Both Off-Grid AND On-Grid Combo Inverter???

x_logo
x_logo Registered Users Posts: 12
I've searched a bit and did not find much. Any advice would be helpful.

Is there an on-grid inverter available (5kW) which, upon utility power failure and once the main breaker is manually placed in the off position, will work off-grid - that is, provide regulated 120VAC to the household branch cricuits?

The on-grid inverters I've studied all shut down and become inoperative during a power failure -- they require the grid voltage to snyc.

It would be nice to use the solar system to backup the grid to provide power during emergency and utility imposed blackouts (like during peak load rationing.)

If there is no such inverter available what might be the other cost effective choices?

Thanks for any info.

Comments

  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Both Off-Grid AND On-Grid Combo Inverter???

    what you are looking for is a battery based gt inverter as there would not be any that are batteryless that will work without grid power. xantrex's xw inverter will handle that much power for a single inverter, but others will work as well if stacked.
  • x_logo
    x_logo Registered Users Posts: 12
    Re: Both Off-Grid AND On-Grid Combo Inverter???

    Thanks for the info.

    The Xantrex is a great hunk of hardware. Except I don't think I need much battery backup power.

    My main concern is that government actions will eventually reduce energy supply (power plant capacity) while population and economic growth will increase demand, resulting in rolling blackouts during peak load periods. (Remember California a few years back?) So the backup is needed precisely when solar output is greatest: when air conditioning, commercial, and industrial demand are high, in late afternoon. My bet is power would likely be restored by nightfall, when the peak commercial and industrial demand is reduced a bit.

    At the moment the most cost effective solution is simply a generator patched temporarily into the breaker box, leaving the solar idle. Pretty dumb but cost effective in keeping the fridge and other stuff running for a few hours for a few days (weeks) during summer. This is only a temporary fix however as generators will eventually be banned under pollution regulations.

    Rock meet hard place.
  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    Re: Both Off-Grid AND On-Grid Combo Inverter???

    be carefull doing something like that as that really isn't allowed due to safety reasons without being properly interfaced. the problem is 2 fold here as one doesn't want a lineman electrocuted and when the power comes on you don't want to see your genny go poof or even bang. what you elect to do is on you as it will be totally your decision.
    even if you won't need an inverter for long you specified 5kw and an inverter like that will need a hefty battery bank.
    i can see banning generators for some non emergencies or when alternative sources of power are reasonably available, but not an all out ban under any circumstance.
  • x_logo
    x_logo Registered Users Posts: 12
    Re: Both Off-Grid AND On-Grid Combo Inverter???

    Of course an approved transfer switch is required for generators to safely connect to the mains.

    On the prohibition of generators -- you are right; on further thought it is doubtful that they would be prohibited outright -- that would be un-American.

    However.....

    In Southern California generators over 50 HP are already limited by law to 200 hours of operation or the owner is subject to a fine. This specifically includes using the generator for emergency backup for intentional blackouts, in addition to routine testing and periodic unplanned outages.

    http://www.aqmd.gov/permit/fact_sheet_emergency_backup_gen.htm

    This is, of course enforced through permits and by physical inspection of hourly meters by the Generator Police. My guess is you don't pay the fine you go to jail.

    So the mechanism is already in place to render your backup generator mostly useless by: 1) reducing the horsepower from 50 to 5 and 2) reducing the maximum hours of use from 200 to 20.

    See, no prohibition, just a little more regulation. California is again blazing the way.
  • vcallaway
    vcallaway Solar Expert Posts: 157 ✭✭✭✭✭
    Re: Both Off-Grid AND On-Grid Combo Inverter???

    Where I am a grid tied system is not cost effective. I'm not even going to bother with a grid tied inverter.

    I have a setup in my house that automatically switches to battery power in the event of a power outage. The automatic switch will use generator power when the genny comes online.

    If I were starting over I would probably buy a Xantrex unit designed for RV use. They have some all in one units that charge the batteries and act as an automatic transfer switch. I would just use the generator to charge the batteries. The sine wave inverter is going to be cleaner power than the generator can put out.

    As others here have stated conservation is really your friend. We spent a lot of time determining what things in our house eat electricity. Because it is cheap here conservation is not really something people pay that much attention to. We found that our clothes dryer was responsible for almost half of our power usage. We have since converted our heat, cooking and dryer to propane. That is more cost effective than increasing capacity. The dryer alone was worth about 300kw a month.

    I am getting ready to start playing with solar. Not for grid tie but to run off of. I'm starting with one room and will go from there. Knowing how much power is needed is step one. It is pretty expensive for an average home to go full solar.

    The fewer things in your home that require power the less you will miss when there is no grid.
  • mike95490
    mike95490 Solar Expert Posts: 9,583 ✭✭✭✭✭
    Re: Both Off-Grid AND On-Grid Combo Inverter???
    x_logo wrote: »
    1) reducing the horsepower from 50 to 5 and
    2) reducing the maximum hours of use from 200 to 20.

    Where did you see 5hp & 20 hours ?
    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 ,

  • stephendv
    stephendv Solar Expert Posts: 1,571 ✭✭
    Re: Both Off-Grid AND On-Grid Combo Inverter???

    SMA have a Sunny Backup system that is approved for this type of setup in Germany and some other European countries - it will automatically switch to backup battery power in the event of grid failure and it will stay isolated from the grid while it's down.
    It is basically a modified Sunny Island with an additional transfer switch. They're slowly modifying the system to comply with more European countries' requirements and may be doing the same for the US.
  • Brock
    Brock Solar Expert Posts: 639 ✭✭✭✭
    Re: Both Off-Grid AND On-Grid Combo Inverter???

    x_logo, that is exactly the setup I have. I have a 200 amp main panel with a few large loads on it, geothermal heat pump, pool panel, dryer a couple of outlets. Then everything else is on a second 200A panel that is fed off the load side of our XW6048 inverter. If the grid fails the inverter takes over without a hiccup powering loads off the batteries or solar array.

    The problem here is our utility won't let you grid tie this inverter because it has batteries. In Wisconsin the PV system must be battery-less and on its own meter. I am looking right now at a second system that is just that and leaving my smaller 1kw system in place. I have found out the hard way if I do back feed the grid the local utility come right over to talk with me. So for now I just disconnect from the grid and power everything, but it is a manual switch.
    3kw solar PV, 4 LiFePO4 100a, xw 6048, Honda eu2000i, iota DLS-54-13, Tesla 3, Leaf, Volt, 4 ton horizontal geothermal, grid tied - Green Bay, WI
  • boB
    boB Solar Expert Posts: 1,030 ✭✭✭✭
    Re: Both Off-Grid AND On-Grid Combo Inverter???
    Brock wrote: »
    The problem here is our utility won't let you grid tie this inverter because it has batteries.

    I wonder why ???


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  • halfcrazy
    halfcrazy Solar Expert Posts: 720 ✭✭✭
    Re: Both Off-Grid AND On-Grid Combo Inverter???

    My guess is they don't trust the inverters because they are still on but not selling. A standard GT inverter will be off. Still makes no sense but then do they usually?