When evaluating the efficiency of an electric motor, it is incorrect to consider only the instantaneous energy efficiency. The real environmental impact must take into account the entire product life cycle, from the materials used to build it to energy consumption during its years of operation.
High-efficiency motors, typically IE3 rated, offer improved performance by reducing electrical losses, but they usually require greater quantities of copper and special steels. There are also solutions with even higher efficiencies, achieved through the use of permanent magnets containing rare earths.
These materials, in addition to representing a significant geopolitical unknown, improve engine performance but generally entail a higher environmental footprint during the production phase. To understand if an engine is truly “green,” it is therefore necessary to evaluate the balance between the initial impact linked to production and the energy savings achieved during the usage phase.
The role of the duty cycle
In this context, two fundamental factors come into play: the duty cycle and the correct sizing of the motor.
An engine that works for many hours a year (e.g., over 4000–5000 hours/year) tends to amortise the environmental impact of its production, because the energy savings accumulated over time compensate for the additional materials needed to achieve higher efficiency.
Conversely, if the engine only operates for around 2000 hours per year, perhaps with variable loads and not always at full capacity, the energy saved could be too limited to justify the use of a greater quantity of raw materials.
For this reason, the environmental assessment of an electric motor should integrate parameters such as operating hours and average load within a type of analysis Life Cycle Assessment. Specific academic studies have addressed these aspects.
The risk of engine oversizing
Another critical element is engine oversizing. Often, out of caution or fear of overheating, engines that are more powerful than necessary are chosen.
However, an oversized engine predominantly operates at partial load, a condition in which efficiency can be significantly lower. This means that for an equivalent amount of work done, energy consumption can be higher.
Furthermore, a larger engine weighs more, contains greater quantities of copper and steel, and therefore generates a higher environmental impact already in the production phase, without offering a real performance benefit.
True efficiency is born from correct sizing
In summary, the true environmental efficiency of an electric motor is not simply the sum of its electrical performance, but the result of a balance between correct sizing, operating hours, average load, and lifespan.
Only when these factors are consistent with each other is a real benefit for the environment achieved.
In Nicolini & C. We are available to customers to support them in these assessments and identify the most suitable electric motor for each application.
For example: Torrent-Burgués et al., IET Electric Power Applications, 2012.
