Thermal Energy Storage Analyses and Designs

Pei-Wen Li, Cho Lik Chan

• Publisher: Academic Press
• Year: 2017
• Print ISBN: 9780128053447
• eBook ISBN: 9780128092330
• Topic: Technology & Engineering
• Subtopic: Energy
• Index: Technology & Engineering

Thermal Energy Storage Analyses and Designs considers the significance of thermal energy storage systems over other systems designed to handle large quantities of energy, comparing storage technologies and emphasizing the importance, advantages, practicalities, and operation of thermal energy storage for large quantities of energy production.Including chapters on thermal storage system configuration, operation, and delivery processes, in particular the flow distribution, flow arrangement, and control for the thermal charge and discharge processes for single or multiple thermal storage containers, the book is a useful reference for engineers who design, install, or maintain storage systems.- Includes computer code for thermal storage analysis, including code flow charts- Contains a database of material properties relevant to storage- Provides example cases of input and output data for the code

Chapter 1

Introduction

Abstract

Energy storage is critical to the development of renewable energy technologies in the future, due to the fact that almost every type of renewable energy is irregular and intermittent regarding its availability and magnitude. Among various energy storage approaches, thermal storage is one of the most promising large-scale energy storage technologies. Here in the introduction the list of topics and technical issues for thermal energy storage are briefly presented as a reader's overview.

Keywords

Energy storage technology; Thermal energy storage; Large-scale energy storage; Concentrated solar power; Industrial energy technology

Contents

1.1 The Significance of Energy Storage to Renewable Energy Technologies

1.2 A Brief Introduction to Energy Storage Technologies

1.3 Examples of Industrial Applications of Thermal Energy Storage

References

1.1 The Significance of Energy Storage to Renewable Energy Technologies

Fossil fuels have been our major energy resources in the past, driving the industrialization and the modernization of human society. There is no doubt that the world economy will continue to largely rely on fossil fuels, such as coal, oil, natural gas, and atomic energy as well, far into the future. More importantly, the demand for energy in general will continue to rise [1]. However, it also has been widely recognized that it is impossible for the worldwide production of coal and oil to keep rising with no limitation. The world has to find new energy resources, or otherwise the current energy technologies have to be improved dramatically so that energy consumption is reduced significantly. The world also has recognized that the heavy use of fossil fuels causes pollution of the air and environment, which could cause hardship and suffering for future generations.

The need for clean energy resources and environmental protection drives the strong demand for developing renewable energy, particularly solar energy and wind energy, around the world. Renewable energy must represent a significant proportion of our energy package in the future, in order for the world economy and environment to have sustainable development.

Almost all types of renewable energy, particularly solar energy and wind power, do not have very high energy density and are available only intermittently or even irregularly. However, the utilization of energy and power in industry, homes, and the workplace often has a different phase compared to the time/period of availability of renewable energy. Therefore, to provide renewable energy and power and follow the load or demand, energy storage and smart energy dispatch technologies are critically needed. Energy storage mechanisms in different forms at a variety of levels of capacities, or quantities, and different periods of time must be better understood. The degradation or loss of stored energy as a function of time will largely determine the energy storage efficiency and length of time. Technologies capable of long-term energy storage and low degradation are very challenging but are in great demand.

1.2 A Brief Introduction to Energy Storage Technologies

The following energy storage technologies have been widely recognized and studied by scientists and engineers in the energy engineering field:

(1) Thermal energy storage including both hot storage and cold storage.

(2) Direct storage of electricity in capacitors or batteries.

(3) Electrical and mechanical energy storage using flywheels.

(4) Pumped hydroelectric energy storage relying on reservoirs.

(5) Compressed air energy storage.

(6) Electrical energy storage using a combination of electrolyzers and hydrogen fuel cells.

The availability and success of these energy storage technologies will significantly affect the success of the renewable energy industry and the directions of technology development. Taking solar energy as an example, the use of solar energy has three major objectives: to produce electricity, make fuels, and directly collect and use heat, as shown in Fig. 1.1. To make electricity from solar energy, photovoltaic panels and solar thermal power plants are often used, which is strategy I in Fig. 1.1. For short-term energy storage, an auxiliary energy storage system can store electricity directly or store thermal energy in a solar thermal power plant. However, for longer-term energy storage or for fuel-energy storage, one needs to consider strategy II in Fig. 1.1. Biofuels, hydrogen, or fuel materials can be stored very long term, and thus using renewable energy for fuel and hydrogen production is receiving more attention recently. Direct use of solar energy for heating can also be assisted with thermal storage, which is categorized as strategy III in Fig. 1.1.

Fig. 1.1 Solar energy for three purposes of energy supply and storage [1].

Of all the energy storage technologies, direct electrical energy storage is the most desirable; for example, the electricity generated by solar PV panels or wind turbines requires storage for dispatch. However, energy storage based on direct electricity storage using batteries and capacitors is limited to small to medium capacity levels, such as supplying energy for portable electronic devices, computers, electrical motorcycles and cars for use in limited operations and over a short time. Electrical and mechanical energy storage using flywheels can also provide a small to medium amount of energy capacity. Storing a very large quantity of energy, such as in a power plant to meet the needs of several hundred megawatts of electrical power output for 4–8 h, is only possible using thermal energy storage, pumped hydroelectric energy storage, or compressed air energy storage. Because of the need for elevated water reservoirs, pumped hydroelectric energy storage is only available in a small number of limited locations. Storing a sufficiently large quantity of energy using compressed air energy storage requires a huge volume for high pressure air, which is only realistic if large-volume natural caverns are available. The technology of electrical energy storage using a combination of electrolyzers and hydrogen fuel cells is considered to a long-term energy storage technology. However, it requires hydrogen storage, and this technology still needs more research and development. Therefore, thermal energy storage turns to be the most viable technology that is readily available with no limitation on location or quantity of energy storage for a short time, up to 12 h.

Thermal energy storage can be either hot or cold storage, for different periods of time and with various scales of capacity. Hot thermal energy storage can provide heating, while cold thermal energy storage may provide cooling as needed at another time. Hot thermal energy storage is widely applied in industry, such as for concentrated solar thermal power generation, thermal storage for room heating, greenhouse heating and industrial drying, etc. In the current state-of-the-art, the maximum temperature for hot storage can go as high as 850°C in a concentrated solar thermal power plant. Cold thermal energy storage is used to provide house cooling, or cooling of food, vegetables, and fruit for storage and transportation. For example, cold packs or cold mass are increasingly commercially available for temporary house cooling, or for keeping food cold during transportation or for a short period of storage.

From the viewpoint of the materials used for thermal energy storage, there is sensible energy storage (with no state change in the material), latent heat storage (using phase change materials), or thermochemical energy storage, which involves cyclic chemical change from an original material to a midstage material and back to the original material. In a thermochemical energy storage process, thermal energy is absorbed or released during cyclic chemical reactions/changes of the materials. With the midstage material stored, the energy is stored. Therefore, long-term energy storage and a large storage capacity are possible using thermochemical energy storage.

1.3 Examples of Industrial Applications of Thermal Energy Storage

Thermal energy storage (hot) has been widely applied in concentrating solar thermal power (CSP) plants for solar thermal energy storage during the day, to provide needed heat during the night to generate electrical power for 4–6 h. Solar thermal energy storage offers the advantage of a CSP plant against photovoltaic-based solar power generation. Therefore, almost every commercial CSP plant worldwide has a solar thermal storage system. Details including electrical power supply, power system thermal efficiency, the area of solar field, heat transfer fluid, thermal storage media, cooling mode, etc., for worldwide power plants and projects of concentrating solar power are available at the website of the U.S. National Renewable Energy Laboratory [2].

Ice or cold water storage is another thermal storage technology for energy conservation in industrial applications [3]. A large percentage of electricity (50%–75%) goes into buildings, and much of that runs air conditioning, either cooling or heating. To cope with the peak loads, particularly in summer, ice storage has been widely used. Typically, ice is made at night, when electricity is cheaper and it is cooler; while ice-melting provides cooling for air condit...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• Preface
• Chapter 1: Introduction
• Chapter 2: Thermal Storage System Configurations and Basic Operation
• Chapter 3: Thermal Energy Storage Materials
• Chapter 4: Mathematical Models and Numerical Solutions for Thermal Storage Processes
• Chapter 5: Discharged Fluid Temperatures From a Thermal Storage System—The Key Parameter for Utilization of Stored Thermal Energy
• Chapter 6: Volume Sizing for Desired Energy Storage Tasks
• Chapter 7: Thermal Storage System Construction and Mechanical Issues
• Chapter 8: Thermal Insulation of Thermal Storage Containers
• Index