Large Off Grid System

Philip CPhilip C Posts: 45Solar Expert
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

Comments

  • stephendvstephendv Posts: 1,571Solar Expert
    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.
  • dsp3930dsp3930 Posts: 66Solar Expert ✭✭✭✭
    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
  • AntronXAntronX Posts: 462Solar Expert ✭✭✭✭✭✭
    Re: Large Off Grid System
    Philip C wrote: »
    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?
  • Philip CPhilip C Posts: 45Solar Expert
    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.
  • Solar GuppySolar Guppy Posts: 1,959Solar Expert
    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.
  • System2System2 Posts: 6,290 admin
    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 it’s 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.
  • stephendvstephendv Posts: 1,571Solar Expert
    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

    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/island-project-gallery.htm
    and www.sma.de/en for other case studies.
    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.
  • stephendvstephendv Posts: 1,571Solar Expert
    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.
  • Dave AngeliniDave Angelini Posts: 2,203Solar Expert ✭✭✭✭
    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!
    "we go where power lines don't" Sierra Mountains near Mariposa CA
     http://members.sti.net/offgridsolar/
    E-mail offgridsolar@sti.net

  • stephendvstephendv Posts: 1,571Solar Expert
    Re: Large Off Grid System
    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).

    Compared to outback maybe that's true, but there are a whole bunch of other inv/chargers that offer the same features as the XW. All of the below offer gen support and surge of 100% or even more against their rated nominal output:
    - Xantrex XW = surge of 100% nominal
    - Victron Multiplus and Quatro = 100%
    - Sunny Island = 100%
    - Studer XTH = 137%

    I'm not disputing that the XW is a great piece of kit, but it's not the only kid on the block.
  • Philip CPhilip C Posts: 45Solar Expert
    Re: Large Off Grid System

    I think the biggest thing pushing me towards the SI, is the ability to push both PV and Generator power.
    If I have a 18kW XW, the max con't power is 18kW and surge up to 36kW
    If a 20kW SI, with 20kW PV, and 10kW Gen Set, I have the ability to use up to 50kW on the AC side with surges up to 70kW.

    Where on the xantrex I can not push AC power from the gen set or PV system straight to the loads.
    Is this right?
  • stephendvstephendv Posts: 1,571Solar Expert
    Re: Large Off Grid System
    Philip C wrote: »
    If a 20kW SI, with 20kW PV, and 10kW Gen Set, I have the ability to use up to 50kW on the AC side with surges up to 70kW.

    Where on the xantrex I can not push AC power from the gen set or PV system straight to the loads.
    Is this right?

    Not entirely. Both the SI and the XW will let you boost power from the genset, and it appears that both have a maximum passthrough current of 56A. Now, I don't believe you can use PV + gen power through the SI at the same time because then the SI has no way of preventing battery overcharging (SMA support would be able to give you a definite answer here).
    So you can only do SI + gen or SI + PV but not SI + gen + PV.

    The Xantrex can also work in an AC connected configuration (as can most battery based inverter/chargers), but it wasn't designed for the task, so it won't automatically protect your batteries from being overcharged if you connect grid-trie inverters (GTI) to the AC bus. You would have to setup your own system for either disconnecting the GTIs when batteries are charged, or turning on an appropriate dump load. There has been some discussion on this, try a search for "backfeed" on the forum.
  • Solar GuppySolar Guppy Posts: 1,959Solar Expert
    Re: Large Off Grid System
    Philip C wrote: »
    I think the biggest thing pushing me towards the SI, is the ability to push both PV and Generator power.
    If I have a 18kW XW, the max con't power is 18kW and surge up to 36kW
    If a 20kW SI, with 20kW PV, and 10kW Gen Set, I have the ability to use up to 50kW on the AC side with surges up to 70kW.

    Where on the xantrex I can not push AC power from the gen set or PV system straight to the loads.
    Is this right?

    Keep in mind, this type of "surge" is only useful when the PV is generating energy, not particularly useful for an off-grid home, are you going to tell the client he can only run the big loads at solar noon and only if its clear conditions?

    the SI is a distributed system, meaning if you have a small village, your depending on two things for this to work, one, there is excess generation to handle a subset of users peak needs and two, you are requiring that non-solar hours must have serverly restricted allowed usage, in the above example you would have less than 1 hour of power with that small battery bank or have grid-backup or other alternative AC source

    The XW could be expanded beyond 18kw simple by having some loads ( like the heat pumps ) on there own sub-panel. I hope you understand the battery bank size you will need for this to work, probably in the order of 10k+ ah@48V if your going to be handling 20kw+ loads and dealing with days without PV production

    For a single offgrid home, the only advantage with the SI is you can use 3,000 dollar SB GT inverters to act as 500 charge controllers, that's it. With what, 50kw of PV, your looking at 20k+ increase in system cost to be able to run high string voltages using the SB.
  • Philip CPhilip C Posts: 45Solar Expert
    Re: Large Off Grid System

    For example with a XW 6048, I can get more than 25A on the AC side when using a gen set? When the gen set turns on, does the XW/SI use the signal from the gen set to push current? Seams like we would have two different signals otherwise.

    Lets assume a chain of events using the XW 6048

    Loads exceed the 6kW, the XW has the ability to handle these for short term. A signal is sent to the gen set to power up, a warm up time elapse, the XW then supplements the load with gen power, the loads drop below 6kW, the gen is then turned off?
  • Solar GuppySolar Guppy Posts: 1,959Solar Expert
    Re: Large Off Grid System

    A good starting point for many XW questions:

    http://www.xantrex.com/web/id/1871/docserve.aspx

    Table 2-1
    pages 3-21

    The XW is completely user configurable on in start/stop of the generator, you configure what condition you want the AGS to start/stop the Genny. Also read up on why a single vs parallel units deal with generators.

    The XW can supply a maximum of 60 amps, 25 from the inverter, the remainder from the AC1 or AC2 lines ( known as generator or grid support )
  • Dave AngeliniDave Angelini Posts: 2,203Solar Expert ✭✭✭✭
    Re: Large Off Grid System
    stephendv wrote: »
    Compared to outback maybe that's true, but there are a whole bunch of other inv/chargers that offer the same features as the XW. All of the below offer gen support and surge of 100% or even more against their rated nominal output:
    - Xantrex XW = surge of 100% nominal
    - Victron Multiplus and Quatro = 100%
    - Sunny Island = 100%
    - Studer XTH = 137%

    I'm not disputing that the XW is a great piece of kit, but it's not the only kid on the block.

    I do not dispute you either and I can't say that I see that gear above except the XW in an offgrid application on this side of the pond, ever! My experience only! The other thing about surging with deep well pumps is the " time" that the inverter can surge for not just the percentage. Having the generator supported by the battery avoids the blown breaker when the generator is too small for the job. This happens all the time when the main generator dies and a smaller back-up is used. Real world situations.
    "we go where power lines don't" Sierra Mountains near Mariposa CA
     http://members.sti.net/offgridsolar/
    E-mail offgridsolar@sti.net

  • MangasMangas Posts: 463Solar Expert ✭✭✭
    Re: Large Off Grid System

    We have a real world larger off grid system which has been in operation for 5 years.

    We used the split panel approach for peace of mind. If we loose one half of the house/ranch, we've still got A/C and heat in the other. For redundancy purposes we wouldn't do it any other way. Rough wiring and set up costs a little more but makes living less stressful if something should go wrong.

    The SWs' (now XWs') are the way to go. With our two A/C and air handler zones, we wanted plenty of inverter surge capacity (we have 4) when everything else is coming on too. Each of our HVAC zones are on two inverters and we have two 100 Amp service panels at the house splitting up the house's power loads. So far, we haven't had a surge capacity problem and we've hung a lot of stuff on our system.

    However, we did use two very high efficiency 2.5 ton central air conditioning compressors and variable speed air handlers. Off surge, I think they each run below 8 amps with a starting surge only slightly above that. Amazing.

    In winter, our main power consumption are the harder running air handlers (propane fired furnaces) and summer mainly the air conditioning compressors with lower running air handlers which is why judicious conservation and efficient contruction materials are so important. We turned off the heat pumps because they idled too much power. The system works better without them.

    I would not have a large off grid system without an 1800 rpm propane or diesel generator to back it all up.
    Off Grid System: 2 x pair stacked Schneider XW 5548 Plus inverters (4), 2 x Schneider 800 Charge Controllers, 2 Xanbus Generator Start and Air Extraction System Modules, 64 Trojan L16 REB Flooded Cel Batteries w/Water Miser Caps, 44 x 185 Sharp Solar panels, Cummins Onan RS20 KW Propane Water Cooled Genset, Rastra House Construction, 2 x high efficiency three ton Central A/C units and 2 x Air handlers
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