Alternative energy storage systems
Johan Beukes
Overview
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Utility applications
Requirements
Capacitors
Flywheels
Compressed air systems
Fuel cells
Flow batteries
Comparisons
Application in network
Other electrochemical systems
1
Utility applications
• Backup power during interruptions (standby)
• Match supply and demand (cycling)
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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
2
Electrolytic capacitors
W (t ) = − q (t ) ∫ E (t )dz =
d
0
where, C =
εA
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High specific power
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•
15 years (45 OC)
No maintenance
High eff, no loss
1 q (t ) 2 1
1
= Cv(t ) 2 = v(t ) q(t ) • Low specific energy
2 C
2
2
• Life: 1 000 000 cycles,
d
Ultra capacitors
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High specific power
Specific energy 10 times
EC
Life: 500 000 cycles, 10
years
45 OC
No maintenance
High eff, no loss
• 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)
3
Beacon Flywheel
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Low specific power
Low specific energy
20-year Design Life
High Temperature Tolerance
No maintenance
88% eff, 2% loss
Rotational energy as a function of moment of inertia
and angular velocity
1
Ek = · J ·ω 2
2
Optimise for angular velocity with the square
relationship to energy
Composite materials, hydrodynamic or
magnetic bearings, vacuumed
Beacon Flywheel
4
Urenco Flywheel
CAESS (Pnu Power)
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Low specific power
Low specific energy
20-year Design Life
High Temperature Tolerance
No maintenance
Low complexity
80% (11%) eff, no loss
5
Scroll technology
Ideal gas law for isothermal process and first law of thermodynamics:
PV = nRT = constant
WA→ B = ∫ P dV = ∫
VB
VB
VA
VA
nRT
V
= nRT (ln VB − ln VA ) = nRT ln
where, PAVA = PBVB and so
VB
1
VA
V
dV = nRT ∫
VB
VA
VB
VA
=
= nRT ln
dV
PA
PB
= PV ln
PA
PB
PA
Fixed scroll
PB
Orbiting scroll
Fast response, only one moving part
Fixed
scroll
High pressure air input
Air pocket expands through sequence
Orbiting scroll
Fuel cell
(Plug Power 5 kW)
H 2 → 2H + + 2e −
2H + + ½ O 2 + 2e − → H 2 O
H + ½ O2 → H 2O
• Independent sizing of
power and energy
• No degradation of
electrodes
• 45 OC
• Low maintenance
• 40% (11%) eff, no loss
6
Flow batteries (VRB)
• Independent sizing of
power and energy
• No degradation of
electrodes
• High cycle
• 62-80% eff, 2% loss
• Low specific power
• Low specific energy
• Life: unlimited cycles, 15
years (45 OC)
• No maintenance
• Complex system
3.3 kW, 10 kWh
Flow batteries (VRB)
VO 2+ + H 2O VO2+ + 2 H + + e −
V 3+ + e − V 2 +
E0 = 1.004 V
oxidation
reduction
E0 = −0.255 V
reduction
oxidation
2H +
e
Vanadium(II) sulphate = violet
vanadium(III) sulphate = aqua green
vanadium(IV) sulphate = blue
vanadium (V) sulphate = yellow
−
+
-
7
Battery assembly
Electrical system
Anode
Cathode
n×
n×
+
-
n×
N2
N2
n×
H2O
P=<140 kPa
Volume control
P=<140 kPa
King Island installation
200 kW, 800 kWh
8
Overview
1 Wh = 3.6 kJ
1000000
Hydrogen @ 1 bar (Wiki)
Hydrogen @ 200 bar (Wiki)
100000
Diesel (Wiki)
FC @ 200 bar (Plug Power)
Carbohydrates (Wiki)
Specific Energy [kJ/kg]
10000
1000
CAES @ 300 bar (Wiki)
LIB (Thunder Sky)
VLAB (FN)
100
VLAB (Delco)
VRB (Wiki)
NCB (Alcad Vantage)
FW (Beacon)
VRB (VRB Power)
CAES @ 300 bar (Pnupower)
UC (EPCOS)
10
1
EC
0.1
1
10
100
1000
10000
100000
Specific Power [W/kg]
Overview
100000
Diesel (Wiki)
Carbohydrates (Wiki)
10000
Hydrogen @ 200 bar (Wiki)
Energy Density [kJ/l]
1000
FC @ 200 bar (Plug Power)
NCB (Alcad Vantage)
LIB (Thunder Sky)
VLAB (Delco)
CAES @ 300 bar (Wiki)
VRB (Wiki)
100
VLAB (FN)
FW (Beacon)
Hydrogen @ 1 bar (Wiki)
CAES @ 300 bar (Pnupower)
10
VRB (VRB Power)
UC (EPCOS)
1
EC
0.1
0.01
0.1
1
10
100
1000
10000
100000
1000000
Specific Energy [kJ/kg]
9
Overview of cost
1000
UC (EPCOS)
100
Cost/Energy [$/kJ]
EC
10
FW (Beacon)
CAES @ 300 bar (Pnupower)
1
VRB (VRB Power)
NCB (Alcad Vantage)
LIB (Thunder Sky)
FC @ 200 bar (Plug Power)
0.1
VLAB (FN)
1
10
100
1000
10000
100000
VLAB (Delco)
0.01
Cost/Power [$/kW]
Overview of cost
LCC comparisons between a 2 kW Pnu Power CAES system and a 288 Ah VLAB system
000's
R 400
R 350
R 300
R 250
R 200
R 150
R 100
R 50
R0
0
1
2
3
4
5
6
7
8
9
Years
10
11
12
13
14
15
16
17
Annual cash flows (VLAB)
Annual cash flows (FCC)
Discounted aggregated cash flow (CAES)
Discounted aggregated cash flow (CAES)
18
19
20
10
Castle Valley Installation
Castle Valley Installation
11
King Island installation
System overview
12
23 :2 2:53
22 :3 2:35
21 :4 2:17
20 :5 1:59
20 :0 1:41
19 :1 1:25
18 :2 1:07
17 :3 0:51
16 :4 0:32
15 :5 0:14
14 :5 9:57
14 :0 9:38
13 :1 9:20
12 :2 9:03
11 :3 8:46
10 :4 8:29
09 :5 8:14
09 :0 7:56
08 :1 7:42
07 :2 7:33
06 :3 7:24
05 :4 7:14
04 :5 7:05
04 :0 6:55
03 :1 6:46
02 :2 6:36
01 :3 6:27
00 :4 6:18
00 :0 0:13
System overview
250 kW, absorbing 50 kVAR
1250 kW, 800 kVAR
850 kW, 0.98 lead to 0.95 lag
Matching load to generation
4500
4000
500 kW wind, 1 MW diesel, variations ESS
3500
3000
2500
P [kW]
2000
Q [kVAR]
1500
1000
500
0
13
Matching load and generation
Time [s]
Frequency control
Time [s]
14
Voltage control
Time [s]
Voltage and frequency control
Time [s]
15