Commercial off-grid application? [RE-wrenches]

[Darryl Thayer]

HI David
This is sort of like the Outback system that I built. 
However sort of on steriods.  

The system that I have mentioned several times on
wrenches is a 40 kW plus, 3 phase, 208 volts, Outback
system.  However mine is heavly grid tied.  On weekend
days the system runs by supplying all the power and
selling power to the grid.  During the week the system
sells early in the morning and late in the afternoon,
during the middle of the day the building draws more
power the the Solar can supply.  During power outages
only emergency circuits are powered.    

I have 13 MX60s and 12 GVFX inverters stacked four per
phase, that function as grid tied during the day.  The
battery system is by C&D battery. The smaller
emergency load allows the solar to completly recharge
the battery every day and gives continous emergency
power.  The system has been flawless for its first 18
mounths of service.  

During the design phase I did some comparisons with
modular and single large inverter, I found that I
could get higher efficiency and lower cost with the
modular approach.

Thanks Darryl  

--- David Brearley <david at meridiansolar.com> wrote:
> Esteemed colleagues,
> 
> We are under contract to install a 42 kW
> grid-interconnected, commercial PV
> system, one that includes a UPS for critical loads
> and a lg. commercial
> diesel generator for back up power.  This is on new
> construction.  The
> proposed service is a three-phase wye at 208Vac.
> 
> The customer has recently requested that we shift
> the entire system to a
> modular, off-grid architecture.  This is driven by
> the customer's new-found
> abhorrence for fossil fuel generators.  Their
> conceptual model of late is to
> install (4) 10.5kW solar arrays each w/ multiple
> charge controllers on (4)
> 1500Ah battery banks feeding (4) 17.5 kVA inverters.
>  The output of these
> inverters would be paralleled, and then run to a
> 1600A, 208Vac transfer
> switch.  This is nominally sufficient to run the
> proposed building loads.
> According the one-line I am looking at, in a low
> battery situation the
> building loads would run off the grid.
> 
>  
> 
> We have presented our customer with a list of
> concerns about this proposed
> design, not the least of which is that it requires
> 12 tons of batteries.  
> 
>  
> 
> The question I have is really more fundamental than
> budgetary or energy
> efficiencies.  Is it even possible to build the
> system that this customer
> requests with available technology?  Satcon
> indicated, for example, that
> they could build a 50kW grid-tie inverter with
> battery back-up.  But our
> customer is requesting something modular, something
> that operates primarily
> in off-grid mode.  This suggests using an OutBack
> platform or an AC coupled
> SMA system.  What is the upper size limit of these
> architectures in a
> 208-wye configuration?  I recall that OutBack can
> stack only three inverters
> in a 3-phase system.  Is this correct?  SMA ignored
> my inquiry about using
> their product for this application.  Does anyone out
> there know how
> expandable the AC coupled architecture is?
> 
>  
> 
> Any input is appreciated.   
> 
>  
> 
> Sincerely,
> 
>  
> 
> David Brearley
> 
> NABCEP Certified Solar PV System Installer (TM)
> 
>  
> 
> Meridian Energy Systems
> 
> 2300 S. Lamar, Suite 107
> 
> Austin, TX 78704
> 
> 512-448-0055 (ph)
> 
> 512-448-0045 (fax)
> 
> www.meridiansolar.com
> 
>  
> 
>  
> 
> 
> [Non-text portions of this message have been
> removed]
> 
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