Critical materials for low -‐ carbon infrastructure : the analysis of local vs global properties

Introducing new technologies into infrastructure – wind turbines, electric vehicles, information systems, low-carbon materials etc. – will change its materials mix. Many of the new materials required by infrastructure are ‘critical’; their supply is highly likely to be subject to disruption owing to combinations of limited geological reserve, geopolitical instability, environmental issues, increasing demand and limited substitutability and recyclability. Other materials not currently considered critical may become so if introduced into infrastructure, owing to the giga-tonne scale of its annual growth. This potentially poses significant risk to the development of a resilient, lowcarbon infrastructure. Analysis of this risk is the subject of increasing study. One previously overlooked aspect of this study is the relationship between the properties that determine the selection or commissioning of a material, component or technology – the local properties – and the overall vulnerability of the system; a global property. Many materials or technologies have properties that vary considerably and treating them as elements having fixed properties overlooks the possibility that there may be optima within the local-global variable space that could be exploited to minimise vulnerability whilst maximising performance. In this study, we present a framework for such analysis and a review of studies that have informed our approach. We define a measure of relative materials criticality RMC in terms of fraction of critical material, national-scale consumption of the material, a pre-defined criticality index and an output parameter. The analysis is applied to the case study of a wind turbine generator, both at a materials level and a component level. Preliminary analysis suggests that even where the introduction of critical materials (in this case, rare earth metals) enhances technical performance by up to an order of magnitude, the associated increase in criticality may be two or three orders of magnitude. Analysis at the materials and component levels produce rather different results, suggesting that design decisions should be based on analysis at several levels. The relative materials criticality values derived here should be treated as preliminary, as the relationships between its component parameters and the probability of supply disruption are not know with confidence. Nonetheless, this analysis serves to highlight the importance of analysing the introduction of critical materials into infrastructure and introduces a methodology for further development.