Low Emission Power Generation Technologies and Energy Management E-Book

• Herausgeber: John Wiley & Sons
• Kategorie: Wissenschaft und neue Technologien
• Sprache: Englisch

Seitenzahl: 577

Veröffentlichungsjahr: 2013

Beschreibung

This title is dedicated to energy storage, low emission technologies and energy management, with discussions on the future of nuclear energy, combined heat and power, using hydrogen as an energy vector and fuel cells, as well as chapters on energy saving and control of the demand for power.

Leseprobe

Table of Contents

Preface

1.1. Electric energy

1.2. The new paradigm

1.3. Dispersed generation

1.4. The new energy generation and management

Chapter 1 Energy Storage: Applications to the Electricity Vector

1.1. Energy density

1.2. Storage problem

1.3. Types of storage

1.4. Bibliography

Chapter 2 Nuclear Fission, Today and Tomorrow: from “Renaissance” to Technological Breakthroughs

Summary

2.1. Introduction: all energy options kept open in 2006 Green Book

2.2. Nuclear energy: 50 years of industrial experience

2.3. Main actors: common needs, international vision and strategic instruments

2.4. On the eve of a technological breakthrough: six challenges for research and development

2.5. Generation II: supply security and environmental protection

2.6. Generation III: continuous improvements in safety and competitiveness

2.7. Generation IV (2030 forecast): technological breakthroughs in competitiveness and sustainability

2.8. Education and training: main objectives (modules, mutual recognition, and mobility)

2.9. Conclusion: nuclear energy – a part of the solution in a sustainable energy mix

2.10. Bibliography

20.11. List of acronyms

Chapter 3 Co-generation

3.1. Co-generation

3.2. Overview of existing technologies

3.3. Co-generation installation dimensioning

3.4. Assessment of the energy advantage of co-generation

3.5. Energy advantage allocation

3.6. The electrical aspects of co-generation installations

3.7. Cooling by absorption and tri-generation

3.8. Estimation of the potential of co-generation

3.9. Influence of co-generation on the environment

3.10. Conclusions and perspectives

3.11. Bibliography

Chapter 4 Hydrogen: An Energy Vector

4.1. Context

4.2. Hydrogen: an energy vector for the future?

4.3. How do we produce hydrogen?

4.4. Hydrogen transportation

4.5. Distribution

4.6. Hydrogen storage

4.7. Applications of hydrogen as energy vector

4.8. Risks, standards, regulation and acceptability

4.9. A hydrogen economy

4.10. The hydrogen players

4.11. Conclusions and perspectives

4.12. Bibliography

Chapter 5 Fuel Cells

5.1. Introduction

5.2. Operation principles in different cell types

5.3. The system aspect

5.4. Energy conversion efficiency

5.5. Main applications

5.6. Bibliography

Chapter 6 Toward Energy Positive Buildings

6.1. Introduction

6.2. Energy and buildings: some key figures in Europe

6.3. How to move from buildings “addicted to fossil energy” toward “low energy buildings” (LEB) and, further, toward buildings as power plants (BaPP)

6.4. The Minergie trademark

6.5. The PassivHaus label (passive house)

6.6. The zero-energy houses: zero-energy house – zero-energy home (ZEH) – zero-energy buildings (ZEB)

6.7. The energy-positive house

6.8. Comparison of the three types of houses: Minergie, PassivHaus and ZEH

6.9. Beyond the positive-energy building

6.10. Bibliography

Chapter 7 Light Sources and Lighting: from Technology to Energy Savings

7.1. Lighting in the past and today

7.2. Light sources and energy conversion

7.3. Energy savings in the lighting field: some typical case studies

7.4. What is the future for light sources?

7.5. Bibliography

Chapter 8 Distributed Generation: Impact and Solutions

8.1. Introduction: a threat or an opportunity?

8.2. Deregulation

8.3. New generation equipment

8.4. Impact of distributed generation on electric networks

8.5. Solution elements

8.6. Conclusion: a challenge and a development opportunity for the electricity sector

8.7. Bibliography

Chapter 9 Control of the Energy Demand: Network Load Shedding

9.1. Nomenclature

9.2. Introduction

9.3. Stakes of the load control

9.4. Choice of loads to control

9.5. Needs in communications, measurements and monitoring to control the loads

9.6. Model and algorithm needs for load control

9.7. Conclusion

9.8. Bibliography

List of Authors

Index

First published in France in 2007 by Hermes Science/Lavoisier entitled: Nouvelles technologies de l'énergie volumes 2 et 4 © LAVOISIER, 2007

First published in Great Britain and the United States in 2009 by ISTE Ltd and John Wiley & Sons, Inc. Translated from the French by Professor Albert Foggia and Ms Florence Martin.

Apart from any fair dealing for the purposes of research or private study, or criticism or review, as permitted under the Copyright, Designs and Patents Act 1988, this publication may only be reproduced, stored or transmitted, in any form or by any means, with the prior permission in writing of the publishers, or in the case of reprographic reproduction in accordance with the terms and licenses issued by the CLA. Enquiries concerning reproduction outside these terms should be sent to the publishers at the undermentioned address:

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© ISTE Ltd 2012

The rights of Jean-Claude Sabonnadière to be identified as the author of this work have been asserted by him in accordance with the Copyright, Designs and Patents Act 1988.

Library of Congress Cataloging-in-Publication Data

Stockage et technologies à émission réduite. English

Low emission power generation technologies and energy management / edited by Jean-Claude Sabonnadière.

p. cm.

Originally published: Paris : Hermes science, 2006: under title: Nouvelles technologies de l'énergie, Pt. 2. Stockage et technologies à émission réduite.

Includes bibliographical references and index.

ISBN 978-1-84821-136-0

1. Power resources--Management. I. Sabonnadière, Jean-Claude II. Title.

TJ163.3.S74713 2009

621.042--dc22

2009017411

British Library Cataloguing-in-Publication Data

A CIP record for this book is available from the British Library

ISBN: 978-1-84821-136-0

Preface

1.1. Electric energy

Energy, which was the basis of the industrial revolution, has had an exponential growth since the birth of industrial electricity at the end of the 19th century. The discovery of the rotating field by Nikola Tesla and the invention of the transformer allowed the expansion of three phases: alternating currents for generation, transmission, and delivery and uses of electric energy in the cheapest way.

At the beginning of the 20th century the development of large electric power grids enabled many countries throughout the world to bring the benefits of electric energy to their citizens, while intensively developing the industrial and tertiary applications of electricity. This growth led to generalization of the use of electric energy in domestic applications and all sectors of industry.

Generation, transportation, transmission and distribution of electric energy were considered to be such strategic operations by most countries that they decided to build them as monopolistic state companies in order to control their development. These decisions and the heavily capitalistic nature of generating and transmission systems led to a vertical integration of electric energy utilities for economic reasons. This is the classic paradigm that for more than a century has allowed the creation of an industry that reached the heights of its power in a slow but constant improvement of the reliability of equipment, the main objective being to ensure the supply of electricity to domestic and industrial customers connected to the grid. The tremendous growth of electric energy consumption during the middle of the last century led to the construction of very large and complex electric power systems (for instance, in the French grid, more than 66,000 MW are flowing at any time in about 1,300,000 km of lines and cables).

Figure 1 shows a schematic representation of these systems.

Figure 1.The historic paradigm

All electric power systems have been built and operated according to this diagram from the beginning, and for almost all, of the 20th century. Their organization and their operation from generation to the consumer were integrated inside only one, generally monopolistic, private or public company.

The deregulation that started at the beginning of the 1980s introduced a tremendous change by imposing the unbundling of the functions of generation, transmission and distribution. This change introduced a new mode of organization according to a broken up model we shall describe in the next paragraph as the new paradigm.

1.2. The new paradigm

The goal aimed at by the instigators of the deregulation of electric systems has always been to promote a new organization of the electric systems in order to create the conditions of commercial competition among all the stakeholders: the aim is to lower the price of electric energy supply for consumers.

The setting up of new regulations took place in a context where geographic constraints were prominent due to the territorial settlement of power grids that were in fact naturally monopolistic.

However, the new system instituted in the UK at the beginning of the 1990s, and then in the USA, is now installed in almost all developed countries, although with some difficulties of adaptation. As a matter of fact, the systems designed and built on to be operated as an integrated company in a well-defined territory must today be operated on a continental scale without prior modification of the infrastructures of transmission and interconnection.

1.2.1. The energy system in a deregulated context

The major functions which must be carried out in order to satisfy consumer demand are the same as previously described but with a different mode of interaction, and they are operated by different actors according to the five essential links described in Figure 2.

Figure 2.The new organization of electric systems

This new organization creates a total hierarchical independence between the producers and the other members of the system. The producers of course are in charge of the generation. They sell to consumers according to several kinds of contracts for short or medium term delivery. The traders are the link between generation and consumption, taking into account the power transmission capacity through transmission and distribution grids.

The power grids must ensure the transmission of energy to the consumers according to the trading exchanges they had with the producers, insuring equitable treatment for all producers. Independent system operators for transmission and distribution grids are in charge of this duty.

This new set of concepts generates not only drastic changes in the economic conditions of the electric system's operation, but also significant technical changes that favor the new technologies with dispersed generation, especially renewable energy technologies that will continue to be the foundation of consumer power.

1.3. Dispersed generation

The economic issues arising from the new regulations incite the big consumers to buy internal generation units in order to smooth the price fluctuations coming from deregulation. They are of course small generation units of limited power, generally connected to distribution grids. These units will be able to control the power imported by the consumer, who will be able to sell his energy on the market by injecting it into the grid if price conditions are favorable. The development of a large number of small generation units from solar, wind, small hydraulic or thermal units, with combined heat and power, alongside classical large generation machines, will superimpose a new phenomenon on the normal operation of the distribution grids: bidirectional energy flow, generally intermittent and random according to wind and sun production.

This phenomenon will create new difficult problems such as the management of these energies while keeping the grid security at the required level.

The new paradigm, which integrates dispersed generation with the economic environment, will lead to a new operation scheme for electric power systems, one that will increasingly be a substitute for the present scheme as described in Figure 3.

Figure 3.The new electric power system

1.4. The new energy generation and management

Independently of these new schemes of grid operation, in the following chapters we shall describe the main characteristics of the emerging generation technologies that will be installed on the grid of the next decades.

In the first volume, Renewable Energies, we reviewed the new energy technologies in terms of the types of renewable energy. This second volume, Low Emission Technologies and Energy Management, will deal with reduced emission technologies and energy saving.

Volume 1 includes various forms of solar energy such as photovoltaic, thermal and thermodynamic energy conversion.

Wind technologies are in full development today. The chapters dedicated to them describe the state of the art, taking into consideration the question of insertion into the grids of a large quantity of this intermittent energy.

Energy from the sea completes this general view, with a chapter discussing very small hydraulic plants that become of interest when fossil energies become more and more expensive.

We then provide an analysis of geothermal energy, followed by energy from biomass. This entails a full description of biofuels and biogas, and especially energy from wood as a substitute to fossil energy heating.

Volume 2 is dedicated to energy storage, low emission technologies and energy management.

We start with the new generation of nuclear energy, which is presently at a crossroads of its history with these future new generations. It then analyzes combined heat and power generation, by which it is possible to produce heat and electricity jointly as a complement to heat generation in order to improve the efficiency of heat plants. A very careful analysis of the economic conditions of the operation of combined heat and power leads to a description of the economic conditions for which this technology is advantageous.

Energy storage describes the various means and methods of storage in association with intermittent energies like photovoltaic and wind energy plants. Their efficiency and cost are strongly dependent upon their operational facilities and investment costs.

A projection of the use of hydrogen as an energy vector similar to electricity will give readers a comprehensive view of the way to create, store and transport this gas. which is generally improperly considered as very dangerous. Its future using fuel cells as a conversion facility allows us to foresee significant development of this energy vector with a large set of applications.

Finally, we take up the very important subject of energy management, control of energy demand, and energy saving. We describe positive energy houses, low consumption public and domestic lighting, and power moderation by control of the load from the grid.

Jean-Claude SABONNADJÈRE

Chapter 1

Energy Storage: Applications to the Electricity Vector1

Energy is a fundamental need for human beings. We can extract it from nature and use it in the way best adapted to our needs, either directly (heat, mechanical energy, etc.) or by transforming it into a more polyvalent form, such as electricity.

The human body is itself an energy source, and also an efficient converter of biochemical energy.

Exploitable energy is stored in nature in various forms and densities:

– fossil storage, in the terrestrial geological layers;

– gravitational storage, e.g. using water;

– biochemical storage, for biomass or the human body (glycogen);

– thermal storage for the sun, the effects of which also influence wind and water energy;

– electromagnetic storage, in electric and magnetic fields.

1.1. Energy density

The level of energy stored in materials is very different to that stored in storage components. Figure 1.1 shows the great advantage of fossil sources over secondary storage sources. Nuclear sources are even more concentrated since we obtain 108 Wh/kg from the natural fission of uranium.

Figure 1.1.Energy density

Once the energy has been extracted and generated in an easily transportable form by an energy vector, it is brought to the consumer in the form best suited to the needs of the consumer. Electricity is one of the most versatile vectors known to date (Figure 1.2).

Figure 1.2.Main energy vectors

In the energy chain, storage may be implemented at each step. Storage is particularly important for electricity networks since the balance between delivered supply and demand must be assured. The most suitable choice of storage technology must be made taking into account the intended application and economic parameters such as cost of investment, energy or power densities, life cycle, and impact on the environment (Figure 1.3).

Figure 1.3.Constraints and criteria for storage choices versus applications

There are so many application ranges that it is better to start with some simple applications. What can we do with 1 kWh?

– drive 1 km in a car that uses 8 liters of fuel for 100 km;

– run a refrigerator for one day;

– light a house for one evening;

– manufacture 200 g of steel or 100 g of plastic.

On average, the total energy used in France, per capita and taking in to account all types of energy, corresponds to 40 MWh/year, which means 4.5 kWh/hour per person.

1.2. Storage problem

All energy sources are stored, either on a geological scale, or in the case of the sun, for even longer, and then released as they are needed. The notion of renewable energy makes sense only in terms of human timescales.

We can distinguish the primary storage of fossil sources that exist naturally, and for which we only have to pay for extraction, and the secondary storage created by man, for which we have to pay for the storage and extraction. This chapter focuses on secondary storage.

Table 1.1. Rechargeable time constants of the sources (source: [HER 05])

Sources

Units of time

Biomass

Years

Thermal gradient of oceans

Hundreds of years

Fossil fuels

Millions of years

Tides, waves

Hours

Geothermal

Days or years

Thermal masses

Hours

Batteries

Minutes

Super conducting magnetic energy storage (SMES)

Seconds

Capacitors

Seconds

Hydraulic pumping

Hours

1.2.1. Electrical networks

Storage is essential in mobile applications (vehicles, onboard systems, portable equipment) in order to carry the necessary energy for their operation.

In the case of electrical networks, electricity cannot be stored efficiently and in a sufficient quantity so supply must always be able to meet demand, taking into account the daily and seasonal changes in consumer requirements (Figure 1.4).

Figure 1.4.Forecast curves of electric energy consumption in France

It is therefore necessary to store energy in an auxiliary physical form (mechanical, thermal, chemical) and to convert this stored energy into electricity (battery, generator). This can be done using converters and energy adaptors, which have an efficiency rating of 80 to 90%, but it results in both energy and financial costs.

1.2.2. Electric energy in France: forecast and consumption curves

To provide the differential energy in relation to the average value of daily consumption would lead to a potential storage requirement of dozens of GWh.

The financial cost resulting from momentary or prolonged interruptions (blackouts) of the electricity network is very important because it concerns all the economic sectors (such financial cost is estimated at many tens of billions of dollars per year in the USA) and this cost must be compared to that of energy storage that is capable of reducing the risk of interruptions.

Power and energy including distributed generation sources must also be globally managed at the network-operator level, by means of network operation systems like ICT (information and communication technology).

ICT, in addition to its classic control-command functions, is also able to manage production, storage, and load in the form of virtual plants.

Storage increases the flexibility and the reliability of electricity networks at each level of the electricity chain (Figure 1.5):

– at the generation level, by reducing the investment and operating costs: power reserve, frequency regulation, deferral of necessary new investments (lines, plants, etc. (see Figure 1.6);

– by enabling supply during momentary failure of classic generation sources;

– as electricity prices vary at different times of the day and year (due to the law of supply and demand in an increasingly open market), by enabling the cost of energy to be evened out, but it also provides the opportunity to speculate on its cost (although this operation has its own limits, see Figure 1.11);

– by enabling the reduction of losses in the transmission lines (see Figure 1.7);

– by giving flexibility and compensating for the intermittence of renewable energies, facilitates their integration in the networks (because of the intermittence of wind energy and its low unitary production capability, the penetration of wind energy is limited to 30% (Figure 1.8));

– by increasing the use rate of transport and distribution lines, it allows for delay in purchasing new equipment, and participates in voltage regulation;

– by guaranteeing the quality of energy at consumer levels (UPS: uninterruptible power supply) and reducing costs by taking care of peak power demands;

– by permiting the supply to isolated zones that are not connected to the grid.

Figure 1.5.Insertion points of storage means in a grid

Figure 1.6.Storage. One of the systems facilitating investment reports: a storage source ofl MWh, 0.5 MW can avoid the implementation of a new production source

Figure 1.7.Line losses reduction by insertion of a storage unit near the charge

Figure 1.8.Intermittent renewable sources and storage association

At a consumer level, the problem is slightly different since the energy and power quantities are far less important; it might therefore be interesting to consider storage solutions closer to the point of use1 (Figure 1.9).

In electricity networks, the types of applications can be distinguished depending upon their energy and power ranges. For each type of application, the preferred choice of storage technology depends on the quantity of power and energy required.

Table 1.2.Storage needs according to application types

Table 1.3. Storage types according to applications

Energy Storage

Distributed Generation

Energy Quality

Pb acid batteries

Pb acid batteries

Pb acid batteries

NaS batteries

NaS batteries

Li-ion batteries

Redox flow

Redox flow

Flywheel

Zn-Br batteries

Li-ion batteries

Super capacitors

Ni-Cd batteries

Zn-Br batteries

SMES

Hydroelectric storage

Ni-Cd batteries

Hydraulic pumping

Flywheel

Super capacitors

Super capacitors

Compressed air

Compressed air Fuel cell

Fuel cell

Any storage problem must integrate the technical-economic aspects. We must pay for energy storage and restorage operations, with each operation having its own efficiency.

For each application it is important to optimize the choice of the storage type according to the primary fuel prices and the investment and operating costs. It is also important to manage the storage/restorage strategy (Figure 1.10).

Figure 1.10.Battery recharge strategy by consumption smoothing, [GER 02] with and without recharge power limitation

Hydraulic pumping or compressed air storage (CAES) is, for example, more interesting when the price difference of electricity between off-peak hours and peak hours is important. A generalized development of local storage (batteries, fuel cells, etc.) may even lead to a smoothing of load curves, which could reduce the economic interest of some types of storage (Figure 1.11).

Figure 1.11.Relevant limits of storage using the differential off-peak hours/peak hours

1.2.3. Relevant limits of storage using the differential off-peak hours/peak hours (Figure 1.11)

During the loading period, low-cost electricity is used (off-peak hours). This energy (storing time may be large compared to charging time and discharge time). When it is used, the stored energy, minus losses (leakages), Ed < Es, is converted into electricity and used during peak hours, when electricity costs are high.

If we consider the economics of such a cycle, ∂ represents the producer cost with for a system with storage and Δ represents the same cost for a system without storage which requires specific equipment, e.g. gas turbine, with both systems giving the same service to the consumer. As long as ∂ < Δ, the system with storage is economically profitable.

Once energy is stored, it is restored according to the target applications, either in its power form (W), or in its energy form2 (J or Wh), e.g. power for a certain period of time. Sometimes we will use storage sources that associate a quantity of stored energy with instantly available power. Different storage strategies may lead to different choices of solutions (Figure 1.12).

Figure 1.12.Needs of an electric vehicle: a hybrid vehicle needs to store power whereas an electric vehicle will need both power and energy. For a hybrid vehicle, the objectives to be targeted are around 12 Wh/kg and 500 W/kg, with an available energy of 300 Wh and available power of 10 kW during 2 s and a 15-year life

Figure 1.13a.Rangone diagrams of power and mass energy densities of a selection of storage sources

The different storage sources can thus be characterized by their power densities and energy per mass or per volume (Figures 1.13a and b).

Figure 1.13b.Rangone diagrams of power and mass energy densities of some storage sources

Storage technologies offer ranges of power and energy extending over many orders of magnitude and adapted to very different needs; the efficiencies of storing and restoring operations and the number of cycles used are also relatively different (Figures 1.14 and 1.15).

Figure 1.14.Use range of storage sources

Figure 1.15.Efficiency and lifetime of storage sources

Moreover, in order to define the quality of a type of energy storage, the concept of exergy, which measures the absolute energy efficiency, must be considered.

Whilst energy efficiency is clearly defined for the main energies (mechanical, hydraulic, electric), usable thermal energy depends on its temperature; we are richer if we have a 2,200x00B0; source than a 80x00B0; source because when a thermal motor is used, more main energy can be extracted from the high temperature source than from the low temperature source.

The exergy concept, which takes into account the quality of energy, quantifies this property. The choice of a storage mode, e.g. heat, will take into account the required quality (Figure 1.16).

Figure 1.16.Electrical heat efficiencies

1.3. Types of storage

Storage technologies use different physical or chemical principles. These technologies can be classified according to physical-chemical phenomena they are based on.

Table 1.4. Physical principles and storage technologies

Origin of stored energy

Technologies

Mechanical

Hydraulic Flywheel Compressed air Spring

Electrochemical

Batteries Hydrogen/fuel cell

Electromagnetic

Capacitor/supercapacitor Inductance/magnetic storage (SMES)

Thermal

Sensitive energy (CΔT): water, thermal masses Latent heat (L): melted salts with phase change

These technologies are characterized by:

– storable quantity of energy;

– available power (discharge capacity);

– time constants of charge and discharge;

– lifetime;

– mass and volume densities;

– charge and discharge efficiency;

– ease of conversion to electricity – thermo-dynamic machines, e.g. gas turbines coupled to synchronous generators, and direct conversion technologies (batteries, fuel cells) are used;

– investment and maintenance costs;

– availability and local feasibility (especially mass storage sites);

– social and environmental considerations.

At very low scales, we can also consider micro-energy storage sources for personal applications of microelectronic technologies in the power range less than 100 mW. The range of potentially usable sources may then be enlarged with the sources using ambient radiation, a few temperature differences, mechanical distortion energy, etc.

The advantages and disadvantages of each storage system are outlined in the following table. The concept of power source is linked to the speed with which the energy is available. Thus, if the hydraulic pumping is able to supply large amounts of power, it will take a few minutes to start up.

The main storage technologies are detailed in the following sections.

1.3.1. Gravity storage

The use of gravity leads to low-energy densities: with a difference in height of 100 m for 3.61 of water we can store 1 kWh.

The stored energy and power are:

where is the mass flow and h the height difference, which gives mass and volume densities equal to g h, i.e. respectively in the order of 0.2 to 2 Wh/kg and of 102tol03W/kg.

This type of storage is, thus, an excellent source of continuous power (starting times are around one minute) which requires large volumes in order to store significant energy, and strong flows in order to increase the power.

Some water reserves are mainly primary reserves (there is no storage cost apart from the investment for building the dam): they fill naturally. A dam that prevents water from flowing leads to a differential in water height. This water height differential, possibly increased by a pipe, produces energy converted into electricity by means of a turbine generator. Considerable amounts of power are thus obtained:

– the world hydroelectric production is of 2,600 TWh/year;

– the Churchill Falls (Canada) site has a reservoir of 6,988 km2, a fall height of 312 m and an installed power of 5.4 GW for a flow of 1,700 m3/s; this power is available for more than 50 days if a level reduction of 1 m is accepted;

– the Three Gorges plant (China) will have an installed power of 18 GW for a 85 TWh/year production.

Pumping station plants (STEP) are secondary storage sources. They use the cost differential between peak and off-peak hours to make storage profitable. The efficiency is about 70–80%, the cost is small, but this type of storage needs adapted sites (Figure 1.17).

For example, the Grand-Maison site stores 137,000,000 m3 of water for a lake surface of 2.19 km2, with a fall height of 955 m. It generates 1,800 MW with a flow of 217 m3/s, and could store 1.3 TWh if the water reserve is completely emptied.

Figure 1.17.Gravity storage STEP

The hydraulic potential remains considerable – around 12,000 TWh/year (more than 50% of this is in Asia) – even if about half of this equipment is not considered economically profitable.

1.3.2. Inertial storage

[1.1]

As shown in Table 1.6 the best materials are therefore carbon-fiber composite materials, which can reach more than 300 Wh/kg.

Table 1.6.Materials characteristics for inertial storage

In order to limit friction losses, a flywheel is placed in a vacuum enclosure using contactless magnetic bearings and, possibly, superconductors. A motor generator directly coupled to the shaft enables the wheel to rotate at its own speed and recover energy (Figure 1.18).

The pulse power can reach 2 kW/kg and an efficiency rate of 90%.

Figure 1.18.Principle of a flywheel

Many industrial installations, with single flywheels3 (vehicles, UPS) or wheel stocks for network stability4 have been set up. Rotating speeds may reach 100,000 rpm.

Low-speed flywheels (<10,000 rpm) use standard bearings and steel rotors, and therefore have densities limited to about 10 Wh/kg. Up to 20,000 rpm, standard bearings are used with composite material rotors to reach densities of about 150 Wh/kg.

For higher speeds, magnetic bearings (superconductors) must be used and the rotating parts are in a vacuum.

1.3.3. Compressed air energy storage (CAES)

This technique consists of storing energy in the form of compressed air, either in large geological caverns, e.g. salt mines (Figure 1.19), or, on a simpler scale, in pressurized gas bottles.

Figure 1.19.Principle of a compressed air storage plant (photo courtesy of CAES Development Company)

The air is compressed at about 100 bars during the periods of low-cost/off-peak electricity. This pneumatic energy, improved while heated in a combustion chamber of a gas turbine, is restored in its electric form by a synchronous generator coupled to the gas turbine during peak hours.

Because a standard gas turbine uses around two-thirds of the available power on the shaft to compress the combustion air, by separating the two processes it is possible to generate three times more power using the same amount of gas.

Figure 1.20.Principle of a single cycle gas turbine operation

Figure 1.21.Principle of a compressed air storage system coupled to a gas turbine operation

The problems with this system are the high energy costs of compression which have an impact on cost effectiveness, the slow start up time of around 15 min, and the high cost of investment. Therefore it is necessary to have a significant Δ between the peak rates and off-peak rates, and to find nearby underground caverns. Gas consumption is also significant, even if it is lower (30–40%) than in the case of a standard gas turbine.5

For example, a CAES source can be connected to a wind farm in order to create a flexible plant. The latter can be used in a quasi-permanent manner, thus smoothing the intermittent problems and taking benefit from the low operating cost of the wind energy (Figure 1.22a).

Coupling CAES and heat (thermal and compressed air storage (TACAS)) is also an alternative – for a few minutes – to batteries and flywheels for power of some MW (Figure 1.22b).

1.3.4. Electrochemical storage: batteries

A battery generates electricity from an oxidation/reduction chemical reaction. A battery contains one or more cells in series that are made of three basic components:

– Anode and cathode. An anode is a negative reductive electrode, which supplies the electrons to the external circuit; it is generally a metal component. A cathode is a positive oxidant electrode, which recovers the electron from the external circuit; it is generally a metallic oxide component.

– Electrolyte. The electrolyte is where the electrochemical reactions take place; this is an ionic conductor with no conductivity for electrons; the current flow is due to the motion of the ions affected by the electric field between the electrodes; this is generally an aqueous solution.

– Membrane. The membrane which is permeable to the electrolyte may sometimes separate the electrodes.

Figure 1.22a.Integration wind and CAES

Figure 1.22b.TACAS6system

During the discharge, electrons move in the external circuit and the positive ions go from the anode to the cathode in the electrolyte.

A battery may be (see Table 1.7):

– Primary: the electrochemical reaction is not reversible (not rechargeable). The chemical transformation slowly destroys one of the electrodes, e.g. Zn-C, Zn-Hg, Zn-Cd, Zn-Air batteries, manganese alkaline batteries or lithium batteries. Lithium batteries are often used in portable equipment.

– Secondary: the electrochemical reaction is reversible. The battery may be recharged and the initial component restored, e.g. Pb-Acid, Ni-Cd, NaS, NiMH, and Li-ion.

Table 1.7. Classification of electrochemical components (source: E.Vieil, LEPMI, Grenoble – private communication)

Process

Non renewable fuel

Renewable fuel

Non-reversible

Battery (primary battery)

Fuel cell

Reversible

Battery (secondary battery)

Fuel cell

The density of the stored energy is proportional to the number of electrons per mole (in this respect lithium is a very interesting material) and to the volume mass of its components. Very reductive and very oxidant anode-cathode couples will be considered. The chemical reactions are very temperature-sensitive and each type of battery will have an optimal operating temperature range.

The first battery was made by Volta, in 1800, by piling up alternating copper and zinc disks, each pair being separated from the other by a cloth saturated with salt water.

In 1839, the lead or lead-acid battery was invented by Gaston Planté. It was made of lead and lead oxide electrodes (PbO2). The electrolyte was an aqueous solution of sulfuric acid (Figure 1.23).

Figure 1.23. Lead acid battery during discharge: cathode: PbO2 reacts with sulfuric acid ==> lead sulfate + water, anode: Pb reacts with sulfate ions ==> lead sulfate, plus electrons, sulfuric acid is consumed. During charge, the lead sulfate is destroyed, making lead and lead oxide; water is consumed and acid is formed

This type of battery is used extensively, even for equipment of many MWh7, because of its cost, despite its short life span.

Liquid electrolyte batteries require regular maintenance (level control of the electrolyte).

Batteries requiring no maintenance (valve regulated lead acid (VRLA)) have an electrolyte like a gel which enables the limitation of hydrogen evolution. They are equipped with a regulation valve which allows the gas recombination.

Lead batteries remain in use today and their lifetime is consistently being improved (Figure 1.24).

Figure 1.24.Typical discharge of a lead acid battery and discharge curves of Zn-C and Zn-Hg batteries

A battery has an internal resistance which varies according to its capacity (Ah), its discharge state and its temperature. At the end of discharge, the limit value EF of its voltage must not be exceeded, otherwise there is a risk of rapidly draining the battery (in the case of primary batteries) and of reducing its recovering capacity during the charge (in the case of secondary batteries).

The discharge depth is the percentage of the discharge capacity; a battery has self-discharge characteristics due to parasitic electrochemical reactions which represent a loss of capacity and energy.

A number of other pairs may form interesting batteries:

– Ni-Cd: these batteries use a nickel hydroxide cathode Ni(OH)2, a cadmium anode, and a potassium hydroxide electrolyte KOH.8 This type of battery is expensive and its components are toxic. The discharge reactions are:

– metallic Ni-Hydrides:9 metallic hydrides can store hydrogen and may be used as negative electrodes; the positive electrode is a nickel hydroxide. These batteries are of the same type as Ni-Cd batteries, but the hydrogen is used as an active element at the anode. The electrolyte is a potassium hydroxide that must absorb and transport the H+ (KOH) ions. The batteries have a large stored-energy density in an extended temperature range. They are not toxic. They could be possible replacements for Ni-Cd batteries, but, like them, they do not recover their full capacity if they are not completely discharged (memory effect);

– Li-ion: the electrodes can accept or deliver Li ions and electrons (insertion phenomena) (see Figure 1.25). The electrolyte is a non-aqueous organic component (lithium reacts with water) in which there is no chemical reaction, but it plays the part of a reversible ionic conductor. In this type of battery there are no gaseous elements such as H2 or O2 (Figure 1.25). These batteries have very good energy density since lithium is very light. They are thus very compact and can be used in all personal equipment. Li-polymer batteries (ACEP) contain a very thin, solid electrolyte (100 Lim) between the lithium electrode (anode) and the vanadium oxide electrode (cathode) which looks like ribbons, leading to combinations with a density > 150 Wh/kg;

Figure 1.25.Principle of Li-ion battery operation

- NaS: sodium is interesting because of its high reduction potential (2.7 V), its low cost, and its low toxicity. It can, however, be used in its liquid form only at temperatures higher than 98°C (Na fusion temperature), around 270°C, which leads to thermal and corrosion problems. The batteries are mainly used in the military field or in stationary applications;10 despite their high-energy densities (> 100 Wh/kg) and their excellent efficiency (90%), they tend to be replaced by Li- ion batteries. The Na-NiCl2 "zebra" system, which also operates at high temperature (300°C) with a ceramic electrolyte which allows the Na+ ions pass, is more secure than the NaS and can reach mass energies of 85 Wh/kg;

Table 1.8.Electrochemical couples (*practical values)

– redox flow: these batteries use Vanadium ions of different valences. The ions are separated by a membrane which is permeable by the protons. Both reservoirs contain slightly acid electrolytes that are pumped into the cell where they remain separated by an ionic membrane. The electronic exchanges in the aqueous phase near the carbon electrodes correspond to an oxidation state change of the vanadium. (Figure 1.26).

In this type of battery, the functions of energy and power are dissociated; the storage capacity (kWh) is defined by the quantity of electrolytes used; the power (kW) depends on the active surface of the cells (membranes). Many industrial-size prototypes (>400 kWh, >100 kW) have been made11 along with modular batteries of some kW/kWh for mobile applications. Some models do not have electrolyte circulation.

Figure 1.26.Operation principle of a vanadium Redox flow battery

Bromine polysulfide (PSB)12 or zinc-bromine13 have the same design, with oxide-reduction relations of the type:

Lead batteries are often used and have definite advantages: their cost is low, but their lifetime is limited according to the charge and discharge procedures.

For other batteries, the main problem is their cost, which is justified for portable applications only.

The main objective is to find new electrochemical pairs, to reduce reliance on active materials, and to use less expensive and less polluting materials.

The redox flow batteries, using Vanadium circulation systems, are attractive for high power output, but the membrane remains a critical point.

Charge and discharge strategies depend on the type of usage. In the case of hybrid vehicles for example, the autonomous operation will be distinguished from the external charge from the grid.

Battery recycling is a necessity because of the toxic level of the material used (Pb, Cd, Br, etc.). Chemical14 or thermal (cremation) techniques are used.

Figure 1.27.Rangone diagram of batteries

Table 1.9a.Evolution perspectives of battery performance, (source: [EU 05])

Table 1.9b.Storage costs

1.3.4.1. Hydrogen

1.3.4.1.1. Production

There are many methods of producing hydrogen:

– fossil hydrogen, carbon or biomass gasification with a risk of secondary production of CO and CO2;

– water electrolysis from electric sources (nuclear, renewable energies) or at high temperature;

– bio-photosynthesis, fermentation, photo-electrolysis phenomena;

– high temperature thermo-chemistry (800°C to 1,300°C) on metal oxides.

1.3.4.1.2. Storage

For mass storage, natural or artificial15 caverns may be used. Hydrogen may also be transformed into hydrocarbon or alcohol with a density that enables ease of storage; these components are then recombined efficiently to obtain hydrogen.

In order to store smaller quantities of hydrogen, e.g. for mobile applications, new solutions are under development, but as yet the ideal solution has not been found:

– gas: at 350-700 bars, in composite tanks (metal and glass fiber, carbon) is still expensive. This type of storage still presents problems of reliability, security and, above all, tank durability,16 and we must take into account the compression energy cost;

8 g of hydrogen, which represents 110 cm3 per m2 of surface per hour, evaporate;

– reversible metal hydrides: absorption and desorption mechanisms and their modeling are not yet fully understood. The quantity of stored hydrogen is still low:

– alloys (LaNiH6, Mg2NiH4, TiFeH2, etc.): the cost and mass of which are high (per mass, 6% of H2 can be stored);

– complex light hydrides: alanates (NaA1H4), hydrides of Mg, hydro-borides alkalis;

– high pressure carbon nano=structures (200 bars);

– porous organo-metallic materials;

– micro-organisms (seaweed), enzymes.

In all cases, the mass densities are put at a disadvantage because of the storage reservoirs (under 350 bars pressure, with a composite reservoir, 1.7 kWh/kg can be obtained).

1.3.4.2. Fuel cells (FC)

The fuel cell, which was invented by Sir William Grove in 1839, is a renewable cell (see Table 1.6). It generally uses hydrogen and oxygen which are converted into water.

1.3.4.2.1. Operation

A fuel cell is a generator which directly converts the internal energy of a fuel into electrical energy by means of a controlled electrochemical process.

Figure 1.28.Combustion principle (source: LEPMI, Grenoble)

Combustion of fuel and oxygen is initiated by an activator. If this combustion is not controlled, it produces an explosion which makes heat and work and gives off combustion waste (Figure 1.29).

This combustion may be monitored, while controlling the exchanges between fuel and oxygen in order to recover heat and electricity. This can be done by separating the electrons from the ions in the electrolyte with a selective membrane. Batteries are made using this method – as are fuel cells, which are renewable – but not reversible batteries (Figure 1.29).

A fuel cell is different from other electrochemical batteries because the agents are permanently renewed and the products permanently evacuated (Figure 1.30).

Figure 1.29.Principle of controlled combustion (source: LEPMI)

Figure 1.30.Renewable cell (source: LEPMI)

The reaction H2 + l/2O2H2O may be separated into two half reactions:

The chemical potential of the reaction (-237 kJ/mole) gives a voltage of 1.23 V.

The different types of fuel cells depend on the ions exchanged between anodes and cathodes; they also depend on the fuels and oxidizers, and on the type of membrane and electrolyte.

They can be divided into six categories: AFC (alkaline fuel cell), PEMFC (polymer exchange membrane fuel cell), DMFC (direct methanol fuel cell), PAFC (phosphoric acid fuel cell), MCFC (molten carbonate fuel cell), SOFC (solid oxide fuel cell).

The tables below outline the characteristics of each type of fuel cell and specify the type of electrolyte that gives the operating temperature range.

The high temperature operation of SOFC allows their coupling with gas17turbines.

Table 1.10.Main electrochemical reactions in fuel cells

Table 1.11.Properties of fuel cells

1.3.4.2.2. Advantages of fuel cells

Fuel cells have the following advantages:

– fuel cells directly transform chemical energy into electrical energy; their chemical agents are stored outside the cell, thus separating stored energy and power;

– their efficiency does not depend on a Carnot cycle;

– they have a low acoustic emission;

– they allow modular manufacturing;

– they give a co-generation possibility efficiencies of 50% to 80%;

– they produce water and emit few green-house gasses.

1.3.4.2.3. Disadvantages of fuel cells

Fuel cells have the following disadvantages:

– some technologies require very pure hydrogen;

– their low unitary voltages (≈ 1 V) require series connections (stack) and power electronic interfaces which introduce losses (Figure 1.31) and reduce their efficiency;

– current densities remain in the order of 1 A/cm2;

– there are losses during transient states;

– current distribution is modified with the generated magnetic field and when the plates surfaces increase;

– thermal and water management operating point control;

– mass and volume;

– cost: catalysts, membranes, current collectors, waterproof joints (at high temperature);

– lifetime, although theoretically the active material of the electrodes is not consumed.

Figure 1.31.Fuel cell/PE coupling

Table 1.12. Fuel cell characteristics (source: [EU 05])

1.3.5. Storage in the electromagnetic field

1.3.5.1. Electric field: capacitors, supercapacitors

In electronic systems, especially in power electronics, the most common buffer storage elements used are the capacitor and the inductance, either in their usual form or directly integrated into silicon chips (Figure 1.32).

Figure 1.32.Integration of planar components LCT (inductance, capacitor, transformer)

Stored energy is weak, in the order of some tens of Wh. The main technologies used are:

– foil capacitors, which in the process of disappearing;

– electrolyte capacitors with a solid or liquid electrolyte. They have good value, but are voltage limited (600 V) and have important leakage currents;

– polymer electrolyte capacitors (polyester, polycarbonate, polystyrene) have low losses and high service voltages. The polypropylene capacitors are used in power electronics because of their good response under a pulse regime;

The electric field stores energy with a volume density equal to:

[1.2]

Table 1.13. Dielectric properties of materials

Dielectric

Dielectric rigidity (MV/m)

ε

r

Dry air

3

1

SF

6

30

1

Pyranol

12

4.5

Epoxy

20

3.3

Mineral oil

10

2.2

Mica

40-240

7

Impregnated paper

14

4-7

PET (polyethylene terephthalate)

700

3

Polypropylene

800

2.4

Polyimide

200

3.8

Porcelain

4

6

Glass

25–100

5–7

Supercapacitors22 (double layer capacitors) are capacitors that operate like classic capacitors, but their technology is similar to the operation principle of the electrochemical batteries (Figure 1.33).

They perform better than batteries in terms of power densities and have energy densities higher than their capacities.

The capacitors of the layers between every two electrodes, made of porous carbon, and the electrolyte ions (surface capacitors of 30(μ F/cm2) are connected in series.

There is no chemical reaction. The energy may be transferred very quickly and as this phenomenon creates charges at the surface of solid faces, the lifetime is very good (>> 10,000 cycles) with an efficiency of 95%. A porous dielectric membrane stops the charge flow between the electrodes. The element voltage remains in the order of 2 to 3 V.

The asymmetric systems, which use one carbon electrode and one metal electrode, have even higher energy densities.

The huge surface (1,000 m2/g) of the porous electrodes (typically made of carbon powder or fiber polymers) and the very thin separation space (1 nm) enable the storage of very significant energy. Capacities of many kFarads and volume energies of around 10 Wh/kg may be obtained. The supercapacitors that deliver a voltage depending on the charge state are connected to power converters.

Figure 1.33.Operating principle of a supercapacitor

1.3.5.2. Magnetic field: Superconductor Magnetic Energy Storage (SMES)

The magnetic field stores energy with a volume density in the air equal to

[1.3]

which allows, if superconductors are used, densities in the order of 10 kWh/m3 and in large volumes. Since μ0 >> ε0, then the electric and magnetic fields E and H are in the same order of magnitude, the magnetic storage in the air is then more efficient and enables large systems.

The first SMES used superconductors (NbTi) requiring a liquid helium temperature cooling (4.2 K), which lead to high insulation and cooling costs, as well as high maintenance and operating costs.

The improvements to superconductor materials now enable the cooling of the coils (Bi2Sr2CaCu2O) at temperatures of about 20 K in order to optimize the operation of the conductor, thus reducing the necessary cold power.

The absence of resistance from the conductors in their superconductor state allows energy storage in the short-circuited coil, theoretically infinitely.

A converter system charges and discharges the current. The charge and discharge times are limited by the over voltage Ldi/dt which appears at the coil terminals, and are also limited by the component reverse voltage. Valuable power can then be delivered with a very high level of efficiency (> 95%) since the AC losses in the conductors are low (Figure 1.34).

Figure 1.34.Connection principle of SMES to the grid

The maximum transferable power varies as Qstored1/2

[1.4]

To date, this kind of storage has been used for network stability (P and Q control) and to improve the network quality (D-SMES, μSMES)23. It has also been used for boost systems (electromagnetic launchers).24

Solenoid geometry is used for large volumes, but generates high leakage fields. The toroidal geometry drastically reduces the parasitic fields.

Figure 1.35.Toroidal and solenoid geometries for a SMES

The main drawback of SMES cryogenic cooling should disappear if HCT (high critical temperature) super-conductors work at temperatures ≥ 77 K (temperature of liquid nitrogen).

1.3.6. Heat

Heat is stored naturally in the ground and is used in geothermal technology (with useful ΔT of 200°C) or in the ocean (with useful ΔT of 20°C) and represents a source used in some accessible sites. Heat storage must be limited to applications directly using this form of energy (buildings). When heat is used, the material characteristics to be taken into account are the thermal capacity (C in Jkg-1K-1) and the thermal diffusivity (D in m2s-1) which will characterize, for a given thermal load, the restoring time of the stored heat. The endothermic latent heat due to the state changes of some materials (L in Wkg-1) may be used; the material absorbs energy when it exceeds the transition temperature and gives it back when it is re-cooled. It is the change of state from solid to liquid that is used. Some of these materials may be integrated into construction materials, e.g. concrete.

Water is often used, e.g. for solar heaters, but its storage capacity remains low (30 kg of water heated with a 30° difference stores little more than 1 kWh). Time constants are rather long and the heat storage may fulfill daily or even season storage needs. Storage temperatures are in the order of 100°C (low temperature storage) or higher (high temperature storage) for use with a gas turbine for example. Insulation measures must also be taken to avoid thermal losses. Cold may also be stored for some specific applications.

Table 1.14.Thermal properties of storage materials

We can envisage a system similar to that of the CAES, which stores energy in its thermal form, in refractory materials electrically heated at 1,400°C during off-peak periods. This stored energy could be recovered in its electric form by means of a temperature turbine with an efficiency of 60%, during peak hours.

The stored energy density is high (360 Wh/kg, 1 MWh/m3). Storage of 100 MWh of electricity, with an efficiency of 60%, would only occupy a volume of 170 m3 (Figure 1.36).

Figure 1.36.Principle of refractory thermal storage at high temperature. A heat exchanger between the cooler and the compressor would achieve a permanent operation cycle, the storage reservoir being a classical boiler

1.3.7. Small-scale storage

In the field of microsystems, especially for embedded systems, the problems of energy storage are of prime importance for reasons of mass, volume, and autonomy. The smaller the microsystem, the greater the problem.

Lithium mini-batteries only deliver mAh/cm2 (HEF group) on surfaces of a few cm2 with thicknesses of a few hundred Lim.

Lithium batteries of 200 μAh have been manufactured directly onto a silicon sublayer, and are able to deliver hundreds of μA /cm2 per hour (Figure 1.37). These batteries may be integrated in the circuits they supply; they are flexible and may be made with a large range of surfaces and in a large range of shapes.

μfuel cells delivering 0.1 W to 10 W may be associated with these μbatteries to create a complete μsource.

Figure 1.37.Schematic of a μbattery Li-ion (source CEA)

Figure 1.38.Schematic diagram of a fuel cell on silicon

Figure 1.39.Portable systems consumption

At these energy scales, the stored energy may be recovered in other, less commonly used forms, macroscopically speaking, particularly the environmental energy:

– thermal energy: the human body used as a heat source for the thermoelectrical effect;25

– mechanical energy (body motion, etc.), in the case of piezo electrical materials;

– thermo-mechanical energy in the case of shape memory materials (nitinol. Figure 1.40);

– thermo-magnetic energy in temperature-commutable magnetization materials such as GdCoCu.

Figure 1.40.Shape memory alloy

Figure 1.41.2 Environmental energy usage

1.4. Bibliography

[AND 97] M.D. ANDERSON, et al, "Assessment of utility-side cost savings for battery energy storage", Proceedings of IEEE Trans on Power Systems, 12–13, 1997.

[BAX 02] J. BAXTER, "Energy storage: enabling a future for renewables? " Renewable Energy World, July-August 2002.

[BOB 05] J.L. BOBIN, E. HUFFER and H. NIFENECKER, L'énergie de demain, EDP Sciences, 2005.

[CAR 99] F. CARDARELLI, Materials Handbook: A Concise Desktop Reference, Springer, 1999.

[CON 99] B.E. CONWAY, Electrochemical Supercapacitors: Scientific Fundamentals and Technological Applications, Kluwer, 1999.

[EPR 03] EPRI-DOE, Handbook of Energy Storage for Transmission and Distribution Applications, EPRI, Product n°1001834, December 2003.

[EU 01] European Commission, Storage: a key technology for decentralised power, power quality and clean transport, Eur 19978 report, European Communities, Belgium, 2001.

[EU 05] European Commission, Energy Scientific and Technological Indicators and References, Eur 21611 report, European Communities, Belgium, 2005.

[EVA 98] D. EVANS, "Hybrid capacitor applications", Proceedings VIII International Seminar, Double Layer Capacitor and Similar Energy Storage Device, Florida, US, 7-9 December 1998.

[FAU 98] J.F. FAUVARQUE, "Présentation générale des super condensateurs à double couche électrochimique", Journées d'études sur les super condensateurs, Paris, 1998.

[GER 02] O GERGAUD, Modélisation énergétique et optimisation économique d'un systéme de production éolien et photovoltaïque couplé au réseau et associé à un accumulateur, PhD Thesis, Cachan, 2002.

[HER 05] WA. HERMANN, Quantifying Global Energy Resources, Science Direct, Elsevier, 2005.

[KIN 99] A. KTNSHI et ah, "Micro thermoelectric modules and their application to wirstwatches as energy source", XVIII International Conference on Thermoelectrics, Baltimore, 1999.

[LAS 01] J.C. LASSÈGUES, Super condensateurs, Techniques de l'ngénieur D3334, 2001.

[LEV 02] A. LEVASSEUR et al., Les micro accumulateurs, Journeés du club EEA, Cachan, 2002.

[LIN 01] D. LINDEN and T.B. REDDY, Handbook of Batteries, 3rd edition, McGraw-Hill, 2001.

[LUC 02] P. LUCCHESE, Pile à combustible, possibilité de miniaturisation, Journées du club EEA, Cachan, 2002.

[MAR 98] A. MARQUET et al, Stockage d'électricité dans les systèmes électriques. Techniques de l'ngénieur D4025,1998.

[MUL 03] B. MULTON and J. RUER, "Stacker l'électricité: oui, c'est indispensable et c'est possible! Pourquoi, où, comment". Club Ecrin, Conference énergies alternatives, Paris 2003.

[MUL 96] B. MULTON and J.M. PETER, "Le stockage de l'énergie: moyens et applications", Revue 3EI, vol. 6, June 1996.

[OHS 04] H. OHSAKI et al, "Development of SMES for power system control: present status and perspective", Physica C, 412, 2004.

[RIB 01] P.F. RIBEIRO et al., "Energy Storage Systems for Advanced Power Applications", Proc of IEEE 89, December 2001.

[SAR 01] C. SARRAZIN, Piles électriques, Techniques de l'Ingénieur D3320, 2001.

[SUR 05] C. SURDU et al, "La centrale virtuelle, un nouveau concept pour favoriser l'insertion de la production décentralisée d'énergie dans les réseaux de distribution", Revue 3EI, vol. 40, March 2005.

[VAN 03] S. VAN DER LINDEN, "The commercial world of energy storage: a review of operating facilities", Annual Conference of the Energy Storage Council, TX, US, March 2003.

[ZIN 97] J.C. ZINK, "Who says you can't store energy", Power Engineering, vol. 101, no. 3, March 1997.

1 Chapter written by Yves BRUNET.

1. EPRI 2.4 kW, 15 kWh, Salt River Residential Photovoltaic-Battery Energy Storage System Project 1997 [EPR 03].

3. Beacon Power System 7 kWh, 2 kW, Powerbridge.

5. AEC 110 MW, 3 GWh, 540,000 m3 at 70 bars, McIntosh plant, Alabama; 290 MW, 580 MWh Huntdorf Germany.

6. CoolAir™ Active Power Co.

7. Chino, 40 MWH, 10 MW (California).

8. 40 MW, Golden Electric Association (Alaska).

9. ElectroEnergylnc 350 V, 500 A 700 W/kg.

10. 6 MW 1999 (TEPCo Ohito substation).

11. Mitsubishi/Osaki Kansai power station; Mitsubischi/Kashima Kita Power Station, Regenesys®: TVA 120 MWh/12 MW; Sumitomo 500 kW/5 Mwh, JPH-NEDO 6 MW.

12. Regenesys 120 MWh, 15 MW Innogy's Little Bradford (UK) station.

13. ZBB 2 MW/2 MWh transportable for PG&E substation (California); VRB Inc King Island.

14. Recupyl.

15. Beynes experimentation.

16. Quantum, Dynetek, CEA.

17. Example of Mitsubishi: efficiencies of 65% with natural gas.

18. Example of Ballard.

19. Example of ONSI Corp.

20. Example of Fuel Cell Energy, Ansaldo Fuel Cell SpA, Hitachi.

21. Example of Technology Sulzer Hexis, experimentations: Siemens (100 kW), 220 kW.

22. Becker patent (1957).

23. Examples of devices achieved by Chubu Electric Co 5 MW/5 MJ and by NEDO 2.9 MJ; Rhineland loop ATC (Wisconsin): 6 units 3 MW, 3 MJ.

24. Example of SMES 20 K, 800 MJ made by LEG.

25. For example, Seiko and Citizen watches.