International audienceThis paper highlights the energy errors made for the design of supercapacitors used as a main energy source. First of all, the paper presents the two definitions of capacitance of a capacitance-voltage dependent material. The number of supercapacitors is important for the application purchasing cost. That is why the paper introduces an analytical model and an electrical model along with an identification method for the capacitance variation. This variation is presented and compared to the manufacturer value in order to underscore the energy error between the manufacturer, the constant approximation and the first order approximation which interests us here. This paper also presents the sizing aspect considering the losses associated to a constant-current charging mode in order to minimize the electrical losses. At last, an application case compares the number of supercapacitors for different approximations of the capacitance
