Advise sought for large off grid PV system; 480 volt 3-phase [RE-wrenches]

[Drake Chamberlin]

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One concern about the cost effectiveness of extremely large off grid 
systems is the price of the battery bank, battery maintenance costs, 
the volatility of the investment, as well as the eventual replacement cost.

One possible approach to this system would be to keep at least one 
generator on line to create a local grid, and to feed this local 
system with grid interactive inverters.  There are a lot of possible 
variables to such a system, including smaller distributed battery 
banks as well as a number of Sunny Island type inverters feeding 
input from various arrays.

With such a system, the high voltage line could be fed from the solar 
at the secondary voltage of the transformers.  The existing 
transformers would step up the voltage from the inverters to the high 
voltage transmission line potential as in any utility situation.

With distributed PV sources and two generators that could work 
together or cover each other during fault or maintenance episodes, 
the system should be relatively reliable.

Drake


At 09:53 PM 3/28/2007, you wrote:

>Larry
>
>I suggest you must think outside the box a little on
>this one.
>
>When and how big is the max load?  When and how big is
>the Min load?  When during the day or night does the
>min load occur? How abrupt and how big are the load
>changes?
>
>What make are the Diesels?  Can the Diesels now load
>share?  (Or do they only transfer on command?)  Are
>the load transfers synchronous or asynchronous?
>
>HOw much 3 phase?
>First Brian's idea, how much 480 Three phase or any
>real 3 phase do you need?  What is the distribution of
>the 3 phase load? Just a short distance then splitting
>into single phase loads?  (If it is just a few motors,
>use VFD's).  I imagine your generators are 480 volt
>three phase and you distribute with 3 phase? Is it
>distrubuted 480-277 such that you have a neutral?  Is
>the neutral carried on the distribution system or just
>the 480? (Delta to Star or star-star to serve the
>distribution loads)
>
>Power sources
>Transfer switches are easy, (sychronus) but do you
>want to deal with the momentary loss of power during
>transfer.  Diesels are good under part load, can you
>unload the diesel via single phase loading of the
>legs, (assuming "Star 3phase" some where near the
>power house, or a Zig-Zag transformer where the solar
>source is applied.  Where I am leading is the use of
>single phase inverters to support the 3 phase
>ggeneration, reducing loads, allowing a load reduction
>on the engine. Unlike SI engines the Diesels BSFC
>(brake specific fuel consumption)follow load over a
>relatively large load range. (Efficiency is not as
>strong due to load changes)  When the loads are light
>enough, transfer to a smaller 3 phase source Diesel or
>inverter to generate the core 3 phase. The trick here
>is to unload the diesels until a small 3 phase source
>such as solar can handle it. Would it be possible to
>possible to add a low capacity Diesel as a core source
>and support until a large Diesel is needed?.
>
>Outback and xantrex can support generator power, I
>have a 3 phase support system that was originally to
>be 55kW, and I found it to be cost effective up to the
>55 kW.  Also Outback, and Xantrex, and SMA have
>products that can generator support and inverter
>support.
>
>What is wrong with using transformers?
>
>Darryl
>   .
>--- Brian Teitelbaum <brian at aeesolar.com> wrote:
>
> >


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