Off-grid with Diesels? [RE-wrenches]

Steve Johnson stevejohnson at comcast.net
Sat Apr 14 07:13:05 PDT 2007


Darryl,

Thanks for the good info.
I don't have info to develop load profile yet.  The peak load I referred 
to is basically a worst case situation, i.e. air conditioners starting 
at the same time etc. and I believe it would be very short duration, a 
minute or two.  However I am not privy to this data yet.  Until load 
profile is developed it is hard to go further.

I am out of town and don't have the Cat genset specs but am interested 
in the data you present.  

<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.

Not sure how to interpret this.  If we call .98, 1, and call 0.45,0.5
- does that mean that each kwh of solar generated would save generation 
of 2kwh of diesel?

If I could equate kwh of solar generated to gallons of diesel saved this 
would be really useful.
I guess I need the load profile to get diesel usage in a 24 hr period. 
The 500kw genset could use 1/2 to $1m of diesel per year.  It seems a 
shame to throw that kind of money away when a good portion of it could 
be spent in a much more benficial manner.

The solar will not be large enough to run everything.  Maybe in peak 
hours, but they want 24/7 availabilty.  I'm thinking over a 24 hr period 
one third solar, one third batteries, one third diesel.  Of course the 
batteries would actually be diesel and maybe some solar.  Their function 
would be to soak up excess gneset while it is running and provide quiet 
time, reduce runtime on genset.
The genrator has to be able to charge batteries early am and evening 
while it runs grid.  Solar handles about six hours in middle of day, and 
batteries pitch in inbetween to hold gen runtime down to 8 hours a day.

Steve 


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