The financial valuation of power plants is an important instrument for investment planning. The environment of the energy sector, which is strongly influenced by renewable energies, is changing. The shift to decentralized supply has an impact on the technical complexity of the energy system and requires congestion management. In such a transitioning system, flexibility is gaining a more important function in the valuation of power plants. Existing valuation methods are examined as to how flexibility and marketing options are taken into account. The comparison of the existing valuation methods showed that the valuation results are strongly dependent on the method used and the technology investigated. There is a lack of validation of the methods through quantitative evaluation.