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Thread: Solar with UPS systems

  1. #1
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    Solar with UPS systems

    Current project is new build, 600amp 3phase, 208v service with an MDP feeding a 10kva UPS cabinet expandable up to 50Kva with a 200amp 3phase line to feed all the lights and outlets in the building. The customer now wants solar on the roof.

    I had the idea of utilizing the UPS battery system so we can generate power and be off-grid when the power goes out. Has anyone tried this?
    In designing the system, what would be the problems installing the solar system on the UPS load side panel to help feed the batteries? Or do most UPS systems not allow power generation/back-feeding into the battery bank?

    In researching, found one site offering 'Hybrid' UPS systems that incorporate solar but I expect the cost to triple.

    Because the UPS system has power optimizers and conditioners, wouldn't I be able to feed the UPS system through an ATS allowing solar to continue connection to the line side of the UPS even if the UPS is not a 'Hybrid' type? I guess this would mean connection of solar to a battery bank after the 3-phase inverters on each panel combined on the line side of the UPS feed and I don't know code on this.

  2. #2
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    A standard UPS is not designed to work with a PV system. So your results could be anything, but I don't think it would end well.

  3. #3
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    The specific problem is that a standard PV inverter (grid tie inverter) has no way of throttling back its output below what the PV is producing. That will cause problems when the load drops below that point.
    There is also the problem with providing a suitably stable reference voltage.
    On the other hand you can take a standalone battery powered inverter and feed it into the AC input of a UPS. But that requires a battery powered inverter and a PV driven charger, and there will be no benefit from the PV when the grid is up.
    The hybrid inverter gives you both functions at (hopefully) less than the cost of both systems separately.

    Sent from my XT1585 using Tapatalk

  4. #4
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    As said above, trying to do this with a UPS not designed for integration with solar it probably won't end well.

    At the UPS specs you mentioned, the newest generation of lithium storage solutions that are designed to work with solar are probably approaching the same price range. It would be a shame if those technologies were not considered early enough in your project to plan properly if they would be desired. Although, 3-phase options haven't really come along yet, with possibly Tesla Powerpack being the feasible exception. I'm a bit surprised you expect costs to triple, since the actual energy storage (and not inverters) is the bulk of the expense in such systems, and it's essentially the inverter that needs to change. But I'm not familiar enough with standard UPS offerings to say you're wrong on that. (Also, things will change a lot in the next few years.)

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