An expression for the aerodynamic optimization of aerofoils for 2D lift driven vertical-axis wind turbines is derived as a function of lift slope and drag. As lift slope is proportional to aerofoil thickness, the aerodynamic optimum is found in thick aerofoils, which are also structurally advantageous. Using a genetic optimization algorithm, the objective function is used to generate aerofoils whose performance in a vertical-axis wind turbine is calculated using a potential flow solution of the induction field and 2D polars calculated with XFOIL. The results demonstrate power and structural gains. This approach can lead to reductions in rotor mass due to the thicker and thus stiffer aerofoils, without compromising aerodynamic performance. Copyright © 2014 John Wiley & Sons, Ltd.