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Thread: Large Off Grid System

  1. #1

    Default Large Off Grid System

    I'm working on a very large off grid system approx 20kW to 30kW.
    What are the pro's and con's of each type of system SunnyBoy & Sunny Island, Xantrex, and Outback?

    Thanks,
    Philip

  2. #2

    Default Re: Large Off Grid System

    That's a big question.

    Firstly I don't think the OBs should even be in the running since they probably can't scale to 20kW and even if they can, they don't offer generator support (i.e. boost generator provided power). That would be a deal breaker in my book for such a large system.

    For that size of system I'd think that an AC connected sunny island + sunny boy has advantages over DC connected Xantrex:
    • Will probably work out cheaper to buy a pair of high power sunny boys than many Xantrex charge controllers.
    • You'd have more choice in array configurations as you could use any grid-connect panels and go for a high voltage array configuration, saving you cabling costs.
    • You could use fewer sunny islands since some of the power will be provided by the sunny boys, i.e. a system designed to provide 20kW peak, could have 10kW worth of sunny islands and 10kW worth of sunny boys since they're all on the same AC bus. With a DC system, all 20kW have to come from the battery inverters.

  3. #3
    Join Date
    Aug 2009
    Location
    Northwest Ohio
    Posts
    66

    Default Re: Large Off Grid System

    The following assumes completely off grid and are using standard household 120/240 single phase.

    If using Xantrex, up to three Xantrex XW 6048 inverters can be linked together for a total of 18kw via their "Load" out line to your off grid panel. (Load does not sync to grid) If you need more than the three, then you'll have to start getting a bit creative.

    IE.
    - Two main panels for two seperate groups of XW linked units
    or
    - A main panel with a much larger rated bus bar with the second group of XWs backfeeding and syncing off the first group using their AC1/To/From/Grid lines ??

    You'll also need a pretty big battery bank.
    1200AH @ 48V as a minimum

    I would think the two main panel approach would be a better plan. You have a spare in case one leg goes out. In a pinch the two main panels could both be run off one set of XWs if there is an issue with the other half of the setup or maintenance is needed.

    David
    Xantrex XW6048, XW-MPPT-60 SCC, Midnite E-Panel, 36 SunXtender PVX-890T @ 801ah, Briggs Elite 8kw, Midnite PV Combiner, 12 Sharp 224s / 2.6kw , Bogart Tri-Metric Meter, 2 EKM Meters (On AC1 and Load)

  4. #4

    Default Re: Large Off Grid System

    Quote Originally Posted by Philip C View Post
    I'm working on a very large off grid system approx 20kW to 30kW.
    What are the pro's and con's of each type of system SunnyBoy & Sunny Island, Xantrex, and Outback?

    Thanks,
    Philip
    What are your loads?

  5. #5

    Default Re: Large Off Grid System

    I am still working on putting a load analysis together. But I like the idea of passing generator power through the Sunny Island, as loads will go way up during Christmas and other holidays. There will be three geothermal AC units, but a section of the house will only be used with family and guest come in.

  6. #6
    Join Date
    Apr 2007
    Location
    Lakeland Florida
    Posts
    1,959

    Default Re: Large Off Grid System

    SI/SB is really intended for Gridtie with small backup on the battery side, not 20-30kw AC loads, unless your only going to power the AC during the day

    If your going to have enough SI's to power the full 20-30kw, they the SB's turn into 3,000 dollar charge controllers and for a system this size, that's a very expensive solution.

    For a True Off grid the XW is you only choice, and it has full generator support and every feature possible and its a fully integrated solution, the inverter, all the BOS and chargers in on nice package.
    Last edited by Solar Guppy; May 19th, 2010 at 18:16 PDT.

  7. #7
    woodman Guest

    Default Re: Large Off Grid System

    I did a lot of research on the Sunny Island setup when I was trying to decide what brand to go with. The product seams to have some great fetchers but itís also missing a lot of fetchers other brands have.

    With a system that size I would look at XW and might look load sharing with generator on the heavy load days.

  8. #8

    Default Re: Large Off Grid System

    Quote Originally Posted by Solar Guppy View Post
    SI/SB is really intended for Gridtie with small backup on the battery side, not 20-30kw AC loads, unless your only going to power the AC during the day
    Have to disagree with this SG. The SI units were specifically designed for off-grid use (in fact you can't grid tie them in Europe) and are available in multicluster boxes to power up to 300kW in 3 phase configuration and have also been used in numerous completely off-grid setups to power entire villages.
    See:
    http://www.windandsun.co.uk/Projects...ct-gallery.htm
    and www.sma.de/en for other case studies.

    Quote Originally Posted by Solar Guppy View Post
    If your going to have enough SI's to power the full 20-30kw, they the SB's turn into 3,000 dollar charge controllers and for a system this size, that's a very expensive solution.
    Yep, I thought the SB's would scale better, but they don't:
    For 30kW using Xantrex MPPT controllers, you'd need about 9 controllers =~ 4 800 USD
    For 30kW using SB, you could use 4 x SB 7000 =~ 14 000 USD!!

    Woodman, I'd be interested in hearing which features the XW has that the SI doesn't have, as by my scorecard the SI is the more flexible unit. AFAIK, the only feature where the XW trumps the SI is that it offers 240V/110V split phase, whereas the SI is 110V only (or 240V only).

    The SI offers the following that the XW does not:
    - The option of doing safe AC coupling with SB and Windy Boys.
    - State of Charge measurement for DC input and ouput, all you need is an additional shunt. With the shunt you can use any DC charge controller and the SI will still correctly measure the SoC of the battery: no comms cable or other accessories necessary.
    - Can scale to 300kW systems. The XW only seems to get to 18kW.

    For all of the features that matter, the two systems are very similar, 100A PF corrected chargers. Both offer gen boost.

  9. #9

    Default Re: Large Off Grid System

    ...The Isle of Eigg project (link in previous post) is particularly interesting:

    • 12 x Sunny Island 5048 for 60kW of battery power
    • 48V 2242 Ah battery
    • 10kW PV
    • 12kW Hydro
    • 24kW Wind
    • Backup diesel generators


    All of the above to create a single mini-grid to power 37 residences and 5 commercial properties.

  10. #10
    Join Date
    Apr 2009
    Location
    California Sierra near Mariposa
    Posts
    1,317

    Default Re: Large Off Grid System

    Stephendv,

    The SW and now the XW have always had 2 things that no other Inv/Chg has been able to provide. They are the ability to gen support and surge for huge amounts of time (deep well pumps). If you do not need these features there other choices. There are also some interesting things coming around the next corner!
    http://members.sti.net/offgridsolar/
    "we go where the power lines don't"

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