1. Solar Power Plant Technologies

M. Nageswar Rao,
Sr.Mgr.(EMD)
Date: 24.10.2015
Venue: EDC, Simhadri

Presentation layout
 Solar radiation & resources
 Solar power technologies
 Govt. policies
 Solar PV
 Solar Thermal
 Solar power distribution
2

Solar energy
 The surface receives
about 47% of the total
solar energy that
reaches the Earth. Only
this amount is usable.
4

NTPC Solar projects
 Commissioned (110 MW)
 Under execution (8MW)
 8 MW hydro energy based project at NTPC-Singrauli in Uttar
Pradesh. 5

Insolation
 Insolation is a measure of solar radiation energy
received on a given surface area in a given time.
 It is commonly expressed as
 average irradiance in watts per square meter (W/m2), or
 kWh/sq. m/day
6

Direct insolation
 Direct insolation is the solar irradiance measured at a given location
on Earth with a surface element perpendicular to the Sun's rays,
excluding diffuse insolation (the solar radiation that is scattered or
reflected by atmospheric components in the sky).
 Direct insolation is equal to the solar constant minus the atmospheric
losses due to absorption and scattering.
 While the solar constant varies with the Earth-Sun distance and solar
cycles, the losses depend on the time of day (length of light's path
through the atmosphere depending on the Solar elevation angle),
cloud cover, moisture content, and other impurities.
 Insolation is a fundamental abiotic factor affecting the metabolism of
plants and the behaviour of animals.
7

Solar radiation
 Solar radiation is received as heat and light.
 Availability of reliable solar radiation data is vital for
the success of solar energy installations in different
sites of the country.
 Solar radiation data is available in the form of
8
solar radiation data Application
Global Horizontal Irradiance (GHI) for flat solar
collectors
Solar PV
Direct Normal Irradiance (DNI) for solar
collectors/
concentrators.
Solar Thermal

GHI
 Most parts of India
receive good solar
radiation 5.5- 6
kWh/sq. m/day

DNI
 Most parts of India
receive good solar
radiation 5- 5.5
kWh/sq. m/day

Solar power applications
 Solar PV
 Roof-top
 Solar farms
 Solar thermal
 Power Tower
 Parabolic Trough
 Parabolic dish
 Grid connectivity
 Off-grid
 On -grid

Solar power technologies
 Solar PV
 Certain semiconductors when exposed to light
produce an electric current.
 Efficiency of Solar PV systems range from 14% - 36%.
 Solar thermal
 Heat from the sun is used to heat large amounts of
water which is then used to drive turbines.
 Efficiency of Solar Thermal system is around 22%.
13

Tilt of panel
 Maximizing exposure
with direct sunlight is
achieved by
 Avoiding shade
 Exposing the panels to the
most direct sunlight for
greatest amount of time
 Tilt and azimuth
14

Tilt and azimuth
 Tilt of the array
 is the angle of inclination from horizontal (0° = horizontal, 90° =
vertical).
 installers aim for a tilt equal to the geographic latitude minus 15 degrees
in order to achieve yearly maximum output of power.
 An increased tilt will favor power output in the winter months, which is
often desired for solar water heating, and a decreased tilt will favor
power output in summer months.
 The azimuth
 is the angle clockwise from true north of the direction that the PV array
faces (0 or 360 = North, 180 = South).
 Solar installations in the Northwest should generally be designed with
an azimuth within 45 degrees of true south (180) to maximize energy
production.
 Increasing the azimuth angle favors afternoon energy production, while
decreasing the azimuth angle favors morning energy production. 15

Solar tracker
 A tracking system is one that moves to track the sun.
 There are two different axes that can be tracked
 the tilt which would change over the course of a year, and
 the azimuth, which would change over the course of a day.
 Tracking with either a one or two axis system allows the PV
production to stay closer to maximum capacity for many additional
hours.
 Note:
 All modules wired to one inverter (or all modules sharing a string in the
case of a multi-string inverter) should be mounted at the same tilt and
azimuth.
 This is to maintain consistent voltage production throughout the array
(or string).
 If voltage differences occur, energy production from the entire array may
be compromised. 16

JNNSM
 The Jawaharlal Nehru National Solar Mission was
launched on the 11th January, 2010 by the Prime Minister
under National Action Plan on Climate Change.
 The Mission has set the ambitious target of deploying
20,000 MW of grid connected solar power by 2022 is
aimed at reducing the cost of solar power generation in
the country through
 (i) long term policy;
 (ii) large scale deployment goals;
 (iii) aggressive R&D; and
 (iv) domestic production of critical raw materials, components and
products, as a result to achieve grid tariff parity by 2022.
18

19
JNNSM - 3 phase approach
Application segment Target for
Phase I
(2010-13)
Cumulative
Target for
Phase 2
(2013-17)
Cumulative
Target for
Phase 3
(2017-22)
Grid solar power
incl. roof top &
distribution grid
connected plants
1,000 MW
100 MW
4,000 MW
10,000 MW
20,000 MW
Off-grid solar
applications
200 MW 1,000 MW 2,000 MW
Solar collectors 7 million
sq meters
15 million
sq meters
20 million
sq meters

JNNSM- RPO
 The key driver for promoting solar power is through
a Renewable Purchase Obligation (RPO) mandated
for power utilities, with a specific solar component.
 This will drive utility scale power generation,
whether solar PV or solar thermal.
 The Solar Purchase Obligation will be gradually
increased while the tariff fixed for solar power
purchase will decline over time.
 As per the National Tariff Policy, it is envisaged that
the targets for Solar RPO shall be
 0.25% by 2012-13 extending to 3% by 2022

JNNSM- RPO
 Solar Power Capacity Requirement By 2022

JNNSM- REC
 Another mechanism being used by the Government is the REC.
 Renewable Energy Certificate (REC) mechanism is a market
based instrument to promote renewable energy and facilitate the
compliance of RPOs.
 Through RECs, states that do not have sufficient potential for
renewable energy can trade with those that have surplus of such
resources.
 One REC is treated as equivalent to 1MWh.
 RECs are available for solar as well as non solar applications.
 Revenue for the renewable energy generator can come from the
sale of electricity as well as from the sale of environmental
attributes in the form of these certificates.
 The RECs shall be exchanged through Power Exchanges
authorised by CERC.
 The price range shall be within the band of floor price and
forbearance price to be determined by CERC from time to time.

JNNSM- REC
 Forbearance Price: It is the highest difference between the CERC tariff
and the APPC across states.
 Floor Price: This is the price to keep the project viable in terms of
meeting the O&M expenses, Interests on loan and working capital,
principal repayment etc. It is taken as the highest difference between the
minimum requirement for project viability and respective state APPC of
pervious year.
 The proposed downward revision is in line with the practices in other
countries (say Germany) where the Feed-in-Tariff (FiT) is periodically
reduced. It is known as digression and is done to ensure that the subsidy
(offered as FiT) follows the falling market prices of the renewable energy
systems.

Solar PV power
 Roof-top application
 Solar farms
26

How does power produce
 Sunlight is composed of photons, or bundles of
radiant energy.
 When photons strike a PV cell, they may be
reflected or absorbed (transmitted through the
cell). Only the absorbed photons generate
electricity. When the photons are absorbed, the
energy of the photons is transferred to electrons
in the atoms of the solar cell.
 Solar cells are usually made of two thin pieces
of silicon, the substance that makes up sand
and the second most common substance on
earth.
 One piece of silicon has a small amount of
boron added to it, which gives it a tendency to
attract electrons. It is called the p-layer because
of its positive tendency.
 The other piece of silicon has a small amount of
phosphorous added to it, giving it an excess of
free electrons. This is called the n-layer because
it has a tendency to give up negatively charged
electrons.

PV cell types
 Crystalline-Silicon Solar Panels
 Thin-Film Solar Panels
30

Crystalline-Silicon Solar Panels
 Advantages
 stable,
 efficiencies in the range of 15% to 25%,
 relies on established process technologies
 proven to be reliable most common solar cells in
use.
 Disadvantages
 poor absorber of light, it needs to be fairly thick
and rigid.
 Construction
 A basic c-Si cell consists of essentially seven
layers.
 A transparent adhesive holds a protective glass
cover over the anti-reflective coating that
ensures all of the light filters through to the
silicon crystalline layers.
 N layer sandwiches against a P layer and the
entire package is held together with two
electrical contacts: positive topside and negative
below. 31

Thin-Film Solar Panels
 Potentially cheaper
 less efficient
 Types of thin-film solar cells:
 amorphous Silicon (a-Si) and
 Thin-film Silicon (TF-Si);
 Cadmium Telluride (CdTe);
 Copper Indium Gallium Deselenide (CIS or
CIGS); and
 Dye-sensitized Solar Cell (DSC) plus other
organic materials.
 Construction
 consist of about six layers.
 a transparent coating covers the antireflective
layer.
 These are followed by the P- and N-type
materials, followed by the contact plate and
substrate.
 And, obviously, the operating principle
(photovoltaic) is the same as c-Si cells.
32

Crystalline vs. thin film
33
Cell Technology Crystalline Silicon Thin Film
Types of Technology
Mono-crystalline silicon (c-Si)
Poly-crystalline silicon (pc-Si/ mc-Si)
String Ribbon
Amorphous silicon (a-Si)
Cadmium Telluride (CdTe)
Copper Indium Gallium Selenide (CIG/ CIGS)
Organic photovoltaic (OPV/ DSC/ DYSC)
Voltage Rating (Vmp/ Voc)
(Higher is better as there is less gap
in Voc and Vmp)
80%-85% 72%-78%
Temperature Coefficients Higher
Lower
(Lower is beneficial at high ambient temperatures)
I-V Curve Fill Factor
(Idealized PV cell is 100%)
73%-82% 60%-68%
Module construction With Anodized Aluminum
Frameless, sandwiched between glass;
lower cost, lower weight
Module efficiency 13%-19% 4%- 12%
Inverter Compatibility and Sizing
Lower temperature coefficient
is beneficial
System designer has to consider
factor such as temperature coefficients,
Voc-Vmp difference, isolation resistance due to external
factors
Mounting systems Industry standard
Special clips and structures may be needed. In some cases
labor cost is significantly saved
DC wiring Industry standard May require more number of circuit combiners and fuses
Application Type Residential/ Commercial/ Utility Commercial/ Utility
Required Area Industry standard
May require up to %50 more space
for a given project size
Example Brands
Kyocera, Evergreen, Sanyo, Schuco,
Canadian Solar, Sharp,
Yingli, ET Solar, Solon, Schott, Conergy, REC,
Solarworld
First Solar, Solyndra, UniSolar, Konarka, Dye Solar, Bosch
Solar, Sharp, Abound Solar

I-V characteristics
34
 The usable voltage from solar cells depends
on the semiconductor material. In silicon it
amounts to approximately 0.5 V.
 Terminal voltage is only weakly dependent on
light radiation, while the current intensity
increases with higher luminosity.
 A 100 cm² silicon cell, for example, reaches a
maximum current intensity of approximately
2 A when radiated by 1000 W/m².
 The output (product of electricity and voltage)
of a solar cell is temperature dependent.
 Higher cell temperatures lead to lower output,
and hence to lower efficiency.
 The level of efficiency indicates how much of
the radiated quantity of light is converted into
useable electrical energy.

P-V characteristics
 MPPT
36

Growth in India PV production
37
20 23 36 45
65 80
135
240
300
600
20 22 25 32 37 45
110
175
240
320
2001-02
2002-03
2003-04
2004-05
2005-06
2006-07
2007-08
2008-09
2009-10
2010-11
Year
0
100
200
300
400
500
600
700
ProductioninMW
Solar
Cell
PV
Module

Status of PV in India
38
Lights
90
Pumps
14
Off grid Plants
62
Grid Plants
1044
Railways
55
Telecom
65
Others
270
Int Projects
1000
2600 MW : 53,00,000 SYSTEMS

Grid solar PV in India
 1044 MW capacity new Grid Solar Power
projects commissioned by September, 2012 in
16 States.
39
Gujarat
680
Rajasthan
199
A. P.
22
Maharashtra
20
Jharkhand
16
T. N.
15
Karnataka
14
Others
80

PV Capital Cost & CERC
Tariff Trends
40

Proposed cost target for
PV by 2017
 PV Module : < Rs. 30 per Wp
 BoS : < Rs. 25 per Wp
 Cost of Electricity : ~ Rs. 4 - 6 per kWh
41

Projection for Grid Parity in
India
42
0
2
4
6
8
10
12
14
2010-11 2011-12 2012-13 2013-14 2014-15 2015-16 2016-17 2017-18 2018-19 2019-20 2020-21 2021-22
Solar
Tariff 5%
Tariff 3%
HT Tariff 3%

Efficiency and disadvantages
 Efficiency is far lass than the 77% of solar spectrum
with usable wavelengths.
 43% of photon energy is used to warm the crystal.
 Efficiency drops as temperature increases (from 24%
at 0°C to 14% at 100°C.)
 Light is reflected off the front face and internal
electrical resistance are other factors.
 Overall, the efficiency is about 10-14%.
 Underlying problem is weighing efficiency against
cost.
 Crystalline silicon-more efficient, more expensive to
manufacture
 Amorphous silicon-half as efficient, less expensive to
produce. 43

Reflector/ Collector types
 Linear Fresnel
reflectors with Linear
collector tubes
 Heliostats with
Central receiver
 Parabolic dish with
receiver
 Parabolic trough with
Linear collector tubes
45

Parabolic Trough
 Sunlight focused on heat transfer fluid (HTF), which
then runs steam turbine

Parabolic Trough power plant
49

 All the collectors track the path of the sun on their longitudinal axes.
The mirrors concentrate the sunlight more than 80 times on a metal
absorber pipe in the line of focus. This pipe is embedded in an
evacuated glass tube to reduce heat loss.
 A selective coating on the absorber tube surface lowers emission
losses. Either water or a special thermal oil, runs through the
absorber tube.
 The concentrated sunlight heats it up to nearly 400 °C, evaporating
water into steam that drives a turbine and an electrical generator.
After passing through the turbine, the steam condenses back into
water that is returned to the cycle . 50

 A fossil burner can drive the water-steam cycle during periods
of bad weather or at night.
 In contrast to photovoltaic systems, solar thermal power
plants can guarantee capacity. This option increases its
attractiveness and the quality of planning distribution over
the grid.
 Thermal storage can complement or replace the fossil burner
so that the power plant can be run with neutral carbon
dioxide emissions. In this case, heat from storage drives the
cycle when there is no direct sunlight.
 Biomass or hydrogen could also be used in the parallel burner
to run the power plant without carbon dioxide emissions. 51

Power tower
• A solar thermal plant
consists of mirror
reflectors called
heliostats
• Produces electricity
by reflecting sunlight
on to the central
receiver.
53

Heliostats
• They direct and
concentrate the solar
radiation onto a central
receiver.
• Many parameters must
be optimized, in the
design of a solar thermal
plant
• The parameters are
– Location
– Shading and
– Blocking
54

Shading & blocking
 Shading occurs when
a heliostat casts its
shadow on another
heliostat located
behind it
• Blocking occurs when
a heliostat in front of
another heliostat,
blocks the reflected
suns energy on its
way to the receiver. 55

Power tower
 General idea is to collect the light from many reflectors spread over a
large area at one central point to achieve high temperature.
 Example is the 10-MW solar power plant in Barstow, CA.
 1900 heliostats, each 20 ft by 20 ft
 a central 295 ft tower
 An energy storage system allows it to generate 7 MW of electric
power without sunlight.
 Capital cost is greater than coal fired power plant, despite the no cost
for fuel, ash disposal, and stack emissions.
 Capital costs are expected to decline as more and more power towers
are built with greater technological advances.
 One way to reduce cost is to use the waste steam from the turbine for
space heating or other industrial processes.
56

Power tower power plant
57
Power tower in Barstow,
California.

Power tower power plant
 The solar field of a central receiver system, or power tower, is
made up of several hundred or even a thousand heliostats,
placed around a receiver at the top of a central tower.
 A computer controls each of these two-axis tracking heliostats
with a tracking error of less than a fraction of a degree to
ensure that the reflected sunlight focuses directly on the
tower receiver, where an absorber is heated up to
temperatures of about 1000 °C by the concentrated sunlight.
 Air or molten salt transports the heat and a gas or steam
turbine drives an electrical generator that transforms the heat
into electricity.
58

Parabolic dish
 Because they work best
under direct sunlight,
parabolic dishes and
troughs must be steered
throughout the day in the
direction of the sun.
60

Solar Generated Electricity
Distribution Approaches
 Centralized (CSP)
 Distributed (PV Roof Installations)

Centralized
 Advantages
 Traditional model of
distribution
 No fuel costs
 Disadvantages
 Non-Constant Power
 Vulnerability
This PV Array is part of the
Sacramento Municipal Utility
District, generating 3.2 MW,
enough for 2,200 homes.

Distributed Solar (PV)
 Advantages
 Net-metering
 Grid Storage
 Flexibility
 Reduced vulnerability to
terrorist attack
 Almost no maintenance
 Negligible environmental
impact
 Domestic Production (?)
 Disadvantages
 Cost
 Extensive Individual
Investment
 Low Conversion Efficiency
 CCR’s
 Intermittency

Roof top grid connected
 The cost of setting up a 5-KW unit is around Rs 7.5
lakh and requires 2,000 sq feet of roof space.
 After signing a Power Purchase Agreement with the
discoms, the house owner will pay Rs 3 lakh, on
which he will get returns of close to Rs 60,000 per
annum.
66

Net-Metering
 Peak generation from PV occurs during the day
 Net-metering allows users to “bank” electricity they generate, and
credit it against the electricity they use
 Most states won’t pay users if they generate more electricity than they
use, but they can “zero-out” their accounts
 As of 2007, net-metering is offered to some degree in 41 states and
D.C.
 California, New York, Texas
 Net-metering is offered in Illinois by one or more individual utilities
 EPAct of 2005 requires all states to offer net-metering by 2008

1. Solar Power Plant Technologies

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