higher voltage off grid systems

mahendra
mahendra Solar Expert Posts: 188 ✭✭✭
in Off Grid Solar & Battery Systems #1
question midnite solar claims its charge controller can charge battery systems of up to 72v and 120v on the classic 250ks,But is any inverter that would stand up to continuous use for this type of application.Are there really battery based systems that use above 48 volts?
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  • stephendv
    stephendv Solar Expert Posts: 1,571 ✭✭
    #2
    Re: higher voltage off grid systems

    Some of the UPS systems like APC use higher voltage batteries. And then there's this company that makes off-grid inverters that work with 250V and 120V batteries: http://www.ingeteam.com/EN/ProductsandServices/Energy/Photovoltaic/Products.aspx?TIPO=PTD&ITEMID=11693&IDIOMA=EN&PRT=SBP&PRTID=2
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  • mahendra
    mahendra Solar Expert Posts: 188 ✭✭✭
    #3
    Re: higher voltage off grid systems

    What i meant to ask also are higher volt systems safe,reliable and efficient ?
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #4
    Re: higher voltage off grid systems

    as with any and all electricity it can be dangerous and needs respect and care around it. higher voltages can give better efficiencies and the reliability is a manufacturer deal. another manufacturer option is exeltech.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #5
    Re: higher voltage off grid systems

    The issue (for me) is that AC Transformers (and those on poles used by the power company too) are designed to only pass so much current before they "saturate" and cannot pass any more.

    DC power systems do not have that natural limiting action. So, if you have a big lead acid battery bank, 12/24/48 volts into a dead short can pass hundreds to thousands of amperes. Bump that up to 170 VDC or so, and it gets even a bit more frightening.

    Plus, there is the issue that DC voltage/current sustains arcing much better than 60 Hz AC... You will find that DC rated switches are much heftier than their similarly rated AC cousins.

    But--If you can find a reasonably priced load/AC Inverter out there that meets your needs--Look at it. It might be very nice.

    However, that does lead us back to another issue--I have not seen any home sized solar power controllers that are designed to work with >~48 volt battery banks. It is probably one of those self fulfilling policies... Regulatory agencies consider >60 VDC to be "hazardous", so anything that is "high voltage" is locked behind cabinets and not user serviceable. So, even for smaller inverters/charge controllers, you may not see any "high voltage" DC equipment because it would never get UL/NRTL approved.

    Not to say that large DC systems (even less than 60 VDC) do not strike a little fear into my heart.

    But there are many higher voltage DC/AC systems out there that are very reliable and very efficient.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • niel
    niel Solar Expert Posts: 10,300 ✭✭✭✭
    #6
    Re: higher voltage off grid systems

    reminder bill that the classic can and does go higher than the 48vdc limit most others have.
    http://www.solar-electric.com/misocl.html
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  • Dave Angelini
    Dave Angelini Solar Expert Posts: 6,894 ✭✭✭✭✭✭
    #7
    Re: higher voltage off grid systems
    mahendra wrote: »
    What i meant to ask also are higher volt systems safe,reliable and efficient ?

    No, not in Guyana ! You should only consider 24V or 48V battery systems.
    "we go where power lines don't" Sierra Nevada mountain area
       htps://offgridsolar1.com/
    E-mail offgridsolar@sti.net

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  • inetdog
    inetdog Solar Expert Posts: 3,123 ✭✭✭✭
    #8
    Re: higher voltage off grid systems
    BB. wrote: »
    The issue (for me) is that AC Transformers (and those on poles used by the power company too) are designed to only pass so much current before they "saturate" and cannot pass any more.

    But do not count on that too heavily. If the secondary voltage is held near zero and the primary and secondary are closely wound on the same core, saturation will not occur until you get into the range of current where the resistive impedance of the secondary coil starts to become a limiting factor too. In an ideal current transformer, the core will not be magnetized at all. In a physical current transformer, core saturation becomes a limiting factor at a much higher current than you might expect as a ratio to the "idle" current expended just magnetizing the core.
    SMA SB 3000, old BP panels.
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  • mahendra
    mahendra Solar Expert Posts: 188 ✭✭✭
    #9
    Re: higher voltage off grid systems

    well the main reason for all these questions is how big a system can one get or use to make sure it operates within acceptable standards ,because i am aware of the limits of 12,24 and 48 volts system .thanks anyways
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  • mahendra
    mahendra Solar Expert Posts: 188 ✭✭✭
    #10
    Re: higher voltage off grid systems

    Dave we in Guyana have certain limitations but not with the voltage limits once its for single home use electrical codes are not applicable once you don't start a fire its ok or kill someone
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  • stephendv
    stephendv Solar Expert Posts: 1,571 ✭✭
    #11
    Re: higher voltage off grid systems
    mahendra wrote: »
    well the main reason for all these questions is how big a system can one get or use to make sure it operates within acceptable standards ,because i am aware of the limits of 12,24 and 48 volts system .thanks anyways

    You can go quite big with 48V, for example power an entire country, 1MW and 1,344 batteries: http://www.sma.de/en/media-newsroom/current-news/news-details/news/3943-tokelau-becomes-the-worlds-first-100-solar-powered-country.html
    Technically, it's a number of smaller systems linked together. The biggest of the SMA multi-cluster boxes, which is 36 5kW Sunny Islands connected together is capable of 180kW and is based on a 48V battery.
    Here's another example of quite a big system built using a 2500Ah 48V Rolls battery: http://www.windandsun.co.uk/case-studies/islands/horse-island.aspx

    If you're looking for big batteries, then try "OPzS" style batts, most manufacturers like Exide and Hoppecke have them in 3000Ah or bigger 2V cells.
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  • mahendra
    mahendra Solar Expert Posts: 188 ✭✭✭
    #12
    Re: higher voltage off grid systems

    well an answer like this i was looking for , initially on an earlier post i was wondering how 48v systems can be integrated to work effectively to produce more than 4000w of power for prolonged periods.thank you
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  • mahendra
    mahendra Solar Expert Posts: 188 ✭✭✭
    #13
    Re: higher voltage off grid systems

    it would be nice if someone can shed some light on how they actually connected those batteries to the stacked inverts to work effectively.thanks in advance
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  • Eric L
    Eric L Solar Expert Posts: 262 ✭✭
    #14
    Re: higher voltage off grid systems

    For the bigger SMA systems, they stack the Sunny Island inverters in clusters of three to generate three-phase AC, which is then sent to a multicluster box that is the main AC distribution point (the multicluster box can take several of the 3-phase clusters, up to 300 KW for the biggest ones). Each cluster of 3 Sunny Islands can have its own battery bank so that the batteries can be distributed at various points around the network.

    Lots of details on their site; you can access all the documentation online: http://www.sma.de/en/products/off-grid-inverters/multicluster-boxes-for-sunny-island.html
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