An embodiment of the invention includes a computer-readable medium storing instructions that, when executed by at least one computer, cause the at least computer to carry out a method for estimating a time-varying energy balance of a power system. A mission plan for a mission is received. The mission plan includes at least one activity and at least one route. Each route of the at least one route includes at least one time and at least one location. A plurality of power load identifications is received for at least one time-varying power load for use in the mission plan. A time-varying power requirement to complete the mission plan is determined. A baseline plurality of energy storage devices required to satisfy the time-varying power requirement is determined by the energy analysis code. The baseline plurality of energy storage devices includes a baseline number and type of energy storage devices.