Comparative life cycle assessment of electric motors with different efficiency classes: a deep dive into the trade-offs between the life cycle stages in ecodesign context

Current ecodesign instruments usually focus on improving single life cycle stages, like the energy efficiency classes for motors put on the European market, which focus on the use stage. Resulting trade-offs between the life cycle stages are however often not integrated properly, like for instance trade-offs between manufacturing stage and use stage.

The goal of this study was to evaluate the trade-offs between the additional efforts of producing energy-efficient motors (achieved, e.g., via different materials for certain components) and the advantages gained from the improved efficiency in operation.For this case study, a life cycle assessment methodology according to ISO 14040/44 was applied for the whole life cycle (cradle to grave) of three electric motors, each from a different efficiency class, and one serving as baseline.

The motors under study have the following specifications in common: asynchronous technology, 110 kW nominal power, cast iron series, and 4-poles. To evaluate the use stage, two different operational profiles were studied for 20 years' service life.The results clearly indicated the dominance of the use stage in the motors' life cycles and that an increase in efficiency pays off environmentally within the first month of operation in the applied load-time profiles.

The dominating environmental impact categories, like ionizing radiation and global warming potential, relate to the consumption of electricity. The study results indicated also that the increase of the analyzed motors' efficiency encompasses trade-offs between the stages materials, manufacturing, and end-of-life versus the use stage in regard to toxicity and (metal) resource depletion aspects, i.e., a burden shifting between energy-related impacts and the toxicity- and resource depletion-related impacts.In the analyzed study set-ups, including the modeled energy generation scenarios for Europe in 2050, an environmental break-even is achieved in less than a month in all impact categories except for human toxicity.

Thus, the further improvement of energy efficiency of drive systems is and will stay a central ecodesign lever. However, toxicity and resource depletion trade-offs should be considered carefully within decision support and decision-making, and further research on related characterization models is necessary.

Further, it is concluded that the load-time profile as well as the motors' service life have a high influence, and therefore, designing drive systems in context with the application seems to be an important approach to facilitate ecodesign.