Energy Storage

The following sections are included:

• Foreword to the World Scientific Series on Current Energy Issues
• About the Editor
• Contents

This chapter describes the role that energy storage can play in the present and in the short–medium term future energy scenario. Both stationary and automotive applications will be considered and the main features required by each of them for an energy storage system will be explained. A very brief description of the proven and most promising storage technologies will be given with the aim of providing an overview of the peculiarities of each one and consequently its better suited applications. Finally, the state-of-the-art, the opportunities and the barriers to the spread of energy storage systems will be summarized.

This chapter describes some current trends and future challenges related to pumped-hydro energy storage (PHES) with special emphasis on the mechanical aspects of hydraulic machinery, power electronics devices used for variable speed operation, and utilities’ operation strategies. After a brief introduction and historical background, the new generation of PHES is presented with particular focus on those equipped with variable speed technology. Typical configurations of pumped-storage hydropower plants (PSHPs) are also briefly described. The next section focuses on reversible pump-turbines, discussing their operating limits and presenting the state-of-the-art of the research on their unstable behavior. The operating principle and some basic aspects of the electrical machines most widely used in PSHPs are next described. Power electronics devices typically used in PSHPs for variable speed operation are described in detail, along with some recent developments on variable speed drives. Finally, utilities’ operation strategies are reviewed in detail, and some future challenges to make the best possible use of PHES assets according to their new role are identified.

With the rapid increase of power generation from renewable energy sources, electrical power networks face a great challenge in maintaining operation stability and reliability. Various solutions are currently under investigation, which include energy storage (ES). Compared with all the ES technologies under consideration, compressed air energy storage (CAES) has the power rating and scale comparable to pumpedhydro ES. This distinguishes CAES from other ES technologies in grid scale applications. This chapter explains how CAES works and what its advantages and disadvantages are. The recent developments in CAES technology are reviewed and the application potential of CAES in supporting power network operation is analyzed. The research challenges and needs are also highlighted in this chapter.

This chapter discusses the use of batteries for storage of electrical energy. It covers the general principals of how batteries work, with more specific details on the common types of rechargeable batteries available: viz. Lead acid, NiCd, NiMH, NaS, and Li-ion. Some of the practical aspects of connecting the cells together into energy storage systems are discussed, as well as the management systems need to operate the battery systems safely and efficiently. The chapter finishes with a brief section on a selection of applications that exist for battery energy storage, with a focus on electric vehicles (EVs).

Capacitors are electrical devices for electrostatic energy storage. There are several types of capacitors developed and available commercially. Conventional dielectric and electrolytic capacitors store charge on parallel conductive plates with a relatively low surface area, and therefore, deliver limited capacitance. However, they can be operated at high voltages. As an alternative, electrochemical capacitors (ECs) (also called supercapacitors) store charge in electric double layers or at surface reduction–oxidation (Faradaic) sites. Thanks to the large surface area of the electrode and the nanoscale charge separation, electrochemical capacitors provide much higher capacitance, filling in the gap in the energy and power characteristics between batteries and conventional capacitors. However, they offer a lower energy density than batteries and commonly lower power than traditional capacitors. In the past decade, intensive research on ECs brought about the discovery of new electrode materials and in-depth understanding of ion behavior in small pores, as well as the design of new hybrid systems combining Faradaic and capacitive electrodes, which are essential for the enhancement of the performance of ECs.

This chapter presents the classification, construction, performance, advantages, and limitations of capacitors as electrical energy storage devices. The materials for various types of capacitors and their current and future applications are also discussed.

The present chapter summarizes the current state and perspectives of fuel cells and hydrogen energy. First of all the relevant fuels and fuel chemistry are discussed focusing on hydrogen, hydrocarbons and oxygenates, then the basics of fuel cell technology and applications are discussed. The different types of fuel cells are presented with particular attention on solid oxide fuel cells, and thermodynamics and the factors influencing efficiency reviewed.

Ubiquitous in rotating machinery, flywheels smooth the flow of energy in rotary systems ranging from small engines to large reciprocating machines. A new class of standalone flywheel energy storage system has been in use since the late 20th century. These systems are electrically connected to the applications that they serve. They may be found in applications as diverse as uninterruptible power supplies, racecars, and large physics research facilities. This chapter presents the theoretical and practical foundations of flywheel design, the history of flywheels from ancient times to the present, flywheel subsystem technology, and a survey of applications where flywheel energy storage systems are currently in service.

The following sections are included:

• About the Contributors
• Index