Method 2 is used to calculate the appropriate size based on the needed energy. Energy needed is Power * td 60 W * 5 sec = 300 Joules. Equation 8 is the formula to calculate energy stored in a capacitor. Rearrange the equation to solve for C and get 3.43 F, using Equation 7, the designer can calculate Ccell capacitance which is 25 F.