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Sunny Boys, with AC Coupling Later?

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  • Sunny Boys, with AC Coupling Later?

    I've been thinking long and hard about the difficulties of a charge controller + battery system, mindful of all the warnings here about the immense cost and babysitting required. Even though the idea of having some independence from the grid is very appealing and a primary reason why I got interested in all this in the first place, I'm about ready to make this summer's project just hooking up a couple of SMA Sunny Boys to the four PV strings I'm planning, get the grid-tie interconnect wired and approved, and wait for further signs of the apocalypse (kidding--well, sort of) before doing the batteries plus big old 48V inverter plus critical loads panel.

    I know that DC coupling is the best approach if you are planning on a battery from the get-go. But it seems that the Outback could AC couple the Sunny Boys just fine if I decided to add all that off-grid crap later on, and they don't cost any more than a pair of Morningstar TS-600V 60A charge controllers. It wouldn't be ideal; if the grid is down, the remote relay in the Outback's AC-coupling load center would be switching the Sunny Boys in and out to keep the battery from overcharging. But the 6000W PV power being well within the <90% of 8KW Outback power requirement. Also, if I'm actually having to run off-grid for any extended amount of time, I seriously doubt if I'd be getting much overcharging done, with all the loading of the PV power I'd be doing at that point. The challenge seems like it would be more one of giving the Sunny Boys a chance to backfeed the Outback's H-Bridge to charge the batteries instead of drawing from them, and running a generator when they can't keep up.

    There would also be the Sunny Island option for AC coupling, for a bit more money. But, hey, what's a few thousand extra if you are willing to spend ten grand on a ton of expensive lead and sulfuric acid that gradually degrades into a pile of heavy toxic junk in less than a decade?

  • #2
    Originally posted by BackwoodsEE View Post
    I know that DC coupling is the best approach if you are planning on a battery from the get-go. But it seems that the Outback could AC couple the Sunny Boys just fine if I decided to add all that off-grid crap later on, and they don't cost any more than a pair of Morningstar TS-600V 60A charge controllers. It wouldn't be ideal; if the grid is down, the remote relay in the Outback's AC-coupling load center would be switching the Sunny Boys in and out to keep the battery from overcharging.
    You can shut down but you can't regulate, so you won't be able to completely charge your batteries from your solar arrays. Breaking it down into two loads (so you can enable 3kW or 6kW) will help but not solve the problem. It might work if you rarely have power outages.


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    • #3
      The trend in the industry is definitely toward combining storage with solar, but I have not seen any storage solutions that are even close to being ready for mainstream. I do some battery backed and AC coupled systems occasionally (for you/us fearful types) but always have ongoing trouble from them (the batteries). The general advice is to be "storage ready" - like you are proposing, start with a cost-effective, easy to permit, reliable grid-tied setup - then be able to add storage later when "better" batteries come to the fore. (Have you heard about Liquid Metal Batteries?)
      BSEE, R11, NABCEP, Chevy BoltEV, >2000kW installed

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      • #4
        Originally posted by solarix View Post
        The trend in the industry is definitely toward combining storage with solar, but I have not seen any storage solutions that are even close to being ready for mainstream. I do some battery backed and AC coupled systems occasionally (for you/us fearful types) but always have ongoing trouble from them (the batteries). The general advice is to be "storage ready" - like you are proposing, start with a cost-effective, easy to permit, reliable grid-tied setup - then be able to add storage later when "better" batteries come to the fore. (Have you heard about Liquid Metal Batteries?)
        Thanks! This is the direction I'm leaning towards now, and your comment helps my decision. I really want to get the panels out of my garage and sitting out in the clearing with power going to good use.

        Instead of AC coupling the Outback ($4000 + $1300 load center for unregulated 8KW), I think when I do go for the battery backup (next summer, probably) I'm going to pay a little extra for the solution designed to work with the Sunny Boy, the Sunny Island. Around $7200 for a pair of them (to do split-phase 240V) with around 9KW of potential power.

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        • #5
          Have you considered putting in the SolarEdge SE7600 which can be upgraded to the StorEdge latter. This would be DC coupled and a single integrated solution.
          you could use it with the LG Chem RESU10H battery.
          OutBack FP1 w/ CS6P-250P http://bit.ly/1Sg5VNH

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