(242g) An Optimization-Based Framework for Material Selection and System Design for Integrating Thermochemical Energy Storage in Solar Power Systems

A promising approach to manage intermittency in concentrating solar power (CSP) plants is to integrate them with thermal energy storage (TES). It is estimated that CSP plants integrated with TES can contribute to 11% of the global electricity generation by 2050.¹ The commercially deployed CSP plants, which are typically integrated with two-tank molten-salt sensible heat storage unit, however, are less efficient because they deliver heat to the power block at low temperature (565 ^oC). Furthermore, the energy density of molten-salt systems is low and it can become too expensive to be used in large-scale systems. Thermochemical energy storage (TCES), which is based on converting solar-thermal energy to chemical energy, is a promising option because it allows high operating temperatures, high storage density, and low heat loss over long periods.

Today, TCES is in its infancy due to, among other reasons, the system complexity. It remains unclear which configuration and reaction should be used for the integrated CSP-TCES system. Towards this goal, we make contributions in three aspects. First, we identify nine major TCES strategies by combining three representative types of reactions (oxides, hydroxides, and carbonates) and six configurations. Second, we develop a novel two-stage stochastic programming optimization model for the design and operation of CSP plants under seasonal solar variability^2,3. Third, using this model, we obtain the optimal performance of all TCES strategies. This analysis allows us to develop general guidelines for the selection of optimal process configurations.

In the second part of the talk, we discuss an extensive reaction screening to generate a ranked list of promising reaction candidates. To do this, we first generate a comprehensive list of reaction candidates. Then, we perform a preliminary screening, and choose the reactions with positive reaction enthalpy and equilibrium temperatures between 400 ^oC and 1500 ^oC. Finally, the model is solved for the reaction candidates obtained after preliminary screening and the reactions are ranked based on the cost of electricity production. The analysis identifies available promising TCES materials. Finally, we formulate a “material optimization” problem by treating key material properties as decision variables. This analysis provides insights in the material and reaction properties that are most suitable for CSP-TCES plants and serve as guidelines for the development of novel TCES systems.

References

1 IEA publications, Energy Technology Perspectives 2017 - Catalysing Energy Technology Transformations, 2017.

2 X. Peng, T. W. Root and C. T. Maravelias, AIChE J., 2019, 65, e16458.

3 X. Peng, M. Yao, T. W. Root and C. T. Maravelias, Appl. Energy, 2020, 262, 114543.