System Modelling

System modelling has so far been confined to the assessment of individual system components such as reactors and heat exchangers using steady-state performance models, with subsequent integration of such component results. Using TRNSYS, preliminary work is however in progress regarding the performance modelling of complete, ammonia-based solar thermochemical power systems that operate in transient mode.

TRNSYS, a computer code developed by the Solar Energy Laboratory of the University of Wisconsin-Madison (USA), relies on a modular approach to solve systems of components, whereby each component is described by a tailor-made model which serves as a FORTRAN subroutine of the entire system model.

Modelling makes use of a library of subroutines of proven components that are typical for conventional power plants as well as for solar thermal systems, with the incorporation of new ammonia-specific component subroutines. The key ammonia-specific subroutines such as for ammonia dissociation and for the associated counter-flow heat exchange will be adapted versions of ANU's experimentally verified performance models.

With the help of a graphical icon-based assembly program, the user directs TRNSYS to connect the relevant subcomponent models together to form a whole system, whereby calculated model outputs can serve as inputs to other component models. The TRNSYS engine then calls all system components, links them according to the user-specified input/ output correlations and finally iterates at each specified timestep until the system of equations is solved.