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11397RE: [hreg] Solar Backup System - comment

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  • kevin conlin
    Aug 24, 2012
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      Excellent answer, Jim, well written and very helpful


      I learned a lot, thank you





      Kevin Conlin

      Heliosolar Design Inc

      13534 Quetzal

      Houston TX 77083-3525


      281 202 9629


      From: hreg@yahoogroups.com [mailto:hreg@yahoogroups.com] On Behalf Of Jim Duncan
      Sent: Friday, August 24, 2012 10:07 PM
      To: hreg@yahoogroups.com
      Subject: RE: [hreg] Solar Backup System




      The Sunny Island also works very well for grid-tied battery backup systems as well as off-grid. The real advantage of the SI or other similar inverter/chargers is that the system will isolate itself from the grid the instant that there is a blackout but will continue to allow the PV array and inverter to work normally as long as the sun is shining. This is known s islanding.

      The SI acts as the grid “fooling” the Sunny Boy inverter into staying in operation and charging the battery bank while powering loads thru the inverter. This turns your system into an off/grid system with all of your critical loads powered by the batteries.

      When the grid power returns the SI reconnects to the grid and grid power will recharge the batteries where they await the next grid outage.

      The Sunny Boy grid-tie inverters work flawlessly with the SI and will communicate with them in several important ways during islanding. The SI also works with some non-SMA inverters but does not communicate with them.

      They are expensive but it’s about as simple a solution to battery backup as you’ll find in the US market.

      One thing to consider concerning an oversized inverter to accommodate more PV in the future, The modules that you used on the first system may not be available in a few years. Also an oversized inverter in a hot climate may tend to shut down during very hot days since the PV voltage will be reduced due to the high temps. If the PV voltage falls below the minimum input level of the inverters DC input the inverter will shut down. This also might happen if it’s cloudy or just a passing cloud on a hot day.

      Your installer should have warned you of the potential loss of power due to voltage drop in these situations.


      Jim Duncan

      North Texas Renewable Energy Inc


      NABCEP PV 031310-57








      From: hreg@yahoogroups.com [mailto:hreg@yahoogroups.com] On Behalf Of Chris and Kathy Denison
      Sent: Friday, August 24, 2012 1:46 PM
      To: hreg@yahoogroups.com
      Subject: [hreg] Solar Backup System



      would appreciate some input on this.  We have a grid tied, 5k solar array and are waiting a year to get an idea how much electricity we'll use per annum. Our 1250sq home is all electric with geothermal cooling/heating (we're in south Texas).  We plan to add more panels next year to come close to our annual usage, perhaps another 3-4k (we had the larger SMA inverter installed to accommodate additional panels).

      So if the grid goes down, the panels automatically shut off for safety. Meanwhile we have no power despite the panels sat up top so would need a generator for the basics (fridge, freezer, PC, lights, etc).  Seems a little crazy to have panels up there we can't utilize during the day. Ideally would like to use something like the SMA Sunny Backup (SB) which has a small battery array just to keep basics going thru the night. In daylight, the panels are back to operating and powering the house and recharging the batteries.  Basically we're looking for a hybrid system so are covered for all eventualities (the house has been pre wired to accommodate this possibility).

      Some of you have suggested the Sunny Island but understand this is designed primarily for off grid and is considerably more expensive than the Sunny Backup, plus needs a different, more expensive inverter.  Also that the panels to first recharge the large battery array before powering the house, then any surplus leccies go to the grid. The SB costs about $2800 in Europe.

      Innovative electricity insurance for private homes: as an add-on to the PV plant, the Sunny Backup set S switches automatically to off-grid mode within 50 milliseconds in the event of grid failure. Whether in summer or winter, if the power goes out, owners of small to medium-sized PV plants and inverters from SMA can supply their most important consumer loads themselves. Our affordable complete solution is suitable for both new PV plants as well as existing PV plants, which can be easily retrofitted with our certified Sunny Backup set S.

      SMA in the USA told me the SB is not UL listed and 50hz so can't be used here.  But surely there's a market in the US for this?  The technology is there, how difficult is it to re-engineer for the US market?   I'm not an engineer, am I not understanding some basics?

      Thank you, Kathy

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