TR A5610

Overview on different types of energy storages.

Nils Arild Ringheim

February 2002

TECHNICAL REPORT SUBJECT/TASK (title)

Overview on different types of energy storages

CONTRIBUTOR(S)

Nils Arild Ringheim

CLIENTS(S)

SINTEF Energy Research Address: NO-7465 Trondheim, NORWAY Reception: Sem Sælands vei 11 Telephone: +47 73 59 72 00 Telefax: +47 73 59 72 50 www.energy.sintef.no Enterprise No.: NO 939 350 675 MVA

Norsk Hydro

TR NO. DATE CLIENT’S REF. PROJECT NO.

A5610 2002-02-28 Torgeir Nakken 12x207 ELECTRONIC FILE CODE RESPONSIBLE (NAME, SIGN.) CLASSIFICATION

020106nar111849 Nils Arild Ringheim Unrestricted ISBN N0. REPORT TYPE RESEARCH DIRECTOR (NAME, SIGN) COPIES PAGES

82-594-2268-9 Petter Støa 12 68 DIVISION LOCATION LOCAL FAX

SINTEF Energiforskning AS Sem Sælands v. 11 +47 73 59 72 50 RESULT (summary)

Electrochemical capacitors have low specific energy, but very good specific power, and are applicable for power pulse durations between 0.01-100 s. Typical applications are power quality related problems, UPS applications and transmission line stability, and as a complementary storage with batteries, fuel cells and diesel electric systems. Batteries are very diverse in characteristic and application. Well-known technology like lead-acid and nickel-cadmium are used in large battery energy storages (tens of MWh). Flow batteries (Regenesys, Redox and Zinc/Bromine) are promising for very large-scale storages (>100 MWh). High temperature sodium-sulfur batteries (NaS) are also installed in some MWh-plants. New technology like Li-ion batteries shows promising characteristics, but is not mature for larger energy storage application. Lead-acid is a clear winner on initial cost, followed by NiCd and then NiMH and at last Li-ion. Li-ion is not inherently expensive: Cost is very volume sensitive. (Metal-air batteries are the least expensive alternative, but are not mature for energy storage applications with electrical recharge.) In addition, flow batteries are cost effective in very large-scale energy storages. Life cycle cost is more important in energy storage than initial costs. It is therefore important to consider effect of operating conditions on life. Main influence comes from temperature and cycling. (E.g. lead acid batteries shorten their lifetime with 50 % for every 8˚C increase, while NiCd only cuts by 20 %.) Flywheels are appropriate for time durations up to some minutes and energy densities in the kWh-range. Low-speed flywheels are commercial available, while high-speed solutions with higher energy densities are limited. Applications like battery replacements in UPS are reported. The initial cost of low-speed flywheels is rather low, and they can be an alternative to batteries at low energy ratings. SMES applications are short-time, high power pulses, like power quality improvements in industrial plants or voltage/VAR support and transmission stability in utility transmission lines. Their maturity and availability is limited (one commercial manufacturer worldwide), and they are expensive: For most application, investment costs and losses are too high compared with other storage devices. Diurnal load leveling is not a cost-effective application for SMES now or in the long term.

KEYWORDS energy storage electrochemical energy storage SELECTED BY

AUTHOR(S) flywheel superconducting magnetic energy storage

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TABLE OF CONTENTS

Page 1 SUMMARY ..............................................................................................................................4 2 INTRODUCTION.....................................................................................................................7

2.1 REFERENCES..................................................................................................................7 3 BATTERIES..............................................................................................................................8

3.1 FUNCTIONAL DESCRIPTION.......................................................................................8 3.1.1 Electrode basics .........................................................................................................8 3.1.2 Electrolyte basics.......................................................................................................8 3.1.3 Definitions and nomenclature....................................................................................9

3.2 LEAD-ACID TYPES ......................................................................................................12 3.3 ALKALINE BATTERIES ..............................................................................................15

3.3.1 Ni-Cd .......................................................................................................................15 3.3.2 Ni-MH .....................................................................................................................17

3.4 Li-TYPES........................................................................................................................19 3.4.1 Li-polymer...............................................................................................................19 3.4.2 Li-ion .......................................................................................................................21

3.5 SODIUM SULFUR (NaS) ..............................................................................................23 3.6 METAL-AIR BATTERIES.............................................................................................25 3.7 FLOW BATTERIES .......................................................................................................28

3.7.1 Redox batteries ........................................................................................................28 3.7.2 Regenesys batteries .................................................................................................30 3.7.3 Zinc/Bromine batteries ............................................................................................31

3.8 COMPARISON OF BATTERY TYPES ........................................................................34 3.8.1 Energy and power densities.....................................................................................34 3.8.2 Life time ..................................................................................................................34 3.8.3 Life cycles ...............................................................................................................35 3.8.4 Temperature.............................................................................................................36 3.8.5 Efficiency ................................................................................................................36 3.8.6 Summary of battery comparison .............................................................................38

3.9 REFERENCES................................................................................................................39 4 ELECTROCHEMICAL CAPACITORS ................................................................................41

4.1 FUNCTIONAL DESCRIPTION.....................................................................................41 4.2 MAIN CHARACTERISTICS.........................................................................................42 4.3 COSTS AND AVAILABILITY......................................................................................44 4.4 ENVIRONMENTAL ASPECTS ....................................................................................45 4.5 APPLICATIONS, PILOT PLANTS AND OPERATIONAL EXPERIENCE ...............45 4.6 MANUFACTURERS AND CENTRE OF COMPETENCE..........................................45 4.7 REFERENCES................................................................................................................46

5 FLYWHEELS .........................................................................................................................47 5.1 FUNCTIONAL DESCRIPTION.....................................................................................47 5.2 MAIN CHARACTERISTICS.........................................................................................48 5.3 AVAILABILITY AND COSTS......................................................................................49 5.4 ENVIRONMENTAL ASPECTS ....................................................................................50 5.5 APPLICATIONS, PILOT PLANTS AND OPERATIONAL EXPERIENCE ...............50

5.5.1 Applications.............................................................................................................50 5.5.2 Pilot plants and operational experience...................................................................51

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5.6 MANUFACTURERS AND CENTRE OF COMPETENCE..........................................51 5.6.1 Manufacturers..........................................................................................................51 5.6.2 Centre of competence ..............................................................................................52

5.7 REFERENCES................................................................................................................52 6 SUPERCONDUCTING MAGNETIC ENERGY STORAGES (SMES) ...............................54

6.1 FUNCTIONAL DESCRIPTION.....................................................................................54 6.2 MAIN CHARACTERISTICS.........................................................................................55 6.3 AVAILABILITY AND COSTS......................................................................................56 6.4 ENVIRONMENTAL ASPECTS ....................................................................................58 6.5 APPLICATIONS, PILOT PLANTS AND OPERATIONAL EXPERIENCE ...............59

6.5.1 Applications.............................................................................................................59 6.5.2 Pilot plants and operational experience...................................................................60

6.6 MANUFACTURERS AND CENTRE OF COMPETENCE..........................................60 6.6.1 Manufacturers..........................................................................................................60 6.6.2 Centre of competence ..............................................................................................61

6.7 REFERENCES................................................................................................................61 7 COMPARISONS BETWEEN THE DIFFERENT ENERGY STORAGE ELEMENTS AND THEIR APPLICABILITY ..............................................................................................................63

7.1 ENERGY AND POWER DENSITIES...........................................................................63 7.2 APPLICATIONS.............................................................................................................65 7.3 COST COMPARISONS .................................................................................................65 7.4 LOSSES...........................................................................................................................67 7.5 REFERENCES................................................................................................................67

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1 SUMMARY Based on a literature study, four different energy storage technologies are reviewed: Electrochemical capacitors, batteries, flywheels and superconducting magnetic energy storages (SMES). The presentation is general, but emphasizes stationary applications. Portable (consumer) electronics and vehicle specific applications are not included. The applicability of different energy storages is strongly influenced by the application. A general presentation relating the power and energy rating with the duration of the pulse is shown in table 1.1. Table 1.1: Different energy storages and their applications

Energy storage Typical power rating

[MW]

Typical discharge time

Application

Electrochemical capacitor 0,0001-0,1 seconds to minutes Power quality, UPS, complementary storage to batteries, fuel cells, diesel electric etc.

Lead acid 0.001-50 minutes to hours Power quality, reliability, frequency control, reserve, black start, UPS

Advanced (VRLA, NaS, Li) 0,001-1 minutes to hours Various, including utility energy storage Battery

Flow batteries 0,1-100 minutes to tens of hours Power quality, reliability, peak shaving, reserve, energy management, integration of renewables

Flywheel 0,005-1,5 seconds to minutes Power quality, battery replacement in UPS

SMES 0,01-2 < seconds Transmission stability, voltage/VAR support, power quality

Table 1.2 shows typical characteristics of the different energy storages Table 1.2: Typical characteristics of different energy storages.

Energy density Power density Energy storage [Wh/kg] [Wh/dm3] [W/kg] [W/dm3] Efficiency

[%] Life time

[cycles|years] Recharge

time Maintenance Maturity

Electrochemical capacitors 1-10 0,01-20 400-4000 102-106 90-95 >105|>10 Seconds to

minutes None Good, increasing

Batteries 10-200 10-400 20-600 10-1000 50-95 500-104|2-20 Minutes to hours

From weeks to none Very good

Flywheels 30-200 1-? 180-30000 125-667 88-93 105|20 Minutes Months to

annual Good/modest,

increasing

SMES 4 –75 - 103-105 - 90-99 >105|20 Minutes (µ-SMES) Annual

Poor, increasing

slowly

Table 1.3 shows availability, costs and environmental aspects. Table 1.3: Availability, cost and environmental impact. (Guidelines only) Energy storage Capital costs

[$/kWh | $/kW] Availability Environmental impact

Electrochemical capacitors 83500 | 250-1000 Good Very good Lead acid 200-700 | 240-700 1) Very good Advanced (VRLA, NaS, Li)

Very varying dependent of technology, but always more expensive than lead-acid

Good to very good (depending on technology)

Battery

Flow batteries 175-600 | - Modest

Modest to very good Depending on type of battery. (Future ban of cadmium?)

Flywheel 300-25000 | 300-500 Low-speed flywheel available High-speed flywheel hardly available

Good. Uncertainty: Safety problem on mechanical damage of rotor?

SMES ~2,4 million | ~670 Poor. One manufacturer worldwide Good (Magnetic field in surroundings of superconductor. Possible health effect?)

1) Based on cost of plants >1MW in the world in 1995 (1995$)

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Electrochemical capacitors have low specific energy, but very good specific power, and are applicable for power pulse durations between 0.01-100 s. Typical applications are power quality related problems, UPS applications and transmission line stability, and as a complementary storage with batteries, fuel cells and diesel electric systems. Batteries are very diverse in characteristic and application. Well-known technology like lead-acid and nickel-cadmium are used in large battery energy storages (tens of MWh). Flow batteries (Regenesys, Redox and Zinc/Bromine) are promising for very large-scale storages (>100 MWh). High temperature sodium-sulfur batteries (NaS) are also installed in some MWh-plants. New technology like Li-ion batteries shows promising characteristics, but is not mature for larger energy storage application. A graphical presentation of some battery comparisons are given below:

Figure 1.1 Guidelines for typical applications of energy storages plotted in a diagram of discharge time vs. system power rating

Figure 1.4 Capital cost comparisons for different energy storage techniques. Lead-acid is a clear winner on initial cost of different battery technologies, followed by NiCd and then NiMH and at last Li-ion. Li-ion is not inherently expensive: Cost is very volume sensitive. (Metal-air batteries are not mature for energy storage applications with electrical recharge.) In addition, flow batteries are cost effective in very large-scale energy storages. Life cycle cost is more important in energy storage than initial costs. It is therefore important to consider effect of operating conditions on life. Main influence comes from temperature and

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cycling. (E.g. lead acid batteries shorten their lifetime with 50 % for every 8˚C increase, while NiCd only cuts by 20 %.) Flywheels are appropriate for time durations up to some minutes and energy densities in the kWh-range. Low-speed flywheels are commercial available, while high-speed solutions with higher energy densities are rather limited. Applications like battery replacements in UPS are reported. The initial cost of low-speed flywheels is rather low, and they can be an alternative to batteries at low energy ratings. SMES applications are short time, high power pulses, like power quality improvements in industrial plants or voltage/VAR support and transmission stability in utility transmission lines. Their maturity and availability is limited (one commercial manufacturer worldwide), and they are expensive: For most application, investment costs and losses are too high compared with other storage devices. Diurnal load leveling is not a cost-effective application for SMES now or in the long term. The figures in this report vary over a wide range, since different literature sources are not necessarily compatible. In order to get more precise information, two different approaches are possible:

- Inquiry to manufacturers (Technical questions, costs questions etc.) - Visit manufacturers, research organisations or highly skilled users with experience from

usage of the different energy storages. If inquiry to manufacturers is done, it is important to make sure that the answers easily can be compared. This can be achieved if the questions are related to an installation or application, where the necessary requirements are specified.