HOMER Knowledge Base

Fuel Slope

I am running some calculations, and I have the attached some genset information I found on Perkins. This information leads me to believe the slope on the fuel curve should be zero? Having said that I had information from Kohler which resulted in a similar curve to what you have in Homer. Did you have any other information on how that curve was calculated?

The spreadsheet you sent doesn't mention units or fuel type, but for argument I assumed the data show diesel fuel consumption in gal/hr for different power outputs in percent of rated output. Then I took the data for the 880 kVA generator, converted it to L/hr by multiplying by 3.78, and assumed a power factor of 0.9 meaning the rated output is 792 kW. That gives the following table:

Load		Consumption
%	kW	L/hr
100	792	165
75	594	125
50	396	91
25	198	56

(The spreadsheet also gave a fuel consumption of zero at zero output, but I ignored that because it's not true. There is always a nonzero fuel consumption at idle. Obviously when you turn it off it doesn't consume any fuel, but that's irrelevant.)

I entered those four points into HOMER's fuel curve calculator window to get:

So the intercept coefficient is 0.0024 and the slope is 0.182. When you hit the OK button HOMER will enter those values into the appropriate input boxes on the Generator Inputs window.

A full-load efficiency of 50% seems too high to me, but if all my assumptions are correct, that's what the data say.