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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

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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 -

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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+

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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

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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

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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

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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

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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

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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.

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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

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Results of Fraunhofer Stack Development

40 cm²

164 cm²

250 cm²

700 cm²

3600 cm²

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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

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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

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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

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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

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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

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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

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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

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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:

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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]

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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

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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

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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+