The power generation in CubeSats is intricately linked to their size, primarily relying on photovoltaic cells mounted on external surfaces to obtain electrical energy. This configuration, while simple and devoid of deployable solar panels, limits the amount of power a CubeSat can sustainably generate, necessitating engineers to ensure it aligns with mission objectives throughout orbital operations. The required power level of a CubeSat directly impacts the size and costs of the space segment, compelling development teams to establish a realistic electrical power system (EPS) strategy early in project phases, encompassing photovoltaic panel specifications and battery capacity. To address this challenge, this research undertakes modeling and simulating power generation for standard CubeSat sizes: 1U, 2U, 3U, 6U, and 12U. Transient available power during orbits is modeled as a function of incoming solar radiation and photovoltaic panel temperature, important factors influencing efficiency. While higher solar radiation enhances power generation, elevated panel temperatures diminish solar cell efficiency. As expected, the results show that larger CubeSat sizes exhibit greater energy output. Yet, power generation is not strictly proportional to CubeSat size due to interdependencies with attitude and orbit variables. The study reveals that a marginal increase in power can result from larger CubeSats with unfavorable attitude configurations, underscoring the importance of realistic power generation scenarios that incorporate mission attitude control systems. These practical implications can guide engineers and development teams in designing and planning CubeSat missions, ensuring optimal power generation and mission success.