A concentrating photovoltaic (CPV) system with a steady electric output adopting an electrically tunable concentration ratio of the liquid crystals (LC) lens is demonstrated. The distribution of the LC directors of the LC lens can be controlled by an applied voltage in order to adjust the number of incident photons in an area. As a result, the CPV system adopting an LC lens can be operated with a static and maximum output power density under different ambient illuminations because the LC lens with an electrically tunable concentration ratio helps to increase the photocurrent at a low illumination and prevent the effect of the series resistance at a high illumination. The detailed operating principles are discussed, and the experimental results are performed. We believe this letter can help enhance the output power density of CPV systems by using active optical elements whose concentration ratio is tunable.