We fabricated polymer piezoelectric energy harvesters (PEHs) that can generate electric power at wind speed of less than 4.7m/s due to their high sensitivity to wind. In order to optimize their operating conditions, we evaluated three distinct PEH operation modes under the boundary conditions of single-side clamping. We found that a PEH connected to an external load of 120 k Omega shows the largest output power of 0.98 mu W at 3.9 m/s, with wind incident on its side (mode I). We attribute this result to large bending and torsion involved in this operation mode.