04.03.2013 aditya poudyal grid distributed generation renewable energy electrode and membrane design...

04.03.2013 Aditya Poudyal

Grid

Distributed generationRenewable energy

Electrode and membrane design

Energy storage

Electric vehicles

Redox couples

Stack design

Elecrolyte flow circuitoptimizationSimulation

Electrical equivalent modelling Electrochemistry

Trasients phenomena

Electrical interfacing

Cost

Redox flow battery

Basic chemistry and material science

Scale up, structural and operation optimization of flow geometries

Modlellng optimization , and simualtion

System science

Electricity value chain

Fuel/Energy Source

Industry

DistributionGeneration Transmission

householdsCoal Nuclear Hydro.....

Fuel/Energy Source

Industry

DistributionGeneration Transmission

households Office buldings

Coal Nuclear Hydro.....

Renewables (Wind, Solar, ) Energy Storage

Distributed Generation

Office buldings

Traditional way: Regulated utility, bundled functions.

Unbundled servicesUnbundled pricesNew service strategies Privatized services

Electrical energy storage along electricity value chain


Energy storage


Candidates for grid storage (Electrochemical)

Liquid metal batteryLithium Ion Battery

Nickel cadmium

Sodium sulfur

Sodium metal chloride

Lithium Ion Battery

Flow batteries

But they are not meeting the following challenges: Un commonly high power Long service lifetime and Super low cost


Comparison table for various storage systems Active

materialsEfficiency OCV

(V) (wh/kg)(wh/liter)

Run time

Capital cost Response time

Lifetime Self discharge

Maturity Environmental impact

Thermal needs

Energy(€/kWh)

Power(€/kW)

years cycles

Lithium Ion Metal compounds oxides containing Li ions/Carbon

85%(8% self discharge/month, 3% electrical, 4% electrochemical)

3.6-3.8 75-200

(200-500)

min-hrs 500-2000

milliseconds 5-15 1000-10000

0.1-0.3% Developed Toxic remains Room temperature

Lead acid Lead dioxide/lead

85-90%(3%self discharge/month, 4% electrical, 4% heat)

2.10 30-50

(50-80)

secs-hrs 50-270 milliseconds 5-15 500-1000 0.1-0.3% Mature Toxic remains Room temperature

Nickel cadmium

Nickel hydrate/Sponge Cadmium

50-90% 1.3-1.35 40-60

(60-150)

secs-hrs - - milliseconds 10-20 2000-2500

0.2-0.6% Developed Impact of cadmium in the production step and also for human health

-

Sodium sulfur

S/Na 75%(2% heating, 12% chemical efficiency, 10% electrical)

2.1 150-240(150-250)

secs-hrs 210-250 125-150

milliseconds 10-15 2500 20% Developed About 300

Sodium metalchloride

85%(2% heating, 9% chemical, 4% electrical)

600

Flow batteries

Vions/Vions 65-75% (3% electrolyte pumping, 10% electrical losses, 20% electrochemical)

1.4 35,16-33 (wh/liter)

secs-10 hrs

125-150 250-300

<100usec 5-10 12000+ Small Developed Room temperature

Metal air 150-3000(500-10000)

100-300Very small Developing

Small

Vanadium Discovered in 1801 by a Spanish

minerologist Andres Manuel del Rio

Named it after the Scandinavian goddess of beauty Vanadis.

Rediscovered in 1830 by Swedish chemist Nils Gabriel Sefstrom

In 1867 isolated in nearly pure form by Roose by reducing its chloride with hydrogen.

Steel grey metal which exists in number of different oxidation states i.e. -1, 0, +1, +2, +3, +4, and +5

Vanadium couples

Strong acidic solutions

Weak acidic solutions

Neutral and basic solutions

V(V)-V(IV) 1.000 0.723 0.991

V(IV)-V(III) 0.337 0.481 0.542

V(III)-V(II) -0.255 -0.082 -0.486

V(II)-V(0) -1,13 -1.13 -0.820

Table: Stadard potential of vanadium couple s at in aqueous solution at 250O


Why all Vanadium?

1. No problems of cross contamination.

2. High charge and voltage efficiency >> fast kinetics of the vanadium redox couples.3. Low rate of gas evolution during charge rates associated with rapid charging cycles.

4. ”No memory effect” & ”Can be over charged and deeply discharged” without doingpermanent damage to the electrolyte and the cells.

5. Reusability of electrolyte >> Long cycle life 5. Fast response 6. Modularity

6. Safe operation

Challenges1. Specific energy density

2. At high molar concentration precipitation occurs in th V5+ electrolyte at tempertaure above 40oC and solid vanadium oxides in V2+ or V3+ solution below 10oC.


Bipolar electrode

End plate electrode

Membrane

End plate electrode

Positive electrolyte

Negative electrolyte

IN

OUT

Components of cell stack


ELECTROCHEMISTRY

Rxn occurs between electrolytes

No electrodeposition

Electrolytes are stored in external tanks and circulated through the stack.

Simultaeneous reaction occues at the both side of electrolyte

Electrical balance is maintained by proton migration across membranes.

Can be operated under the temperature range of 10-(35)40oC.

Discharge: Electrons are removed from Anolyte and trasnferred to the Catholyte via external circuit.


Vanadium concentrations during battery operation

Salt Charge Discharge Electrolyte

V2+ VSO4 ↑ ↓ Anolyte

V3+ 0.5 V2 (SO4)3 ↓ ↑ Anolyte

V4+ or VO2+ VOSO4 ↓ ↑ Catholyte

V5+ or VO2+ 0.5 (VO2) 2 SO4 ↑ ↓ Catholyte


Electrolyte preparation• Based on the the electrolysis of Vanadyl Sulphate.• Catholyte is obtained from the electrolytic oxidation of VOSO4 solution and anolyte from

the elecrolytic reduction.

V3+ and V2+ (Reduction) V5+ (Oxidation)Negative compartment: Vanadyl Sulphate

Positive compartment: Sulphuric acid solution with a sulphate concentration equivalent to the Vanadium concentration in negative compartment.

Both are filled with the VOSO4 and electric current is applied to the electrodes

23 VeV

OHVeHVO 23 2 2 eHVOOHVO 222

2


Electrolyte stability Depends upon

temperature, the vanadium concentration, the suplphric acid concentration and on the SOC.

At higher temperature Catholyte precipitaion at fully charged state. But not irreversible >> dissloves when discharging

Lower temperature V4+, V3+ and V2+ start to precipitate. Slows the rates of the reactions at the electrodes; operation at 0oC could result iin significantly slower

reaction rates. Increasing the stability

Use of inhibitors Dispersion: decrease the strength of attraction forces betn the particles Comlexing: forms new complexes with one of the ion involved in precipitation Threshold: inhibit the precipitation of certain compunds

Use of heat treatment. Boil the electrolyte for few hours to remove the precipation process.


Electrical equivalent circuit R reaction and R resistive compise the

internal losses, reaction kinetics, mass transport reisistance, membrane resistacne, solution resistance, electrode resistance and bipolar resistance.

Rfixedloss represent the parasitic losses

Ipump stands for the power consumption by recirculation pump, system controller, and power loss from cell-stack-by pass.

Celectrodes represnet the transie component associated with the electrode capacitance.


VRB discharging and charging cycles: Charging take longer time than to

discharge it.

Ipump soars dramatically as the SOC drops >> more catholyte and anolyte are required to provide the same power when the SOC lowers

Stack voltage is higher than the output volatge when dscharging , stack volatge is smaller when charging and it implies internal losses.

Efficiency decreases by 5 % when SOC is 0.2%.


Trasients and response time• Transients are essential

because of the importance of the system ability to respond to the fast change.

• Trasient behaviour is related to the electrode capacitance as well as concentration depletion close to electrodes.

Worst case transients were considered the operation is switched from -65A and then back.Figure shows that it takes 0.045 seconds for battery voltag e to reach steady state


Equilibrium PotentialThe equilibrium voltage corresponds to the sum of equlibrium potential of each cell in stack.

Equilibrium potential is given by the Nernst equation and depends upon vanadium species concentration and the proton concentrations.

is standard potentials and it is important parameter in nersnt equation as it expresses the reaction potentials at standard conditions.

)ln(

)()()(

QnF

RTEE

tUtUtU losseqstack


R is gas constant T is temperatureF is Faraday constant E

Standard potentialAn ideal state where the battery is at standard conditions:

Vanadium species at a concentration of 1

All acticity coefficients equal to 1 and temperature 250C.

Can be detemrined from the thermodynamic principle called the Gibbbs free enthalpy, the conservation of energy and empirical parameter that can be found in electrochemical tables.

ro

ro STHG 0

Standard Gibbs free enthalpy of reaction which represents the change of free energy that accompaniesthe formation of 1M of a substance from its component elements at their standard states: 250C, 100kPa, and 1M

Where the standard reaction enthalpy is the difference of molar formation enthalpies between the products and reagents

and the standard reaction of entropy is the differnce of molar formation entropies between the products and the reagents

roH

reagentfo

productfo

r HHH ,,0

0rS

productfoS , reagentf

oS ,

reagentfo

productfo

r SSS ,,0


= -155.6kJ/mol

=-121.7 J7mol.K

The conservation of energy relates the change in free energy resulting from the transfer of n moles of electrons to the difference of potential E:

Therefore standard potential can e written as

”The standrad potentia is 1.23V at 250C.”

Hfo

VOfo

Vfo

OHfo

OHfo

VOfo

r

HHH

HHHH

,,,

,,,0

222

222

Hfo

VOfo

Vfo

OHfo

OHfo

VOfo

r

SSS

SSSS

,,,

,,,0

222

222

nFEG

nF

STH

nF

GE

ro

roo

o

Inserting thermodynamical data the standard reaction enthalpy ∆H0

r becomes :

and similarly the standard reaction entropy ∆S0

r


Standard potential

Characteristic curve of the equilibrium potential E for a single cell


Electron exchange rate

[mol/s] )()(N

by given is cells N containingstack for the and

-------------------------------------------------------------------------------

[mols/sec] )(1

)(N

is cell singlefor electron of rate flowmolar Therefore

------------------------------------------------------------------------------

number Avgardo theis N where)()(1

iscurrent given afor involved electrons ofnumber the

----------------------------------------------------------------------------

charge elementary thee and electrons ofnumber then time, t thecurrent, thei charge, theis Q where

)(

cell. through flowingcurrent electrical by theset ision concentrat theof pace theandcurrent electrical the

toalproportion are changeion concentrat theTherefore occurs.reaction redox a each time involved

iselectron known that isit also and ratereaction the toalproportion are changeion Concentrat

.

.

A

ec -

tieN

Nt

tieN

t

tdtieN

ne

dttieneQ

A

celle

A

e

A

c


Proton concentrations


Internal loss

)()()()()( tttttU ionohmconcactloss

• When current starts to flow – Cell Voltage ≠ Nernst Voltage

• The losses are called overpotentials– represents the energy required to force the redox

reaction to proceed at required rate

)()( arg/arg, tiRtU edischecheqloss Electrode phenomena and are associated with

the energy required to initiate the charge transfer and Concentration difference between bulk solution and electrode surface

Ohmic loss occurs in electrodes, the bipolar plates and the collector plates.Ionic loss occurs in electrolytes and membranes


Efficiencies

dttP

dttP

ech

edich

)(

)(

efficiencyEnergy

arg

arg

energy

dtti

dtti

Q

Q

ech

edisch

ech

edischcoulombic

)(

)(

efficiency Coulombic

arg

arg

arg

arg

coulombic

energy

ech

edich

dttU

dttU

)(

)(

efficiency Voltage

arg

arg

energy

•Ratio of the charge withdrawn from the system during the discharge to the charge supplied • Can be caused by side reaction such as

oxygen and hydrogen evolution• Cross mixing of electrolyte through

membrane due to ion transfer• Unbalanced flowrates of the electroly

•Defined for charge and discharge cycle for constant currnet. • Is meaure of ohmic and plarization losses

during the cycling.• Can be maximized by contact, electrode,

electrolyte and membrane resistance • By using an electrode material with good

electro-catalytic properties for the reactions.

Enegy released during discharge and energy supplied during charge


Charge and discharge at costant currnet

Efficiencies at various currents.The cycle starts at 2.5% SOC, and charged upto 97.5% SOC and again discharged to 2.5%

Cost breakdown


Thank you for the attention !!!


04.03.2013 aditya poudyal grid distributed generation renewable energy electrode and membrane design...

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