Generator Fuel Runtime and Backup Duration
How long a standby generator runs on its fuel, the fuel-supply companion to generator-sizing and battery-runtime.
Example
You enter
- Fuel tank capacity (gal) 100
- Fuel consumption at load (gph) 3
- Usable tank fraction (%) 90
- Target backup duration (hr, 0 to skip) 72
You get
- Usable fuel 90 gal
- Runtime on a full tank 30
- For the target duration 216
- Tank for target (gal) 240
Details, formula, and sources
runtime = usable fuel / consumption, where usable = tank x usable% (default 90%). A 100 gal tank at 3.0 gph runs 30 hr (1.25 days); for a 72-hour outage design basis it needs 216 gal of fuel and a 240 gal tank, so the 100 gal tank does not meet it. Enter the consumption at load from the genset data plate (a diesel burns ~0.05-0.08 gal/hr per kW at load). Liquid-fuel-tank case; a utility gas feed has no tank limit. A planning aid; the published fuel curve and the AHJ's fuel-storage rules govern.
usable = tank x usable%/100; runtime_hr = usable / consumption_gph; runtime_days = runtime_hr/24; for a target: fuel = consumption_gph x target_hr, tank_needed = fuel / (usable%/100).
Generator fuel runtime from the fuel supply and consumption, first-principles; the genset manufacturer's published fuel-consumption curve governs the rate.
Runtime = usable fuel / consumption is first-principles arithmetic; the consumption rate is from the generator's published data plate / fuel curve.
Estimate. AHJ and licensed professional govern.
Field names used by the API: tank_capacity_gal, consumption_gph, usable_pct, target_runtime_hr, usable_gallons, runtime_hr, fuel_for_target_gal, tank_for_target_gal
- Runtime usable fuel / consumption; usable = tank x usable% (default 90%)first-principles
- Consumption from the genset data plate / fuel curve (~0.05-0.08 gal/hr per kW at load for diesel)manufacturer fuel curve
- Target sizing fuel = gph x target hours; tank = fuel / usable%; a 72-hour basis is common (NFPA 110)backup-power planning