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Photogalvanic cells: Renewable and future energy


Photogalvanic cells: Renewable and future energy devices for solar power and storage By Dr. Pooran Koli Assistant Professor Solar Power & Storage Lab – PowerPoint PPT presentation

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Title: Photogalvanic cells: Renewable and future energy

  • Photogalvanic cells Renewable and future
  • devices for solar power and

  • By
  • Dr. Pooran

  • Assistant Professor
  • Solar
    Power Storage Lab
  • Department of Chemistry, Jai Narain Vyas
  • Jodhpur (Rajasthan) 342033 INDIA

Approach of my talk
  • Introduction
  • Survey of solar power techniques
  • Photogalvanic cells- my research field
  • What is my contribution to the field of
    photogalvanic cells?
  • How photogalvanic cells compares with other
    similar cells?
  • How photogalvanic cells could be future energy
  • What to be done in the field of photogalvanic

  • Some supreme truths
  • - everyone/everything has to die,
  • - sometimes things can happen without
  • - but nothing can happen without the
  • energy.
  • Therefore, the energy is essential and
    unavoidable for life. Therefore, the production
    and use of energy is vital to the social,
    economic and scientific
  • development of all the countries.

  • Presently at world level
  • - about 70 energy (power) is supplied by
    non- renewable sources, and about 30 power is
    supplied by renewable sources (Source IRENA
    database). Total installed power worldwide 2013
    is 5667 GW, solar 173 GW (3 of total)
    Germany(100.9) gtItaly (23.1) gt Japan gt USA gt
    China gtSpain
  • At India level - 71.4 energy (power) is
    supplied by non- renewable sources, and 28.6
    power is supplied by renewable sources (Source
    Report Central electricity authority, Govt. of
    India). Solar power 1 .
  • - India on pace with global trend regarding
    renewable energy.
  • At my home state Rajasthan level - 66
    energy (power) is supplied by non- renewable
    sources, and 34 power is supplied by
    renewable sources (Source Report Central
    electricity authority, Govt. of India). Solar
    power 1 .
  • Rajasthan a bit ahead of global trend regarding
    renewable energy.
  • Attracted to California because sun intensity
    similarity between Rajasthan (5-7 KWH day-1 m-2
    2nd highest in world) on one hand California,
    Nevada, (7-9 KWH day-1 m-2 highest in world) on
    other hand.

  • At India level scenario of total power
  • 2.54 lakh Mega Watt was the established power
  • generation capacity in India as on 30
  • (Report Central electricity authority,
    Govt. of India).
  • Out of this 2.54 lakh MW power -
  • - 69.5 is from fossil fuels ( 60.1
    coal, 85.9
  • gas, 0.47 diesel)
  • - 16.1 is from hydro power
  • - 1.8 is from nuclear power
  • - 12.5 is from renewable sources
    (solar power 1 , small
  • hydro projects, bio-mass,
    wind power, etc.).
  • 2632 MW solar (Guj 1000,
    Raj 700).

  • At Rajasthan level
  • 9500 Mega Watt was the established power
  • generation capacity in Rajasthan as on 31
  • (Report Central electricity authority,
    Govt. of India).
  • Out of this 9500 MW power -
  • - 60.2 is from fossil fuels ( 53.2
    coal, 7.0 gas)
  • - 15.63 is from hydro power
  • - 6.03 is from nuclear power
  • - 18.13 is from renewable sources
    (solar power, wind power, etc.).

  • Levels of needs of energy -
  • At body level- supplied by food and drink
  • At household industrial level- this is
    supplied from non-renewable renewable sources

  • Non-renewable sources
  • (e.g. fossil fuels- coal, petroleum,
    natural gas) are those energy sources which
    cannot be renewed after use.
  • Beauty of Non-renewable sources
  • -Highly developed, highly reliable, high
    energy density,
  • independent of seasonal climatic
  • deep penetration in life, modern life
    owes to them, etc.
  • Limitations of Non-renewable sources
  • polluting, costly, limited in stock, less
    abundant, geographically unevenly distributed
    and fastly depleting, so they cannot be safe and
    lasting source of energy.

  • Renewable sources ( e.g. solar energy,
    tidal energy, geothermal energy ,wind energy,
    hydel energy, bio-energy, etc.) are those energy
    sources which can be renewed after use. Thus,
    their use is safe , clean and lasting .
  • Limitations of Renewable sources
  • Less developed (except hydro), less
    energy density,
  • dependent of seasonal climatic
  • less penetration in life , etc.
  • Beauty of Renewable sources
  • - their use is safe, clean and lasting .

Among the all renewable energy sources, the
solar energy has special significance for some
  • - it is mother of all energy resources
    (except nuclear energy).
  • - It is a renewable, cheap and clean energy
  • It is most abundant source of energy, yet least
  • - It is not certain whether life exists or
    not on planets other than earth but it is
    certain that once we master in solar energy
    techniques, they can be source of power on all
  • - the solar energy only can be source for
    power generation as long as life is on the
    Earth. The life can sustain on Earth only as long
    as the life of sun, because Earth is inhabitable
    due to sun radiations. In the absence of sun, the
    Earth will be a cold planet unable to sustain

Present status of solar energy
at world and India level- World level- About 3
(173 GW solar) of total power (5667 GW) coming
from solar year 2013- India level 1 (2631
MW solar) of total power 2.54 lakh MW - JLN
National Solar Plan has envisaged at least 20,000
MW of solar power generation by 2020 and up
to 200,000 MW by 2050. JLN National Solar Plan
is 3-phase approach (1)first phase
(2010-13),1000-2000 MW, (2) Phase 2
(201317) ,4000-10000 MW, (3) Phase 3
(201722) , 20000 MW  
In theory, the entire present energy consumption
of the world could be met by an area smaller than
1 of the worlds deserts if they were covered
with solar thermal electric plants.
2. Solar power techniques- A survey
  • The solar energy can be directly converted into
  • electricity. This electricity is called
    solar power.
  • Some of the techniques for solar power
    generation are

  • This is based on concentrating solar thermal
    systems which uses lenses or mirrors and
    tracking systems to focus a large area of
    sunlight into a small beam.
  • This concentrated and small solar beam is
    focused on working fluids (like oil, water,
    hydrogen, helium, air, etc.).
  • The working fluid flows through the receiver
    and is heated up to 500 ?C (even up to 1500 ?C)
    before transferring its heat to a distillation or
    power generation system.
  • Thus solar energy can be converted into heat
    energy in turn into mechanical energy then into
    electrical energy.

  • Electricity can be produced directly
    from sunlight with the help of SPV technology.
  • SPV technology is based on the
    photovoltaic effect, which refers to transition
    of electrons from a lower to a higher energy
    state having absorbed photons of the right
  • The photovoltaic effect is like
    photoelectric effect with a little difference.
  • While in the photoelectric effect,
    electrons are ejected from the solid, liquid and
    gaseous elements when light strikes on the
    surface of these elements, in the photovoltaic
    phenomenon the electrons make a transition from a
    lower to a higher energy state having absorbed
    photons of the right energy.

  • The SPV systems consists of two materials in
    contact with each other. Among them, one is wafer
    of electron emitting non-metal and other is
    electron collecting material which pass on
    electrons in form of electron stream (i.e.
    current) to circuit. The electron emitting wafer
    replenishes those electrons which goes out to
  • This technology involves semiconductors as light
    absorber, and electronic species (electrons and
    positively charged holes) as mobile charges
    moving in device due to mainly drift ( under the
    influence of electric field) and some diffusion
    (under the influence of concentration difference).

  • These cells are made up of a porous film of tiny
    (nanometer sized) white pigment particles made
    out of titanium dioxide.
  • The titanium dioxide particles are covered with a
    layer of dye, which is in contact with an
    electrolyte solution.
  • When solar radiation hits the dye, it injects a
    negative charge in the pigment nanoparticle and a
    positive charge into the electrolyte resulting in
    the conversion of sunlight into electrical

  • - Photogalvanic cells are galvanic cells which
    have property of solar energy conversion and
  • - This is the very simple technology on which
    I am working.

2.3. Experimental and calculation method
- Study of variation of various parameters like
conc., diffusion length, Pt size, Temp.,etc. We
fill sollution of dye, reductant,NaOH,
surfactant(if used) in H-shaped tube containing
SCE in one arm and Pt in oppoosite arm.
  • The experimental set up consists of
  • - H-cell (photogalvanic cell),
  • - light source ( different wattage bulbs),
  • -digital pH meter- Systronics Model335 (for
    measuring potential in millivolt-mV),
  • microammeter-OSAW (for measuring current in
  • - a carbon pot log 470 K device (for changing
    the resistance of circuit),
  • water filter (for filtering infrared radiations)
  • a circuit key (for closing and opening

  • The photogalvanic cell is made of glass tube of
    H-shape whose wall is externally blackened, but a
    window is left in one arm.
  • The arm with window acts as illuminated chamber
    and other arm without window acts as dark chamber
  • This glass tube of H-shape is filled with known
    amount of the solutions of photosensitizer,
    reductant and Sodium hydroxide.
  • The total volume of the solution is always kept
    25.0 ml making up by doubly distilled water.

  • A platinum electrode (as negative terminal) is
    dipped in illuminated chamber against window and
    a Saturated Calomel Electrode- SCE( as positive
    terminal) is immersed in dark chamber.
  • The terminals of the electrodes are connected to
    a digital pH meter.
  • Initially, the circuit is kept open and cell
    is placed in dark till it attains a stable
    potential (dark potential - Vdark).
  • Then, the Pt electrode is exposed to light
    radiations emitted from tungsten bulb.
  • On illumination, the photopotential (V) and
    photocurrent (i) are generated by the system.
  • The cell stand charged when maximum potential is

  • A water filter is put between cell and lamp to
    cut off infra-red radiation with the aim of
    curbing heating effect of cell, which otherwise
    may adversely affect the cell leading to lower
  • After charging of the cell, the circuit is
    closed and the cell parameters like maximum
    potential (Vmax), open-circuit potential (Voc),
    maximum current(imax) and equilibrium
    current(ieq) or short-circuit current(isc) are

  • The study of i-V characteristics of the cell
    done by observing potential at different direct
    currents by varying resistance(calculated by Ohm
    law) of the circuit.
  • i-V characteristics shows the highest power at
    which cell can be used.
  • The cell is operated at highest power
    (i.e.,power at power point - ppp) at
    corresponding external load, current( i.e.,
    current at power point - ipp) and potential(
    i.e., potential at power point-Vpp) for study of
    its performance by observing change in current
    and potential with time.
  • The cell performance is studied in terms of
    half change time (t0.5), conversion efficiency
    (CE) and fill factor (FF) in dark.

  • The time taken for fall in the power of the
    cell to its half value of power at power point is
    called t0.5 (which is measure of storage
    capacity of the cell).
  • The average rate of change of current over t0.5
    period (?i/?t) is
  • calculated from (ipp - it0.5)/ t0.5 ,
  • where it0.5 is current at t0.5 .The potential
    corresponding to it0.5 is Vt0.5.
  • The charging time (t) is calculated as,
  • charging time (time at which Vmax is
    obtained) (time at which illumination is
  • Photopotential (?V) is equal to Vmax Vdark .

  • The CE and FF of the cell are calculated from
    equations (1) and (2),respectively.

Where, Vpp is potential at power point and ipp
is current at power point .

. (2)
Where, Vpp is potential at power point, ipp
is current at power point, Voc is
open circuit potential, and isc is
short-circuit current.
The initial pH of the mixture of solutions has
been calculated by the formula,
pH 14 - pOH
Lamps of different wattage have been used to
vary the light intensity.
2.4 Mechanism of solar power generation storage
riplet state being relatively more stable than
singlet state has role in storage capacity.
  • Both singlet and triplet excited states of dye
    are involved here, but triplet state being
    relatively more stable than singlet state has
    role in storage capacity.
  • The main electroactive species are the leuco or
    semi dye and the dye in the illuminated and the
    dark chamber, respectively. However, the
    reductant and its oxidized product act only as
    electron carriers in the path(Tamilarasan R,
    Natarajan P.Photovoltaic conversion by
    macromolecular thionine films. Nature 1981292
    224 225, Kaneko M, Yamada A. Photopotential
    and photocurrent induced by a tolusafranine
    ethylenediaminetetraacetic acid system. Journal
    of Physical Chemistry 1976 81 1213-1215).

Inside the cell, there is only
diffusion controlled motion of ions in solution.
Therefore, photogalvanic cell requires that
incident light be absorbed close to the light
electrode in order to enable the electron-rich
species to reach the electrode by diffusion
within its lifetime. It is intended to be
achieved by blackening H-cell externally and
keeping a small window for illumination of
platinum electrode. Further, the higher
diffusion retards energy wasting reverse reaction
(electron transfer from Pt electrode to dye, and
from dye to reductant in illuminated chamber)
(Gomer R. Photogalvanic cells. Electrochim. Acta
1975, 20, 13-20.)and increases isc leading to
improvement in overall performance of the cell
(Shiroishi H, Yuuki K, Michiko S, Takayuki H.,
Tomoyo N, Sumio T, Masao K. Virtual Device
Simulator of Bipolar Photogalvanic Cell. Journal
of Chemical Software 200284754).
  • 2.4.1 Introduction
  • The photogalvanic cell technique provides a
    promising and unexplored method for solar power
    generation and storage.
  • Photogalvanic cells based on solution of dye
    photosensitizer, reductant, and NaOH are portable
    energy devices for decentralized solar power
    generation and storage. They are cheap,
    renewable, and relatively eco-friendly promising
    energy sources for the future. They have good
    electrical out, power storage capacity and

The photogalvanic cell is a
photoelectrochemical device involving ions as
mobile charges moving in solution through
diffusion process. In this cell, the solution
is the absorber phase contacted by two electrodes
with different selectivity to the redox reaction.
Alternatively, we can say that in the
photogalvanic cell, a dye in solution is
photoexcited (energy rich product), which in turn
can lose energy electrochemically to generate
electricity with inherent storage capacity, which
makes them superior to photovoltaic cells.
There is no consumption of chemicals during
charging and de-charging of these solar
cells(Tamilarasan R, Natarajan P.Photovoltaic
conversion by macromolecular thionine films.
Nature 1981292 224 225).
2.4.2. Survey of photogalvanic cellsFirst
of all, Rideal and Williams observed the
photogalvanic effect during the action of light
on the ferrous iodine- iodide equilibrium,
which later on was systematically investigated by
Rabinowitch in Fe (II)-Thionine system.
Rabinowitch suggested that the photogalvanic
effect might be used to convert sunlight into
electricity. To explore this suggestion, some
photogalvanic cells using the iron-thionine
system as the photosensitive fluid were tested .
The observed maximum power conversion efficiency
was 3 10-4 per cent.
  • The principal reason for the low efficiency was
    shown to
  • be polarization of the polished platinum
    electrodes and
  • rapid loss of the photochemical activity of the
  • Coating the electrodes with platinum black
    reduced polarization sufficiently.
  • In principle, it appeared possible to make
    further increases in efficiency by increasing
    electrode area and decreasing the electrolyte
  • The maximum power conversion efficiency that
    could be
  • achieved from a photogalvanic cell is between
    5 9 .

  • Photogalvanic cells have been studied
  • based on-
  • Chlorophyll-a plated Pt electrode and
  • free Pt electrode separated by a salt bridge,
  • aqueous ferric bromide,
  • ruthenium complex of dye ,
  • chromium complex in a Honda Cell,
  • micro-emulsions with micellar solution, etc.

  • In beginning, photogalvanics emphasized on coated
    Pt electrode with ferrous ion as reducing agent.
  • Later on, the researcher started using
  • - non-coated Pt electrode with saturated
    calomel electrode,
  • - dyes like methylene blue , azure-B , azure-A
    , fluoroscein ,toluidine blue , etc.,
  • - organic reductants like mannitol ,oxalic acid
    ,EDTA , etc. and
  • - surfactants like sodium lauryl sulphate
    ,Tween-80 , etc.
  • Friends, I belongs to this later group of
    researcher. I have chosen it because fabrication
    of cell is very easy, simple, and cheap.

My contribution to the field of
photogalvanics-1. Used following systems--
Brilliant Cresyl Blue dye - Fructose reductant
system Fuel, 90 (2011) p.3336 - Rhodamine B
dye Fructose reductant Renewable Energy, 37
(2012) p.250- Fast Green FCF- Fructose
Photogalvanic cell Applied Energy,118 (2014)
p.231-Naphthol Green B dye photosensitizer in
Photogalvanic cells Applied Solar Energy,
50(2014) p.67- Sudan I dye in natural sunlight
Arabian Journal of Chemistry, ARABJC-14-015,accep
ted on 25 Nov.2014- Comparative study of
various synthetic dye and natural photo
sensitizer present in spinach extract RSC
Advances, 4 (2014) p.46194- shown that under
similar conditions, all sensitizers single as
well as mixed gives nearly same result.
Therefore, people should focus on cheap and
renewable sensitizersRSC Advances, 4 (2014)
My contribution to the field of
photogalvanics- - By very simple means like use
of small size Pt, SCE component of combination
electrode, relatively more NaOH, cleaning Pt,
etc. Interesting fact lack of Pt and SCE proved
blessing in disguise for me.
power current efficiency
My own Arabian Journal of Chemistry, ARABJC-14-015, accepted on 25 Nov.2014. 1081.1 ?W 4200 ?A 13.5 ,
Bhimwal ,M.K. Gangotri, Energy. 36(2011) p.1324. 168.95 ?W 480 ?A 1.62 .
Comparison with other similar cells--There are
various other cells (like Photovoltaic cell- PV,
Dye sensitized solar cells(DSSC), etc.) which
directly converts sunlight in to electricity as
do the photogalvanic cell. -- It is
concluded that photogalvanic cells may be
promising future devices for solar power and
storage. It is also viewed that the photogalvanic
cells, with additional advantage of low cost and
storage capacity, can give electrical output
comparable to that for commercially used power
storage property lacking photovoltaic cells.-The
PV cell may be taken as a yardstick for
comparison and knowing the status of development
of the different kinds of cell as PV is the only
cell which is being used commercially world over.
Cell Current density potential efficiency
PG 52 mA/cm2 1 V 13.5
PV 35mA/cm2 0.6 V 17
DSSC 20 mA/cm2 0.7 V 11
I see photogalvanic cells as promising source for
future due to following beauty of these cells-1.
high electrical output2. short charging time,
3. can be charged even in very low intensity
illumination even inside room lacking direct
illumination4. tremendous inherent storage
capacity,5. easy simple construction,6.
reversibility with cycle of charging and
discharging7. solution if disposed off is
easily degradable as dye chemicals are already
photo decayed to some extant,8. solution can be
used in cleaning9. easy to replace solution10.
SCE and Pt reusable and non-consumable11.
expected cost low as no extra storage device is
needed, and all materials are durable and
What should be done now in photogalvanic cells1.
use of only renewable sensitizers as all
sensitizers give same result 2. design new
electrodes, vessels as all sensitizers give same
result3. study of assembly of cells for actual

At Sudan-I10.37 x 10-5 MFructose 2.37 x
10-3 M, NaLS 1.48 x 10-2 M, Pt electrode
area 0.4x 0.2 cm2, natural sunlight
intensity100 mWcm-2, diffusion length (DL)
6.3 cm,pH 13.74.
Cell Parameters
Voc (mV) 1048
t (min.) 25
imax (?A) 5800
isc (?A) 4200
Ppp (?W) 1081.1
t0.5 (min.) 31
CE () 13.5
FF 0.24
For each system, the cell performance is found to
be dependant on the concentration of the
reductant, and the highest cell performance is
observed at an optimum concentration of
reductant. The reason for this observation may be
that on the lower side of concentration range of
Fructose, there will be limited number of
Fructose molecules to donate electrons to dye,
therefore, there is low electrical output at
lower concentrations of Fructose whereas higher
concentration of Fructose will not permit (i) the
desired light intensity to reach the dye
molecules, and (ii) will also hinder the motion
of dye molecules towards electrodes and hence,
there will be corresponding fall in power of
cell.Reducing agent indeed acts as a regenerable
electron carrier Tamilarasan R, Natarajan
P.Photovoltaic conversion by macromolecular
thionine films. Nature 1981292 224 225 and
Kaneko M, Yamada A. Photopotential and
photocurrent induced by a tolusafranine
ethylenediaminetetraacetic acid system. Journal
of Physical Chemistry 1976 81 1213-1215.
For each system, the cell performance is found to
be dependant on the diffusion length, and the
highest cell performance has been observed at an
optimum diffusion length.Diffusion length
significantly affects performance of
photogalvanic cells as they are based on
diffusion of ionic species. It has been observed
that with an increase in diffusion length, the
photocurrent showed an increase and potential
showed decrease . As diffusion length
increases, the current increases as conductivity
of dye increases due to increase in volume of
solution between electrodes. The potential
decreases with diffusion length. The reason is
that concentration gradient disturbs the dye
(double layer) layer on Pt electrode. As
diffusion length is small, concentration gradient
factor is reduced and potential is increased.
  • With an increase in the temperature, the
    photocurrent (imax) of the photogalvanic cell is
    found to increase with a corresponding fall in
  • The change in voltage is much stronger than
    the change in current.
  • It is observed that with the increase in
    temperature (temperature range under observation)
    the power output of the cell increase slowly
    irrespective of the fall in photopotential. With
    temperature rise, the double layer on Pt is
    disturbed due to thermal motion.
  • So, the potential decreases with temperature
  • With temperature rise, the thermal motion and
    diffusion of ions increases leading to higher

  • The photocurrent and photopotential shows a
    increasing behaviour with the increase in light
    intensity. The increased light intensity
    increases the number of photons per unit area
    (incident power) striking the dye
    (photosensitizer) molecules around the platinum
    electrode and, therefore, an increase in the
    electrical output.
  • At lower light intensity, the number of
    photons may be few in comparison to dye molecules
    leading to few numbers of dye molecules for
    electron donation to Pt electrode .As the light
    intensity increases, the numbers of dye molecules
    for electron donation to Pt electrode increases
    and hence electrical parameters also increases.
  • At very high light intensity, the performance
    of cell decreases for probable reasons (i) the
    dye molecules are limited in number, so large
    number of photons remains unutilized, (ii) there
    is relatively less increase in power but high
    increase in intensity leads to lower efficiency
    as intensity is in denominator of formula of
    conversion efficiency, and (iii) higher intensity
    causes higher heating effect on cell leading to
    relatively poor performance of the cell. A water
    filter is used to cut off the thermal radiations
    and mitigate the heating effect.

For the observed effect of electrode
area, the better cell parameters is found for
small electrodes owing to relatively less
hindrance to diffusion of ions.
the variation of potential with time (during
charging) is as -
Fig. Variation of potential with time
We see that potential rises with time and reaches
to a highest value that is maximum potential as
also shown in Fig.
Variation of current with potential (i-V
characteristic) and power is as -

Fig. Variation of current with potential (i- V
characteristic of the cell) for Rhodamine B-
Fructose System.
We see that there is inverse relation between
current and potential. It means potential
increases as the current is decreased.
The variation of power with current is as in

Fig. Variation of power with current for
Rhodamine B Fructose System.
We see that maximum power from cell is obtainable
at some middle current (460 µA).