Off-grid with Diesels? [RE-wrenches]

[Darryl Thayer]

HI Steve
SI is spark ignition (a throttled engine,and at part
load the BSFC increases sharply)

As for Diesels, I found an old article in my paper
archives that had a Diesel showing 2% increase in
brake specific fuel consumption at 50% of lowest BSFC
power, all at 1800 RPM.  This means if you added solar
to a loaded Diesel, the solar would reduce the fuel
consumption by (kWh fuel saved)= 0.98(kWh
solar)/(engine eff).  Engine eff is about 40 to 45%.  
The same article showed only slight reduction in wear
at lower load.

However it seems that You must have a very short term
very high load period.  And I think you need to study
the load profile and look at load shedding.  It also
looks like you have a problem with the rep, good luck
on diplomacy.  The problem is it is very difficult to
meet these high load requirements.  It takes lots of
inverter power and battery to handle these loads. 
Most solar RE batteries are designed for moderate
discharge rates, you would need a high discharge rate
battery.  

Please keep us informed as this develops.  My take
right now is to use solar to cut fuel consumption, no
batteries.  If the solar is so large that you cannot
use it as produced, then add batteries.  This all
depends upon load profile.  Also there maybe some
outside the box approaches.  
Good luck
Darryl 

   
--- Steve Johnson <stevejohnson at comcast.net> wrote:

> 
> 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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