Inverter with aux generator input

pcguy2upcguy2u Solar Expert Posts: 139 ✭✭✭
I'm contemplating a 6KW grid tie system with batteries and a generator as an alternate input. The Outback systems are very particular about sine waves and accept very few generator's (mine is a Generac 15KW) output.

The Xantrex XW seems to have everything I'm looking for with some exception. The PV array power feeds into the charge controller and not the inverter - seems strange. And the product has very little in the way of a proven track record.

Anyone one care to comment on the reliability of the XW system - I recall the SW suffered some pretty bad press when many of them were rebuilt not so long ago.

Also, I would like to make sure I don't overlook other good inverters that have that auxilliary generator input connection with some tolerance for generators with a fluctuating sine wave, as most seem to have.

Appreciate any input here...............

Many thanks,
Nick

Comments

  • Solar GuppySolar Guppy Solar Expert Posts: 1,962 ✭✭✭
    Re: Inverter with aux generator input

    The XW is no different than all other inverters, they run off batteries. If you want solar to charge the battery pack, then you need a solar charge controller, its an independent function. Same for the old SW line, Outback ect
  • pcguy2upcguy2u Solar Expert Posts: 139 ✭✭✭
    Re: Inverter with aux generator input

    Hi SG, somehow I missed something here. If an inverter is simply grid tie with no batteries, then isn't the connection made directly to the inverter??? I realize that there are systems that wire up differently, but my observation (hope I figured this out correctly) about the XW is that since the charge controller is limited to 60amps DC, then in order to reach the max of the XW 6k inverter, you need 2 charge controllers in order to pass that much current????

    If the inverter receives the array power directly (up to its max kw) it could then pass the needed current to the charge controller - or am I way off base here?

    Do you have any experience with the reliability of the XW?

    Thank again......
  • BB.BB. Super Moderators, Administrators Posts: 29,500 admin
    Re: Inverter with aux generator input

    Pcguy2u,

    Yes, you are correct... A 60am*60volt charge controller can only output 3,600 watts of power to the battery bank.

    Regarding the standard Grid Tied vs Off-Grid inverter... The functions look similar, but their internal control circuitry is vastly different....

    A typical off-grid inverter assumes an unlimited amount of 12 vdc power (current) and converts that to 120 VAC 60 Hz from 0-max current.

    A typical Grid Tied inverter assumes that the grid is 240 VAC 60 Hz (exactly, more or less), and assumes that the DC input voltage and current is variable, and depends on how much energy the inverter "sucks" out the solar panels, the input voltage and current will change. But the Grid Tied inverter tries to maximize the energy available from the solar panels by measuring I and V , and using the equation P=I*V. That is called Maximum Power Point Tracking (MPPT). It then takes that energy and dumps all of it into the utility power mains... Which, in effect, are the equivalent of a giant AC battery (voltage stays the same, but can supply or sink large amounts of current).

    So--the XW system, the inverters have a DC Battery input (constant voltage, any current available that is needed), and then has two output modes. One is the stand-a-lone inverter (240/120 VAC 60Hz) like any off grid type... The other, is an ability to synchronizes with the AC power line and push energy (current) into the power line as if it was an AC battery.

    I assume there is some sort of algorithm in the XW inverter that monitors the battery voltage/state of charge (and, possibly even the energy coming from the solar charge controller)... When on-grid--it needs to know how much power it should output to the grid--you don't want to discharge your batteries. And when off grid, it supplies the power needed to the home from the batteries--plus the option of starting a generator when the batteries need recharging.

    The batteries are the common point in the system--panels dump power to the solar charge controller to the batteries. The inverter takes power from the batteries, either for grid-tie or off grid power--plus the inverter can take generator power and charge the batteries too.

    It is a complex little piece of equipment--but so far, it does appear to work (don't know how many are out there--and there was some reports of early problems).

    The Xantrex GT 3.0 grid tie inverter I have, so far has been ticking along for almost 3 years with zero problems... I sure hope it continues.

    And, Xantrex, so far, has been pretty good about repairs and lower cost replacements of obsolete, unrepairable out of warranty units.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • pcguy2upcguy2u Solar Expert Posts: 139 ✭✭✭
    Re: Inverter with aux generator input

    Hi Bill, so are we saying that all grid tie inverters with battery backup accept their RE from the battery charge controller rather than directly from the array(s)? Or is the XW an exception, Or?

    Great dialog - thanks,

    Nick
  • BB.BB. Super Moderators, Administrators Posts: 29,500 admin
    Re: Inverter with aux generator input

    Nick,

    Uhhh.... yes, more or less...

    But, there are always exceptions... Solar Guppy has reported (thread somewhere here--but don't have time to look it up right now) where you set up an off grid system (inverter, battery, etc.) just like normal.

    Then, you have a normal Grid Tied inverter+panel setup. And, you connect the Grid Tied Inverter to the Off-Grid Inverter system... The off-grid inverter acts like the "utility" and sets the line voltage/frequency. And supplies current/energy to the AC loads--just like normal.

    The Grid Tied Inverter acts just like normal--tracking the Voltage/Frequency of the Off-Grid inverter, and pumping energy into the AC house circuit--to be consumed by your loads...

    But--it turns out that the off grid inverter is bi-directional... It acts like an inverter when out-putting power, but acts like a battery charger when receiving power from the Grid Tied inverter...

    The Skystream wind turbine system uses this concept with their AC Grid Tied inverter system, for off grid use... The "battery" charge monitor, will notify the Grid Tied wind turbine inverter to "turn off" when the battery is fully charged...

    This system is probably not quite ready for home use with Grid Tied Solar--but it is close--the issue is how to control your battery charging as the typical Grid Tied inverter has no battery feed back controls.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • pcguy2upcguy2u Solar Expert Posts: 139 ✭✭✭
    Re: Inverter with aux generator input

    One other question on the Xantrex XW. Do I understand correctly that the XW never puts power on the output side unless the grid is down. Is that correct and if not, does it make a difference if there is no load for a short or long time?

    Nick
  • BB.BB. Super Moderators, Administrators Posts: 29,500 admin
    Re: Inverter with aux generator input

    Nick,

    I am not sure I understand your question... I don't know the XW in detail--but I would assume it has an internal AC Mains transfer switch of some type...

    When it is in Grid Tied mode (utility lines are within voltage and frequency specifications), the inverter outputs "excess" solar panel power into the home's mains. The power is added with the Utility power--and if your home uses less power than generate, you pump energy "backwards" through your utility meter. If your home is consuming more power than you generate, then your meter spins forwards--just slower than with out the XW inverter.

    When you loose utility power, a transfer switch should open--isolating the XW's output to your home's internal wiring... The XW inverter then "turns on" in Off-Grid mode, powering your local AC wiring with energy from your batteries while monitoring the utility power on the AC mains input...

    Once the utility power is restored and stable for 5 minutes--the XW would turn off it output, switch back to AC Mains for power, then go into "grid tied" operation again (feeding power back into the utility mains).

    The above is a guess--but probably close enough for a first cut at understanding.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Solar GuppySolar Guppy Solar Expert Posts: 1,962 ✭✭✭
    Re: Inverter with aux generator input

    Think of the XW as a large UPS, the output is your load , the input is connected to a branch circuit off the Main breaker panel. Lose AC, the inverter seamlessly keeps the output up, regain AC at the input, the XW's output switches back to using the AC input ( about 10 second delay )

    In addition to being a UPS, it allows a second source of AC power ( generator ), its the only unit on the market that has the dual AC inputs

    The Gridtie is if the battery is above a threshold ( typically say 52V ), it will allow excess energy from the batterys to backfeed the AC mains input, depending of course if things are within UL paramters and the output load of the XW isn't using all the available generation

    The GT inverters ( Xantrex Brand name ) are completely different, they are direct PV to AC converters, but only send energy into an infinate load and have no ability of there own to be stand-alone inverters or use batterys in anyways
  • pcguy2upcguy2u Solar Expert Posts: 139 ✭✭✭
    Re: Inverter with aux generator input
    BB. wrote: »
    Once the utility power is restored and stable for 5 minutes--the XW would turn off it output, switch back to AC Mains for power, then go into "grid tied" operation again (feeding power back into the utility mains).
    -Bill


    Hi Bill, I think this question relates to where the RE power is standing when the XW is in grid tied mode - is the XW providing power to the house wiring when in that mode (via the output side of it's internal transfer switch)? Is it just feeding RE power to the grid/house via the grid tap or is it feed to both the grid and the loads at the same time?

    In other words, in my scenario (whole house feed), I want to feed the grid connection to the XW as a tap off of the grid input to my auto transfer switch. In that case, the 200amp buss is maintained through my existing auto transfer switch and when the grid goes down, the output from the XW would pass through to the whole house via the auxilliary input to my existing auto transfer switch and that auto transfer switch will only activate if the grid has failed (or somehow been turned off) and there is power to a control lead from some power source.

    See my block diagram below.......... BTW, if you are using Internet Explorer, double click on the image and then press F11 for full screen mode - the text will be somewhat clearer. Press F11 again to return to normal mode.

    What I'm trying to find out is whether or not the auxilliary input to my transfer switch will have power sitting on it when the XW is in grid tied mode? And if it does, would it make any difference if there is no load on it until the grid goes down?

    Thanks again Bill,

    Nick
  • pcguy2upcguy2u Solar Expert Posts: 139 ✭✭✭
    Re: Inverter with aux generator input

    Another thought - one other way to accomplish a standing load for the inverter would be to connect a couple of wall warts to the output side of the XW so that it always thinks there is a load (if that is a requirement)???

    nick
  • BB.BB. Super Moderators, Administrators Posts: 29,500 admin
    Re: Inverter with aux generator input

    Nick,

    I don't know--you may have missed Solar Guppy's post just above your a couple minutes earlier... Basically, the XW is a giant UPS with an alternate AC input for generator--very cool...

    Regarding your diagram... It does not make sense to me with using the Generac Transfer Switch. I see you are using it to allow you to turn off heavy loads before the XW transfer over?

    6 kW is a large inverter, and it can handle surges above 6kW (2x???). And given your 400 kWhr per month usage--it would sound like you don't have very large loads (A/C, electric hot water, etc.) that would trip the XW on startup...

    If you do have very heavy, but optional loads... You perhaps would be better to create a third distribution panel for those loads.

    Connect the Xantrex to the existing East/West panels, and move the optional loads to the new optional power panel through your XW+Gen and Utility feed. You can leave the Generac control line off and it will not power those loads until you manually switch.

    I see a question I would ask--What is the XW's transfer switch internal capacity--you are expecting to dump up to 15 kW through it (via the generator)--will it manage that power? Second, if you are planning on the 15+kW through the XW for normal utility operation (since you are worried about surges/short term heavy loads)--you may be over[stressing/over-subscribing/over-loading the XW transfer switch anyway.

    That Generac transfer switch in the middle of the system (your current drawing) sort of has me concerned... It, presumably, is the generator controller (utility monitoring, start, warm-up, operate, cool-down, monthly exercise, etc.)... So, great though needs to be used in using this with the XW system (which also includes generator control--so it can start your generator if your batteries are low and turn it off when done).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • crewzercrewzer Registered Users, Solar Expert Posts: 1,832 ✭✭✭✭
    Re: Inverter with aux generator input

    Nick,

    As you indicated, OutBack’s present line of utility-interactive (U-I) inverters typically do not operate well when using a generator as an AC power source. Additionally, all OutBack inverters must operate from a battery bank; we do not manufacture battery-less inverters.

    However, we’ve found that our U-I inverters do operate satisfactorily when connected to Honda inverter-type generators. Additionally, a fairly small battery bank is all that’s required if you’re not interested if any substantial back-up power capability.

    Please let me know if I can provide you with any additional information.

    Regards,
    Jim Goodnight
    “crewzer”
    Eastern Regional Sales Manager
    OutBack Power Systems
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