Comparative life cycle assessment: Reinforcing wind turbine blades with carbon nanofibers

Wind energy conversion (WEC) is dependent on wind power density, which increases with elevation and swept area of the rotor. Many components are readily scalable and size-independent; whereas, turbine blades have presented a new frontier in aerodynamic design. As the limits of glass fiber-reinforced plastics (GFRP) have been reached in this field, there is now a materials development problem in achieving outlooks for larger, more resilient WEC systems. A hybrid material is under development, which uses vapor-grown carbon nanofibers (VGCNF or CNF) to reinforce the interface of a glass fiber/epoxy matrix. This research aims to determine life cycle effects of substituting GFRP in large turbine blades with the hybrid material. A review of literature, databases, and industry reports on life cycle data for wind turbines helped to establish a baseline descriptive life cycle assessment (LCA). Trends of new installations were assessed to determine appropriate boundaries for comparison. Results indicate that cradle-to-gate processing energy of the new material is 1.4-7.7 times greater than for the original GFRP material on a MJ/kg basis under implicit assumptions of weight savings. Effects on energetic return on investment (EROI) vary from insignificant to substantial according to upstream process choices for CNF manufacture and solvent handling. All conclusions inherently assume that CNF-incorporation would lead to realizable technologies for substantially increasing either size or life span of turbine blades concomitant with weight savings. It is not yet substantiated whether replacement of long carbon fibers is advantageous both mechanically and energetically.