SW 4024

trumpets3utrumpets3u Solar Expert Posts: 35 ✭✭✭
I'm off the Grid here but what I would like to know is, if I did tie to the grid to charge my batteries. Now if my batteries are full from the solar charging will it send power back to the grid? If so is there a setting to stop it from doing so?
Thanks Brian


  • BB.BB. Super Moderators, Administrators Posts: 32,817 admin
    Re: SW 4024

    Most SWxxxx family inverters did not have a Grid Tie option connected (as I understand). So, there should be no physical way for the SW inverter/charger to drive power back to the grid that I am aware of...

    There was an option that allowed SW connections (GTI--Grid Tie Interface)--But that was not common and withdrawn from sale many years ago (did not meet updated GT specifications)... This is all from my memory, so I may have some of this wrong.

    Most all inverter/chargers are one way only--Draw power from the grid for local AC power and battery charging. They are not physically capable of driving energy back to the grid unless specifically designed and configured (like the Xantrex XW or the Sunny Island families).

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • trumpets3utrumpets3u Solar Expert Posts: 35 ✭✭✭
    Re: SW 4024

    Thanks. What I want to do is bring a small line from my barn about 500 feet away (120V 20 amps) and tie it to the inverter, It has a grid tie and and Generator in put on it, so I don't have to run the generator.
    Thanks Brian
  • boBboB Solar Expert Posts: 1,012 ✭✭✭✭
    Re: SW 4024

    The Trace SW inverters were grid tie from the beginning. At least from around
    1993 or so.

    The GTI was WAY later, like, 1999 or 2000 and I understand that
    they actually did sell back even without the GTI attached
    which was basically just an inductor to reduce current distortion.

    That whole GTI thing was a big farce and they were forced into having
    to use it because of the way the SW works and some folks at the competition
    didn't like it.

  • trumpets3utrumpets3u Solar Expert Posts: 35 ✭✭✭
    Re: SW 4024

    So Bob can I safety do this tie with out sending power back to the grid?
  • RCinFLARCinFLA Solar Expert Posts: 1,470 ✭✭✭✭
    Re: SW 4024

    Depends on how old the unit is, somewhere there is tread that I looks up when the software was changed to prevent grid power push. I think I remember it to be around 1998 or 1999 with software rev 4.01 allowing it.

    Then came UL1741 and the design got in trouble that was not easy to remedy. They tried a rather bad grid tie adaptor that was a large series inductor in the grid input line to allow the rather coarse adjustments of SW series to test for grid presences without overloading the inverter and stressing the batteries. It was a bad bandaid.

    On the earlier software if battery voltage is raised above the charger set point the inverter will push out the excess trying to keep the battery charger regulated voltage. It will either be consumed by ACout load or go back out the AC in port. On later software, without the GTI adaptor box there will be a short period of reverse push to grid (or AC loads), if excesss battery voltage continues beyond the allowed time period then the inverter will shut off to prevent reverse power push. (AC passthough to output in not interrupted) Your PV controller would then control the battery charge voltage regulation.

    As to old units in use, they don't pass the present regulations (UL1741) but no damage will occur to your equipment. This is is when the grid goes open circuit with a light enough load to not overload the inverter. This case probably happens about 0.001% of the time the grid goes down. Usually when the grid goes down the inverter see a very heavy load that trips the overload sense immediately releasing the relay that couples the inverter to the grid. (your AC continues on inverter battery supply)

    A case for the 0.001% grid drop might be your common pole transformer primary breaker releasing due to some momentary overload on your particular pole transformer. If your neighbor is also connected and not drawing too much power, your SW4024 could supply you and your neighbor. The primary high voltage side of the pole transformer (with open circuit breaker) will have the the 25kV (depends on your neighborhood setup) which might surprise the power company service man. They are taught to always assume the line they work on is live. Once I had a wild parrot poking around the high voltage primary side transformer insulator. There was a loud pop, toasting the parrot and causing the transformer's primary side breaker to blow. This is exactly what the UL1741 spec is designed to detect but the old SW series would not, unless the neighbor's load overloaded the SW inverter.
  • Ralph DayRalph Day Solar Expert Posts: 986 ✭✭✭✭
    Re: SW 4024

    I have my SW4048 doing just what you want to do. In the garage, where there is grid power (and my generator) there's a "generator panel". You can select generator or grid supply to it, and your house feed is just one of the circuits. It's all using the AC2 input intended for generator. The inverter's generator controls are used to control the charge. Right now the system is float charging the batteries until the sun comes up in the morning (and the time of use price goes up).

    If the grid goes out, or you need to exercise your generator, you just flip the breaker from utility to generator. No chance of backfeeding if your inverter is in FLOAT mode and you're on AC2.

  • SolaRevolutionSolaRevolution Solar Expert Posts: 410 ✭✭
    Re: SW 4024

    The SWs will not sell (with or without the GTI) unless you set it to "SELL" in menu 9.

    Inverter Setup 9
    Set Grid Usage

    "FLT mode does not sell excess power into the utility grid" - SW manual (With Revision 4.01 Software)

    -Alex Aragon
  • boBboB Solar Expert Posts: 1,012 ✭✭✭✭
    Re: SW 4024

    Another thing that happened around the time of the GTI was when Sandia labs (with a push from certain others) found that connecting
    a 60 Hz resonant R-L-C circuit up to the SW's grid side was that it was able to make it island.

    UL1741/IEEE1547 then added this circuit to the testing requirement and later lowered the "Q" requirement for some reason. That resonance had a very low
    chance of happening of course.

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