The true cost of motors

ELECTRIC MOTORS account for a significant share of industrial power consumption, making them a major contributor to both operating costs and environmental impact. While buying a motor is a one-time expense, it represents less than two per cent of the total cost of ownership (TCO), meaning that the other 98% consists almost entirely of energy usage.

What running costs can tell you

Understanding a motor’s consumption offers financial and operational advantages. Regular monitoring is essential — without it, reducing energy use is nearly impossible. Tracking consumption not only shows where costs come from but also creates a baseline to spot changes.

The data can also highlight issues that might otherwise be undetected. For example, if a motor consumes 50kW one week and 75kW the next, that variation may reflect a problem on the line, a motor that is over or undersized, or even a difference in power consumption between processes or products on a production line. This can affect product pricing, margins and maintenance planning. Recording trends and fluctuations in motor running costs can provide helpful insights to put strategies in place to improve overall operation efficiency and positively impact the bottom line. 

Calculating the cost

Motor running costs are primarily dictated by electricity prices, the power rating of the motor and its annual running hours. It is also important to remember when choosing a motor that its rated power tells you how much mechanical output it can deliver, not how much electricity it consumes. For example, a 7.5 kW motor can always provide 7.5kW of mechanical power, but the amount it draws from the power supply depends on its efficiency. A less efficient motor will absorb more input power to deliver the same output, while a high-efficiency motor achieves the same output using less energy. This means that not all the power taken from the grid is always used productively.

Motor running costs are directly linked to power along with several other parameters. This information can be found on the motor nameplate or manual. Modern energy meters also offer convenient way to measure energy usage, and this data can be used to work out the running cost of a motor.

First, calculate the energy usage in kWh by multiplying the annual operating time by the rated power of the motor. Losses can be calculated using its efficiency rating, and this combined with the energy use gives the total chargeable kWh. When this is multiplied by the tariff a business pays per kWh, this gives the total annual motor running costs. For example, a 45 kW IE3 motor running continuously (8760 hours) at €0.28/kWh could cost over €40,000 per year. 

Cost cutting strategies

Once businesses understand how their motors are performing, there are several ways to reduce energy use and operating costs. Consulting with an expert to evaluate the entire system is a helpful first step to identify opportunities to improve operational efficiency. One of the most commonly used strategies is smarter control. It is important to remember that overall, the best energy you will save is the energy you don’t use. By fitting variable speed drives (VSDs), motors can run at the speed the application requires and even a small reduction in speed can deliver large energy savings. 

Correct sizing and careful selection also play a crucial role. A motor that meets the actual demands of the application will operate closer to full load, improving both efficiency and power factor. Beyond the motor itself, evaluating other plant equipment is important. Worm gear units, for example, may operate at efficiencies as low as 45%, while switching to a bevel-helical unit can increase efficiencies to around 90% significantly cutting wastage. 

Maintenance also matters. While motors are often quite low-maintenance, the machinery they drive may require more frequent intervention. Worn or seized components can force motors to work harder, drawing more current than necessary. 

Finally, minor adjustments such as switching equipment off when not needed can offer easy savings without major investment or disruption. Together, these strategies show that savings often come from a combination of smarter choices across motors, drives and the wider plant rather than a single change.

An efficiency success story

An example of just how effective a holistic approach can be seen in an industrial exhaust fan project. The objective was to improve flow control of the vacuum level in a dryer while reducing overall energy consumption. Fitting a VSD allowed more precise control of the fan, with its speed adjusted according to the pressure requirements. 

Technidrive also downsized the motor to 110kW and upgraded it to an IE4 model. The results were measured across a week of production and the data showed significant improvements. 

Energy costs were reduced by 22% on a weekly comparison, and energy consumption per tonne of material fell by 19%. Comparing hourly operation, the fan consumed 38% less energy, even though it ran for 26% longer, delivering more than €30,500 in annual savings and cutting CO₂ emissions by 757 kilograms per year.

The bigger picture

Calculating motor running costs is an important step for any operation to manage its energy use, reduce expenses and meet sustainability goals. This allows companies to make informed decisions on investment priorities and identify where improvements can be made using valuable insights into where energy is going. 

However, some of the biggest opportunities lie beyond the motor. Poor system design, inefficient equipment or insufficient control can all drive up costs, and evaluating the entire operation can highlight the true savings potential. By combining accurate cost calculations with a holistic view of systems and processes, businesses can achieve meaningful reductions in both costs and energy consumption. 

David Strain is technical director at Technidrive

www.technidrive.co.uk