Brazil is a country whose energy matrix is strongly dependent on generation by hydropower plants. Within this scenario, the use of biomass power plants represents an attractive alternative, since it associates the diversification of the Brazilian energy matrix with the use of renewable sources, and is not as polluting as their counterparts moved to non-renewable fossil fuels such as oil and gas. This study aimed to conduct the economic evaluation of an investment in a project of a biomass power plant, considering strategies with and without managerial and operational flexibilities, in order to identify the best methodology for evaluating the project in question. In the strategy without flexibilities, the discounted cash flow method was adopted. In the strategies with uncertainties and flexibilities, the uncertainties related to the electricity market and flexibilities related to the possibility of selling the electricity generated in the long or short term markets were incorporated into the analysis. Moreover, there is the possibility of installing a briquetting plant, which would allow the plant to choose between selling electricity in the short term market or briquettes, whichever is more economically interesting. The results indicate that the existence of uncertainties and managerial flexibilities increases the value of the project and reduces significantly the risk of failure, which reinforces the idea that the evaluation with real options, though more complex, can be more appropriate to determine the actual value of the project.