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1 KW All-Vanadium Redox Flow Battery

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  • Fraunhofer ISE

    Design, characterisation and operation strategies of 1 KW all-vanadium redox flow battery

    Martin Dennenmoser, Kolja Bromberger, Felix Owald, Karsten Korring, Tobias Schwind, Tom Smolinka, Matthias Vetter

    Fraunhofer Institute for Solar Energy Systems ISE

    The second International Flow Battery Forum,

    Edinburgh - Scotland, 4th, 2011

  • Fraunhofer ISE

    2

    Introduction to redox flow batteries

    Applications

    Overview energy losses

    Stack design

    System description

    Measurement results

    Smart Redox flow Control

    Summary

    Agenda

    V4+ V3+ V5+ V2+

  • Fraunhofer ISE

    3

    General layout of a RFB

    Vanadium redox flow batteries:

    Decoupling capacity from power

    Modular design facilitates different applications

    Fast response time

    Efficiency >75 % possible

    No irreversible cross-over of active mass over the membrane

    Long calendar life, cycle stability (> 10.000)

    Introduction to redox flow batteries

  • Fraunhofer ISE

    4

    General layout of a RFB

    Vanadium redox flow batteries:

    Decoupling capacity from power

    Modular design facilitates different applications

    Fast response time

    Efficiency >75 % possible

    No irreversible cross-over of active mass over the membrane

    Long calendar life, cycle stability (> 10.000)

    storage

    Electrochemical converter

    Introduction to redox flow batteries

  • Fraunhofer ISE

    5

    Fields of application:

    Off-grid / mini-grid

    kW/kWh range

    Long term storage

    Distribution network

    MW/MWh range

    Energy management

    Industrial

    Backup power

    Load management

    Introduction - application

  • Fraunhofer ISE

    6

    System overview

    Components of a redox flow storage system

    Stack

    Pumps

    Tanks

    Valves

    Pipes

    Inverter

    Controlling

    Process technology

  • Fraunhofer ISE

    7

    System overview energy losses

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    8

    System overview energy losses

    For an optimal process/energy efficiency inverter, pump control and stack design has to be optimized.

    Energy efficiency of the stack is depending on:

    Diffusion through the membrane

    Internal shunt currents

    Ohmic losses

  • Fraunhofer ISE

    9

    Hydraulically in parallel configuration causes

    --> internal shunt currents

    Stack design

  • Fraunhofer ISE

    10

    Hydraulically in parallel configuration causes

    --> internal shunt currents

    Stack design

    Electrolyte is electrically conductive!

    Internal shunt currents

  • Fraunhofer ISE

    11

    Hydraulically in parallel configuration causes

    --> internal shunt currents

    It is very important to minimize internal shunt currents

    The internal shunt currents effects:

    Coulombic efficiency

    Self discharge

    Operation strategies

    Corrosion of the bipole plate

    Stack design

    Electrolyte is electrically conductive!

    Internal shunt currents

  • Fraunhofer ISE

    12

    Modelling of internal shunt currents

    Appropriate design of manifolds and in/outlet of the cells minimizes the internal shunt currents

    But trade off between shunt currents and pressure drop has to be found

    Stack design

    Electrolyte is electrically conductive!

    Internal shunt currents

  • Fraunhofer ISE

    13

    Stationary analysis of

    Pressure drop

    Fluid distribution

    Parameter studies of

    Porosity, permeability of porous electrodes

    Velocity of electrolyte

    Geometric design of manifolds

    Fluid simulation of a half cell

    CFD s imulation of an 700 cm half cell

    Pre

    ssu

    re P

    a

  • Fraunhofer ISE

    14

    Porosity: 95 %

    Velocity: 19 ml/min to 76 ml/min per half cell

    Stoichiometric flow rate 1 to 4

    700 A/m2 current density

    1.6 mol/l vanadium

    2.0 mol/l sulfuric acid

    Parameter study of electrolyte velocity

  • Fraunhofer ISE

    15

    Parameter study of electrolyte velocity

    manifold inflow

    manifold outflow

    porous electrode

    Velo

    city

    (m

    /s)

    Velocity: 19 ml/min

    Stoichiometric flow rate

  • Fraunhofer ISE

    16

    Velocity: 38 ml/min

    Parameter study of electrolyte velocity

    Velo

    city

    (m

    /s)

  • Fraunhofer ISE

    17

    Velocity: 57 ml/min

    Parameter study of electrolyte velocity

    Velo

    city

    (m

    /s)

  • Fraunhofer ISE

    18

    Velocity: 76 ml/min

    Parameter study of electrolyte velocity

    Velo

    city

    (m

    /s)

  • Fraunhofer ISE

    19

    Velocity: 76 ml/min

    Line plots for velocity magnitude at electrode inflow and outflow

    Comparison of fluid distribution at electrode inflow and outflow

    Parameter study of electrolyte velocity

    Velocity field at electrode inflow

    Velocity field at electrode outflow

    Velo

    city

    (m

    /s)

  • Fraunhofer ISE

    20

    Electrode outflow

    Velocity field is homogenous

    Electrode inflow

    Velocity field is not homogenous

    depends strongly on velocity of electrolyte

    Velocity field, electrode inflow and outflow

    Optimized geometric design of manifolds to reach homogenous velocities at electrode inflow

    Line graph: Velocity field, y component (m/s)

    0,0

    0,5

    1,0

    1,5

    2,0

    2,5

    3,0

    150 200 250100500

    X 10-3

    X 10-3

    4,0

    3,5

    3,0

    2,5

    2,0

    1,5

    1,0

    0,5

    0,0

    150 200 250100500

    X

    X

    19ml/min

    38ml/min

    57ml/min

    76ml/min

    19ml/min

    38ml/min

    57ml/min

    76ml/min

  • Fraunhofer ISE

    21

    Design of a 1 kW stack

    18 cells

    700 cm active area

    Ca. 1.3 V nominal cell voltage

    Max. 800 A/m

    Max. charge power 1.6 kW

    Flow through electrodes

    Electrically in series and hydraulically in parallel

  • Fraunhofer ISE

    22

    Design of a 1 kW System

    Measuring of

    Pressure

    Temperature

    Single cell voltage

    Electrolyte level in the tanks

    Balancing of the electrolyte level

    Valve control

    Pump control

    SoC determination over OCV measurement

    1 kW redox flow system

  • Fraunhofer ISE

    23

    Voltage, current and power curves

    cc-cv charging

    cc discharging

    600 A/m

    Initialization plus 4 test cycles

    Results power-voltage and current curve

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    24

    Influenced by

    flow rate

    cell design

    different SoC in the stack

    Homogenous single cell voltages are a sign for a good stack design

    Results single cell voltage

    1

    1,1

    1,2

    1,3

    1,4

    1,5

    1,6

    1,7

    0:00 1:12 2:24 3:36 4:48 6:00 7:12 8:24 9:36

    duration [h:mm]

    vo

    ltag

    e [

    V]

    cell 1 cell 3 cell 4 cell 8 cell 10 cell 12 average cell voltage

  • Fraunhofer ISE

    25

    Without pumps

    Stack disconnected from electrolyte fluid cycle

    100 % SoC after 2 h

    Deinitialization begins after 15 h

    Results single cell voltage self-discharge

    0,8

    0,9

    1

    1,1

    1,2

    1,3

    1,4

    1,5

    1,6

    1,7

    1,8

    0:00 4:48 9:36 14:24 19:12 24:00

    duration [h:mm]

    vo

    ltag

    e [

    V]

    cell 16 cell 12 cell 10 cell 8 cell 6 cell 4 cell 3 cell 2 cell 1

  • Fraunhofer ISE

    26

    Energy efficiency around 70 %

    Coulombic efficiency > 90%

    Voltage efficiency depends on the flow rate

    Results with very low flow rate

    Results - efficiencies

  • Fraunhofer ISE

    27

    System integration in the Messib project - Smart Redox Flow Control

    Smart Redox Flow Control:

    Battery management system

    Interface between EMS, inverter and battery

    Overview of the integration in the Solarhaus Freiburg

  • Fraunhofer ISE

    28

    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

  • Fraunhofer ISE

    29

    Smart Redox Flow Control

    Smart Redox flow Control

    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

    30

    Smart Redox Flow Control

    AC-Grid VRB +

    PeripheryInverter

    Pu

    mp

    co

    ntr

    ol

    Cu

    rre

    nt A

    C S

    et

    Me

    asu

    rem

    en

    t

    va

    lue

    s

    Actual values

    SOC-forecast

    Power AC Demand

    Smart Redox flow Control

    Energy

    Management

    System

    (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

    31

    Hardware implemen-

    tation

    Control algorithm

    System validation

    Parameter fitting

    System modeling

    Smart Redox Flow Control - development

    Required steps for the development:

  • Fraunhofer ISE

    32

    Modelled components:

    Inverter

    Tanks

    Stack

    Pipes

    Pumps

    Reference cell

    Smart redox flow control

    Smart Redox Flow Control modelling in Modelica

    System modelling in Modelica / Dymola

  • Fraunhofer ISE

    33

    Electrochemical characteristic:

    Voltage according to depth of discharge and current density

    Equivalent circuit

    Results for discharge mode

    Cel

    l v

    olt

    age

    [V]

    Smart Redox Flow Control modelling in Modelica

  • Fraunhofer ISE

    34

    Electrochemical characteristic:

    Dynamic of the stack

    RC equivalent circuit

    Important for control algorithm

    Dynamic model of the voltage according to the SoC and the current density

    Very fast response time!

    Smart Redox Flow Control modelling in Modelica

  • Fraunhofer ISE

    35

    Energy loss model out of the inner resistance and coulombic efficiency model

    The model shows the losses for charge and discharge according to SoC and the nominal power

    SoC forecast

    Optimized control strategies with several stacks

    System layouts / design

    Smart Redox Flow Control simulation in Modelica

  • Fraunhofer ISE

    36

    Stoichiometric flow rate depends on current and SOC

    SOC difference between stack and tanks should not too large

    Current density

    600 A/m

    discharging

    Smart Redox Flow Control pump control

  • Fraunhofer ISE

    37

    Smart Redox Flow Control pump control

    Stoichiometric flow rate depends on current and SOC

    SOC difference between stack and tanks should not too large

    Current density

    600 A/m

    discharging

  • Fraunhofer ISE

    38

    Stoichiometric flow rate depends on current and SOC

    SOC difference between stack and tanks should not too large

    Pump control is important for the energy efficiency of the VRFB

    Smart Redox Flow Control pump control

  • Fraunhofer ISE

    39

    Stoichiometric flow rate depends on current and SOC

    SOC difference between stack and tanks should not too large

    Pump control is important for the energy efficiency of the VRFB

    SOC Range also influences the energy efficiency

    Smart Redox Flow Control SOC range variation

    70

    70,5

    71

    71,5

    72

    72,5

    73

    5-95 %

    10-90 %

    15-85 %

    20-80 %

    25-75 %

    30-70 %

    35-65 %

    40-60 %

    45-55 %

    SOC Range

    S

    yste

    m [

    %]

  • Fraunhofer ISE

    40

    Summary

  • Fraunhofer ISE

    41

    May the flow be with you, and thank you for your kind attention!

    Martin Dennenmoser

    Fraunhofer ISE

    Heidenhofstr. 2 / 79110 Freiburg / Germany

    Ph: +49 761 4588 5682

    [email protected]

    www.ise.fraunhofer.de

    Questions?

    BMU 1-MWh-Netzspeicher

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