1. A modular method of modeling a power plant, the power plant comprising a plurality of major components including at least one of a gas turbine, a heat recovery steam generator, a steam turbine, and a condenser/cooling tower, said method comprising: selecting a major component module model from a library of component module models for each major component of the power plant, each major component module representing a power plant major component of a unique configuration; inputting initial model information into a database for the selected modules, the initial model information including at least one of operating parameters, deign data, convergence criteria, and a maximum number of passes; and running the modular model by running each selected module and enabling data exchange between the selected modules.