Design and Control of a Small-Scale Isolated Concentrated Solar Power Generation Unit

Electricity generated by small-size concentrated solar power (CSP)-driven Rankine cycle (RC) is an increasingly explored alternative for powering isolated homes/small communities. In these units, solar energy is captured to raise the temperature of a heat transfer fluid (HTF). The hot FITF drives a low-temperature Rankine cycle to generate electricity-for the household(s). Because the solar flux follows the diurnal transient cycle along with high variability in the power demand, very large inventory of the HTF is needed to store the solar energy and supply heat to the Rankine cycle, including when the solar flux is zero at night. There then is no steady state for the process and it must be designed for inherently transient operation over a very large operating window. Simultaneous design and control evaluation to ensure robust operation for such a large operating window is then essential. This work presents the same for a small scale 20 kW isolated CSP-RC power generation unit. Three enhancements to the basic flowsheet are developed with quantified benefits in terms of improved overall process efficiency, significantly reduced HTF inventory and the flexibility of capturing extra solar energy. A robust control strategy with appropriate overrides for handling process constraints is developed for the enhanced flowsheet and tested using rigorous dynamic simulations. The closed loop results are used to size the necessary HTF inventory. These results demonstrate the robustness of the control system in the face of extreme disturbances in power demand and the captured solar flux.