Purchase price does not equal total cost
Anyone procuring an electric drive usually compares catalog prices: Motor, gearbox, frequency inverter. However, with continuously operated industrial drives, these acquisition costs are only 5-15 % of the total life cycle costs out. By far the biggest cost driver is energy - and this is hardly calculated when purchasing.
For an 11 kW drive with 6,000 operating hours per year and a service life of 15 years, the energy costs alone amount to over €190,000 - the purchase price of the motor is between €800 and €1,200. Total Cost of Ownership (TCO) makes this imbalance visible and provides the basis for well-founded purchasing decisions.
Key message
At 6,000 h/year of operation, over 80 % of the TCO are energy costs. An improvement in overall efficiency of just 5 percentage points saves more over 15 years than the motor actually costs.
TCO components in the drive context
The total costs of a drive system are divided into five blocks. The following table shows typical proportions for continuous industrial operation at 6,000 h/year over a service life of 15 years:
| TCO block | Typical contents | Share of TCO |
|---|---|---|
| CAPEX components | Motor, gearbox, frequency inverter, clutch | 3–8 % |
| CAPEX installation | Installation, cabling, commissioning | 1–4 % |
| Energy costs | Electrical energy over the entire operating time | 70–90 % |
| Maintenance costs | Lubrication, bearing change, seals, oil change | 3–10 % |
| Downtime costs | Production downtime, emergency repair, express delivery | 1–8 % |
| Waste disposal | Waste oil disposal, metal recycling, dismantling | < 1 % |
The shares vary depending on the operating profile: drives with a few hundred operating hours per year have relatively higher CAPEX shares; continuous operation systems (pumps, compressors, fans) are at the upper end of the energy range.
Energy cost model with sample calculation
Basic formula
The annual energy costs of a drive are calculated as follows:
E_year = (P_mech / η_total) × t_operation × c_current
- P_mech - Mechanical effective power at the output shaft [kW]
- η_total - Overall efficiency motor × gearbox (dimensionless)
- t_Operation - annual operating hours [h/year]
- c_current - Industrial electricity price [€/kWh]
Example calculation IE3 vs. IE4 over 15 years
Boundary conditions: 11 kW mechanical output power, 6,000 h/year, electricity price 0.18 €/kWh, planetary gearbox η = 0.96, motor efficiency according to IEC 60034-30-1.
| Parameters | IE3 (η = 0.915) | IE4 (η = 0.932) | Difference |
|---|---|---|---|
| η Motor | 0.915 | 0.932 | +1.7 % |
| η total (motor × gearbox 0.96) | 0.879 | 0.895 | — |
| Electrical power consumption P_el | 12.51 kW | 12.29 kW | 0.22 kW |
| Energy consumption / year | 75,065 kWh | 73,741 kWh | 1,324 kWh |
| Energy costs / year | 13,512 € | 13,273 € | 239 € |
| Energy costs over 15 years | 202,672 € | 199,096 € | 3,576 € |
The table shows the overall system comparison including the gearbox. Isolated to the motor (without gearbox), the difference in efficiency IE3→IE4 is even clearer: IE3 consumes 12.02 kW, IE4 only 11.80 kW - a difference of 1,320 kWh/year or €238/year.
Maintenance Costs: Lubrication, Bearings, Wear Parts
Lubrication intervals
Transmission mineral oil should be changed after 10,000-15,000 operating hours or every two years at the latest - regardless of the operating time. Synthetic gear oils (PAO, PAG) last up to 30,000 hours and reduce maintenance costs despite their higher cost price. For a complete method of calculating intervals, see the guide to Set lubrication intervals correctly.
Bearing replacement after L10 service life
Rolling bearings are wear parts with a calculable service life. The dynamic load rating and the load profile provide the L10 service life (10 % probability of failure). Typical guide values for rolling bearings in gearboxes:
- Lightly loaded bearings (deep groove ball bearings, n < 1,500 1/min): L10 = 20,000-50,000 h
- Medium-loaded bearings (tapered roller bearings, worm gear bearings): L10 = 10,000-25,000 h
- Highly loaded bearings (planetary gears, hollow shaft): L10 = 15,000-30,000 h with good lubrication
Preventive bearing replacement after reaching 80 % of the L10 service life typically costs € 200-600 (bearing + labor). Reactive replacement after bearing damage causes additional consequential damage to shafts and housings as well as downtime costs - often five to ten times higher.
Other wearing parts
- Rotary shaft seals (RWDR): every 15,000-20,000 h or in the event of visible oil leakage - neglected leakage leads to bearing damage
- Coupling elements: Check elastomer inserts every 5-10 years depending on the load spectrum
- Brake pads (for holding brakes): according to manufacturer's specifications; typically every 3-5 years in continuous operation
Rule of thumb: Preventive maintenance costs amount to approx. 1-2% of the purchase price per year. For a gearbox worth €1,500, this amounts to €15-30 per year - a minimal TCO item, but one that prevents downtime costs in the four-digit range.
Comparative Calculation: Worm Gearbox vs. Planetary Gearbox
The difference in efficiency between worm gearboxes (η ≈ 70 %) and planetary gearboxes (η ≈ 96 %) has a massive impact on the TCO over the service life. The following calculation shows the pure energy cost comparison with the same effective mechanical power.
Boundary conditions: 11 kW mechanical output power, IE3 motor (η = 0.915), 6,000 h/year, 0.18 €/kWh, 10-year observation period.
| Parameters | Worm gearbox η = 70 % | Planetary gearbox η = 96 % | Difference |
|---|---|---|---|
| Gearbox efficiency | 70 % | 96 % | 26 % |
| η total (motor × gearbox) | 0.641 | 0.879 | — |
| Electrical power consumption P_el | 17.16 kW | 12.51 kW | 4.65 kW |
| Energy consumption / year | 102,971 kWh | 75,065 kWh | 27,906 kWh |
| Energy costs / year | 18,535 € | 13,512 € | 5,023 € |
| Energy costs over 10 years | 185,347 € | 135,115 € | 50,232 € |
| CO₂ over 10 years (0.38 kg/kWh) | 391 t CO₂ | 285 t CO₂ | 106 t CO₂ |
Result: The worm gearbox costs around €50,000 more in energy over 10 years. A planetary gearbox of this size costs around €500-1,500 more to purchase - amortization takes less than 4 months. Further efficiency considerations can be found in the guides Calculate gearbox efficiency and Worm gearbox vs. planetary gearbox.
IE3 vs. IE4: Motor classes and amortization
The IEC 60034-30-1 standard defines the efficiency classes IE1 to IE5 for three-phase motors. IE4 (Super Premium Efficiency) exceeds IE3 by approx. 1.5-2.5 percentage points in efficiency. The additional price for 11 kW motors is 15-20% (approx. €150).
| Parameters | IE3 | IE4 |
|---|---|---|
| Motor efficiency (11 kW, 4-pole) | 91.5 % | 93.2 % |
| Electrical power consumption | 12.02 kW | 11.80 kW |
| Energy consumption / year (6,000 h) | 72,131 kWh | 70,813 kWh |
| Annual energy savings (0.18 €/kWh) | — | 238 €/year |
| Typical purchase price | approx. 800 € | approx. 950 € (Δ +150 €) |
| Amortization of the additional price | — | approx. 8 months |
Calculation: Δ = €150 surcharge / €238/year Savings ≈ 0.63 years (approx. 8 months). For any drive with more than 2,000 operating hours per year, IE4 is clearly the economically superior choice. An overview of all efficiency classes IE1-IE5 can be found in the guide IE Efficiency Classes: IE1 to IE5 Explained.
CO₂ balance Scope 2: Emissions from operating electricity
Scope 2 emissions are caused by purchased electricity. According to data from the German Federal Environment Agency (UBA), the emission factor for the German electricity mix in 2025 is:
CO₂ [kg] = E_Consumption [kWh] × 0.38 kg CO₂/kWh
Source: Federal Environment Agency, emission factor electricity mix DE 2025. For green electricity contracts, the factor is reduced to 0-0.10 kg CO₂/kWh.
Based on the comparative gearbox calculation (11 kW, 6,000 h/year, 10 years), the following Scope 2 emissions result:
| Drive | Energy consumption 10 years | CO₂ emissions |
|---|---|---|
| IE3 + worm gear unit (η=70 %) | 1,029,706 kWh | 391 t CO₂ |
| IE4 + planetary gearbox (η=96 %) | 708,127 kWh | 269 t CO₂ |
| Savings through optimal selection | 321,579 kWh | 122 t CO₂ |
122 tons of CO₂ correspond to the mileage of a mid-range car of around 750,000 kilometers. For companies with ESG reporting and CO₂ reduction targets, gearbox selection is therefore a directly measurable lever - without changing the process, just by selecting better components.
Influence of the frequency inverter: Cubic characteristic curve
For applications with variable load requirements - especially pumps, fans and compressors - a frequency inverter (FI) offers the greatest energy-saving potential. The reason for this is the cubic dependence of the power on the speed (affinity laws):
P₂/P₁ = (n₂/n₁)³
With speed reduction to 80 %: P₂ = (0.8)³ × P₁ = 0.512 × P₁ - i.e. only 51.2 % of the rated output, a saving of 48.8 %.
Example: Pump Drive 11 kW
A pump runs continuously at full load without a frequency converter. With frequency converter and demand-based control at an average speed of 80 %:
- Without FI: 11 kW × 6,000 h/year × 0.18 €/kWh / 0.879 = 13,512 €/year
- With FI (80 % speed → 51.2 % load): 0.512 × 13,512 = 6,918 €/year
- Savings: 6,594 €/year - a VFD (approx. €800–1,500) pays back in less than 3 months
This cubic characteristic curve does not apply to all load profiles. Conveyor belts, strokes and constant-torque-loaded drives follow a linear P ~ n dependency - the savings through speed control are lower in these cases. More on this in the guide Frequency inverters: When is it worth using them?
10-point checklist for purchasing (B2B)
This checklist helps purchasers and designers to anchor TCO-relevant requirements in specifications and bid comparisons:
Specify efficiency class
Require motor class IE3 as minimum, IE4 for >2,000 h/year. Specify minimum gearbox efficiency in the specification (e.g., η ≥ 94%).
Select gearbox type based on operating hours
Worm gearbox only for <2,000 h/year or when self-locking is absolutely required. Specify planetary gearbox for continuous operation.
Request L10 bearing service life
Require minimum L10 for all load-bearing bearings in the offer (e.g., L10 ≥ 20,000 h at n = 1,500 rpm).
Have lubrication intervals documented
Oil/grease change intervals and recommended lubricant grades must be included in the delivery scope.
Ensure spare parts availability
Manufacturer commitment for bearings, rotary shaft seals, and gearbox assemblies for at least 10 years after delivery.
Check variable frequency drive compatibility
Motor must be designed for VFD operation (insulation class F minimum, bearing protection for VFD use).
Operating hour counter / condition monitoring
For drives >15 kW or critical machines, plan operating hour counting or vibration/temperature monitoring.
Include TCO calculation in bid comparison
Calculate not only the purchase price, but energy costs over 5–10 years as a comparison metric (use the formula from this article).
Request manufacturer warranty and MTBF
Mean Time Between Failures (MTBF) and warranty scope (incl. consequential damages) must be explicitly requested and compared.
Disposal plan for operating fluids
Waste oil disposal certification and recyclability of gearbox housings (aluminum/gray cast iron) for ESG documentation.
TCO analysis for your drive project?
Our application engineers will calculate the total cost of ownership for your application - free of charge and without obligation. Bring along your operating profile (performance, operating hours, electricity price) and receive a well-founded recommendation.
Request a consultation now →