It depends on the duty rating and fuel supply. Portable diesel units typically run 10-72 hours between refueling. Prime power (PRP) units can operate up to 250 hours continuously before requiring a 24-hour rest period per ISO 8528. Continuous power (COP) units are designed for unlimited runtime with adequate fuel and maintenance. Standby (ESP) units are limited to 200 hours annually. Our calculator factors in your specific duty rating.

Fuel consumption varies by generator size, engine efficiency, and load percentage. As a rule of thumb, industrial diesel engines consume approximately 0.20-0.28 liters per kWh depending on load and engine brand. A 100kW generator at 75% load uses roughly 18-22 L/hr. A 500kW unit at the same load consumes 90-110 L/hr. Our calculator uses specific fuel consumption curves from Cummins, Perkins, Yuchai, and Weichai engines for precise estimates.

Altitude reduces air density, which decreases engine power output and increases fuel consumption per kWh. Standard derating is approximately 3-4% per 300 meters above sea level. At 2,000 meters, a generator produces roughly 20% less power and consumes proportionally more fuel per kWh, reducing runtime accordingly. Our calculator applies ISO 3046 altitude corrections automatically.

Wet stacking occurs when a diesel generator operates below 30% rated load for extended periods. At low loads, combustion temperatures are insufficient to burn fuel completely, causing carbon and unburned fuel to accumulate in the exhaust system. This reduces engine efficiency, increases fuel consumption, and can permanently damage the turbocharger and exhaust components. The practical effect is that runtime at very low loads is worse than calculated because fuel is wasted rather than converted to power.

Required tank capacity equals Hourly Consumption x Desired Runtime x (1 + Safety Margin). For critical facilities, ZC Power recommends a 20% safety margin. For a 500kW generator consuming 100 L/hr requiring 72 hours of runtime: 100 x 72 x 1.20 = 8,640 liters minimum. For compliance applications, use the specific mandated duration — CMS requires 96 hours for healthcare, while NFPA 110 specifies requirements based on risk classification. Our calculator includes pre-built compliance modes.

Not proportionally, and not safely. While fuel consumption in liters per hour decreases at lower loads, fuel efficiency per kWh actually worsens below 30% load due to wet stacking. The optimal efficiency band for most diesel engines is 70-85% rated load. Running continuously below 30% load wastes fuel, damages the engine, and often voids warranties. Our calculator flags when your load profile falls into the wet-stacking danger zone.

A quality 100kW industrial diesel generator typically consumes: 25% load: 6-8 L/hr | 50% load: 11-13 L/hr | 75% load: 18-22 L/hr | 100% load: 24-28 L/hr. Exact figures depend on engine brand, alternator efficiency, ambient conditions, and fuel quality. Our calculator provides precise estimates using manufacturer test data rather than generic rules of thumb.