This study presents a system dynamics model to analyze how renewable electricity can reduce carbon emissions in Iran. It investigates the effects of population growth and the substitution of fossil fuels with renewable energy. Four population scenarios are considered: decreasing, moderate, stable, and high fertility. The results show that a high fertility scenario (2.6) leads to a sharp increase in carbon emissions by 2051, underlining the importance of demographic trends in energy planning. The study also tests three levels of renewable electricity substitution: high, medium, and low. Higher substitution levels lead to greater emission reductions. The simulation results provide both absolute and relative production values, showing how much additional renewable electricity is needed to replace fossil fuel-based generation. This model helps policymakers understand the long-term impact of energy and population policies on emissions. It also demonstrates how dynamic modeling can capture complex feedback between population and energy systems. The approach offers a flexible tool for testing future scenarios and supporting strategic decision-making. Future work can improve the model by including economic analysis, carbon absorption capacity, and detailed investment scenarios.