Computational Modeling of Solar Energy Storage in Rock Beds

Over the last 60 years, technology for harvesting solar energy has been extensively developed and used. Examples of applications incorporating this technology include the following: heating and cooling of residential and commercial buildings; solar water heaters; photo-voltaic conversion to electricity; solar-thermal-electric power generation; and solar desalination of seawater. In parallel, thermal energy storage (TES) systems have also been extensively developed and employed for enhancing the efficiency of energy conversion systems, typically by matching thermal energy supply and demand during summer-winter, day-night, and peak-off-peak periods. In this work, the focus is on computational modeling of flat-plate solar-thermal collectors and sensible diurnal TES systems consisting of rock beds, both with air as the working fluid. Such collectors and TES systems are inexpensive, relatively simple, easy to construct, and quite effective for many solar energy and building engineering applications. Numerous publications on flat-plate solar-thermal collectors and rock-bed TES systems are available, but there is a need for efficient computational methods for designing and optimizing them. The contributions of this work are the following: proposal of cost-effective mathematical models of fluid (air) flow and heat transfer through flat-plate solar-thermal collectors and rock-bed TES systems; adaptation of a finite volume method (FVM) for the solution of the aforementioned mathematical model of rock-bed TES systems; testing of the proposed computational methods; and applications of the proposed models and methods to two demonstration problems. In one of these problems, a sample rock-bed TES system is simulated and assessed. In the other one, actual meteorological data from three different geographical locations are used to estimate the performance of a system that couples a flat-plate solar-thermal collector with a rock-bed TES system.