grid tie inverter idle load

Ralph DayRalph Day Posts: 873Solar Expert ✭✭✭
During the process of planning a feed in tarrif grid tie installation I was asked the question by my wonderful wife:"what load does the grid tie inverter have, and powered by grid or solar?


Our off grid home Xantrex 4048 has a tare load of about 1kw per day. Our plan for the grid tie is to only have a revenue meter...no loads, or load meter. So, do grid tied inverters have a standby load or do they shut down after sunset and wake up after sunrise...or do they feed their electronics with grid power?

Just curious. Also curious about string inverter vs Enphase inverters. Any more comments there?

Thanks

Ralph

Comments

  • Solar GuppySolar Guppy Posts: 1,959Solar Expert ✭✭✭
    Re: grid tie inverter idle load

    Most GT inverters are 1 watt or less as they physicality disconnect from the AC when DC is not present with an internal relay

    As for you XW Tar, mine SCP is showing 11-14 watts idle load and that with the AC air handler as a 24/7 load ... how did you arrive at the 1kwh number?

    According to this

    http://www.xantrex.com/web/id/1858/DocServe.aspx

    "Idle consumption - search mode < 8 W"
  • Ralph DayRalph Day Posts: 873Solar Expert ✭✭✭
    Re: grid tie inverter idle load

    smack self on forehead...meant that having the inverter always on, no search mode, the tare load is about 1kwh per day. I still make that mistake...kw when I meant kwhour. (we need a dohh! smilie)

    I only calculated the tare load by observing the T500 meter amp display when the house ac was zero (open main breaker), and multiplied by 24, multiplied by 50vdc (actually closer to 1.5kwH). When first commisioned i used a 1kw inverter for parasite loads (vcr, fans always on), but found that it only saved about 50watt hours in a day while the main inverter was in search mode (ie overnight). Not worth the bother.

    So if my grid tied setup disconnects from ac automatically, and no other ac source is available (revenue only hookup), are any user difined settings held in non-volatile memory...or does that depend on the brand? (any kind of industry standard?)

    THanks

    Ralph
  • Solar GuppySolar Guppy Posts: 1,959Solar Expert ✭✭✭
    Re: grid tie inverter idle load

    You need to be careful of using something with a 500 amp shunt to find a Tar load, the meters resolution is in the noise floor at sub amp levels which is what your trying to measure.

    I'm certain the XW isn't 1kWh/Day Tar load. Typically accuracy of the 500 on the end of scale might be quarter to half and amp, best case using this large shunts and at 50 volts is a BIG difference in the watts measured for checking Tar.
  • mikeomikeo Posts: 385Solar Expert ✭✭✭
    Re: grid tie inverter idle load
    meant that having the inverter always on, no search mode, the tare load is about 1kwh per day. I still make that mistake...kw when I meant kwhour.

    This is in line with the power draw I found for my SW4024 when in SELL mode. The idle mode does not work in sell mode so the inverter is on 24/7 drawing power. The manual specs 16 watts for no load when the inverter is on but I believe it to be more. I have a kw/hour meter on my inverter AC1 input and when I would harvest say 4 kw by sunset (output to the grid) by the next morning the kw/hr meter would read closer to 3 kw. This is why I built the Basic Stamp controller that turns off the SW inverter after the MX60 indicates PV current drops to less than 1 amp.
  • Solar GuppySolar Guppy Posts: 1,959Solar Expert ✭✭✭
    Re: grid tie inverter idle load

    For the casual reader, the SW ( 1994-2004 ) have nothing in common with the current XW line produced by Xantrex.

    The XW is every way is more efficient than the old SW line.
  • RCinFLARCinFLA Posts: 1,280Solar Expert ✭✭✭
    Re: grid tie inverter idle load

    If the inverter is running (switching) the SW series is about 35 watts, the XW is about 25 watts.

    You can probably set time of day or battery voltage based sell mode allowing inverter to go into bypass mode at night.

    On XW, being UL1741 certified, I think it will push to grid if battery is raised by solar controller above inverter float charge setting and AC load is not able consume the solar power pushed at batteries. This would be regardless of whether sell mode was invoked. The power has to go somewhere and pushing it to grid is much better alternative then running the batteries at a solar controller higher float voltage.

    I am not super familar with XW but the only way it could avoid the grid push is if the Xanbus tells the solar controller to back down on power pull from solar panels. The only reason I can see this making any sense, versus pushing to grid, is if the grid is actually down.
  • Solar GuppySolar Guppy Posts: 1,959Solar Expert ✭✭✭
    Re: grid tie inverter idle load

    XW requires sell mode enabled in two places too sell, it will not by default sell if battery voltage is raised. If the Battery's hit the Over Voltage threshold, the inverter will turn itself off
  • RCinFLARCinFLA Posts: 1,280Solar Expert ✭✭✭
    Re: grid tie inverter idle load

    Sounds like only solar controller that can be used with XW inverter is XW solar controller.
  • Solar GuppySolar Guppy Posts: 1,959Solar Expert ✭✭✭
    Re: grid tie inverter idle load

    Why is that?, I have run 4 different manufactures chargers with mine ... no issues
  • RCinFLARCinFLA Posts: 1,280Solar Expert ✭✭✭
    Re: grid tie inverter idle load

    I don't see why you wouldn't want the XW inverter to push to grid if solar power output exceeds ACout load demand unless the power company forbid it.

    Without Xanbus, on say MX60 controller, even if float voltages are set the same there is tolerances that may have solar controller float voltage slightly higher then XW float level. If you want good UPS functionality you don't want inverter to shut down.

    It takes several cycles to get large hunk of iron transformer to steady state from an inverter inactive state versus less then one cycle for parallel active inverter running condition just opening AC1 relay.
  • Solar GuppySolar Guppy Posts: 1,959Solar Expert ✭✭✭
    Re: grid tie inverter idle load

    Possibly your confusing the different components and their regulation for the batteries

    For starters, the charge controllers will never push the battery above there safe voltages ... If I understood your post you were concerned that to much solar will boil the battery's, that's simple not how it works.

    The Solar and Charge controllers are independent of the inverter and ANY charge controller properly rated can be used with any inverter , the only common link is the battery bank.

    Now Outback and Xantrex have link ability's to help improve smooth selling, but its not required and works fine without this data link.

    So I'm at a loss at what your point is?.
  • BB.BB. Posts: 27,354Super Moderators admin
    Re: grid tie inverter idle load

    If I understand the XW setup correctly.. The XW Inverter is a proportional "dump controller"... Basically "diverting" excess battery charging current from the solar panels to the AC Grid (a good thing). The XW does the charge controlling and, normally, just sets the float voltage of ~52 VDC (for 48 VDC battery system) after the batteries have been charged.

    The Solar MPPT controller has its levels set above the XW float/charging settings so that the MPPT controller is (most of the time) just transferring as much power as possible from the solar PV array to the battery bank. The MPPT charge controller will only take over in the case if the XW Inverter is unable to "dump" the load (Utility Grid is down, XW inverter is running in Off-Grid Mode, XW Inverter is down, etc.).

    So the MPPT Charge Controller only control's the battery bank state of charge when XW is off-grid or as a "back up controller" when necessary. There is no need for communications between the XW Inverter and a good quality MPPT Charge Controller.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • RCinFLARCinFLA Posts: 1,280Solar Expert ✭✭✭
    Re: grid tie inverter idle load

    Guppy said XW inverter will shut down to avoid pushing to grid if battery voltage rose above its battery float setpoint. I take this to mean if the solar controller's setpoint is slightly higher then XW's, and there happens to be light load on ACout, the XW inverter will shut down to avoiding having to push excess power to grid.

    Maybe the Xanbus communication between XW inverter and XW charge controller can resolve this but with an MX60 the communication doesn't exist.

    I have equipment that is sensitive to glitches in power and need to keep inverter running to get the less then a cycle switchover.

    If no sell means totally no grid push then why not let the inverter ride up on the higher then XW inverter float voltage set point battery voltage resulting in no push to grid and keeping the inverter active. I don't see the reason to shut inverter off if battery rises above XW inverter float set point. If sell is enabled, or ACout load is sufficient THEN let the inverter parce power off the excess battery voltage.
  • BB.BB. Posts: 27,354Super Moderators admin
    Re: grid tie inverter idle load

    A Grid Tied Inverter always tries to push as much energy to the utility grid as it can. It just checks that the grid voltage/frequency is in specifications, and that the battery input voltage is in specifications--and of course, that its total power (say 3kWatts for a 3kW inverter) meets its internal settings.

    A grid tied inverter is always trying to output the maximum power available (such as the panel Vmp and Imp for a panel connected inverter, or the Battery Set Point voltage for a battery based GT inverter).

    When the wiring system is designed... the breaker panel, the circuit breaker for the GT inverter circuit, and the wiring to the GT inverter are all designed to handle the maximum current for the particular installation. You could have too small of gauge of wiring, or too small of breaker--and the GT inverter will not know the difference (until the wire fails or the breaker opens).

    The XW is a hybrid inverter such that it can do GT (Grid Tied) or Off Grid (behind a an internal transfer switch)--depending on the mode required (GT for grid, or Off-Grid when the power fails or it is an off grid system). Because the operations of the Hybrid Inverter are so different (GT is "slaved" to the grid voltage and frequency and outputs current based on how much energy is available from the battery input--vs the Off Grid Mode where the inverter sets the Voltage and Frequency and only output current based on needs of the load)--It is difficult to explain "how the XW functions" without describing which mode you are talking about.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Solar GuppySolar Guppy Posts: 1,959Solar Expert ✭✭✭
    Re: grid tie inverter idle load
    RCinFLA wrote: »
    Guppy said XW inverter will shut down to avoid pushing to grid if battery voltage rose above its battery float setpoint. voltage.

    I suggest you re-read my posts, I said over voltage would shutdown the inverter ( default is 66V I believe ) I said nothing about a float voltage. That specific post was to correct your post about the XW selling un-commanded if the battery voltage was raised due to it having UL-1741 listing which is false

    Maybe I'm to short with my responses so I'll say this, BB is 100% correct in explaining how these Hybrid inverter can sell. This isn't meant to be a personal thing but what you have written isn't correct for how the XW-6048 works and I was just trying to point out some specific points.

    Having a All Xantrex is nice, but not for performance, more from the monitoring, BTS sharing and fit and finish using all the boxes that match.
  • RCinFLARCinFLA Posts: 1,280Solar Expert ✭✭✭
    Re: grid tie inverter idle load

    I know all what you and BB said. I also know you are a Xantrex advocate.

    If the XW is not allowed to push to the grid unless absolutely commanded to, then it must allow the battery voltage to rise (from solar controller) without drawing any more power from the battery input then can be consumed by ACout. Other alternate would be to shut down the inverter.

    On the old SW series the battery float set point was a strict regulated value. I wrote a long time ago on how this caused an undesireable issue when putting multiple SW's on same battery bank, like series stacking. One inverter would suck power from the battery lines while the other pushed power to battery lines. During float, net 0.3 amps going to maintain battery while inverters were throwing 5 to 20 amps between them. Aggrevating the issue was the incremental temp comp steps from temp sensors. They increment on discrete steps on about 2 deg. change. Due to tolerance between the two inverters one may have jumped to higher temp comp voltage increment while the other inverter was on lower increment point. This cause the thrashing between inverters to go almost to there max charge current setpoint limits.

    I just don't like idea of shutting down inverter if not allowed to push to grid. Again, I am saying this to give UPS quicker recovery then if inverter was shut off.
  • BB.BB. Posts: 27,354Super Moderators admin
    Re: grid tie inverter idle load
    RCinFLA wrote: »
    If the XW is not allowed to push to the grid unless absolutely commanded to, then it must allow the battery voltage to rise (from solar controller) without drawing any more power from the battery input then can be consumed by ACout. Other alternate would be to shut down the inverter.
    ...
    I just don't like idea of shutting down inverter if not allowed to push to grid. Again, I am saying this to give UPS quicker recovery then if inverter was shut off.

    I am not quite sure which mode you are typing about (I am guessing here--but I type longer sentences than Solar Guppy so it may be easier to understand me--assuming I am correct :roll:)...

    If the first paragraph is in GT Mode (connected to utility), The AC1 In and AC Out connections would be just "pass through" -- I.e., just a copper to copper electrical connection. The GT inverter (in GT Mode) would not care which direction energy was passing (out AC out or through the AC1 In -- ignoring current limit settings--if any).

    The GT Inverter (for a guess) sees 52.00 VDC, it "turns on", sync's with the AC1 Input voltage/frequency, and outputs 0% power. If it sees the battery at 52.5 VDC, it outputs 50% of rated power. If it sees >53.00 VDC, it outputs 100% of rated power. (This could be a PID controller too--but that would make the issue more complex and really does not change the fundamental operation of the GT inverter). Basically--it is probably "that simple" (remember, the devil is in the details).

    If the inverter detects AC1 Input voltage/frequency out of specifications, the transfer switch opens the AC1 Input connection and switches over to Off-Grid Mode (should be able to do this within ~1/2 cycle--that is the "typical" UPS specification for fail-over operation). From this point on, the XW inverter operates just like any other ordinary Off-Grid Inverter pumping 120/240 VAC out AC Out and supplying the energy needed to keep the loads happy; with an integral battery charger powered from AC2 In (again--with respect to Solar Guppy and Xantrex--there are a lot of details and a lot of work to make something like this work well--I am way over simplifying for basic understanding--and making lots of guesses on how it works).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • RCinFLARCinFLA Posts: 1,280Solar Expert ✭✭✭
    Re: grid tie inverter idle load

    Guppy was referring to the the 70 vdc red-line (for 48v versions) for inverter shutdown. In the context of previous discussion of selling when solar raised battery above inverter charge setup, I mis-interpreted his statement of inverter shutdown to exceeding voltage of inverter charge setpoint.
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