Optimal operation of Concentrating Solar Collector fields using exergy-based hierarchical control

Abstract

This work develops an exergy-based hierarchical control for the ACUREX solar collector field. The objective is to simulate and to determine the optimal control operation based on exergy. The control structure uses a nonlinear exergy optimization layer that sends the steady-state optimal temperature set-point to a nonlinear Model Predictive Control layer. The simulations show that the control can track references, reject disturbances, and optimize the production considering process intermittency (start-up, operation, shut-down), operational constraints, and pump power. The study compares the proposed control to common literature approaches such as energy-based and maximum outlet temperature reference generation. The main findings are: (i) the proposed exergy-based controller design gives an enhanced second law of thermodynamics performance independently of solar collector process parameters; (ii) despite modest energy production and efficiency advantages (1%) on ACUREX solar field, the real application of the control law does not imply any new investments or hardware changes; (iii) seeking the maximum temperature is a simple, quasi-optimal strategy for the ACUREX solar field; and (iv) energy-based optimization is not a suitable strategy for ACUREX solar field from the second law of thermodynamics (exergy) perspective.