Molten silicon storage of concentrated solar power with integrated thermophotovoltaic energy conversion

A new kind of systems combining latent heat energy storage in molten silicon and thermophotovoltaic (TPV) heat-to-power conversion are under development within the AMADEUS (www.amadeus-project.eu) project. The extremely high latent heat of silicon (1230 kWh/m3) plus the very high electrical power density of TPV (several 10’s of kW/m2) will eventually enable the fabrication of ultra-compact CSP systems that integrate thermal energy storage and power generation in the same unit. This work deals with the search of the optimal geometry of the PCM vessel, enabling the highest energy transfer to the TPV converter. Two kinds of geometries are explored: the inverted truncated pyramid (ITP) and the hollow cylinder (HC). A simplified quasi-1D semi-analytical model for the heat transfer in the PCM coupled to a TPV optical cavity model is used to simulate the system and determine some key figures of performance such as discharge efficiency, discharge time or electrical power. On top of that, the assumptions made in the 1-D model are verified against a well advanced 3-D Computational Fluid Dynamics (CFD) model, which takes into account buoyancy effects, dendrites formation and the PCM expansion during solidification, being thus in position to describe in more detail the induced complicated fluid structures governing both the phenomena of PCM melting and solidification. We find that both the analytical model and the advanced 3D CFD model coincide for most of the simulation time, enhancing the validity of the analytical model that can be implemented during the initial stages of the system design. Finally, the article discusses on the best geometries resulting in the maximum system efficiency and output power, as a result from the 1D analysis.