Zero-emission chemical sites – combining power purchase agreements with thermal energy storage

The chemical industry is adopting increasingly ambitious greenhouse gas emission targets. This work examines the decarbonization concept of a chemical site utility system based on renewable power purchase agreements and green hydrogen. To this end, a model of a zero-emission utility system including all typical components, demand profiles and energy prices was developed. The model was used to investigate the effect of flexibility options such as curtailment, power-to-heat and thermal energy storage by means of energy system optimization. Sensitivity studies were carried out with respect to the green hydrogen price, thermal energy storage investment costs and on-site steam turbine capacity to gain a deeper understanding of the various influencing factors. Thermal energy storage, e.g. molten salt technology, can achieve cost savings up to 27 % through efficient integration of renewable electricity from PV and wind. Furthermore, the concept with thermal energy storage proved to be more resilient to variations in the green hydrogen price. In the best-case scenario, a 30 % higher green hydrogen price only results in a 6 % increase in annual expenditures. Even when very high investment costs are assumed, thermal energy storage still remains an integral component of the cost-optimal zero-emission utility system.