Motor Energy Consumption and Efficiency Calculator
Calculate annual electric motor energy consumption (kWh/year) and the kWh savings achieved by upgrading from IE2 to IE3 or IE4 efficiency classes.
Formula used
P_in = (P_shaft × k_load) / η · ΔE = (P_in1 − P_in2) × t (kWh/yr)
IEC 60034-30-1 motor efficiency classes (4-pole, 50 Hz) and annual kWh savings
Nominal efficiency values for 4-pole (1,500 rpm) 50 Hz three-phase asynchronous motors. The last column shows annual energy saved (kWh/year) when upgrading from IE2 to IE4 at 80% load factor and 4,000 operating hours/year.
| Motor power (kW) | IE2 efficiency | IE3 efficiency | IE4 efficiency | IE2 → IE4 savings (kWh/yr) |
|---|---|---|---|---|
| 0.75 | 79.6% | 82.5% | 85.7% | 215 |
| 1.1 | 81.4% | 84.1% | 87.2% | 288 |
| 1.5 | 82.8% | 85.3% | 88.2% | 355 |
| 2.2 | 84.3% | 86.7% | 89.5% | 485 |
| 3 | 85.5% | 87.7% | 90.4% | 609 |
| 4 | 86.6% | 88.6% | 91.1% | 730 |
| 5.5 | 87.7% | 89.6% | 91.9% | 917 |
| 7.5 | 88.7% | 90.4% | 92.6% | 1,140 |
| 11 | 89.8% | 91.4% | 93.3% | 1,470 |
| 15 | 90.6% | 92.1% | 93.9% | 1,862 |
| 18.5 | 91.2% | 92.6% | 94.2% | 2,067 |
| 22 | 91.6% | 93.0% | 94.5% | 2,359 |
| 30 | 92.3% | 93.6% | 94.9% | 2,850 |
| 37 | 92.7% | 93.9% | 95.2% | 3,354 |
| 45 | 93.1% | 94.2% | 95.4% | 3,729 |
| 55 | 93.5% | 94.6% | 95.7% | 4,327 |
| 75 | 94.0% | 95.0% | 96.0% | 5,319 |
Example: 15 kW motor at 80% load for 4,000 hours/year (IE2 90.6% → IE4 93.9%)
- Electrical input power: P₁ = (15 × 0.80) / 0.906 = 13.25 kW; P₂ = (15 × 0.80) / 0.939 = 12.78 kW.
- Annual consumption: 52,980 kWh/year (IE2) vs 51,118 kWh/year (IE4).
- Annual energy savings: 1,862 kWh/year (0.47 kW demand reduction).
How is electric motor annual energy savings (kWh) calculated?
Electrical input power is P_in = (P_shaft × load_factor) / η. Upgrading from efficiency η₁ to η₂ over t annual operating hours saves ΔE = P_shaft × load_factor × t × (1/η₁ − 1/η₂) kWh per year.
Why does electrical input power exceed motor shaft kW?
The kW rating on a motor nameplate is mechanical shaft output; active electrical power drawn from the mains equals shaft power divided by motor efficiency (P_in = P_shaft / η).
What do IE2, IE3 and IE4 efficiency classes mean?
Defined in IEC 60034-30-1, IE2 is high efficiency, IE3 is premium efficiency and IE4 is super-premium efficiency, cutting internal losses in high-duty pumps, fans and compressors.