Energy Systems Analysis seeks to compare various energy technologies on the basis of "Second Law" thermodynamic efficiency. The analysis uses a software framework whereby different component models communicate process information to each other and a user. This information can be used to describe energy and material flow from exergy reservoirs to the environment. Exergy destruction can be quantified and opportunities for technological improvement can be identified. The results of Energy Systems Analysis provide input to the Technology Assessments and a set of benchmarks which can be used by the Integrated Assessment team.