1. A system for calculating an incremental heat rate and a maximum capacity for at least one power generating unit, comprising: a current performance model, for calculating one or more performance characteristics for a first time period for the power generating unit, using at least one of data describing the unit's physical configuration, data describing the unit's operating parameters, and data describing the unit's fuel constituency; a database, for storing at least one of the performance characteristics; and a predictive performance model, for calculating an incremental heat rate and a maximum capacity for the power generating unit, using at least one of data describing the unit's physical configuration, data describing the unit's fuel constituency and performance characteristics.