Wind turbine blades' basic physics and economics are relatively simple. For one, their power output is roughly proportional to the square of blade length. This relationship pushes designers to create increasingly longer blades for harvesting additional energy. Secondly, as blades get longer, weight increases – by about the cube of the length – which raises raw material costs. This correlation sends designers in search of weight-efficient geometries that are strong and rigid enough to weather the increased loading inherent in longer blades.