01-12-2012, 01:38 PM
Battery energy storage technology for power systems—An overview
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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 andmethods 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
[1–5]. 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.
Battery energy storage technology
The battery energy storage system (BESS) comprises mainly of
batteries, control and power conditioning system (C-PCS) and rest
of plant. The rest of the plant is designed to provide good protection
for batteries and C-PCS. The battery and C-PCS technologies are the
major BESS components and each of these technologies is rapidly
developing. So the present state-of-art of each of them have been
discussed separately.
Batteries
The batteries are made of stacked cells where-in chemical
energy is converted to electrical energy and vice versa. The desired
battery voltage aswell as current levels are obtained by electrically
connecting the cells in series and parallel. The batteries are rated in
terms of their energy and power capacities. Formost of the battery
types, the power and energy capacities are not independent and
are fixed during the battery design. Some of the other important
features of a battery are efficiency, life span (stated in terms of number
of cycles), operating temperature, depth of discharge (batteries
are generally not discharged completely and depth of discharge
refers to the extent to which they are discharged), self-discharge
(some batteries cannot retain their electrical capacity when stored
in a shelf and self-discharge represents the rate of discharge) and
energy density.
Controls and power conditioning system (C-PCS)
The C-PCS form a vital part of the BESS. It interfaces the batteries
to the loads (utility/end user) and regulates the battery
charge/discharge, charging rate, etc. The C-PCS cost is significant
and it can be greater than 25% of the overall energy storage system.
However, this technology is maturing rapidly due to the recent
developments in the power conditioning systems of the renewable
and distributed energy sources. At present research is being carried
out to reduce the overall cost, improve reliability, and develop more
efficient and better packaging of power conditioning system.
Generally, the BESS C-PCS are designed to use the BESS to
achieve many functions [16,17]. Such multi-function BESS have
been designed in an attempt to make the BESS technology more
economical and cost effective. In order to develop multi-functional
BEES several investigators have suggested many control philosophies.
Some of the studies design controls BESS to directly improve
the power system reliability and operation and the others are
indirect applications (normally in the form of adding new features/
providing greater capabilities to custom power devices, SVC,
STATCOM, etc.). Here the controls designed for direct and indirect
BESS applications have been discussed separately.
Use of electric drive vehicles (EDV) batteries for power
systems
The possibility of using EDV as BESS in power system has been
recognized in [2,32] as early as the last decade. Of late a fewinvestigations
have been carried out [33] to examine the role of renewable
energy/storage technologies for the EDV. Even though it is well
known that the BESS used for EDV could also be used for power
system applications, only recently in [34,35], the practicality has
been examined. In [34], an attempt has been made to assess the
economic benefits of using different vehicle types (fuel cell, battery
and plug-in hybrid electric vehicle) for providing base load,
peak power, spinning reserve and frequency regulation services to
the power system has been carried out. While in their companion
paper [35], the authors examine the systems and processes needed
to tap energy in vehicles and implement vehicle-to-grid power. Further,
this study also examines the applicability of vehicle-to-grid
power for serving as a back-up for the renewable sources, i.e., wind
and solar.