Fuel Consumption Calculator
Estimate fuel usage and operational costs for your diesel generator. Our technical tool uses specific fuel consumption (SFC) metrics to provide accurate budgeting data.
Operational Parameters
Calculated Power Output
At 75% load, your generator is producing approximately 0 kW of real power.
Consumption Summary
Technical Guide to Diesel Generator Fuel Consumption
Fuel is the single largest operating expense for any diesel generator system. Understanding exactly how much diesel your engine consumes is vital for budgeting and operational planning.
The Science of SFC
Engineers measure fuel efficiency using a metric called Specific Fuel Consumption (SFC). This is the mass of fuel consumed per unit of power produced. A modern diesel engine typically consumes between 0.24 and 0.28 liters of diesel for every kilowatt-hour (kWh) generated, though that figure worsens noticeably below 50% load, which is why the calculator above uses a sliding SFC scale rather than a single fixed number.
Worked Example: 150kVA Generator, 8-Hour Outage
Take a 150kVA generator running at 80% load with a 0.8 power factor. Actual electrical output is generator size × power factor × load percentage: 150 × 0.8 × 0.8 = 96kW. At 80% load the engine sits in its efficient operating band, so SFC stays at the base rate of roughly 0.27 litres per kWh, giving fuel burn of 96 × 0.27 ≈ 25.9 litres per hour.
Over an 8-hour outage, that's approximately 207 litres of diesel consumed. At a typical pump price of KES 165 per litre, the fuel cost for that single outage comes to roughly KES 34,000. Running the same generator at just 30% load instead — a common mistake when a unit is oversized for the connected equipment — pushes SFC up to around 0.30 L/kWh even though the kW output is lower, which is the efficiency penalty behind "wet stacking" and why correct generator sizing affects fuel budgets directly, not just equipment longevity.
Factors Affecting Consumption
1. Load Profile
Running a generator at its peak efficiency point (70-80% load) provides the best "liters per kilowatt" ratio. Low load operation increases SFC significantly.
2. Maintenance Condition
Dirty air filters and worn fuel injectors can cause poor atomization and restricted airflow, directly increasing fuel consumption by up to 15%.
Frequently Asked Questions
How much fuel does a 100kVA generator use?
At 75% load, a 100kVA generator typically consumes about 16-18 liters of diesel per hour.
Does low power factor increase fuel usage?
Yes. A low power factor increases the current the alternator must produce, creating more heat and resistance, requiring more fuel.
Why does running a generator at low load waste fuel?
Diesel engines are most fuel-efficient in their 70-80% load band. Below roughly 50% load, incomplete combustion raises SFC, so the same kW of useful output costs noticeably more diesel — on top of causing wet-stacking if sustained for long periods.
Professional Audit
Calculators provide estimates. For mission-critical facilities, a physical load audit is mandatory to ensure 100% capacity accuracy.