 Through solving the scalar electric potential formula_17 from the surface charges

formula_18 (5)

the Ps can be obtained by

formula_19

This indicates that the output energy per cycle E can be calculated as the encircled area of the closed loop in the V–Q curve, and all V-Q cycles are named as ‘cycles for energy output’ (CEO).By periodic transformation between in load and short circuit conditions, cycles for maximum energy output can be obtained.When the load equals infinite, the V-Q becomes a trapezoid shape, the vertices of which are determined by the maximum short-circuit transferred charge QSC,max, and the maximum output energy can be calculated as