Exergy as Criteria for Efficient Energy Systems – Maximising Energy Efficiency from Resource to Energy Service, an Austrian Case Study

The EU aims for complete decarbonisation. Therefore, renewable generation must be massively expanded, and the energy and exergy efficiency of the entire system must be significantly increased. To increase exergy efficiency, a holistic consideration of the energy system is necessary. This work analyses the optimal technology mix to maximise exergy efficiency in a fully decarbonised energy system. An exergy-based optimisation model is presented and analysed. It considers both, the energy supply system and the final energy application. The optimisation is using Austria as a case study with targeted renewable generation capacities of 2030.

The results show, that despite this massive expansion and the maximum exergy efficiency, about half of the primary energy still be imported. Overall exergy efficiency can be raised from today's 34% (Sejkora et al., 2020) to 56%. The major increase in exergy efficiency is achieved in the areas of heat supply (via complete excess heat utilisation and heat pumps) and transport (via electric and fuel cell drives). The investigated exergy optimisation results in an increase of the final electrical energy demand by 44% compared to the current situation. This increase leads to mainly positive residual loads, despite a significant expansion of renewable generation. Negative residual loads are used to provide heat and hydrogen.