A circular economy metric to determine sustainable resource use illustrated with neodymium for wind turbines

The finite capacity of the Earth to provide the resources needed to make products is beginning to dictate policy decisions and citizen behaviours. Herein a methodology is proposed that considers the function (i.e., efficiency and durability) of a product as a way of normalising and hence justifying its resource use. Titled ‘Performance-weighted abiotic Resource Depletion’ (PwRD), this approach allows the resource use of different products to be directly compared, analogous to an absolute sustainability assessment. The PwRD metric quantifies concerns over the supply risk of elements and indicates reasonable actions to sustain a circular economy. This new format of circularity indicator is explained with the case study of neodymium for wind turbine magnets. Individual products as well as larger infrastructure projects such as wind farms can be assessed. It was found that the electrical energy produced by a wind turbine in the USA does not justify the quantity of neodymium required. Demand for the function of products is a variable in PwRD and is equally important as resource use in sustaining a circular economy. In regions of low electricity demand per capita such as the Philippines and Pakistan, the same quantity of neodymium as used in a wind turbine installed in the USA was found to be acceptable for sustaining a circular economy.