Commercial off-grid application? [RE-wrenches]

[David Brearley]

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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

 

 


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