Energy Prices, essential input for the Sectorial Model, consist on the biggest uncertainties of the Electric Sector. These uncertainties enclose all price elements: the supply, the demand and the market rules, making sometimes difficult for the agents to evaluate the price process and the impact that the variation of each process element can produce on the result. The objective is to present Brazilian price process in a structuralized way, evaluating the variables composition that affects this structure: the demand, the electric system expansion and the energy supply availability. The market is modeled in all its physical details, and the calculation is done into the regulatory environment, including a reproduction of the optimal operation model responsible for energy prices. First, a demand forecast model is described, based on Functional Analysis Theory. Then, the focus is on the energy future supply, analyzing the supply expansion in Brazil. Finally, an optimal operation system is simulated, reproducing the sector model (Newave) results from an implementation developed in this work. From these possible future settings, each element (demand, expansion and energy supply availability) variation impact on energy prices can be measured. The simulations show that uncertainties about these variables can have big impacts on marginal costs and, consequently, on the energy future prices.