When is repair environmentally beneficial? The case of high-voltage electric motors

Poster (konferens), 2023

Use extension by repair is a circular economy (CE) strategy that has been advocated to improve products’ environmental performance and resource efficiency. Previous studies have shown that this does not necessarily hold for energy-using products, for instance, when a more energy-efficient product is available for replacement. The requirements for use extension to be beneficial have been found to vary with the product and its use conditions. However, resource depletion is seldom discussed, and the case of very long-lived and energy-intensive products has not been addressed yet.

An example of such an energy-intensive product is high-voltage (HV) electric motors, typically used for more than 20 years and in operation for 50 weeks a year full time. Electric motors represent 50% of the electricity consumption in Europe and despite being few, HV motors represent a significant share of this consumption. The two HV motor designs, induction motors (IM) and synchronous motors (SM), are often used until failure, commonly occurring in stator windings which could be repaired but with the risk of affecting energy efficiency.

This work aims to provide recommendations on important aspects for use extension to be environmentally beneficial for long-lived and energy-intensive products.

Cradle-to-grave LCAs are performed for global warming and mineral resource depletion to compare (1) the two motor designs and (2) each motor with and without use extension through repair. The motors are chosen to deliver the same output of 16 MW and the functional unit is set to one year of operation. The IM has an energy efficiency of 97.3%, the SM has an efficiency of 98.3% and both are run for 20 years. The additional use time and the efficiency reduction after the repair are left as varying parameters between 1 and 20 years and between 0 and 1% respectively.

Results show that, due to high energy use and long lifetime, the impact of electricity use during motor use is dominant for both global warming and resource depletion. This dominance remains with different electricity mixes, including in a scenario with hydroelectricity only. For resource depletion, it is due to copper in transmission lines and resources for electricity production (e.g., uranium from nuclear energy production). The dominance of the use phase results in energy efficiency being key to the environmental performance of HV motors. The more efficient design, the SM, results in lower impacts than the IM in both impact categories. In terms of resource depletion, SM manufacturing is more impactful but lower energy losses during use compensate for the difference. Besides, additional energy losses from a small energy efficiency reduction offset the gain from the repair for both global warming and resource depletion. The gain from the use extension by repair is small compared to the benefit of choosing the more efficient design.

Choosing and maintaining high energy efficiency is key for long-lived and energy-intensive products’ environmental performance due to their high energy requirements and long lifetime. Thus, efforts should be channelled on ensuring high energy efficiency by design and after repair. This is relevant for both policy-making and manufacturers or users when prioritising strategies for improving products’ environmental performance. Finally, as conclusions are similar for global warming and resource depletion, this work demonstrates the importance of including resource use from electricity production and transmission when exploring the use extension of energy-using products.