Jon Van Lew

Analysis of Heat Storage and Delivery of a Thermocline Tank Having Solid Filler Material

Thermal storage has been considered as an important measure to extend the operation of a concentrated solar power plant by providing more electricity and meeting the peak demand of power in the time period from dusk to late night everyday, or even providing power on cloudy days. Discussed in this paper is thermal energy storage in a thermocline tank having a solid filler material. To provide more knowledge for designing and operating of such a thermocline storage system, this paper firstly presents the application of method of characteristics for numerically predicting the heat charging and discharging process in a packed bed thermocline storage tank. Nondimensional analysis of governing equations and numerical solution schemes using the method of characteristics were presented. The numerical method proved to be very efficient, accurate; required minimal computations; and proved versatile in simulating various operational conditions for which analytical methods cannot always provide solutions. Available analytical solutions under simple boundary and initial conditions were used to validate the numerical modeling and computation. A validation of the modeling by comparing the simulation results to experimental test data from literature also confirmed the effectiveness of the model and the related numerical solution method. Finally, design procedures using the numerical modeling tool were discussed and other issues related to operation of a thermocline storage system were also studied.

Experimental investigation of thermal storage processes in a thermocline tank

This paper presents an experimental study of the energy charge and discharge processes in a packed bed thermocline thermal storage tank for application in concentrated solar power plants. A mathematical analysis was provided for better understanding and planning of the experimental tests. The mathematical analysis indicated that the energy storage effectiveness is related to fluid and solid material properties, tank dimensions, packing schemes of the solid filler material, and the durations of the charge and discharge times. Dimensional analysis of the governing equations was applied to consolidate many parameters into a few dimensionless parameters, allowing scaling from a laboratory system to an actual industrial application. Experiences on the system design, packing of solid filler material, system operation, and data analysis in a laboratory-scale system have been obtained in this work. These data are used to validate a recently published numerical solution method. The study will benefit the application of thermocline thermal storage systems in the large scale concentrated solar thermal power plants in industry.

Transient Heat Delivery and Storage Process in a Thermocline Heat Storage System

Parabolic trough power systems utilizing concentrated solar energy have proven their worth as a means for generating electricity. However, one major aspect preventing the technologies widespread acceptance is the deliverability of energy beyond a narrow window during peak hours of the sun. Thermal storage is a viable option to enhance the dispatchability of the solar energy and an economically feasible option is a thermocline storage system with a low-cost filler material. Utilization of thermocline storage facilities have been studied in the past and this paper hopes to expand upon that knowledge. The current study aimed to effectively model the heat transfer of a working fluid interacting with filler material. An effective numerical method and efficient computation schemes were developed and verified. A thermocline storage system was modeled under specific conditions and results of great significance to heat storage design and operation were obtained.Copyright

Heat Transfer in Thermocline Storage System With Filler Materials: Analytical Model

Parabolic trough power systems utilizing concentrated solar energy have proven their worth as a means for generating electricity. However, one major aspect preventing the technologies widespread acceptance is the deliverability of energy beyond a narrow window during peak hours of the sun. Thermal storage is a viable option to enhance the dispatchability of the solar energy and an economically feasible option is a thermocline storage system with a low-cost filler material. Utilization of thermocline storage facilities have been studied in the past and this paper hopes to expand upon that knowledge. The heat transfer between the heat transfer fluid and filler materials are governed by two conservation of energy equations, often referred as Schumann [1] equations. We solve these two coupled partial differential equations using Laplace transformation. The initial temperature distribution can be constant, linear or exponential. This flexibility allows us to apply the model to simulate unlimited charging and discharging cycles, similar to a day-to-day operation. The analytical model is used to investigate charging and discharging processes, and energy storage capacity. In an earlier paper [2], the authors presented numerical solution of the Schumann equations using method of characteristics. Comparison between analytical and numerical results shows that they are in very good agreement.Copyright

Transient Heat Transfer and Energy Transport in Packed Bed Thermal Storage Systems

Compared to fossil fuel energy resources, the major types of renewable energy—such as wind power, solar energy, ocean currents, and tidal energy—generally possess the innate characteristics of intermittence of availability, fluctuation of magnitude, as well as low energy density (Li, 2008). However, the utilization of energy and power in industry, living, and working often requires high energy densities, and demand may be out of phase with the period of availability of renewable energy. In other words, renewable energy is not always load following. This variability creates a demand for energy storage when people develop renewable energy technologies (Kolb, 1998). Among the several types of renewable energy, solar energy has the largest proportion of the total available and may be directly used as thermal energy in conventional thermal power plants, or converted into electrical power directly using photovoltaic panels. Although direct electrical energy storage in batteries or capacitors may have a high efficiency, it is still very challenging and expensive—particularly when storing a large quantity of electrical energy (Spiers, 1995). Electricity may be indirectly stored by pumping water to reservoirs, or by compressing air, or by electrolyzing water and making hydrogen fuel, etc. However, these methods often have low round-trip efficiency (from electricity to electricity), or are restricted by the availability of geographical conditions or suitable locations. In comparison, it has been recognized that direct solar thermal energy storage is relatively easy to approach at a reasonably low cost and high efficiency, and the energy storage capacity can be much larger than that of direct electricity storage (Price et al., 2002; Montes et al, 2009). Thermal energy storage systems use materials that can be kept at high temperatures in insulated containers. The heat retrieved can then be used in conventional thermal power plants for power generation at times when sunlight is not available or when weather conditions are not favorable (Singer et al, 2010; Laing et al, 2010).

Experimental Investigation of Thermal Storage Processes in a Thermocline Storage Tank

This paper presents an experimental study and analysis of the heat transfer of energy charge and discharge in a packed-bed thermocline thermal storage tank for application in concentrated solar thermal power plants. Because the energy storage efficiency is a function of many parameters including fluid and solid properties, tank dimensions, packing dimensions, and time lengths of charge and discharge, this paper aims to provide experimental data and a proper approach of data reduction and presentation. To accomplish this goal, dimensionless governing equations of energy conservation in the heat transfer fluid and solid packed-bed material are derived. The obtained experimental data will provide a basis for validation of mathematical models in the future.Copyright