Install a grid-tie inverter behind a UPS

Hi,
we have quite a few black-outs here, am wondering if I could install a grid-tie inverter on the UPS-supported circuit to push the support-time of the UPS?

Comments

  • waynefromnscanadawaynefromnscanada Solar Expert Posts: 3,009 ✭✭✭✭
    Re: Install a grid-tie inverter behind a UPS
    Hi,
    we have quite a few black-outs here, am wondering if I could install a grid-tie inverter on the UPS-supported circuit to push the support-time of the UPS?

    So what do you propose as a power source to feed the grid-tie inverter? They are designed to take DC power, such as from a solar installation, and feed that energy out into the grid.
  • jaapkrijgerjaapkrijger Registered Users Posts: 6
    Re: Install a grid-tie inverter behind a UPS

    utility feeds ups
    PV feed GTI

    both UPS and GTI outputs are connected to UPS supported circuit(S)

    my main worries are:
    where will excess power from GTI go when running UPS on battery?
    Will GTI adjust to cycles of UPS when switching over to battery?

    rg,
    Jaap
  • GreenerPowerGreenerPower Solar Expert Posts: 264 ✭✭✭✭✭✭
    Re: Install a grid-tie inverter behind a UPS

    There are 2 potential issues with this:
    1 - Most UPS are mod-sine, grid-tie inverters might not sync to "sell" to the UPS AC output. True-sine UPS is OK.
    2 - When grid is down, the grid-tie would "back-feed" the UPS AC output (if it can sync). If the grid-tie "sell" power is more than loads, the UPS AC output might go poof.

    You would be better off using PVs and CC to charge directly the UPS batteries.

    GP
  • jaapkrijgerjaapkrijger Registered Users Posts: 6
    Re: Install a grid-tie inverter behind a UPS

    Thanks for this info, all understood, wouldn't the charging of the batteries limit the power from the solar to be only usefull when operating the UPS on battery, thus during black-outs? I'd like to maximize the power available from the PVs that's why I wanted to use a GTI
  • jaapkrijgerjaapkrijger Registered Users Posts: 6
    Re: Install a grid-tie inverter behind a UPS

    the UPS I have is an APC, as per the manual is't pure-sine so that question is answered OK, as for the feeding back on the UPS.... now that's one of my worries, could a diode help me here?
  • GreenerPowerGreenerPower Solar Expert Posts: 264 ✭✭✭✭✭✭
    Re: Install a grid-tie inverter behind a UPS
    Thanks for this info, all understood, wouldn't the charging of the batteries limit the power from the solar to be only usefull when operating the UPS on battery, thus during black-outs? I'd like to maximize the power available from the PVs that's why I wanted to use a GTI
    If you could find a grid-tie inverter that uses the same battery voltage as the UPS, you could run the inverter from the same UPS battery and "sell" to the AC input of the UPS and set the "sell battery voltage" slightly above float voltage. Well, you might as well replace the UPS with a grid-tie inverter with battery backup system. Or were you thinking of battery-less grid-tie ?
    ...as for the feeding back on the UPS.... now that's one of my worries, could a diode help me here?
    It's AC, so diode won't help. Depending of the DC-AC design of the UPS, if it's "bi-directional", the extra power would be "dumping" unregulated to battery - still no good.

    GP
  • jaapkrijgerjaapkrijger Registered Users Posts: 6
    Re: Install a grid-tie inverter behind a UPS

    from the diode reply, I see you have understood what I want to do, let me ponder over the feeding back by the GTI.
    the idea is to run battery-free on the solar system. in the original plan the GTI sits right at the meter, am just looking at how to maximize the use of the solar system, especially when dealing with a black-out... the outback inverters are extremely expensive... my GTI (250W) is only USD 150, the nearest outback is 10 times that amount...
  • GreenerPowerGreenerPower Solar Expert Posts: 264 ✭✭✭✭✭✭
    Re: Install a grid-tie inverter behind a UPS
    ...the idea is to run battery-free on the solar system. in the original plan the GTI sits right at the meter, am just looking at how to maximize the use of the solar system, especially when dealing with a black-out... the outback inverters are extremely expensive... my GTI (250W) is only USD 150, the nearest outback is 10 times that amount...
    So, you are thinking about the Enphase et al. inverters. You still can connect the AC output of the inverter to the UPS AC output but need to put in a "safe-guard" circuit to disconnect the inverter AC output when "AC in down" AND "load less than AC export" . A NC relay would do and the relay is activated on those conditions.

    GP
  • mike95490mike95490 Solar Expert Posts: 8,239 ✭✭✭✭✭
    Re: Install a grid-tie inverter behind a UPS

    Get a "hybrid" inverter GT & Battery (Xantrex XW series) and that is your solution.

    It is UPS when grid fails, and backfeeds when the sun shines.

    Oh, you need a MPPT battery charger for it. Go with 48V system, 8, 6V batteries in series.
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • jaapkrijgerjaapkrijger Registered Users Posts: 6
    Re: Install a grid-tie inverter behind a UPS

    The xantrex option is running into big figures, I'm going to have a look at the earlier option you gave me, thanks for the support
  • snuffysnuffy Solar Expert Posts: 72 ✭✭✭✭
    Re: Install a grid-tie inverter behind a UPS
    Hi,
    we have quite a few black-outs here, am wondering if I could install a grid-tie inverter on the UPS-supported circuit to push the support-time of the UPS?

    Maybe I misunderstand but it seems to me an inverter/charger and battery bank would do the trick. The inverter/charger keeps the batteries charged from grid power then switches to battery power and outputs 120 volts ac to your UPS when the grid goes down. I don't see where you need a grid tied inverter to solve this problem.
  • BB.BB. Super Moderators, Administrators Posts: 29,002 admin
    Re: Install a grid-tie inverter behind a UPS

    I believe that jaapkrijger is out of South Africa--So he may have limitations on the hardware available (at a good price) too.

    It sounds like he wants to optimize by using the panels to supply AC power when the power is good (save money) and keep the UPS's running when the power is down (save generator fuel).

    With a steady load (computers exceed GT Solar power on UPS)--it could be done--although it is a bit dicey--it would be possible that the UPS could become unstable if the GT solar exceeds the computer loads (something shut down)--would the UPS turn off, over charge the battery bank, or what?

    So, the easiest would be to set up a voltage controlled switch on the UPS battery bank... When the Battery Bank is over 14.5 volts (or whatever), it could turn of the the GT to AC power connection. When battery voltage falls (say 12.7 or so), the AC switch is turned back on (and possible 5 minute timeout on the GT inverter for reconnect).

    More or less, that is what some others have done (attempted) commercially (from what little I have seen).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • snuffysnuffy Solar Expert Posts: 72 ✭✭✭✭
    Re: Install a grid-tie inverter behind a UPS

    I didn't realize he had panels. I thought he was just looking for options to extend the run time of his UPS. Every APC UPS I've ever seen had a built in battery charger that run off 120 or 240 AC. An inverter charger and battery bank would give him the 120 AC the UPS needs and extend his run time on his UPS. Not sure whether his UPS needs pure sine wave to run it's charger but I doubt it.
  • BB.BB. Super Moderators, Administrators Posts: 29,002 admin
    Re: Install a grid-tie inverter behind a UPS

    It is possible that he could "back feed" the TSW UPS that he is using and have both Grid Tied step (used most of the time to reduce power bills) and when power is down, to support/recharge the battery bank with the panels (with the caution that we don't know his UPS is capable of being back fed, and he would probably need to put a battery charging control of some sort in place to prevent battery damage or worse).

    Could be done for much less money than installing a new Hybrid Inverter and stuff. Also, could be handy for the smaller installation where a 4+ kW hybrid inverter may be overkill.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • System2System2 Posts: 6,290 admin
    Re: Install a grid-tie inverter behind a UPS
    So, you are thinking about the Enphase et al. inverters. You still can connect the AC output of the inverter to the UPS AC output but need to put in a "safe-guard" circuit to disconnect the inverter AC output when "AC in down" AND "load less than AC export" . A NC relay would do and the relay is activated on those conditions.

    GP

    Hi, got intrigued by your relay idea. Any further lead as to where to find such thing?
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