Off-grid with Diesels? [RE-wrenches]

[Steve Johnson]

Darryl,

Thanks for the response.
I noticed I had replied to Geofs grid-tied post, this system is off grid 
so I changed the subject line.
The 500 kw generator and a 480 v 3 phase UG distribution was already 
there before I got involved.  They were talking about running it 24/7 
and asked if they could save diesel with battery inverters. Also with 
solar.  Of course I believe they can.  At this preliminary stage I don't 
have a load profile.  Design budget is 1000 kwh per day.

The genset is Cat Prime 500ekw 625 kva.  I am not supplying it.  Owners 
rep insists on it.  Original plan was 500 kw with 500kw backup and 
alternate between the 2 gnerators.  they are both Prime rated. I don't 
see any mention of BSFC on the spec sheets.  What is SI?

As far as the 225kw carrying the load I was thinking that with a huge 
battery bank you could get a quarter of the load and another quarter 
with grid tied PV.  Yeah it is pretty rough so far.  the 420 kw peak 
load will just be for a short period, ie motor start up etc.  I though 
with enough battery/inverters and the 225kw and 60 kw PV (6 hrs sun) it 
would handle that short surge to 420kva.

So basically the big 500kw would run everything OR the 225kw AND the 
battery/inverters AND the 60kw PV would handle every thing.  2 systems 
but only one connected to grid at a time through a 800 amp transfer 
switch.

On the batteries - point well taken.  This could be a problem as 500 to 
600 kw worth of batteries would be required to get 250 to 300 kwh a day 
out of them at 50% discharge.  If the 225 generator could support the 
grid while charging the batteries then shut off while the PV is cranking 
and then hit another lick for a couple of three hours around evening 
time couldn't that work?  The Sunny Islands would have to draw what they 
need from the generator for the taper off while the generator feeds the 
rest to the grid.  The idea is to run the smaller generator about 8 
hours a day so there is 16 hours of down time (not necessarily all in 
one stretch) - thus saving humongous amounts of diesel compared to 
running a 500 kw 24/7.

There has to be a way to do this!


Steve 


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