Turn field readings into reliable efficiency numbers. Supports diesel and custom fuels with live checks. Download CSV or PDF reports for project records easily.
| Scenario | Rated (kW) | Load (%) | Fuel | Fuel rate | LHV | Estimated efficiency | Heat rate |
|---|---|---|---|---|---|---|---|
| Site lighting + small tools | 60 | 50 | Diesel | 8.0 L/h | 35.8 MJ/L | ~37% | ~9,700 kJ/kWh |
| Concrete batching support loads | 150 | 70 | Diesel | 28.0 L/h | 35.8 MJ/L | ~38% | ~9,500 kJ/kWh |
| Temporary HVAC and dewatering | 250 | 80 | Natural gas | 60 m³/h | 35.8 MJ/m³ | ~33% | ~10,900 kJ/kWh |
Generator efficiency relates electrical output to fuel energy input. On construction projects it supports budgeting, temporary power sizing, and performance verification. This calculator standardizes comparisons by reporting efficiency, heat rate, and estimated losses from the same operating point. It also helps compare rented sets against contract targets. Use it after major load changes, unusual fuel burn, or before long shift operations.
For electrical output, use a kW meter when available. Otherwise record voltage, current, power factor, phase, and the measurement window. For fuel-based checks, record consumption rate from a controller, flowmeter, or timed refill method. Log frequency, harmonics, and any derating factors shown on the controller. Note ambient temperature, elevation, and maintenance condition, because these influence combustion, cooling demand, and alternator losses.
Fuel energy input uses the lower heating value (LHV), which excludes water vapor condensation energy. LHV is widely used for engine heat-rate reporting. Supplier blends can shift LHV, so enter a certificate value when available. If not, use a typical preset and document the assumption in your exported report.
Efficiency (%) is electrical energy out divided by fuel energy in. Heat rate (kJ/kWh) is fuel energy required per kilowatt-hour; lower generally means better performance. Losses (kW) are fuel power equivalent minus electrical output and represent heat rejection, friction, and electrical inefficiencies. Compare results at similar load percentages for fair trending.
Use results to keep generators within an efficient load band and to justify resizing or load consolidation. Repeat tests monthly, after major equipment additions, or after servicing. Export CSV for spreadsheet tracking and PDF for site records, then attach notes on instruments, units, and operating stability. Consistent documentation improves cost control and reduces disputes.
Many engine-driven sets show fuel-to-electric efficiency around 25–45%, depending on size and load. Compare your results at similar loads and with the same fuel assumptions to avoid misleading conclusions.
Use LHV for most engine performance and heat-rate reporting because it excludes water vapor condensation energy. If your contract specifies HHV, convert inputs consistently and document the basis in exports.
Fixed losses such as friction, cooling fans, and alternator magnetization consume a larger share of fuel at low load. Running well below the recommended load band can also reduce combustion quality and increase fuel use.
A calibrated kW meter is best. If using V, I, and power factor, measure all three at steady state and ensure three‑phase voltage is line‑to‑line. Unstable loads can cause fluctuating power and errors.
Prefer a flowmeter or generator controller fuel-rate signal. If using timed refills, use a consistent container, stabilize the load, and run long enough to reduce timing error. Record units carefully.
Heat rate is often easier to compare across reports because it expresses fuel energy per kWh. A falling heat rate indicates improvement, while rising heat rate suggests higher losses, poorer fuel quality, or measurement issues.
Yes. Select a preset for gasoline or natural gas, or choose custom fuel and enter your LHV and consumption units. Ensure your fuel rate units match the LHV units for correct energy input.
Important Note: All the Calculators listed in this site are for educational purpose only and we do not guarentee the accuracy of results. Please do consult with other sources as well.