TCO: More Than Just the Purchase Price
The total cost of ownership (TCO) of a drive train is broken down into six categories: purchase, installation, energy, maintenance, downtime, and disposal. In continuous industrial operation (approximately 6,000 operating hours per year, 15-year service life), energy accounts for 70–90%. The purchase price—which is usually the focus of bid comparisons—accounts for only a fraction of the total cost of ownership: components make up about 3–8%, and together with installation, about 5–12% (approximate value). The figure shows the proportions of all six categories.
Description and values of the figure
The energy component (highlighted) by far dominates the life-cycle costs at 70 to 90%—significantly more than purchase (3–8%), installation (1–4%), maintenance (3–10%), downtime (1–8%), and disposal (less than 1%) combined. This explains why investing in higher efficiency usually pays off over the service life, even if the initial purchase is more expensive.
| Name | from (%) | to (%) |
|---|---|---|
| Anschaffung | 3 | 8 |
| Installation | 1 | 4 |
| Energie | 70 | 90 |
| Wartung | 3 | 10 |
| Stillstand | 1 | 8 |
| Entsorgung | 0 | 1 |
Why Efficiency Is the Key Cost Factor
Because energy accounts for the largest portion, the efficiency of individual components has a disproportionately large impact. The overall efficiency η of the motor and gearbox is the key factor determining power consumption. In the example in this learning unit, an IE3 motor (11 kW, 4-pole, η ≈ 91.4 %) drives a load with 11 kW of mechanical output power via the gearbox: With a worm gearbox (η ≈ 70 %), this results in η_ges ≈ 0.64; with a planetary gearbox (η ≈ 96 %), η_ges ≈ 0.877. For simplicity, the motor efficiency is assumed to be the same for both variants (IE3, 91.4 %); in reality, the worm gearbox variant requires a larger motor. For the same net power output, the worm gearbox thus consumes approximately 37 % mehr of electrical energy per year more than the planetary gearbox. The same applies to motors: A higher efficiency class costs more, but quickly pays for itself with many operating hours.
E = P / η · h
E = Annual energy consumption (kWh) · P = Mechanical output power (kW) · η = Overall efficiency of the drive train = η_Motor · η_Getriebe (decimal value) · h = Operating hours per year
Higher energy consumption also means higher CO₂ emissions. The connection is simple:
m_CO₂ = E · f
m_CO₂ = CO₂ quantity (kg) · E = energy consumption (kWh) · f = emission factor of the electricity mix (kg CO₂/kWh), published annually by the Federal Environment Agency; German electricity mix for 2025: f ≈ 0.344 kg CO₂/kWh
In the example provided in this learning unit, over 10 years of operation results in approximately 355 t CO₂ for the worm gearbox compared to approximately 259 t for the planetary gearbox—a difference of approximately 96 t.
Maintenance as a small but important section
As a rule of thumb, preventive maintenance costs about 1–2% of the purchase price per year—a small expense that helps prevent costly consequential damage. This includes changing the oil in the gearbox, replacing rolling bearings in a timely manner, and installing new shaft seals. The standard intervals are listed below the figures for reference.
Procurement costs: more than just the unit price
From a purchasing perspective, the unit price is just one of several cost components—in addition, there are process costs per order, supplier relationship costs, inventory holding costs, and capital tie-up costs. According to a supplier source, consolidating procurement needs with fewer suppliers can yield a 3–8% price advantage on the consolidated volume—though no independent study exists on this topic. A framework agreement is not a cost-free benefit: purchase obligations and contract terms offset the price advantage.
Mnemonic
Worked example: Energy consumption ratio
Based on the example in this learning unit (IE3 motor, 11 kW; η ≈ 91.4%; 6,000 h/year): Worm gearbox (η_ges ≈ 0.64) 103,157 kWh/year; planetary gearbox (η_ges ≈ 0.877) 75,219 kWh/year. For simplicity, the motor efficiency is assumed to be the same for both variants (IE3, 91.4 %); in reality, the worm gear variant requires a larger motor.
(103,157 − 75,219) / 75,219 ≈ 0.371 → approximately 37% higher energy consumption for the worm gearbox—assuming the same electricity price, this results in exactly the same proportion of higher energy costs, also 37%.
Description and values of the figure
Under otherwise identical conditions (IE3 motor, η ≈ 91.4%, assumed to be the same for both variants for simplicity; in reality, the worm gearbox variant requires a larger motor), the worm gearbox consumes approximately 103,157 kWh per year, while the planetary gearbox (highlighted as the more efficient choice) consumes only approximately 75,219 kWh—a difference of about 37%. Both values represent pure energy quantities (kWh), not cost amounts (Price-Policy-Gate).
| Name | Value (kWh) |
|---|---|
| Schneckengetriebe | Lower efficiency, more energy |
| Planetengetriebe | ≈37% less energy than a worm gear |
Reference Figures
You don’t need to memorize these values. They help with classification and when making an inquiry.
| Topic | Guideline value |
|---|---|
| Proportions of cost categories during continuous operation | Purchase 3–8%, installation 1–4%, energy 70–90%, maintenance 3–10%, downtime 1–8%, disposal less than 1% (guideline values) |
| CO₂ in the example: worm gear vs. planetary gear, over 10 years | approximately 96 metric tons more (355 metric tons compared to 259 metric tons; emission factor for the German electricity mix in 2025: 0.344 kg CO₂/kWh, source: Federal Environment Agency) |
| IE4 motor instead of IE3 | The more operating hours the motor runs per year, the faster the additional cost pays for itself; the calculation depends on the actual additional cost and the price of electricity. |
| Changing the Gear Oil | 10,000–15,000 operating hours, at least every two years |
| Preventive Replacement of Rolling Bearing | at approximately 80% of the L10 service life |
| Replacing shaft seals | All 15,000 –20,000 operating hours |
| Bundling with additional specification harmonization | According to the supplier, a price advantage of 10–15% in some cases (3–8% without harmonization) |
Knowledge check
Answer all three questions, then click "Check". From 2 of 3 correct answers, the unit counts as completed. You can retry at any time.
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