How to Calculate Diesel Generator Fuel Consumption and Running Cost

The basic formula

• Fuel consumption in litres per hour equals rated power in kW multiplied by specific fuel consumption in g/kW.h, divided by 1000 and by the diesel density of about 0.84 kg per litre.
• Our air-cooled small diesel engines have a specific fuel consumption of about 295 g/kW.h.

Worked examples

• 5 kW set at full load: 5 x 295 / 1000 / 0.84 = about 1.75 litres per hour.
• 9 kW set at full load: 9 x 295 / 1000 / 0.84 = about 3.16 litres per hour.
• 18 kW set at full load: 18 x 295 / 1000 / 0.84 = about 6.32 litres per hour.

Real running cost is usually lower

• Most standby sites average 40 to 60 percent load, not 100 percent.
• At half load the fuel consumption drops roughly proportionally, so use these figures as an upper limit.

Why specific fuel consumption matters

• A lower g/kW.h figure means the same power for less diesel over the life of the machine.
• When comparing suppliers, always ask for the fuel consumption rate on the datasheet, not just the tank size.