SOLAR ENERGY IN INDIA

1. SOLAR ELECTRICITY
lndian Perspective
NATIONAL SOLAR MISSION

2. Solar Photovoltaic Electricity
Indian Perspective from
2010
NATIONAL SOLAR MISSION

3. • The National Solar Mission, is a major
initiative of the Government of India and State
Governments to promote ecologically
sustainable growth while addressing India’s
energy security challenge.
It will also constitute a major contribution by
India to the global effort to meet the challenges
of climate change.
This is one of the several initiatives that are
part of National Action Plan on Climate Change.
The program was officially inaugurated in 2010
by Prime Minister of India.
•
•

5. NATIONAL SOLAR MISSION
The deployments across the application segments is envisaged
as follows
TARGET
S.
No
Application Segment Phase 1
(2010-13)
Phase 2
(2013- 17)
Phase 3
(2017-22)
1 Solar Thermal
Collectors
7
Million sq.
metres
15
Million sq.
metres
20
Million sq.
metres
2 Off Grid Applications 200 MW 1000 MW 2000 MW
3 Grid power, including
Roof top and small
plants
1,100 MW 4000-10,000
MW
20000
MW

6. Off-Grid Solar Applications
• Support viable business models, which are demand driven
• Multiple channels for rapid up-
scalinq
Renewable Energy Service Provider Companies (RESPCs):
• Provide energy services, including
and installation of equipment and
design, supply, integration
systems, maintenance and
operation and other related services to
consumers.
Micro finance & other financial institutions acting as Aggregators:
• Institutions involved tn consumer finance with customer base in
rural/urban areas and outreach through self help groups, etc.

7. PV
•
•
systems
are easily transportable and Installable.
can be used to generate electricity
where it will be used,
even at locations the electric grid
doesn’t reach.
PV is also modular, so installations can
be scaled to the appropriate size for a
given use
•
•

8. Small as well as medium scale
PV’s scalability allows it to be used for both
large-scale power plants and to
power handheld calculators, and it
•
•
distinguishes PV from fossil fuel based power.
• PV can be installed on buildings, parking lots
and other developed areas without interfering
with human activities.

9. Solar energy can be integrated
every part of Indian life—
into virtually
•
•
•
the
the
the
homes we live in,
offices where we work,
farms and factories that produce the
products we buy, and
the schools where our children learn.
With creativity and sound public policy,
solar energy can make a major contribution
to India’s energy future.
•
•

10. In solar photovoltaics, sunlight is converted into
electricity using a device called solar cell
• A solar cell is a
semiconducting device
made up of silicon or
other materials, which
when exposed to
sunlight, generates
electricity.

11. The nature and availability of
solar radiation
• In reality, the solar flux
density (same as power
density) varies between
250 and 2500 kilowatt
hours per meter squared
per year (kWhm-2 per
year).
As might be expected
the total solar radiation
is highest at the equator,
especially in sunny,
desert areas.
• Solar radiation arrives on the
surface of the earth at a
maximum power density of
approximately 1 kilowatt per
meter squared (kWm-2).
The actual usable radiation
component varies depending
on geographical location,
cloud cover, hours of
sunlight each day, etc.
•
•

12. .
Most parts of India get 300 days of sunshine a year, which makes
the country a very promising place for solar energy utilization.
The daily average solar energy incident over India varies from
4 to 7kWh/m2 with the sunshine hours ranging between 2300
and 3200 per year, depending upon location. The country receives
enough solar energy to generate more than 500,000TWh per year
of electricity, assuming 10% conversion efficiency for PV modules.
It is three orders of magnitude greater than the likely electricity
demand for India by the year 2015. The highest annual global
radiation is received in Rajasthan, northern Gujarat and parts of
Ladakh region. Other parts also receive fairly large amount of
radiation.

14. An example of a complete set of beam normal
insolation data for a given location is shown in Figure

16. Capacities of SPV
modules
SPV modules of various capacities are
available, and are being used for a variety of
applications. Theoretically, a PV module of
any capacity (voltage and current) rating can
be fabricated. However, the standard
capacities available in the country range from
5 Wp to 120 Wp. The voltage output of a PV
module depends on the number of solar cells
connected in series inside the module.
•

18. Science & technology of solar
Cells & Modules
Types of silicon solar cells
(Mono- crystalline, multi- crystalline,
Amorphous, Thin film)
Energy efficiency
and

19. Energy efficiency
A solar cell's energy conversion efficiency (η,
"eta"), is the percentage of power converted
(from absorbed light to electrical energy) and
collected, when a solar cell is connected to an
electrical circuit. This term is calculated using the
ratio of Pm, divided by the input light
irradiance under "standard" test conditions (E, in
W/m2) and the surface area of the solar
cell (Ac in m²).
•

20. Standard Current-Voltage (I-V) Curve
• The I-V Curve is an important technical aspect
of a solar module, the basis for understanding
all PV array design. It represents the possible
values of output current (I) and voltage (V)
that a solar module can deliver under specific
environmental conditions.

21. Standard Current-Voltage (I-V) Curve

22. Reading the I-V Curve
If the module is outputting to a 12-volt
battery, you can determine the watts output
to the battery from the graph. Read up from
12 volts to the IV curve and then over to the
Amperes scale to find that the current output
would be about 5.9 amps. Since power (in
watts) equals voltage times current, this
means that the module would be outputting
into the battery at a rate of about 71 watts.
•

25. Components & configuration
In every configuration all these
•
components are not used. Components
used depend
configuration,
upon the type of
which in other way
depend upon the application. For
example: Storage battery is not used in
case of direct coupled PV system,
inverter is not used in case of DC
load.

26. Important Components other than the PV Module
‘Balance of System’ (BOS)
Batteries for Storage of Electricity
•
• Electronic Charge Controller
• Inverter
• Mounting structure and tracking device

27. Battery banks
• Batteries are
using the DC
SPV module.
charged during the day time
power generated by the
• The battery bank supplies power to loads
during the night or non-sunny hours.

29. Inverter fundamentals
The inverters transform the DC power from
solar modules into AC power to match the grid
and be useful for most house loads.
•
• The inverter is a power conditioner that creates
pure sine wave power (AC.) This power is
cleaner than the grid because it is conditioned
right on site.

30. Maximum Power Point Tracking
(MPPT).
Inverters also maximize the power output of the
solar array in a function known as Maximum
Power Point Tracking (MPPT). Solar modules
produce the power at the voltage they are
connected to.
The maximum power point voltage changes as
the sun moves throughout the day and the
current (amps) gets higher and lower
.
This allows the inverter to produce the most
amount of power at any given time without frying
its circuitry.
•
•
•

31. Inverter failure
Inverters are the one component that needs to be replaced
periodically. Most systems installed today use a single inverter
for the entire system, so when it fails, the whole system stops
providing electricity to the home.
Possibly with an inverter for each panel or small group of
panels may be a solution. This has several advantages:
If an inverter fails, only one panel of the system will be affected,
which will be reported in our daily monitoring.
This allows for better scalability, in that we do not need to have
different inverter capacities for different system sizes.
The efficiency of the system is improved, since DC loses more
energy than AC going through a wire.
•
•
•
•
•

32. Available space
•A crucial factor is having enough space in the sun with
the proper orientation.
•The average home needs about a 5 kW system to offset
their annual usage.
•To calculate the physical size of this system, you can
use this simple rule of thumb:
•10 W / ft2 of space
•A 5 kW system covers about 500 ft2 of roof or ground
area.
•5000 W / 10 W/ft2 = 500 ft 2

33. Charge controllers/regulators -1
Why do you need a controller?
Main function is to fully charge a battery
without permitting overcharge. If a solar array
is connected to lead acid batteries with no
•
•
overcharge protection, battery life will be
compromised. Simple controllers contain a
relay that opens a charging circuit terminating
the charge at a pre-set high voltage and once
a pre-set low voltage is reached, closes the
circuit, allowing charging to continue.

34. Charge controllers/regulators - 2
• More sophisticated controllers have several
stages and charging sequences to assure the
battery is being fully charged. The first 70% to
80% of battery capacity is easily replaced. It is
the last 20% to 30% that requires more
attention and therefore more capacity.

35. Charge controllers/regulators -3
• The circuitry in a controller reads the voltage
of the battery to determine the state of
charge.
Designs and circuits vary, but most controllers
read voltage to reduce the amount of power
flowing into the battery as the battery nears
full charge.
•

37. solar electric generating
The largest solar electric
generating plant in the
world produces a
maximum of 354
megawatts (MW) of
electricity and is located
at Kramer Junction,
California. It produces
electricity for the grid
supplying the greater
Los Angeles area.
plant
•

38. Solar PV has one of the highest capital costs of all renewable
energy sources, but it has the lowest operational cost, owing to
the very low maintenance and repair needs. For solar energy to
become a widely used renewable source of energy, it is imperative
that the capital costs are reduced significantly for Solar PV. For a
solar PV power plant, the approximate capital cost per MW is Rs. 17
crores. This includes the cost of panels, the balance of systems, and
the cost of land and other support infrastructures In India, where
most regions enjoy nearly 300 sunny days a year, is an ideal market
for solar power companies. However, the high cost of light-to-
electricity conversion at Rs. 12 to Rs. 20 per kWh has acted as a
deterrent so far.

39. Standards for balance of system
components

40. Located at the 19th Milestone on the Gurgaon–
Faridabad road just
Solar cell testing
Photovoltaic module
testing
outside the boundary of Delhi.
•
•
•
•
Resource assessment
Technology
demonstration &
assessment
SPV power plant
Research and
Development
•
•
•
Testing of lighting systems
SPV pump testing
•
•
Battery testing for
applications
PV
• Long-term performance
evaluation of PV modules

41. Stand-alone system:
• Stand-alone systems are virtually self
sufficient and not interacted with grid.
Such system may have some
backup/storage system to run during the
no sun or low sun hour.
PV system without storage battery
(Direct coupled PV system)
DC system with storage battery
DC systems powering AC load
(with or without storage)
•
•
•

42. Solar DC Nano-grids –
A promising low-cost approach to village electrification
Several solutions involving solar photovoltaic electricity generation,
such as solar lanterns, solar home systems (SHS), and solar (AC)
mini-grids are being actively pursued to address the energy
requirements of the people. These current solutions each have certain
limitations, such as high cost for the cases of mini-grids and solar
home systems, or limited functionality and expandability in the case of
solar lanterns.
There is an approach to rural electrification – solar DC nano - grids –
which attempts to address these limitations by providing basic energy
services at lowest possible cost, while using a system architecture
which is expandable and future-proof.

43. Consider small clusters of closely-spaced houses (comprising
around 20 to 50 houses). The solar DC nano-grids that are
developed are sized to suit this typical housing arrangement. Each
nano-grid comprises a main solar photovoltaic array for electricity
generation co-located within the housing cluster with a main battery
for energy storage. The individual houses within the cluster are
connected to this main generation and storage facility via cables
and energy meters. Electricity is distributed via low-voltage direct-
current (DC), thus avoiding the cost of an inverter. Highest
efficiency low-power-consumption loads are provided along with
the nano-grid infrastructure to ensure that resistive cable losses are
kept to an acceptable level.

44. A central system monitoring and transmission device sends
information about the system status to the energy meters in the
individual houses which allows for flexible tariffing depending on the
state of charge of the main battery and the solar resource. Any
households within the cluster having existing solar home systems
may also be connected to the nano-grid via an energy meter,
meaning that existing SHS infrastructure is not rendered obsolete by
the arrival of the nano-grid. In future, higher voltage DC
interconnection of nano-grids between clusters may be implemented
to form a wider-area grid by a process of “swarm electrification”(Groh,
Philipp, Brian, & Kirchhoff, 2014).

45. For participation in the DC nano-grid, each household has to sign
up for a membership. The membership fee consists of a one-time
payment that ranges between 500 BDT and 750 BDT (6.4 – 9.6
USD). After signing up for the membership the energy meter is
installed in each house and connected to the nano-grid. The
equipment stays with each household for the time of the
membership. Energy services are provided through energy service
packages. These service packages are based on loads. In a first
approach, there will be three service packages for lighting, ranging
from 120 lm to 240 lm. By signing up for an energy package, the
load and required electricity to run the load are provided to the
household.

46. Energy service packages can be ordered by each household on a
monthly basis, giving maximum flexibility to the end-user. Through
this model, up to 20 h of light can be provided to a household for a
monthly price of only 100 BDT (1.3 USD).
The described payment model ensures that only high efficient loads
are used and furthermore helps to bridge the financing gap for the
end-user. In future, similar energy service packages for fans and TVs
will also be offered. The key concept behind the DC nano-grid
structure is the element of efficiency. The starting point of
implementation was chosen in Bangladesh due to the high level of
local technology development in this area.

47. PV modules, efficient lead acid battery as well as ultra-
efficient LED technology are developed and manufactured
in the country. This results in three critical factors:
a) The overall system sizing can be much smaller than
with regular loads.
b) Cable losses are kept at a minimum even with small
cross sections that would otherwise only be used for
higher voltages
c) The cost portion that is required for the appliances is
significant, reaching 20% of the total hardware costs.

48. Once energy efficient loads are applied, differentiated
electricity amounts can be granted to an individual user
thanks to the smart meter. These programmable devices
can allow a user to opt for different packages of
electricity access. These packages were designed under
guidance of the current ESMAP developments for
measuring energy access on a multi-tier framework
(Muench & Aidun, 2014; Tenenbaum, Greacen,
Siyambalapitiya, & Candelaria, 2014). Hence, the
number of lights, fan or TV and duration of service are
controllable by the user her / himself.

49. The SOLshare solution is an integrative approach, which
allows communities to set up their own efficient nanogrid
in which everyone can proactively participate. SOLshare
nanogrids create business opportunities. They allow
Solar Home System users to connect their system to the
SOLshare network to become electricity suppliers and
generate additional income. The SOLshare solution is
based on the principle of sharing. It is not only a service
for local communities; it is based on local communities.

50. Utilize your local capacities is one of ME SOLshare‘s main principles.
Everyone can decide if he wants to be a producer of electricity, a
consumer, or even both at one time (Prosumer).
Users without own Solar Home System can purchase electricity from
the SOLshare nanogrid. If a user produces more electricity than he
needs, electricity sharing allows him to feed electricity into the
SOLshare nanogrid. Both options are made possible through smart
metering technology. The equipment required to participate in
SOLshare nanogrids is the SOLshare Box. The SOLshare Box
incorporates advanced renewable energy electronics with a simple
and intuitive user interface. SOLshare Box is an advanced technology
product with a simple design. It is easy to understand and provides
access to the most relevant information whenever it is needed.

51. SOLshare Box allows the integration of already existing
and newly set up Solar Home Systems into the grid. This
principle enables the network to grow. To be part of a
SOLshare nanogrid, an own Solar Home System is not
absolutely necessary. As in usual nanogrid approaches,
electricity can simply be bought from the grid via the
SOLshare Box. The difference is that SOLshare allows
to feed electricity into the grid. The SOLshare
technology can be easily connected to most types of
standard Solar Home System.

52. SOLshare has successfully piloted the world’s first ICT-
enabled peer-to-peer electricity trading network for rural
households with and without solar home systems in
Shariatpur, Bangladesh. Along with its implementation
partner, the NGO UBOMUS, its financing partner IDCOL
and research partner United International Universit-
Centre for Energy Research, SOLshare combines solar
home systems and centralized mini-grids to enable more
rural households to access renewable electricity at a
lower cost.

53. The trading network interconnects households via a low-voltage DC
grid and controls power flows through bi-directional metering
integrated with an ICT backend; handling payment, customer service
and remote monitoring. Each SOLshare meter enables the user to
buy and sell renewable electricity with neighboring households,
businesses. People in rural area are now earning additional income
by selling their surplus electricity and at the same time, new users
have gained access to electricity for the first time in their life – without
any large, centralized grid. Trading renewable electricity through a
SOLshare village grid can unlock at least up to 30% excess
generation capacity of existing solar home systems. Through usage of
the full power generation capacity, more people benefit from a clean,
reliable source of electricity at a low cost.

54. MicroEnergy International GmbH. The SOLshare peer-to-peer
electricity trading network enables the interconnection of
households with and without solar home systems (SHS) into local
electricity trading networks; increasing individual SHS utility by up
to 30% and therefore providing more people with access to
renewable electricity at a lower cost.
Each meter is installed in a household with or without an existing
SHS. The device measures power inflows and outflows, contributes
to overall grid control, allows for personal preferences of the users
(i.e. buy or sell-only mode) and optimizes for battery state of
charge. Interconnected SOLshare meters form a SOLshare
electricity trading network, enabling peer-to-peer electricity trading
in the village.

55. DC Systems With Storage
Batteries-2:
Batteries are used to store the electrical
energy generated by the photovoltaic
modules .
Power can be drawn from the batteries
whenever required- during the day or night,
continuously or intermittently.
In addition, a battery bank has the capacity
to supply high surge currents for a short time.
This gives the system the flexibility to start large
motors or to perform other high power tasks.
•
•
•

57. PV power output management can be achieved with battery or other
electrochemical storage, pumped hydroelectric storage, or with diesel-
generator backup.

58. LED lighting
• Recently solar PV are coupled with Light
Emitting Diodes (LEDs) to give energy efficient
• Recent advancements in LED technology have
led to the development
diodes (WLEDs) .
WLEDs provide a bright
for domestic lighting .
The advantage of using
of white light emitting
• white light that's ideal
• LEDs with solar PV
systems is that the LED requires a much lower
wattage (less than conventional high efficiency
light bulbs), therefore
the size and the cost of the solar system is
much reduced for each household.
•

59. Utility grid interconnected
system:
A utility grid interactive photovoltaic system is
•
connected to the utility grid .
A specially designed inverter is used to transform
the PV generated DC electricity to the grid
electricity (which is of AC) at the grid voltage .
•
• The main advantage of this system is that power
can be drawn from the utility grid and when
power is not available PV can supplement that
power.
But again such grid interactive system
• is designed
with battery or without battery storage.

60. Parameters influencing PV
system operation
• Solar irradiation: Power of a solar cell
changes with solar radiation. which is
different for different geographical location,
tilt and orientation .. The change of power is
almost linear with the
a very little change in
(Voe) of the solar cell,
solar radiation. There
open circuit voltage
but the short circuit
is
current (Isc) varies almost linearly with the
solar intensity.

61. Parameters influencing
operation
PV system
• This affects the power,
which decreases at a
rate of about 0.45°/o per
degree rise in temp.
The operating
temperature of the
battery should be
nominal (25-35 degree
C). Higher temperature
may give a higher
capacity of battery but
at the same time 1t
reduces the life of the
battery.
• Temperature: Power
decreases with increasing solar
cell temp. Voltage decreases by
a value of approximately 3mV/K
for each degree rise in temp.
A solar cell with Vol. of 0.6 V at
25, C reaches a value of 0.45V
at 75 C. lsc increases with
rise of temperature but the
reduction in voltage is much
greater than the corresponding
increase in current.
•

62. Shading effect:
Shading has a very bad impact on the performance
of the PV system.
Even a partial shading (on one or two cells) of the
whole module can reduce the output drastically and
if it persists for a longer period, it may damage the
whole system.
To protect the modules from such adverse
effect, a bypass diode is used.
The effect is more prominent in crystalline silicon
solar modules.
Amorphous silicon modules are less affected by
shading.

63. Rural water pumping
applications
Water pumping and treatment systems
pumping for drinking water
pumping for irrigation
dewatering and drainage
ice production
saltwater desalination systems
water purification

64. Security systems &
Miscellaneous
•
•
•
•
•
•
security lighting
remote alarm system
electric fences
ventilation systems
calculators
pumping and
automated feeding
systems on fish farms
• solar water heater
circulation pumps
boat/ ship power
vehicle battery trickle
chargers
earthquake
monitoring systems
emergency power for
disaster relief
•
•
•
•

65. PV Manufacturers
in India
•
•
•
•
•
TATA
BHEL
BP
CENTRAL ELECTRONICS LTD
SELCO INDIA
PHOTON ENERGY SYSTEMS LIMITED

66. 66

67. 67

68. 68

69. While electric mobility powered by battery remains the mainstay of
automotive companies the world over, Tata Motors' dive into Fuel
Cell technology could also have positive ramifications for the
country's focus on lessening dependence on fossil fuels. "We
have successfully supplied 215 EV buses under FAME I and won
orders for 600 EV buses under FAME II. This order to supply PEM
Fuel Cell buses from a company as respected as Indian Oil
Corporation, further encourages our ongoing efforts on developing
India-focused alternative sustainable fuels to transform the future
of mobility in India," said Girish Wagh, President, Commercial
Vehicle Business Unit, Tata Motors.

70. Hydrogen-based fuel cell vehicles are being developed the
world over and are seen by many as a viable option in the
fight for clean and emission-free mobility. As such, Tata
Motors says that it will collaborate with the Research &
Development Centre of IOCL to also study the further
potential of Fuel Cell technology in commercial vehicles.
"This will be done by jointly testing, maintaining and
operating these buses for public transport in real-world
conditions in Delhi-NCR," a press statement from the
company informed. "The buses will be refueled by
hydrogen, generated and dispensed by IOCL."

71. Issues in managing solar electricity: References
• Denholm, P and R. M. Margolis, 2007, ‘Evaluating the
limits of Solar Photovoltaics in Traditional Electric
Power Systems’, Energy Policy, Vol 35, pp 2852 - 2861
Denholm, P and R. M. Margolis, 2007, ‘Evaluating the
limits of Solar Photovoltaics in Electric Power
Systems Utilizing Energy Storage and other Enabling
Technologies’, Energy Policy, Vol 35, pp 4424 – 4433
Lamont, Alan, 2008, ‘Assessing the Long Term System
Value of Intermittent Electric Generation
Technologies’, Energy Economics, , Vol 39, pp 1208 –
1231
•
•

72. Comparison of PV and Diesel-generator power
Kolhe, Mohanlal, Sunitha Kolhe and J.C. Joshi, 2002, “
Economic viability of stand alone photovoltaic system
in comparison with diesel powered system for India”,
Energy Economics, vol24, pp 155 – 165.
Stand alone PV systems in remote areas of India are
compared with the diesel-powered systems through
sensitivity analysis. PV systems are found to be the
lowest cost option for the daily energy demand of 15
kWh/day under unfavourable economic conditions
and upto 68 kWh / day under favourable conditions.
•
•

73. Among the elements of the action plan
are the following aims:
Deployment of 100,000 solar lanterns as
a
substitute for kerosene lanterns rural electrification
through PV systems covering 400 villages / hamlets
a special programme on water pumping systems
intensified R & D on technologies which can lead to
a reduction in cost
commercialisation of PV systems for applications by
giving a market orientation to the programme and
•
•
•
promoting manufacturing and
As a result of these measures
leading countries in the world
and use of PV technolocv.
related activities
India is among the
in the development
•

74. Textbooks of Solar energy Engineering
1. Principles of Solar Engineering, D. Yogi Goswamy,
2nd
Frank Kreith, Jan. F. Kreider, Edition, Taylor &
Francis, 2000, Indian Reprint, 2003, Ch. 9,
Photovoltaics, pp 411-446
2. Fundamentals for Solar Energy Conversion, Edward.
E. Anderson, Addison Wesley Publ. Co., 1983.
3.Fundamentals of Renewable Energy Sources, G. N.
Tiwari and M. K. Ghosal, Narosa Publ. House, New
Delhi, 2007, Ch. 2, Solar Energy, Ch. 3 Photovoltaic
systems pp 52 - 165

75. Textbooks of Solar energy Engineering
4. Wind and Solar Power systems, Mukund R Patel,
2nd Edition, Taylor & Francis, 2001
5. Roger Messenger and Jerry Ventre, Photovoltaic
2nd
Systems engineering, edition, CRC Press. 2003.
3rd
6.Solar Energy, edition, S.P
. Sukhatme and J. K.
Nayak, Tata McGraw-Hill Publ. Co., N. Delhi., 2008,
Ch. 9, Section 1, pp 313 - 331

76. An important reference book for
Systems
Practical Handbook of Photovoltaics:
Fundamentals and Applications
PV
•
Edited by: Tom Markvart and Luis Castaner
[2003]

77. Handbook of photovoltaic science and engineering
• Antonio Luque, Steven Hegedus
John Wiley and Sons, 2003 - 1138
pages
Handbook of Photovoltaic Science
and Engineering incorporates the
most recent technological
advances and research
developments in Photovoltaics. All
topics relating to the photovoltaic
(PV) industry are discussed and
each chapter has been written by
an internationally-known expert in
the field.

78. Photovoltaic solar
Adolf Goetzberger,
energy generation
Volker U. Hoffmann
• Springer, 2005 - Technology
& Engineering - 232 pages
This comprehensive description
and discussion of photovoltaics
(PV) is presented at a level that
makes it accessible to the
interested academic. Starting
with an historical overview, the
text outlines the relevance of
photovoltaics today and in the
future. Then follows an
introduction to the physical
background of solar cells and
the most important materials
and technologies, with
particular emphasis …..
•