Battery energy storage technology for power systems—An overview

Abstract

The penetration of renewable sources (particularly wind power) in to the power system network has been increasing in the recent years. As a result of this, there have been serious concerns over reliable and satisfactory operation of the power systems. One of the solutions being proposed to improve the reliability and performance of these systems is to integrate energy storage devices into the power system network. Further, in the present deregulated markets these storage devices could also be used to increase the profit margins of wind farm owners and even provide arbitrage. This paper discusses the present status of battery energy storage technology and methods of assessing their economic viability and impact on power system operation. Further, a discussion on the role of battery storage systems of electric hybrid vehicles in power system storage technologies had been made. Finally, the paper suggests a likely future outlook for the battery technologies and the electric hybrid vehicles in the context of power system applications.

Introduction

The need for storage devices and their utilization in power systems has long been debated. An overview of the different storage technologies, their applications and limitations are discussed in [1], [2], [3], [4], [5]. The earlier reviews on storage technology [1], [2] focus exclusively on lead-acid battery technology. In [1] the economic models, their controls, ratings and applications found in US power systems are discussed and in [2] the possible future applications are suggested. In [3] the use of battery energy technology to improve the power quality (mainly voltage depressions and power interruptions) and reliability of the power system are discussed. Some of the reviews carried out recently in [4], [5] discuss about the various storage technologies and suggest that so far the battery technology is the most widely used storage device for power system applications. In [4] the authors state the support provided by the DOE (US) and other organizations to demonstrate the application of various storage technologies (predominantly battery technologies) at different power utility companies in North America. Further it is stated that the energy storage technology will be the key to the future development of renewable energy. In [6] some of the commercial successes in electric power storage technologies have been discussed and it also discusses some of the emerging applications in power storage like wind farm power stabilization, etc. The report [7] provides a catalogue of the various current technologies (steam, hydro, wind, etc., and storage being one of them). Their future outlooks, evaluations of security of supply and environmental impacts, climate change evaluations, and technical and economic analysis, in the context of energy planning activities.

In spite of the large number of investigations carried out to apply different storage technologies to power systems, very few of them have been implemented in practice. Some of the main reasons for this limited practical application are:

• The conventional power system had large amounts of generating sources whose generation could be easily varied to match the load demand. Also most of these systems operate in a interconnected manner and the power from generators in other areas can be used to balance the load demand. In such a situation it is very difficult to justify the economic gains obtained in using storage technologies.

• Lack of practical experience and lack of availability of tools which could be used for: (i) operational cost optimization and (ii) assess the benefits of storage technology (considering the market models) during planning.

Now, the scenario is changing and there are large number of generating sources (mostly non-conventional) whose power output cannot be controlled. The power from these generators varies according to the availability of the resources (for example in case of wind turbine, it depends on the availability of wind). Additionally, many of these generating sources would be operating as distributed generators. In this case, during the non-availability of the power system grid, it may be beneficial to operate these uncontrollable sources in an island mode. Also the storage technologies could play a vital role in improving the overall stability and reliability of power system (islolated/grid connected/systems with large share of renewable sources) and could defer the costs need to improve the transmission and distribution capacity to meet ever growing power demand. The storage technologies could also play an important role in the deregulated markets like providing arbitrage, increasing the value of renewable power in some of these markets, etc.

There are many types of storage technologies available at present. Although examining all these technologies is necessary, this paper concentrates only on battery storage technologies and gives an overview of the following:

• Different types of battery energy storage technologies (batteries as well as their controls) available at present.

• State some of the battery energy storage technologies implemented/planning to be implemented in an actual power system.

• Identify the likely future power system applications and analysis tools needed to be developed to examine the economic as well as technological benefits of various battery energy storage technology.

• Discuss the use of electric drive vehicle (EDV) power to improve the reliability of electric utilities.

The various ways in which battery and EDV technologies can help in improving the reliable operation of the future power systems is explained by considering the Danish electricity grid. The Danish electricity grid has a special characteristic of high wind power and distributed generation penetration. This type of electricity grid is being envisioned as the future electricity networks in many other countries. Although about 20% of the total electricity demand was met by wind power alone in 2007 in Denmark, there are ambitious targets set by the politicians to increase the wind power penetration to 50%. In this context, the different technologies which would assist 50% wind power penetration in Denmark (by 2025) are being examined and one such technology is the battery technology, which is presented in this paper.