1

Alternative energy storage systems

Johan Beukes

Overview• Utility applications• Requirements• Capacitors• Flywheels• Compressed air systems• Fuel cells• Flow batteries• Comparisons• Application in network• Other electrochemical systems

2

Utility applications• Backup power during interruptions (standby)• Match supply and demand (cycling)

– Stress relieve on generators and transmission – Control frequency– Control voltage– Optimize losses– Optimal use of installed assets– Store renewable energy when available

• Improve voltage quality (cycling)

Requirements• Total cost of

ownership• Reliability• Temperature tolerance• Cycle depth• Number of cycles• Specific power• Specific energy• Round trip efficiency• Standby losses• Maintenance• Environmental impact

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Electrolytic capacitors2

2

0

1 ( ) 1 1( ) ( ) ( )d ( ) ( ) ( )2 2 2

where,

d q tW t q t E t z Cv t v t q tC

ACdε

= − = = =

=

∫• High specific power• Low specific energy• Life: 1 000 000 cycles,

15 years (45 OC)• No maintenance• High eff, no loss

Ultra capacitors

• Activated carbon electrode material causes high energy content of Ultra Caps vs EC • High specific surface area of about 2000 m2/g and• short distance between the opposite charges of the capacitors (2 ... 5 nm)

• High specific power• Specific energy 10 times

EC• Life: 500 000 cycles, 10

years• 45 OC• No maintenance• High eff, no loss

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Beacon Flywheel• Low specific power• Low specific energy• 20-year Design Life • High Temperature Tolerance• No maintenance• 88% eff, 2% loss

21· ·2kE J ω=

Rotational energy as a function of moment of inertia and angular velocity

Optimise for angular velocity with the square relationship to energyComposite materials, hydrodynamic or magnetic bearings, vacuumed

Beacon Flywheel

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Urenco Flywheel

CAESS (Pnu Power)

• Low specific power• Low specific energy• 20-year Design Life • High Temperature Tolerance• No maintenance• Low complexity• 80% (11%) eff, no loss

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Scroll technology

Air pocket expands through sequenceHigh pressure air input

Orbiting scroll

Fixed scroll

1

(ln ln ) ln ln ln

where, and so

constantB B B

A A A

V V V

A B V V V

B A AB A

A B B

B AA A B B

A B

nRTW P dV dV nRT dV

V VV P P

nRT V V nRT nRT PVV P P

V PP V P V

V P

PV nRT

→ = = =

= − = = =

= =

= =

∫ ∫ ∫

Ideal gas law for isothermal process and first law of thermodynamics:

Fixed scroll

Orbiting scrollFast response, only one moving part

Fuel cell(Plug Power 5 kW)

2

2 2

2 2

H 2H 2e

2H ½ O 2e H O H ½ O H O

+ −

+ −

→ +

+ + →+ →

• Independent sizing of power and energy

• No degradation of electrodes

• 45 OC• Low maintenance• 40% (11%) eff, no loss

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Flow batteries (VRB)

• Low specific power• Low specific energy• Life: unlimited cycles, 15

years (45 OC)• No maintenance• Complex system

• Independent sizing of power and energy

• No degradation of electrodes

• High cycle• 62-80% eff, 2% loss

3.3 kW, 10 kWh

Flow batteries (VRB)

Vanadium(II) sulphate = violetvanadium(III) sulphate = aqua green

vanadium(IV) sulphate = bluevanadium (V) sulphate = yellow

22 2 02 1.004 VVO H O VO H e E+ + + −+ + + = 3 2

0 0.255 VV e V E+ − ++ = −

e−

2H +

oxidationreduction

reductionoxidation

+ -

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Battery assembly

n×

n×n×

n×

Electrical systemAnode Cathode

N2 N2

P=<140 kPa P=<140 kPaVolume control

+ -

H2O

King Island installation

200 kW, 800 kWh

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Overview 1 Wh = 3.6 kJ

LIB (Thunder Sky)

NCB (Alcad Vantage)

VLAB (Delco)

VRB (VRB Power)

EC

UC (EPCOS)CAES @ 300 bar (Pnupower)

Diesel (Wiki)

Carbohydrates (Wiki)

Hydrogen @ 200 bar (Wiki)

VRB (Wiki)

CAES @ 300 bar (Wiki)

VLAB (FN)

FW (Beacon)

FC @ 200 bar (Plug Power)

Hydrogen @ 1 bar (Wiki)

0.1

1

10

100

1000

10000

100000

1000000

1 10 100 1000 10000 100000

Specific Power [W/kg]

Spec

ific

Ener

gy [k

J/kg

]

Overview

LIB (Thunder Sky)

FC @ 200 bar (Plug Power)

EC

UC (EPCOS)

Diesel (Wiki)Carbohydrates (Wiki)

FW (Beacon)

NCB (Alcad Vantage) VLAB (Delco)

VRB (VRB Power)

CAES @ 300 bar (Pnupower)

Hydrogen @ 200 bar (Wiki)

Hydrogen @ 1 bar (Wiki)

VRB (Wiki) CAES @ 300 bar (Wiki)

VLAB (FN)

0.01

0.1

1

10

100

1000

10000

100000

0.1 1 10 100 1000 10000 100000 1000000

Specific Energy [kJ/kg]

Ene

rgy

Den

sity

[kJ/

l]

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Overview of cost

LIB (Thunder Sky)NCB (Alcad Vantage)

VLAB (Delco)

EC

UC (EPCOS)

FW (Beacon)

FC @ 200 bar (Plug Power)

VRB (VRB Power)

CAES @ 300 bar (Pnupower)

VLAB (FN)

0.01

0.1

1

10

100

1000

1 10 100 1000 10000 100000

Cost/Power [$/kW]

Cos

t/Ene

rgy

[$/k

J]

Overview of cost

R 0

R 50

R 100

R 150

R 200

R 250

R 300

R 350

R 400

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

000's

Years

Annual cash flows (VLAB) Annual cash flows (FCC)

Discounted aggregated cash flow (CAES) Discounted aggregated cash flow (CAES)

LCC comparisons between a 2 kW Pnu Power CAES system and a 288 Ah VLAB system

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Castle Valley Installation

Castle Valley Installation

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King Island installation

System overview

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System overview

250 kW, absorbing 50 kVAR

850 kW, 0.98 lead to 0.95 lag

1250 kW, 800 kVAR

Matching load to generation

0

500

1000

1500

2000

2500

3000

3500

4000

4500

00:0

0:13

00:4

6:18

01:3

6:27

02:2

6:36

03:1

6:46

04:0

6:55

04:5

7:05

05:4

7:14

06:3

7:24

07:2

7:33

08:1

7:42

09:0

7:56

09:5

8:14

10:4

8:29

11:3

8:46

12:2

9:03

13:1

9:20

14:0

9:38

14:5

9:57

15:5

0:14

16:4

0:32

17:3

0:51

18:2

1:07

19:1

1:25

20:0

1:41

20:5

1:59

21:4

2:17

22:3

2:35

23:2

2:53

P [kW]Q [kVAR]

500 kW wind, 1 MW diesel, variations ESS

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Matching load and generation

Time [s]

Frequency control

Time [s]

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Voltage control

Time [s]

Voltage and frequency control

Time [s]