Energy Storage: A Vital Element in Mankind's Quest for Survival and Progress

By Joseph Silverman

Energy Storage: A Vital Element in Mankind's Quest for Survival and Progress presents the transactions of the First International Assembly held at Dubrovnik, Yugoslavia, 27 May-1 June 1979. It was the first international gathering of industrial, academic, and government experts to discuss all facets of energy storage: electrochemical, thermochemical and thermal, photochemical, and mechanical. In addition to panel sessions and lectures in these four areas, there were assessments using techno-economic models of the impact of various aspects of energy storage. The volume is organized into three sections. Section I consists of the plenary lectures, which are designed to summarize the progress, problems, and future opportunities in various areas of energy storage technology. Section II consists of Summary Proceedings. It was compiled mainly at the conference site and includes summaries of both the papers and discussions at the plenary and panel sessions. Section III contains the papers presented during the panel sessions.

• Language: English
• Publisher: Elsevier Science
• Release date: Oct 22, 2013
• ISBN: 9781483145488

Book preview

USA

ORGANIZATION OF ASSEMBLY

GENERAL CHAIRMEN

Prof. A. Despić

Dr. R. Smelt

EXECUTIVE COMMITTEE

Prof. C. Newton

Dr. G. Pezdirtz

Prof. L. Rakić

Prof. J. Silverman

Secretary-General

CONFERENCE COORDINATORS

Mr. H. Lowitt (USA)

Mr. N. Ostojić (Yugoslavia)

PUBLICATIONS COORDINATOR

Mrs. W. Stevens

TRAVEL AND ACCOMMODATIONS COORDINATOR

Ms. C. Rice

RAPPORTEURS

Ms. L. Burch

Mr. H. Lowitt

Dr. K. Mead

Mr. L. Oliva

Ms. C. Rice

Mr. M. Siat

Ms. M. Strauss

SPONSORED BY

National Academy of Sciences – USA

Council of Academies of Science – Yugoslavia

PROGRAM

SUNDAY, 27 MAY 1979

REGISTRATION

RECEPTION

MONDAY, 28 MAY 1979

PLENARY SESSION IA: A. Despić (Yugoslavia), Chairman

Call to Order

Chairman’s Remarks

R. Smelt (USA)

Welcome by Deputy Mayor

Introductory Address

J. Silverman (USA)

Keynote Lecture

A. Despić (Yugoslavia)

PLENARY SESSION IB: V. S. Bagotskii (USSR), Chairman

Electrochemical Storage

K. Kordesch (Austria)

Thermochemical and Thermal Storage

G. Wettermark (Sweden)

Photochemical Storage

J. Rabani (Israel)

RECESS

PLENARY SESSION IIA: J. P. Longwell (USA), Chairman

Mechanical Storage

Z. Stanley Stys (USA)

Modeling and Assessment

U. LaRoche (Switzerland)

An Overview of Energy Storage

N. Lidorenko (USSR)

PLENARY SESSION IIB: J. Silverman (USA), Chairman

Discussion of Plenary Papers

TUESDAY, 29 MAY 1979

PANEL MEETINGS

1. Electrochemical Energy Storage Panel

Fuel Cells and Metal-Air Batteries as Electrochemical Energy Storage Systems

H. Cnobloch

Electrochemical Energy Storage on Board of Road Electric Vehicles

P. Montalenti and G. Brusaglino

Lithium Metal Sulfide Batteries for Electric Vehicles

P. A. Nelson

Oxygen Electrodes for Electrochemical Energy Storage Systems

E. Yeager

Electrocatalysis on Surfaces Modified by Foreign Metal Adatoms and Its Application in Fuel Cells

R. R. Adzić

Hydrogen Energy Scenario

S. Srinivasan

Fuel Cells for Transportation

H. Van den Broeck

Ambient Temperature Batteries for Electric Vehicles and Energy Storage

A. J. Salkind

2. Thermochemical and Thermal Energy Storage Panel

Chairman’s Introductory Remarks

N. Kurti

Thermal Energy Storage for Non-Fossil Power Plants

P. V. Gilli and G. Beckmann

A Review of Current Aquifer Thermal Energy Storage Projects

C. F. Tsang

Large-Scale Annual-Cycle Thermal Energy Storage in Aquifers

C. F. Meyer

Thermal Energy Storage for Buildings

A. L. Berlad

Sweden – A Case for Long-Term Thermal Storage

W. Raldow and G. Wettermark

Thermal Energy Storage Using Metal Hydrides

H. Buchner

Summary of the U. S. Thermochemical Energy Storage and Transport (TEST) Program

T. T. Bramlette

Method of Storage and Recovery of Thermal Energy by the Use of the Chemical System: (Ethyl Sulfate) – (Ethylene, Sulfuric Acid)

R. Rigopoulos, P. Yianoulis, A. Cutinas and A. Tsolis

Research on Energy Storage at Risø National Laboratory

1. Ground Storage for Thermal Energy

O. Rathmann

2. Seasonal Heat Storage in Aquifers J. Reffstrup and J. Würtz

3. Natural Gas Storage in Salt Caverns

S. Krenk, N. S. Ottosen, K. Jensen and I. Rassmussen

4. Energy Storage Bssed Upon Metal-Hydrogen Systems B. Vigeholm

Past, Present and Future Thermochemical Hydrogen Production Research

D. van Velzen

3. Photochemical Energy Storage Panel

Limitations of Artificial Photochemical Solar Energy Storage

M. Almgren

Some Recent Progress in Semiconductor-Liquid Junction Solar Cells

A. Heller and B. Miller

Processes in Photogalvanic Cells and Their Possibilities in Solar Energy Storage

O. Haas

Photoelectrical Cell for Conversion and Storage of Solar Energy Based on Photosensitized Redox Reactions

I. Kraljić

Electron Transfer Processes in Micellar Systems

E. Pelizzetti

Photoredox Processes. Catalytic Generation of Hydrogen by Reactions of Metal Ions and Water

O. I. Mićić and M. T. Nenadović

Protection, Size Factors and Reaction Dynamics of Collodial Redox Catalysts Mediating Light Induced Hydrogen Evolution from Water

J. Kiwi and M. Grätzel

Brief Summary of Canadian Research and Development of Interest to Photochemical Panel of the International Assembly on Energy Storage

E. J. Casey and D. R. Snelling

4. Mechanical Energy Storage Panel

Compressed Air Energy Storage Technology Program in the United States

M. V. Loscutoff

Actual C.A.E.S. Technology in Europe

J. Pellin

Demonstration of a Low Cost Flywheel in an Energy Storage System

D. W. Rabenhorst

A Flywheel Energy Storage and Conversion System for Photovoltaic Applications

A. R. Millner

Fluid Bed Augmented C.A.E.S. Systems

A. J. Giramonti

Flywheel Energy Storage Systems Operating on ‘Single Active Axis’ Magnetic Bearings

P. C. Poubeau

5. Modeling and Assessment Panel

Methods of Evaluating and Comparing Energy Storage Devices for Automobiles

H. C. Forsberg and E. Behrin

Energy Storage in Automotive Vehicles: An Analytical Model

R. F. McAlevy III

Heating with Off-Peak Electricity: A Cost-Effective Way to Save Oil and Gas

J. G. Asbury

The Assessment of Energy Storage Systems for Electric Utilities

H. G. Pfeiffer

Prioritization of Research Projects

C. R. Johnson

WEDNESDAY, 30 MAY 1979

PANEL MEETINGS

Development of Panel Summary Statements

PLENARY SESSION III; R. Smelt (USA), Chairman

Report of the Panel on Electrochemical Storage

E. Budevski (Bulgaria)

Report of the Panel on Mechanical Storage

W. Loscutoff and D. Rabenhorst (USA)

Report of the Panel on Thermal and Thermochemical Storage

N. Kurti (UK)

Report of the Panel on Photochemical Storage

M. Grätzel (Switzerland)

Report of the Panel on Modeling and Assessment

K. Hoffman (USA)

BANQUET, D. Wyatt (USA), Chairman

Frederik Pohl (USA), Speaker

THURSDAY, 31 MAY 1979

PLENARY SESSION IV: R. Smelt (USA), Chairman

Plenary Discussion of Panel Reports

Some Impacts of Energy Storage Technologies on U. S. Energy Problems

G. Pezdirtz (USA)

Closing Remarks

A. Despić (Yugoslavia)

Adjournment

FRIDAY, 1 JUNE 1979

EXECUTIVE COMMITTEE MEETING

SECTION I

PLENARY LECTURES

Outline

Chapter 1: CHAIRMAN’S OPENING REMARKS

Chapter 2: INTRODUCTORY ADDRESS

Chapter 3: ELECTROCHEMICAL ENERGY STORAGE

Chapter 4: THERMOCHEMICAL AND THERMAL STORAGE

Chapter 5: PHOTOCHEMICAL STORAGE PLENARY LECTURE - INTERNATIONAL ASSEMBLY ON ENERGY STORAGE - DUBROVNIK, YUGOSLAVIA - MAY 28, 1979

Chapter 6: MECHANICAL ENERGY STORAGE

Chapter 7: MODELLING AND ASSESSMENT

Chapter 8: SOME IMPACTS OF ENERGY STORAGE TECHNOLOGIES ON U.S. ENERGY PROBLEMS

Chapter 9: CHAIRMAN’S CLOSING REMARKS

CHAIRMAN’S OPENING REMARKS

A.R. Despić,     Faculty of Technology and Metallurgy, University of Belgrade, 11000 Belgrade, Karnegijeva 4, Yugoslavia

I am greatly honoured by being given the opportunity to call this important assembly to order.

I wish to greet you all on behalf of the Council of the Academies of Science of Yugoslavia, which readily accepted the proposal to sponsor this meeting. The Council is fully aware of the truth of the motto of our program: Energy Storage – a Vital Element in Mankind’s Quest for Survival and Progress. There is no other assembly of people in the world which could give a more detailed and more qualified answer to how far we have gone in helping fulfill our quest.

I wish to greet also our guests, the representatives of our government, of the press and in particular of the city of Dubrovnik, which is providing such a good and comfortable setting for our work.

We have here the Deputy Mayor of Dubrovnik, Ferdo Zivković, and he expressed his desire to take the floor and welcome you. Also there is my Co-Chairman, Dr. Ronald Smelt of the National Academy of Sciences (USA), who will play such an important role in the conduct of this meeting. I am also pleased to acknowledge Dr. George Pezdirtz from the Department of Energy (USA) who conceived the idea and format of this Assembly. Finally there is the Secretary General of this Assembly and the man whose great vitality, persistence and ability has really made this meeting and to whom we all should be grateful for assembling us here today, Prof. Joseph Silverman of the University of Maryland.

It is proper that at the beginning of the meeting we ask ourselves what has made us gather and it seemed to me appropriate that I should devote opening remarks to try and give more substance to the motto of our programme which I cited a few moments ago.

What makes us say that energy storage is a vital element for our survival and progress? We are witnessing a broadening awareness of the pending energy crisis. What elements make us come to such a situation? I shall try to review them briefly asking forgiveness from those who would consider this so well known as to be trivial.

Pending exhaustion of oil makes for a steep increase in price. Oil is not a barrel of wine – which has a constant price till one hits the bottom of the barrel. Awareness of limited reserves makes the effect of its exhaustion appear much before it is beginning to be physically felt. It is becoming a precious commodity which people are trying to save for themselves or sell at as high a price as they can get.

This shifts attention to employing other primary sources of energy and using other lines of energy conversion. For almost all of them, there are needs for temporary energy storage. This especially concerns transport.

Energy sources are stationary and are likely to stay so. Moving atomic reactors around is hardly a practical solution except for submarines and aircraft carriers. It does not seem to be catching on even with the ship-building industry and certainly no one presently thinks of running passenger and commercial traffic with portable nuclear reactors. Traffic, however, consumes up to 25% of all the energy produced. Hence, we shall always be in need of reservoirs of energy on our vehicles long after our tanks run short of gasoline.

The second major reason is uneven energy consumption. Fig. 1 demonstrates the problem of the city of Belgrade. Obviously, if designed to match the peak power needs, our plants are not being used to full capacity most of the 24 hours of a day. Needless to say, weekly and yearly graphs would show similar patterns. This is where great need for load leveling arises.

Figure 1 Variation in electric power consumption in Belgrade

The third but very important point came to my awareness only a few days ago at the Electrochemical Society meeting in Boston. Hence, I can expect to find at least some of you today in a similar position. It is connected with the total amount of energy we can afford to produce from terrestrial sources.

If we defined the total insolation of the globe as 1 solar unit, the calculations presented at the AES meeting – and there is little reason to doubt them – show that if we produced another solar unit of power on earth from other primary sources, we shall raise the average temperature on earth to the boiling point of water. Hence, the maximum we can allow ourselves without considerable damage to our present world is 1% of a solar unit thereby raising the temperature by 1°C.

Now, it appears that energy production the world average is already at 0.01% of a solar unit and the U.S. is at 0.1%. Hence, a tenfold increase of power is the most we can make in the future before we strike what I would call the absolute energy ceiling. All the needs beyond that must be covered by increasing use of solar energy, which is in any case falling upon us and determining the average temperature as it is.

This is a strong argument for intensifying research on the use of solar energy. At the same time it is an equally compelling argument for the need of research in storage for we must take into account the mismatch in the time dependence of solar radiation intensity (Fig. 1) and the variation with time of electric power needs (Fig. 2).

Figure 2 Variation with time of solar radiation intensity

I know that deliberations of our distinguished participants will advance our understanding of this important area of research and development.

INTRODUCTORY ADDRESS

J. Silverman,     Institute for Physical Science and Technology, University of Maryland, College Park, MD 20742, USA

It all began less than two years ago in a discussion with Dr. George Pezdirtz. As Director of the U. S. Department of Energy’s Division of Energy Storage, he is responsible for the annual expenditure of some 75 million dollars. He was seeking the judgments of the most creative and practical contributors to this field of study for guidance in his difficult and important task.

At the University of Maryland’s Institute for Physical Science and Technology, we have a grant from Dr. Pezdirtz on energy storage research. One of our responsibilities was the sponsorship of a meeting whose objective would be to provide such guidance. When Dr. Pezdirtz began pressing us on this point, what started as a small workshop at Maryland became the first International Assembly on Energy Storage. The principal task of organizing the conference we are now attending fell to us.

I have been a consultant to the Danish Atomic Energy Laboratory at Risø for fifteen years. I have enjoyed my stay in northern Europe enormously and somehow avoided southern Europe until 1975. At that time the persistent efforts of Dr. Vitomir Marković of the Boris Kidrić Institute for Nuclear Science near Belgrade brought me to Yugoslavia beginning a collaboration which still persists. It was love at first sight. I became an unabashed admirer of this country, of its tough, realistic, and generous people, and of the unparalleled beauty of the Adriatic coast. I also became better acquainted with the accomplishments and skill of its scientists, among them, Prof. Despić, widely acclaimed for his stellar achievements in electrochemical storage. Also I encountered a marvelous young man, Negoslav Ostojić from the Serbian Administration for International Scientific, Educational, Cultural and Technical Cooperation; he seemed to know everyone, and seemed to be able to do anything.

The synthesis of all these elements was clear. We would hold, the meeting in Yugoslavia. It would be organized in collaboration with Yugoslav scientists, especially Prof. Despić. Mr. Ostojić would manage the physical and logistic arrangements in Yugoslavia. Dubrovnik was to be the site. The National Academies of Sciences of the U. S. and of Yugoslavia were to provide the organizational framework. These broad outlines were rapidly adopted by all concerned.

The most important item was the substance of the assembly. Was it to be just another meeting of an itinerant scientific freemasonry gathering at another watering spot and sharing a few truths before marching on to the next? Clearly this could not be our purpose. It was Dr. Pezdirtz who came up with the suggestion which forms the basic framework of this assembly. The conferees were to be small in number – perhaps 100 in all. Nevertheless they were to cover all aspects of energy storage. On the first day plenary lectures by outstanding experts would inform all the participants of the broad range of topics to be covered. The lecturers would then assemble as a group to answer the questions raised by their plenary speeches.

On the second day, the meeting would break up into five panels. Each conferee was to be a member of one panel. Some movement from panel to panel could be useful; carried to the extreme, however, it would destroy the cohesive quality of the panels, so that this was to be the exception. Each panel was to examine the status, the problems and the prospects of its field of energy storage. Out of the discussions would emerge panel reports covering the following points:

1. Which are the promising methods leading to practical energy storage systems?

2. What are the obstacles to their development and widespread use?

3. What organized programs can be devised, particularly those of a collaborative international character, to overcome these obstacles?

Each panel chairman was to be a scientist of exceptional stature with the ability to organize his discussion group so as to produce answers to these questions. He was also to provide a statement summarizing the transactions of his panel. These statements would be presented in plenary session on the afternoon of the third day. A plenary discussion on the fourth day would provide further revisions. At the end there would emerge a final executive summary of about 8,000 words. After the conference, the complete proceedings of the Assembly would be published less than one year after the meeting.

As you can see, these plans were set into motion. The National Academies assumed sponsorship of the meeting. Their interests were represented by Professors Newton and Rakić on the Organizing Committee, and by our distinguished Co-Chairmen, Professor Despić and Dr. Smelt. Dr D. Wyatt of the National Academy of Sciences (USA) was particularly helpful in the scientific aspects. Mr. Lowitt of Resource Planning Associates, Inc. and the redoubtable Mr. Ostojić of the Serbian Administration for International Scientific, Educational, Cultural and Technical Cooperation are responsible in a large measure for the physical circumstances of the meeting. Dr. Pezdirtz (who incidentally stems from Slovenian antecedents) contributed so much to the conception, organization, and conduct of these proceedings that he must accept the principal credit.

The rest is up to you.

ELECTROCHEMICAL ENERGY STORAGE

K. Kordesch,     Institute for Inorganic Chemical Technology, Technical University Graz, Austria, 8010

Publisher Summary

The storage of massive amounts of energy is an inherent requirement of modern technology, but not all types of storage are equal in cost, efficiency, or convenience. A selection between storage technologies is timely. Interconnections with several storage means are necessary because there is no practical system known that can store electricity as such. For electricity to be stored in larger amounts, it must be converted into another form of energy first, then stored, and finally reconverted again. This rather complicated process is accepted because electricity is the most convenient and universally useful form of energy available to mankind. This chapter discusses the application of rechargeable batteries for electrochemical energy storage. Rechargeable batteries are also called accumulators or secondary batteries are distinguished from primary batteries by the feature of electrical rechargeability. Alkaline rechargeable batteries such as nickel-iron batteries, Ni–Cd batteries, Aq-Zn cells, and Ni–Zn cells have an excellent cycle life. The chapter also presents several battery systems that are to be considered as future electrochemical storage devices surpassing the present conventional batteries, such as metal–air systems, metaloxide–hydrogen systems, alkali metal–high temperature cells, and fuel cells.

1 THE NEED FOR ENERGY STORAGE

Fossil fuels contain stored chemical energy produced through the action of sunlight over past geological eras in a compact and conveniently convertible form. Unfortunately, the supply will only last a few more generations. Renewable resources such as sunlight, wind or the kinetic energy of the ocean waves have the problem of variability. Technology must therefore use devices which can’ store energy.

Nuclear fuels, fossil fuels, solar and geothermal energy, even the temperature gradient of the ocean, can be used to generate electricity, but the consumer and industry need energy at different levels. The typical demand load of the utilities, as an example, varies during the day, over the weekend and seasonally. As a result, expensive, rarely utilized equipment must be kept available to be pressed into service when required.

The use of a flashlight for a short time is a storage problem on a small scale, the operation of an automobile is a storage problem for larger quantities of energy to be released on demand.

The purpose of storage devices is to match the production of energy with the consumer’s needs. A suitable storage system is also a means to provide flexibility at lower cost.

The storage of massive amounts of energy is an inherent requirement of modern technology, but not all types of storage are equal in cost, efficiency or convenience. A selection between storage technologies is timely. Interconnections with several storage means are necessary because there is no practical system known which can store electricity as such. For electricity to be stored in larger amounts it must be converted into another form of energy first, then stored and finally reconverted again. This rather complicated process is accepted because electricity is the most convenient and universally useful form of energy available to mankind.

2 ENERGY STORAGE TECHNOLOGIES (1)

Energy storage methods may be classified into the following groups:

Mechanical (physical) methods:

Hydro-pumped-storage facilities

Compressed air

Flywheel energy storage

Superconductive magnets

Thermal (physical and chemical) methods:

Heatcapacity-storage (liquids, solids)

Reactionheat-storage (chemical recombination)

Electrochemical (chemical) methods:

Galvanic cells, batteries (primary and secondary)

Chemical storage (after electrolysis) and

Converters (fuel cells)

The established production of batteries is a multi-billion Dollar business worldwide:

The automotive industry is presently the biggest customer of electrochemical storage devices in the form of the starter battery, based on the lead-acid system.

Industrial lead-acid batteries number about one third of the automotive batteries.

The electric automobile could drastically increase the demand for storage batteries, lead-acid type for the near future and improved systems for the years around 1990.

Solar power converted to electricity needs galvanic storage systems of perhaps tremendous quantities and sizes. Applications on Earth and in space are abundant.

Large power-storage for utility companies may be a future field for electrochemical storage considering the features of batteries: instant availability, compatibility with the city environment and diversification, just to name a few credits.

Portable power for the consumer should not be underestimated. The rate of growth of the dry-cell industry is in the range of 10 – 15 percent per year. The annual consumption of small cells in the USA alone represents a value of Dollar 600 million and similar figures are estimated for Europe and Japan. The numbers of radios, tape recorders and especially calculators is still rising, the market for electric watch batteries is flourishing, the use of battery powered medical devices is getting wide-spread.

The underdeveloped Countries are just beginning to build their own industry to produce automobiles and electrical gadgets, representing a huge increase in need for electrical power storage.

3 INTRODUCTION TO ELECTROCHEMICAL STORAGE

Rechargeable batteries, also called accumulators or secondary batteries are distinguished from primary batteries by the feature of electrical rechargeability. Significantly, both, accumulators and primary batteries contain all the chemical reactants within the cell boundaries. Contrary to this, fuel cells are chemical converter systems (generators) which have the capability to convert the energy of chemicals stored outside of the cells into electricity.

The word capacity is often used. It has in this context nothing to do with electrostatic charges. Ah-capacity is the number of Ah which can be delivered per unit weight or volume.

The energy density is Ah-capacity multiplied by the cell voltage. There are maximum (theoretical) values and practical values. The units Wh/kg or Wh/liter are often just given for a commercial unit in consideration of a specified application. The numbers may change for different power densities, expressed in w/kg or W/l.

To illustrate the problem of varying capacity under different load conditions, the specific energies of several battery systems are plotted against their specific power output in Fig. 1. To illustrate the practical significance of such a graph, an over-layed grid marks the projected range an electric automobile of 1, 3 ton weight could travel at certain speeds (2).

Fig. 1 Specific Power and Specific Energy Diagram for the Lead-Acid Battery and Advanced Systems. A Grid of the projected Ranges of a 1300 kg Automobile with a 300 kg Battery at different Speeds is drawn in.

As a general rule-of-thumb it should also be mentioned that technical batteries, manufactured on a large scale, can only be counted on delivering about one fourth of the calculated maximum energy of their electrode systems.

4 RECHARGEABLE BATTERIES – CONVENTIONAL TECHNOLOGY

4.1 The lead-acid cell (3,4)

It took approximately 60 years from the time of Volta’s discovery of the galvanic cell in 1800 for its application to Plante’s electric storage battery. Over the last 20 years the weight of an automobile battery again decreased by about 25 percent and the service life rose to 5 years. As far as material utilization is concerned only marginal improvements can be expected in the future, but cycle life under higher current densities and at deep discharge conditions is worth looking at, especially in respect to electric vehicles. Hermetical sealing and overcharge capability are the goals for small lead-acid batteries, partly already achieved.

Figure 2 shows the weight analysis of a typical starter battery. Improvements were obviously limited to small steps, mainly of design-nature. For instance, lightweight containers and through-the-wall connectors made the batteries much lighter. Low maintenance was achieved by changing from antimony grid-alloys to calcium alloys.

Fig. 2 Weight Analysis of a typical Lead Acid Battery (Type SLI: Starting, Lighting, Ignition).

The cycle life of starter-batteries – if deep-discharged – is in the 100 – 500 range (the shallow cycles of the vehicle applications with a generator providing immediate recharge go into the 100000). The cycle life of an industrial or traction battery is between 1500 and 5000.

Big strides were also made in stationary batteries. They are produced in sizes up to 15000 Ah, have a service life up to 25 years. In the Bell-Telephone System there are an estimated total of over one million cells in the capacity range of 180 to 1680 Ah in service for dc filtering of rectified ac, instantaneous power reserve for outages (milliseconds to minutes) and extended reserves for periods of 3 to 48 hours.

The lead-acid battery was and still is the workhorse of the electrochemical rechargeable storage systems. Its economy is not surpassed by any other system yet.

4.2 Alkaline Rechargeable Batteries

Table 2 compares the lead-acid battery with alkaline storage battery systems (5)

TABLE 2

The Energy Densities, Power Densities and Cycle Life of Rechargeable Batteries (Existing Technology)

Nickel-iron batteries have an excellent cycle life and the system was preferentially used in mining locomotive-traction applications. Today it may find a new field of application in electric vehicles for over the road use (6). In a recent development a special sintered iron electrode is used, which shows a low gassing characteristic and a charge behavior which makes the iron electrode better compatible with a nickeloxide cathode.

Ni-Cd batteries are sometimes used for traction purposes due to their long life properties, but they are too expensive for large applications. The hermetically sealed Ni-Cd batteries are widely used in small portable devices (tape recorders, radios) where the feature of being overchargeable makes them suitable for rather uncritical customer use.

Ag-Zn cells are manufactured in the open and sealed version. The most valued property is the high energy density, a serious disadvantage is the poor cycle life of the zinc electrode and the high cost of the silverelectrode.

Ni-Zn cells are a recently renewed development. With a theoretical energy density of 375 Wh/kg and a presently achieved energy density of 60 to 70 Wh/kg, about 300 cycles are obtainable. The cycle life is limited by the zinc electrode which has a tendency to produce zinc dendrites which short the cell. Batteries have been developed for vehicle propulsion and represent efforts to increase the range of electric cars twofold in the near future (7).

5 RECHARGEABLE BATTERIES – FUTURE SYSTEMS

Table 3 lists several battery systems which are to be considered as future electrochemical storage devices surpassing the present conventional batteries by a factor of 2 to 4.

TABLE 3

Projected Performance of Future Batteries for Energy Storage

5.1 Metal – Air Systems

Zinc-air batteries have been the subject of particular attention. The advantages of zinc are: reactivity, low cost and a reasonable rechargeability. The theoretical value for the specific energy content is 1050 Wh/kg. Primary air zinc cell are old technology, such applications as signal lights and navigational aids were widely found. During the last 15 years (with the improvement of air electrodes for fuel cells) high current air electrodes emerged. Rechargeability became possible through special electrode structures which were not damaged by the oxygen evolved during charging (7, 8). The problem of CO2 removal from the air is a serious restriction for alkaline air cells, if not done, the pores system pluggs prematurely and the current drops. Mechanical recharging (9) circulating electrolytes (10) are system variations.

Īron-air cells combine the stability of the newly developed iron electrodes with the features of an air electrode (11, 12, 13).

Aluminium-air cells have been studied extensively because the low equivalent weight of Al (3 e−) gives that system an advantage over any other room temperature aqueous system. Energy storage systems up to two kW have been built, but the rechargeability is not satisfactory, the reaction products must be removed mechanically. Aluminium corrosion problems are also high (hyrogen evolution). Theoretically at least the Al-air (O2) battery is still a promising project for future developments (14, 15, 16, 17).

Sodium-air and Lithium-air systems using the alkali metal/water electrode are powerful systems recently developed (18).

5.2 Metaloxide – Hydrogen Systems

These sealed cells have been developed for communication requirements (COMSAT) because the cycle life of the combinations Nickeloxide – hydrogen or Silveroxide – hydrogen turned out to surpass that of any other system. Solar cell charging in relatively short intervals (90 minutes) is taking advantage of the high cycle life and is not too much concerned with the comparatively high self discharge rates of these systems (19) (see Fig. 3, Ni-H2 cell).

Fig. 3 Nickel-Hydrogen Cell Construction (COMSAT)

Low cost commercial systems (D-size cells) seem possible.

5.3 Alkali Metal – High Temperature Cells

Sodium-sulfur cells have been in development since 1966 with the objective of developing an electric vehicle battery. The principle is to separate the molten reactants, sodium and sulfur by a sodium ion-conducting membrane of beta-alumina. Graphite felt makes the sulfur conductive. The reaction products are polysulfides. Means of minimizing cracking and increasing the life of the ceramic membrane were found after years of development. In a somewhat modified form, this battery system is now considered to be suitable for large scale energy storage. The main points are the low cost of the reactants and the high power density of the sodium-sulfur battery, operating at 350° C. The goal for energy density was stated at 80 – 100 Wh/kg and the power density as 200 – 300 W/kg (20, 21). See Fig. 4 for Na-S cell construction.

Fig. 4 Construction of a Sodium-Sulfur Cell (Ford Motor Co.)

Lithium-alloy/Metalsulfide systems are preferred for safety and easier operation. The electrolytes are LiClKCl eutectica. Summarizing the best data on Li.Si / FeS2 cells it was stated that 1000 cycles at a depth of discharge of 80% and an energy density of 180 Wh/kg were demonstrated in 1978, a big improvement over the previous 300 cycles (22). Figure 5 shows a Li-Al / Fe S2 cell.

Fig. 5 Li.Al-FeS2-Cell Construction (Argonne Natl.Laboratory)

In the Zinc-Chlorine Hydrate System zinc can be plated out of zincchloride solutions. A rechargeable system using a non-alkaline electrolyte is considered to be a big step forward. Because air electrodes perform very poorly in neutral electrolytes, chlorine was chosen as a substitute. Chlorine-hydrate, Cl2 . 6H2O, which can be prepared by bubbling chlorine gas into water under cooling, is a useable chlorine storage. The energy density is theoretically very high: 830 Wh/kg. A prototype system was used to propell a Vega automobile with a 200 V, 100 A power plant. This system is also under serious consideration as a large utility energy storage system (23). 45 kWh-modules have been built.

5.4 Fuel Cells

In the following Table 4 a list of the many different types of fuel cell systems is given (24, 25).

TABLE 4

A fuel cell is an electrochemical cell which can continuously change the chemical energy of a fuel and oxidant to electrical energy by a process involving an essentially invariant electrode-electrolyte system. In accordance with this definition, fuel cells can be used as converters in combination with stored fuels (26). As such one can consider: hydrogen (from electrolysis, compressed or liquid), H2 + CO, ammonia, methanol or any chemical which is part of an energy cycle. In this respect the redox and regenerative types listed under D in Table 4 are especially suited.

An example which obtained recent consideration is the thermocyclic use of benze n – cyclohexane. Hydrogen is carried as chemical compound and released at the end of a pipeline. This system would be well suited for a fuel cell system operating on hydrogen and air (27). A similar concept is the chemical heat pipe system which uses the chemical equilibrium CH4 + H2O → CO and H2 as energy carrier (EVA-ADAM-loop).

Figure 6 shows a fuel cell system (phosphoric acid cells) operated on steam reformed fuel.

Fig. 6 Hydrocarbon Converter and Fuel Cell System (U.S.Army)

Figure 7 shows a principal system which could convert heat directly into electricity. Carnot’s law is valid in this case!

Fig. 7 A Thermally Regenerative System (MSA-Corp.)

5.5 Primary Batteries

The available primary battery systems will not play any major role in a large scale electrochemical storage scenario, but the place of those batteries on the industrial manufacturing scene is quite important (28). Small batteries made a tremendous leap forward in volume production and value, mainly due to the progress of the electronic and solid-state industry. The alkaline Manganese dioxide primary battery, for instance, had a growth rate of 15 percent annually, the non-aqueous batteries, which practically did not exist 1970 are entering the market now. The underdeveloped nations have a staggering need for