A model of the power coefficient of a mid-scale Magnus wind turbine using numerical solutions of the Blade Element Momentum Theory and symbolic regression is presented. A direct method is proposed for solving the nonlinear system of equations which govern the phenomena under study. The influence of the tip-speed ratio and the number, aspect ratio, and the angular speed of the cylinders on the turbine performance is obtained. Results show that the maximum power coefficient is on the order of 0.2, which is obtained with two low aspect ratio cylinders, a dimensionless cylinder speed ratio of 2, and a turbine tip-speed ratio between 2 and 3. The predicted power coefficient at low tip-speed ratio suggests that a Magnus turbine may be adequate in the urban environment.