Positive ground with batteries? [RE-wrenches]

[Geoff Greenfield]

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Here's a unique one:
I am asked to design a grid tied system with battery back up using the new
positive grounded Sunpower PV cells.  (not the Sunpower modules, but the
cells assembled in flat roof laminates from a company called solar roofing
systems).

Question # 1 - any battery based inverters allow positive ground?

Question #2 - Assuming NO to #1, this looks like a great application for AC
bus, with an appropriate battery free box tied to a sub panel served by
either a Sunny Island or Outback system.

We have not yet done an Island, it looks like they require an additional
transformer to serve/tie into 120/240.  Advantage is modulation of SBs.
Outback is talking about this being a viable use of their product as well,
with either a 5 minute countdown based charge control during off grid
operation or a Batt voltage controlled relay based modulation (both seem
rough).  Add to this the ability to use the Bergey Gridtek inverter and we
are all very interested in an AC bus approach.

OK John B and Chris F (and others) lets lay out the pluses and minuses of
each approach.  Efficiency during normal grid operation?  Scalability and
capacity? Warranty coverage?  Field experience/reliability/surprises?



For a brighter energy future,

Geoff Greenfield
NABCEP Certified Energy Practitioner

THIRD SUN SOLAR & WIND POWER Ltd.
340 West State Street
Athens, OH 45701

www.third-sun.com
(740) 597-3111

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