Using grid inverters without solar/wind

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  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Using grid inverters without solar/wind

    Well #1 isn't right: PV does not connect directly to an off grid inverter.

    #2 could work if the off grid inverter is the right kind (i.e. one that can handle the AC coupling of the grid tie inverter).

    The GTI's are "self regulating" in that they are only going to supply power when the sun shines. They will not care if it goes to household loads or to the utility.

    Controlling an off grid inverter to allow time shifting to help with peak demand times can be done with a timer, as I've already explained. If you want the utility to have the ability to control it - I'm not so sure that's a good idea even, as it would require a substantial interaction with them (they'd need to know the battery power was actually available before switching it on) and probably would not be practical on a small-scale house-to-house basis. More simply; they wouldn't want to bother. Power companies tend to think in megawatts, not kilowatts. :D

    I once proposed a similar scheme for them to handle generation from GTI's via smart meters (existing technology) and thankfully no one went with it (yet).

    You have two possible operation plans that I can see: management at the home and management by the grid. For many independent installations management at the home would be simpler and more practical.
  • DellyDelly Registered Users Posts: 16
    Re: Using grid inverters without solar/wind
    Well #1 isn't right: PV does not connect directly to an off grid inverter.

    Right, that's what I thought too, but in the AC coupling document from Outback, all the drawings are directly connected to the inverter except in one case, I think, where it was connected through a cc. Other than that, would #1 work if it was connected to the cc like the dotted lines? If yes, is it correct to also connect it to the enphase inverter too?

    Well, not sure how much time left I have to work with the company options since I've used more time than what I had expected and calculated, so I might have to drop the programming part of the control device. But that is not of any concern in this thread. What I'm more interested in/concerned about is finding a couple of dealers offering the same large inverters to compare the prices and have a more basic understanding of what to aim for.

    Best regards,
    Delly
  • CariboocootCariboocoot Banned Posts: 17,615 ✭✭✭
    Re: Using grid inverters without solar/wind
    Delly wrote: »
    Right, that's what I thought too, but in the AC coupling document from Outback, all the drawings are directly connected to the inverter except in one case, I think, where it was connected through a cc. Other than that, would #1 work if it was connected to the cc like the dotted lines? If yes, is it correct to also connect it to the enphase inverter too?

    With AC coupling the PV would connect directly to a grid-tie inverter and its AC output would go to the off-grid inverter. Enphase is a grid-tie inverter too, and as such powered directly by the PV.

    What usually confuses the plans are hybrid inverters which are powered by batteries but are grid-tied and are usually the kind used for AC coupling installs. As such you can have the option of either charging the batteries from PV through a charge controller as in a conventional off-grid system or by back-feeding them with an AC coupled grid-tie inverter.
  • DellyDelly Registered Users Posts: 16
    Re: Using grid inverters without solar/wind
    With AC coupling the PV would connect directly to a grid-tie inverter and its AC output would go to the off-grid inverter. Enphase is a grid-tie inverter too, and as such powered directly by the PV.

    What usually confuses the plans are hybrid inverters which are powered by batteries but are grid-tied and are usually the kind used for AC coupling installs. As such you can have the option of either charging the batteries from PV through a charge controller as in a conventional off-grid system or by back-feeding them with an AC coupled grid-tie inverter.

    Right, I'll be chewing on that a little bit and see what I can do. Meanwhile I came to a conclusion that a large scaled system is not cheaper even if it is divided amongst many, although I still can not confirm this since I haven't been able to get prices for the different products yet. :/

    OT question: Someone asked me how big should the battery bank be based on an 600w inverter he had. He wanted to supplement the house(i guess) with 600w for 3 hours and use no more than 50% of the battery cap. I'm not sure whether the inverter is of a good quality or if its a Chinese jack inverter. Anyhow I suggested that he shouldn't use more than 50% of max inverter capacity, thus I made this calculation:

    300w x 3 = 900wh
    24v battery system (just something I decided)
    900/24 = 37.5Ah
    37.5 * (1/0.8 ) * ( 1/0.5) = 94Ah
    94*24 = 2256Wh

    He also wanted a battery charger so I suggested him to use something between 10-20% of max battery cap. (preferably 13% for PV array)

    I'm used to size the system based on my battery bank, and not the inverter size. Therefore I'm a bit unsure if I could use the same logic to size his system or not. I mean, there should not be a problem using 600w inverter for a 2256wh battery bank as long as he is using only a small amount of the max battery capacity over 3 hrs? I've calculated it so that it would only use about 375w (2256wh/[2*3h]).

    Please do correct my calculation if it is wrong.

    EDIT:
    Ok, there is one thing that is really confusing me. Do the SMA multicluster boxes actually include the island 5048 inverters in their price, or not? I mean take a look at this: http://www.windandsun.co.uk/products/147/.aspx
    compared to:
    http://www.sonnenshop24.eu/en/Photovoltaik-Solar/Iland-Solar-Systems-storage-Systems/SMA/SMA-Sunny-Backup-Set-XL-80-extra-large.html

    There is a huge gap between the prices, which makes me think that the multicluster boxes are only pre-wired boxes supporting up too 300kw. But then again if this is true, isn't it crazy to pay $ 18k for a pre-wired box?!!

    Best regards,
    Delly
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