Photogalvanic cells: Renewable and future energy
devices for solar power and storage
By
Dr. Pooran Koli
Assistant Professor
Solar Power & Storage Lab
Department of Chemistry, Jai Narain Vyas University
Jodhpur (Rajasthan) – 342033 INDIA
1
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 source?
*What to be done in the field of photogalvanic cells?
1. INTRODUCTION
Some supreme truths
- everyone/everything has to die,
- sometimes things can happen without money,
- but nothing can happen without the time &
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.
3
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) >Italy (23.1) > Japan > USA > China >Spain
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.
4
At India level scenario of total power
2.54 lakh Mega Watt was the established power
generation capacity in India as on 30 Sept,2014
(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).
5
At Rajasthan level
9500 Mega Watt was the established power
generation capacity in Rajasthan as on 31 Dec,2011
(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.).
6
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
7
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 variations,
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.
8
* 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 variations,
less penetration in life , etc.
Beauty of Renewable sources –
- their use is safe, clean and lasting .
9
Among the all renewable energy sources, the solar
energy has special significance for some reasons –
-
-
-
it is mother of all energy resources (except nuclear energy).
It is a renewable, cheap and clean energy source.
It is most abundant source of energy, yet least harvested.
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
planets.
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 life.
10
In theory, the entire present energy consumption of the world could be met by an area smaller than 1% of the world’s deserts if they were covered with solar thermal electric plants.
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 (2013–17) ,4000-10000 MW,
(3) Phase 3 (2017–22) , 20000 MW
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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 :
2.1. SOLAR CONCENTRATING POWER
2.2. SOLAR PHOTOVOLTAIC (SPV)
TECHNOLOGY
2.3. DYE- SENSITIZED SOLAR CELL
TECHNOLOGY
2.4. PHOTOGALVANIC CELLS,etc.
12
2.1 SOLAR CONCENTRATING POWER
* 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.
13
2.2 SOLAR PHOTOVOLTAIC (SPV) TECHNOLOGY
*
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 energy.
*
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.
14


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 circuit.
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).
15
2.3 DYE- SENSITIZED SOLAR CELL TECHNOLOGY



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 energy.
16
2.4 PHOTOGALVANIC CELLS

- Photogalvanic cells are galvanic cells which have property of solar
energy conversion and storage.
- This is the very simple technology on which I am working.
17
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.
18
* The experimental set up consists of –
- H-cell (photogalvanic cell),
- light source ( different wattage bulbs),
-digital pH meter- Systronics Model:335 (for measuring
potential in millivolt-mV),
- microammeter-OSAW (for measuring current in microampereµA),
- a carbon pot log 470 K device (for changing the resistance of
circuit),
- water filter (for filtering infrared radiations) and
- a circuit key (for closing and opening circuit).
19
* 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.
20
* 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 obtained.
21
* 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 performance.
* After charging of the cell, the circuit is closed and the
cell parameters like maximum potential (Vmax), opencircuit potential (Voc), maximum current(imax) and
equilibrium current(ieq) or short-circuit current(isc) are
measured.
22
* 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.
23
* 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 started).
* Photopotential (∆V) is equal to Vmax – Vdark .
24
* The CE and FF of the cell are calculated from equations (1) and
(2),respectively.
…(1)
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.
25
riplet state being relatively more stable than singlet state has role in storage capacity.
2.4 Mechanism of solar power generation & storage
-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 1981;292: 224 – 225, & Kaneko M, Yamada A. Photopotential and
photocurrent induced by a tolusafranine ethylenediaminetetraacetic acid system. Journal of
Physical Chemistry 1976; 81: 1213-1215).
26
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, 1320.)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
2002;8:47–54).
.
27
2.4 PHOTOGALVANIC CELLS
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 ecofriendly promising energy sources for the future. They
have good electrical out, power storage capacity and
efficiency.
28
* 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 decharging of these solar cells(Tamilarasan R, Natarajan P.Photovoltaic
conversion by macromolecular thionine films. Nature 1981;292: 224 – 225).
29
2.4.2. Survey of photogalvanic cells
*First 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.
30
* 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 dye.
* 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 resistance.
* The maximum power conversion efficiency that could be
achieved from a photogalvanic cell is between 5 & 9 % .
31
*
Photogalvanic cells have been studied
based on-
- Chlorophyll-a plated Pt electrode and Chlorophyll-a
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.
32
•
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.
33
My contribution to the field of photogalvanics1. 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-14015,accepted 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
sensitizers[RSC Advances, 4 (2014) p.46194].
34
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 %.
35
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.
-
Cell
Current density
potential
efficiency
PG
52 mA/cm2
1V
13.5 %
PV
35mA/cm2
0.6 V
17 %
DSSC
20 mA/cm2
0.7 V
11 %
- 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.
36
I see photogalvanic cells as promising source for future due to following beauty of
these cells1. high electrical output
2. short charging time,
3. can be charged even in very low intensity illumination even inside room lacking
direct illumination
4. tremendous inherent storage capacity,
5. easy & simple construction,
6. reversibility with cycle of charging and discharging
7. solution if disposed off is easily degradable as dye chemicals are already photo
decayed to some extant,
8. solution can be used in cleaning
9. easy to replace solution
10. SCE and Pt reusable and non-consumable
11. expected cost low as no extra storage device is needed, and all materials are
durable and reusable.
37
What should be done now in photogalvanic cells
1. use of only renewable sensitizers as all sensitizers give same result
2. design new electrodes, vessels as all sensitizers give same result
3. study of assembly of cells for actual application
38
Thanks
39
*At [Sudan-I]=10.37 x 10-5 M
[Fructose] = 2.37 x 10-3 M,
[NaLS] = 1.48 x 10-2 M,
Pt electrode area = 0.4x 0.2 cm2,
natural sunlight intensity=100
mWcm-2,
diffusion length (DL) = 6.3 cm,
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
pH =13.74.
40
ductant.
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 1981;292: 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].
41
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.
42
* With an increase in the temperature, the photocurrent
(imax) of the photogalvanic cell is found to increase with a
corresponding fall in Voc.
* 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 rise.
* With temperature rise, the thermal motion and diffusion
of ions increases leading to higher current.
43
* 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.
44
* 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.
45
* 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.
46
* 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.
47
* The variation of power with current is as in Fig. –
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).
48