Thermodynamic modelling and real-time control strategies of solar micro gas turbine system with thermochemical energy storage

Abstract

Distributed solar gas turbine systems with thermal energy storage are expected to overcome the intermittence and instability of solar irradiance and produce reliable and flexible electricity for remote districts and islands. Here, a mathematical model is developed for a 10 kWe solar micro gas turbine (MGT) system with thermochemical energy storage (TCES) to study the system thermodynamic characteristics at real-world direct normal irradiation (DNI) variations. Real-time control strategies aiming for stable operation and set point tracing are proposed and implemented in transient simulations to analyze the control effect against both short- and long-term DNI disturbances based on system dynamics. Results show that, by regulating the output power, rotational speed (N) is kept constant, and system responses are smoothened (e.g., less than 5.8% fluctuation of the mass flow rate). Power regulation also enables a constant turbine outlet temperature (TOT) and the optimal overall performance (e.g., output power and total efficiency exceeding 14 kWe and 14%, respectively). By combining power and bypass regulations, N and TOT can simultaneously remain constant while outputting a stable power of 12.6 kWe ±5% under 750–820 W/m2, with a sharp drop to 500 W/m2. For favorable weather, N-TOT simultaneous control can guarantee the high and stable system performance. If massive clouds appear, constant TOT operation is more advantageous during peak load demand for larger electricity generation, while constant N operation is preferable during low power demand for smoother turbine operation.

Furthermore, the addition of TCES smoothens the performance variation and prolongs the generation duration. TCES also allows constant TOT operation to store up to 32% more energy than constant N and output 18–28 kWh more energy during daytime operation, thanks to the higher operating temperature. Overall, the proposed real-time control methods reduce the dependency on fossil fuel combustion and contribute to the stable, safe, and efficient operation of a distributed high-percentage-solar-share MGT system.