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© Fraunhofer ISE
Latest Achievments of the Project »Advanced Energy Storage«
Redox Flow Batteries – Electric StorageSystems for Renewable Energy
Tom Smolinka1, Sascha Berthold2, Martin Dennenmoser1, Christian Dötsch2, Jens Noack3, Jens Tübke3, Matthias Vetter1
Fraunhofer Institute for1Solar Energy Systems ISE2Environmental, Safety and Energy UMSICHT3Chemical Technology ICT
First International Flow Battery Forum 2010 Vienna, June 15th/16th, 2010
© Fraunhofer ISE
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Itzehoe
BerlinGolm
Magdeburg
Hannover
Braunschweig
Bremen
OberhausenDortmund
Duisburg
AachenEuskirchen
SchmallenbergSt. Augustin
IlmenauJena
Dresden
Chemnitz
Würzburg
Erlangen
Pfinztal
DarmstadtKaiserslauternSt. Ingbert
SaarbrückenKarlsruhe
Stuttgart
Freiburg
Freising
Rostock
Teltow
CottbusHalleSchkopau
Paderborn
Nürnberg
Efringen-Kirchen
MünchenHolzkirchen
Leipzig
Itzehoe
BerlinGolm
Magdeburg
Hannover
Braunschweig
Bremen
OberhausenDortmund
Duisburg
AachenEuskirchen
SchmallenbergSt. Augustin
IlmenauJena
Dresden
Chemnitz
Würzburg
Erlangen
Pfinztal
DarmstadtKaiserslauternSt. Ingbert
SaarbrückenKarlsruhe
Stuttgart
Freiburg
Freising
Rostock
Teltow
CottbusHalleSchkopau
Paderborn
Nürnberg
Efringen-Kirchen
MünchenHolzkirchen
Leipzig
Fraunhofer Gesellschaft
60 institutes
17,000 employees
1.5 bn € budget
Fraunhofer Research Team»Advanced Energy Storage«
- Coordination -
© Fraunhofer ISE
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Agenda
Introduction to redox flow batteries
System layout for two different applications
Stack development with performance data
Material optimisation
Development of a model based control
Summary V4+ V3+V5+ V2+
© Fraunhofer ISE
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AnolyteV2+/V3+
CatholyteV4+/V5+
Source/SinkPump Pump
Electrolyte tank
Electrolyte tank
MembraneElectrode
Fields of application:
Off-grid / mini-grid
kW/kWh range
Seasonal storage
Distribution network
MW/MWh range
Grid management
Industrial
Backup power
Load management
Redox-Flow Batteries Have a Great Potential
General layout of a RFBStorage tanks
Electrochemicalconverter
© Fraunhofer ISE
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Standard Potentials of Possible Redox Couples
Advantages Vanadium
High OCV in thepotential window
Cross-over is notirreversible
Long life time
Drawbacks Vanadium
Low energy density
Limited temperaturerange
Costs electrolytesolution?
Oxygen evolution
-1.0 -0.5 0.0 +0.5 +1.0 +1.5 +2.0 (vs. NHE)Standard Potential [V]
V (2/3) V (4/5)
Fe (2/3)Cr (2/3)V (3/4)
Ti (3/4)
Cu (1/2) Cr (3/6) Mn (2/3) Ni (2/4)Co (2/3)Mn (4/7)
OCV
Hydrogen evolution
Possible Potential Window
Source: CRC Press Handbook of Chemics and Physics
© Fraunhofer ISE
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RFB in general:
Decoupling capacity from power
Modular design facilitate different applications
Fast response time (μs – ms)
VRFB in particular:
High efficiency (>75 % possible)
No irreversible cross-over of active mass over the membrane
Long calendar life, excellent cycle ability (> 10.000)
Low self discharge
Low maintenance costs
Why Vanadium Redox-Flow Batteries?
Compared to other storage technologies VRFB has many advantages:
Energy storage of fluctuating RESin the range from kW / kWh to MW / MWh
© Fraunhofer ISE
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Hausnetz
DieselGenerator
230 V AC brigde
PV panel Solar Charger
Inverter
Diesel Gen
VRFB
Hous grid
Wind millRectifier
48 V DC bar
230 V AC bar
Rectifier
Rappenecker Hof in the Black Forest
Applications from kW to …
Off-grid application:
Coupled with PV + wind turbine
1 stack à 5 kW
50 kWh (~ 2x 1.25 m³electrolyte)
1.2 kWP
3.9 kWP
9.6 kW
5.0 kW
© Fraunhofer ISE
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Applications from kW to …
Cost analysis
„Rappenecker Hof“:
Output power: 5 kWmax
ALCC including:
Investment
Maintenance
Replacement
0
2000
4000
6000
8000
10000
12000
14000
0 5 10 15 20 25 30
Autonomy time [h]
ALL
C [€
]
Lead acid( 6 years)
Lead acid (4 years)
VRFB (4.8 years)
Annualized life cycle cost
© Fraunhofer ISE
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… to MW: Scale-up Concept
2 MW / 20 MWh concept:
Medium sized wind farm
56 stacks à 35 kW
8 strings
2 x 500 m³ electrolytetanks
Source: VRB Power Systems Inc.
© Fraunhofer ISE
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From Cell Design to Stack Construction
Reduced stray current within the stack
Uniform electrolyte distribution in the cell
40 cm²
700 cm²
3600 cm²
Neg. half cellPos. half cell
Manifold
FeltCarbon
Bipolar Plate
Filter press configuration
Electrically in series and Hydraulically in parallel
Flow through electrode
© Fraunhofer ISE
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Results of Fraunhofer Stack Development
40 cm²
164 cm²
250 cm²
700 cm²
3600 cm²
© Fraunhofer ISE
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Test facilities for material and stack development
5 cm² 40 cm² 250 cm² 700 cm² 3600 cm²
Cell area:
ICT ICT ISE UMSICHTISE
Material optimisation
Modelling and Control
Stack and System
© Fraunhofer ISE
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Stac
k V
olt
age
[V]
Complete charge / discharge cycle
@ ~ 40 mA/cm²
Typical Charge / Discharge Characteristic
Time [h]
Cu
rren
t[A
]
5-cell stack à 700 cm²
cc-cv charging
cc discharging
VoltageCurrent
© Fraunhofer ISE
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Single Cell Voltages During Charging / Discharging
Time [h]
Cel
lvo
ltag
e[V
]
Cell 1
Cell 2
Cell 3
Cell 4
Cell 5
5-cell stack à 700 cm²
Complete charge / discharge cycle
@ ~ 40 mA/cm²
cc-cv charging
cc discharging
© Fraunhofer ISE
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Efficiencies
At different currentdensities
Complete charging / discharging
CE: Coulombic Efficiency
EE: Energy Efficiency
0
0,2
0,4
0,6
0,8
1
1 2 3 4 5Current density [mA/cm²]
Effic
ienc
y [-]
CE EE
10 20 40 60 80
5-cell stack à 250 cm²
Mea
nce
llvo
ltag
e[V
]
SOC [ - ]
Currentdensity
© Fraunhofer ISE
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Optimisation of Cell Materials: Membrane
Types of membrane:
DuPont Nafion(cation exchangemembrane)
FuMA-Tech FAP(anion exchangemembrane)
Activation by
Pretreatment in salts
Boiling in acid
0 10 20 30 40 50 60 70 800,0
0,2
0,4
0,6
0,8
1,0
ene
rgy
effic
ienc
y
current density [mA/cm2]
Nafion untreated FAP-0 24h 2M NaCl 24h 2M Na2SO4 30min 3% H2O2 FAP-0 30min 2M H2SO4 FAP-0 30min 0,5M H2SO4
FAP-0 24h 2M NaCl 24h 2M Na2SO4 FAP-0 30min 3M H2SO4
FAP-0 untreated Nafion 60min 3% H2O2 30min H2O 30min 1M H2SO4 FAP-0 24h 1M NaCl 24h 1M Na2SO4 FAP-0 30min 1M H3PO4
FAP-0 30min 3% H2O2
© Fraunhofer ISE
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KFA untreatedGFD untreated
GFA untreatedGFD acid
GFD acid heatGFA acid heat
GFA acid
0,0
0,2
0,4
0,6
0,8
1,0
Energy Efficiency Discharge Power
Ener
gy E
ffici
ency
0
5
10
15
20
25
30
35
Dis
char
ge P
ower
[mW
/cm
²]
20 mA/cm²
Optimisation of Cell Materials: Electrodes
Screening of different materials for electrodes
© Fraunhofer ISE
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Optimisation of Cell Materials: Electrodes
Thermal and acid treatment at different times and temperatures
0 20 40 60 80 1000
20
40
60
80
100
disc
harg
e po
wer
den
sity
[mW
/cm
²]
current density [mA/cm²]
GFA5 untreated GFA5 5 min conc. H2SO4 RT GFA5 5 min 400°C GFA5 heat
GFA 5
0 20 40 60 80 1000
20
40
60
80
100
ener
gy e
ffici
ency
[%]
current density [mA/cm²]
GFA5 untreated GFA5 5 min conc. H
2SO
4 RT
GFA5 5 min 400°C GFA5 heat
GFA 5
heat ramp > 1 ½ h heat ramp > 1 ½ h
© Fraunhofer ISE
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Development of a “Smart Redox Flow Control“
Smart Redox Flow Control:
Control loops for devices of redox flow battery
Determination of set points (e.g. inverter, pumps)
Optimization of the process cycle
energy efficiency
Interface with energy management system (e.g. UESP)
Smart Redox flow Control
Pump control
Charge/ Discharge controller
SOC forecast
SOC Determination
© Fraunhofer ISE
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Development of a “Smart Redox Flow Control“
AC-Grid VRB + PeripheryInverter
Pum
p co
ntro
l
Cur
rent
AC
Set
Mea
sure
men
t va
lues
Actual values
SOC-forecast
Power AC Demand
Smart Redox flow Control
EnergieManagementSystem (EMS)
Pump control
Charge/ Discharge controller
SOC forecast
SOC Determination
Smart Redox Flow Control:
Control loops for devices of redox flow battery
Determination of set points (e.g. inverter, pumps)
Optimization of the process cycle
energy efficiency
Interface with energy management system
© Fraunhofer ISE
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Hardwareimplemen-
tation
Controlalgorithm
Systemvalidation
Parameterfitting
Systemmodeling
Development of a “Smart Redox Flow Control“
Required steps for the development:
© Fraunhofer ISE
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Modeling in Modelica
Modeled components:
Inverter
Tanks
Stack
Pipes
Pumps
Reference cell
Smart redox flow control
Measure & ControlElectrolyteElectrical current
Anolyte Catho-lyte
© Fraunhofer ISE
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Fitting of measured charging / discharging data
Internal resistance model
Result of discharging
IRVV Icell ⋅+
Parameter Fitting
= 0
RI
V0 U
I∆V
Cel
lvol
tage
[V]
DOD [-]
Current density [A/m²]
© Fraunhofer ISE
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Outlook (I): Test facilities for large RFB stacks
RFB laboratory at Fraunhofer UMSICHT: total power (bi-directional):
80 kWmax. 100 V, max. 900 A
Temperature controlled: 15 - 40 °CElectrolyte tank:
2 x 0,5 m³2 x 0,3 m³
Stack size up to 1 x 1 x 1 mmax. 60 cells 500 kg85 VNom
Flow rate: 5 m3/h and 3 m3/h
© Fraunhofer ISE
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Outlook (II): EU project MESSIB
“Solarhaus Freiburg”:
1 kW / 6 kWh VRFB
Smart Redox Flow Control (SRC)
Test site with AC demand control
Connected to a PV system and the grid
PV installed:
3.8 kWp
© Fraunhofer ISE
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Summary
VRFB are long-lasting and high efficient ESS which can be tailored to many applications
Two different concepts are under developement in the kW - MW range at Fraunhofer
Within the Fraunhofer project the VRFB technology is pushed forwarded:
Material optimisation for higher efficiencies and power densities (membrane, electrode)
Stack design and construction from 1 – 35 kW units
Model based VRFB control for optimised system operation under development
Further work will focus on system integration and field tests
© Fraunhofer ISE
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Thank you for your kind attention!
Tom Smolinka
Fraunhofer ISE
Heidenhofstr. 2 / 79110 Freiburg / Germany
Ph: +49 761 4588 5212
tom.smolinka@ise.fraunhofer.de
www.ise.fraunhofer.de
Questions?
V4+ V3+V5+ V2+
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