Environmental sustainability of high voltage motors: do better efficiency and repair lead to improved environmental impact?

Conference poster, 2022

Various circular economy (CE) strategies, for instance lifetime extension by repair or reuse, have been suggested to improve products’ environmental performance. The literature emphasises the need to better understand the consequences of those CE strategies with assessment tools such as life cycle assessment (LCA). From previous assessments, Böckin et al. (2020) identifies energy use reduction and use extension by maintenance, repair or remanufacturing as relevant CE strategies for durable and active products. However, this conclusion is based on assessments of small- and medium-size electronic products, leaving out more durable and more energy consuming bigger products. In this study, the implementation of two CE strategies, energy use reduction and use extension by repair, is explored for high voltage (HV) motors delivering 135GWh per year over at least 20 years.

Electric motors are prominent active products, representing 50% of the electricity consumption in Europe. Even in small numbers, HV motors represent a significant share of this consumption due to their more intensive use and high output power. Two main HV motor technologies exist: induction motors (IM) and synchronous motors (SM), which are more energy efficient. Both are often used until failure, which frequently occurs in stator windings but could be repaired by rewinding at the expense of a slight decrease in efficiency.

This study aims to compare the life-cycle environmental impact of the two motor technologies and to explore their lifetime extension by repair in comparison to their replacement.

For each motor technology, a cradle-to-grave LCA is performed for global warming and mineral and metal resource depletion impact categories. The IM has an efficiency of 97.3%, the SM an efficiency of 98.3% and both are run 20 years. Results show that the impact of electricity consumption during use is dominant. Besides, the SM has a lower environmental impact than the IM. In term of resource depletion, SM manufacturing is more impactful but lower energy losses during use compensate for the difference.

Repair is modelled with the production of a new stator winding and a decrease in efficiency of 0.7%. Three scenarios are compared. The IM is initially used for 20 years, and an additional 10 years of use is provided by either 1) replacing with an IM with the same efficiency, 2) replacing with the SM, or 3) repair by rewinding. LCA results show that the additional energy losses after repair in scenario 3 offset the gain from avoiding the production of a new motor compared to scenarios 1 and 2.

This study shows that the long lifetime and high energy requirements of HV motors lead the energy efficiency to be an essential factor for the life-cycle environmental performance. Choosing and maintaining high energy efficiency is key in this situation, especially for lifetime extension strategies to be beneficial for the product environmental performance.

Reference:
Böckin et al. (2020), How product characteristics can guide measures for resource efficiency. Resources, Conservation and Recycling 154, 104582.