The most significant challenge associated with employing small-scale H-Darrieus wind turbines is to ensure that they self-start without compromising their efficiency at the design operating condition. One of the key and straightforward methods to improve the turbine performance is to choose an optimized blade profile. It has been shown that by creating rounded protuberances (tubercles) around the blade leading edge, not only do the blades demonstrate a more gradual stall characteristic but also that the tubercles significantly increase the blade lift performance in the post-stall regime at the expense of slightly degraded lift performance in the pre-stall regime. This effect might be beneficial for the H-Darrieus turbine application where the blades experience extreme incidence range during the turbine start-up period. Therefore, in this study the performance of standard NACA0021 blades is compared experimentally to a modified set of blades which have a sinusoidal tubercle configuration along the original NACA0021 blade leading edge (0 ≤ x ≤ 0.3c). Time-accurate, self-starting data were recorded from wind tunnel tests under different flow conditions and the power coefficient (Cp) versus tip speed ratio (λ) curve was calculated. It is demonstrated conclusively that blades with an appropriate configuration of tubercle leading edges can considerably improve turbine self-starting capability. To the best of the authors’ knowledge, this study provides the first experimental data of H-Darrieus wind turbine performance with tubercle leading edge blades and the data are valuable for future designs and for the validation of simulation models.