Multi-objective optimization of helium power cycle for thermo-chemical energy storage in concentrated solar power

Concentrated Solar Power is an increasingly widespread technology because of its potential for efficiently converting solar radiation into electricity. The discrepancy between the time evolution of solar radiation and power demand makes it appropriate to include a Thermal Energy Storage in the plant operation. Calcium-Looping represents an interesting opportunity to store solar energy in chemical form thanks to high energy density and null thermal losses. Several aspects must be taken into account for the choice of the thermal cycle in the discharging process and its optimization. Process components operating conditions, heat transfer processes, layout complexity and investment costs are the most important characteristics for which an appropriate investigation must be developed. In this context, thanks to the high achievable temperatures and efficiencies, the use of helium power cycles constitutes an attractive option to analyse. The present work is devoted to the study of this thermal cycle integration and its optimization in energy and economic terms; a multi-objective optimization is performed with the aim of evaluating possible compromises between these two aspects. The system synthesis, design and operating conditions are optimized thanks to the adoption of a coherent and comprehensive strategy, which is the HEATSEP method. To evaluate the effect of deviations in the estimation of helium turbomachinery price, a sensitivity analysis is performed, showing that the plant configurations obtained do not change even for considerable errors in the prediction of this cost. He turbine inlet temperature and minimum temperature difference of He regenerator are demonstrated to strongly impact the cost of the system. Results show total plant efficiencies in a range between 18.1% and 21.9% and novel system layouts are designed for the most significant configurations. The strategy for the power block thermal feeding appears to be a key element in both energy and economic terms.