - A resistive element is a standard choice for "dumping" excess power. A standard water heater element will work just fine on DC, though keep in mind that the "220vAC" rating on such elements is the RMS rating (yes, it peaks intermittently at 360v), but the equivalent DC rating would be 220vDC. (You could put two heating elements together to get 440vDC rating.) If you ran a 220vAC element on 400vDC, it'll use way more power than it's rated for, and likely burn out fairly quickly. Yes, you could connect it to the DC terminals WITH A PROPERLY DC-RATED BREAKER! 100vDC will easily throw a one-inch arc. 400vDC? I don't want to know.
                  - A synchronous AC motor (capacitor start, etc.) will NOT run on DC. Actually, putting DC voltage on such motors will turn them into a very nice brake (though they will quickly burn out if run at such DC voltages.)
                  OP has a SolarEdge DC optimizer system. Are you familiar with this type of system?
                  Any set up as suggested is going to void the warranty, is not to code as well. The inverter would likely throw an error and shut down if a major resistive load were tossed into the mix and would likely make the rapid shutdown system behave erratically.
                  OP needs a larger inverter or second inverter.
                  OutBack FP1 w/ CS6P-250P http://bit.ly/1Sg5VNH

                    Comment

                    • NochiLife
                      Member
                      • Jun 2019
                      • 63
                      #6
                      ButchDeal No, I am not familiar with that type of system; I fully agree with all of your statements. Grid tied systems are a completely different beast, and for very good reason.
                      Perhaps the problem is that I'm the kind of person who looks at something and says, "I wonder what other way I could use it?" I personally have wired up a waterbed heating mat through a solid state relay and thermostat to my solar panels (at MY risk) to keep my LiFePo4 battery bank warm in wintertime charging conditions. It absolutely kills output power from the MPPT (which is automatically switched off via MODBUS until the bank warms up above freezing)...but it gets the job done.

                      As you pointed out earlier, OP is well over the maximum input voltage of the inverter anyway (likely the cause for the audible buzzing)...and if the warranty is already void, well...enough of my reasoning . But I would not do any such experiments to a grid-tied system. Which this is.

                        Comment

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