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

Wed Mar 28 21:53:51 PDT 2007

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:

> 
> Larry,
> 
> Big system. Trace Technologies (now Xantrex) used to
> build a battery based
> version of their PV Series inverters (now Xantrex PV
> Series of course), that
> was called the HY Series (for "hybrid"). They listed
> models up to 300kW. My
> understanding is that they only made a few of them,
> and they were so much
> trouble that they dropped them. Biggest problem was
> dealing with the 360VDC
> battery banks!
> 
> Are there any actual loads using the 480VAC power?
> Or are they just going
> 480V for long distance distribution?
> 
> The reason I ask is that it may be better to look
> into using separate
> systems at each building rather then one central
> power system.
> 
> 
> 
> Brian Teitelbaum
> AEE Solar
> 
> 
> 
> -----Original Message-----
> From: larry crutcher
> [mailto:larry at starlightsolar.com] 
> Sent: Tuesday, March 27, 2007 1:59 PM
> To: RE-wrenches at topica.com
> Subject: Advise sought for large off grid PV system;
> 480 volt 3-phase
> [RE-wrenches]
> 
> 
> 
> RE-Wrenches,
> 
> I am designing an off grid PV system and am looking
> for input and 
> recommendations from experienced installers.
> Although I have years of 
> building battery based systems, this is a big one.
> The customer has been 
> running 60kW diesel generators 24/7 for about 2
> decades. They want a PV 
> system with batteries that will allow the generators
> to be shut down 
> during the winter and low load periods. Summer loads
> can be above 
> 500kWhs per day but winter drops to less than
> 100kWhs which I can do 
> with PV's.
> 
> Power details: The site has 480 volt, 3-phase Y
> distribution and 6 
> transformers. There are only two 480 volt
> distribution circuits leaving 
> the generator building. I have failed to locate
> power equipment that 
> will produce 480 volt 3 phase for off grid use.
> Telecom equipment does 
> not look suitable. I have found inverters to produce
> 60 kW @ 208 volt 3 
> phase (Exeltech) and a 75 kva step up transformer
> for 480Y. I don’t like 
> the transformer idea. The generator must be
> available at any time to 
> take over loads. I am thinking of transfer switching
> @ 480 volts. I 
> really would like automation for generators, battery
> charging, and 
> transfer switches.
> 
> One generator is scheduled for rebuild and it will
> have auto-start added 
> to it. The site has room for several large ground
> mount arrays of PV. 
> Wind power does not look viable, < 5 m/s @ 30
> meters. I am in a desert 
> location that has very high ambient temperatures
> above 115°. A building 
> for the batteries and inverters will be climate
> controlled to 80° F. 
> 
> So, how would you propose a solution for this type
> of site? Do you know 
> where I can get 480 3-phase inverters?
> 
> Next post I'll ask about batteries, BIG batteries.
> No, even bigger!
> 
> Larry Crutcher
> Starlight Solar
> 
> 
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