A better diversion for an AC coupled battery system?

SolaRevolutionSolaRevolution Solar Expert Posts: 407 ✭✭✭✭✭✭
I've done a few AC coupled projects; SMA Sunny Islands, Fronius into an Outback , Sunny Boy into an Outback. I have seen situations where I'd like to AC couple enphase systems to provide grid back-up or just to add to an existing off grid system. I keep ending up looking for the elusive perfect diversion controller. I would like to provide regulated charging while avoiding the use of a diversion load controller which dumps current directly from the battery bus. A shunting regulator can complicate EQ and other charging protocols for a non technical system owner.

Has anyone got any experience with AC-coupling a grid-tie type wind controller? It seems to me that this could make the wind generator "self contained" and allow the wind to disconnect via a simple high voltage disconnect relay.

Is there a big, reliable diversion controller? A large grid-tie PV inverter (>3kW) AC-coupled to a battery system can be a challenge too. (Not required for a Sunny Island System) It can be a challenge to properly regulate battery charging with a diversion load from a 6kW (or larger) source with no way to throtle it down. So far I've had to have the big GT inverters on or off and rely on a smaller DC-coupled array to provide regulated "finish" charging. One complication has been AUX voltage controlled relays without temp comp.

Any suggestions?:confused:

Comments

  • SolaRevolutionSolaRevolution Solar Expert Posts: 407 ✭✭✭✭✭✭
    Re: A better diversion for an AC coupled battery system?

    I've been checking out the Schneider XW (battery inverter) and GT (non battery inverter) AC coupling application note:
    http://www.global-download.schneider-electric.com/852577A4005D7372/all/8FA29D94B918A0FB8525781F0072FCA7/$File/ac-coupling-app-note(976-0240-01-01_rev-a).pdf

    (I have installed XW systems in many applications both on-grid and off. I have not yet AC coupled any of them.)

    The system has a firmware upgrade available which supports AC frequency shifting to disable the GT once the XW's battery voltage exceedes the Bulk set point.

    "The AC Coupling Module is a control strategy that varies the line frequency
    according to a predetermined pattern to cause a grid-tie inverter to cease
    producing power to avoid overcharging the system battery." - From the App Note.

    This is not regulated charging. This is Bulk Voltage Disconnect for the full output of the PV array.

    To have regulated charging with the XW/GT combination, or for that matter the XW/any non-battery inverter, requires either a seperate DC coupled PV Array or diversion system large enough to regulate the entire capacity of the non-battery inverter's PV output.
  • stephendvstephendv Solar Expert Posts: 1,571 ✭✭
    Re: A better diversion for an AC coupled battery system?
    Has anyone got any experience with AC-coupling a grid-tie type wind controller? It seems to me that this could make the wind generator "self contained" and allow the wind to disconnect via a simple high voltage disconnect relay.

    Sorry, no experience here, but I do like the idea of AC coupling a wind turbine :) I think the Xantrex XW or Sunny Island provide the most flexible solution for this, because you can then buy a standard wind turbine grid tie kit (turbine + GTI + dumpload) and then reprogram the GTI to cut out at exactly the right frequency, e.g. 62Hz. So instead of turning on the dump load at high voltage, it would start to dump when the SI or XW change the frequency, which means that you can put the turbine up anywhere along your AC line.

    Another idea might be to stick a frequency dependent relay anywhere on the AC line to turn on loads when there's excess power, e.g. turn on at 61Hz before the turbine disconnects at 62Hz. See DILCs at the bottom of this page: http://www.windandsun.co.uk/Inverters/sunny_island_inverters.htm
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