Solar Energy, Solar Thermal and Solar Photovoltaic Basic Introduction

1. Solar Energy - Power from the Sun
• Most renewable energy comes either directly or indirectly from the sun.
• Direct solar energy is used every day, like when the sun shines on a
window and heats the room
• Solar energy can also be used indirectly to generate electricity in solar
cells

2. SOLAR ELECTRIC
Electricity can be generated in two
ways
i. Solar Thermal Electric
• Solar heat is used to drive heat engines,
which can be coupled to a generator to
produce electricity.
ii. Solar Photo Electric
• Sun rays can be converted directly to
electricity using Semi-Conductors Semi
Conducting photovoltaic cells i.e. Solar
Cell

3. Passive solar heating/cooling

4. Active solar heating
• Active solar heating is the gathering of solar energy by collectors that
are used to heat water or heat a building
• Solar collectors, usually mounted on a roof, capture the sun’s energy
• A liquid is heated by the sun as it flows through solar collectors
• The hot liquid is then pumped through heat exchangers, which heats
water for the building.

5. Active solar heating

6. Solar Concentrating
Collectors

7. Introduction
• For applications such as air conditioning, central power generation,
and numerous industrial heat requirements, flat plate collectors
generally cannot provide carrier fluids at temperatures sufficiently
elevated to be effective.
• Alternatively, more complex and expensive concentrating
collectors can be used.
• These are devices that optically reflect and focus incident solar
energy onto a small receiving area.
• As a result of this concentration, the intensity of the solar energy is
magnified, and the temperatures that can be achieved at the
receiver (called the "target") can approach several hundred or
even several thousand degrees Celsius.
• The concentrators must move to track the sun if they are to
perform effectively

8. Concentrating collectors
• Concentrating, or focusing, collectors intercept direct radiation over
a large area and focus it onto a small absorber area.
• These collectors can provide high temperatures more efficiently
than flat-plate collectors, since the absorption surface area is much
smaller.
• However, diffused sky radiation cannot be focused onto the
absorber.
• Most concentrating collectors require mechanical equipment that
constantly orients the collectors toward the sun and keeps the
absorber at the point of focus.
• Therefore; there are many types of concentrating collectors

9. Types of concentrating collectors
 Parabolic trough system
 Parabolic dish
 Power tower
 Stationary concentrating collectors
There are four basic types of concentrating collectors:

10. Parabolic trough system
Parabolic troughs are devices that are shaped like the letter
“u”. The troughs concentrate sunlight onto a receiver tube
that is positioned along the focal line of the trough.
Figure 3.1.2 Parabolic trough system
Figure 3.1.1 Crossection of parabolic trough

11. Parabolic troughs often use single-axis or dual-axis
tracking
Figure 3.1.3 One Axis Tracking Parabolic Trough
with Axis Oriented E-W
Figure 3.1.4 Two Axis Tracking Concentrator

12. Temperatures at the receiver can reach 400 °C and
produce steam for generating electricity. Multi-megawatt
power plants have been built using parabolic troughs
combined with gas turbines (California).
Figure 3.1.5 Parabolic trough combined with gas turbines

13. Parabolic dish systems
A parabolic dish collector is similar in appearance to a large
satellite dish, but has mirror-like reflectors and an absorber
at the focal point. It uses a dual axis sun tracker
Figure 3.2.1 Crossection of parabolic dish

14. A parabolic dish system uses a computer to track the sun
and concentrate the sun's rays onto a receiver located at
the focal point in front of the dish. Parabolic dish systems
can reach 1000 °C at the receiver.

15. Power tower system
A heliostat uses a field of dual axis sun trackers that
direct solar energy to a large absorber located on a
tower. To date the only application for the heliostat
collector is power generation in a system called the
power tower (solar tower)
Figure 3.3.2 Heliostats
Figure 3.3.1 Power tower system

16.  A heliostat (from helios, the Greek word for sun, and
stat, as in stationary) is a device incorporating a
mirror which moves so as to keep reflecting sunlight
toward a predetermined target or receiver, despite
the sun's apparent motions in the sky.
 The target is stationary relative to the heliostat, so
the light is reflected in a fixed direction.
 Most modern heliostats are controlled by computers.
The computer is given the heliostat's position on the
earth (latitude and longitude) and the time and date,
and uses them to calculate the direction of the sun as
seen from the mirror.

17. A power tower has a field of large mirrors that follow the
sun's path across the sky. The mirrors concentrate
sunlight onto a receiver on top of a high tower. A
computer keeps the mirrors aligned so the reflected rays
of the sun are always aimed at the receiver, where
temperatures well above 1000°C can be reached. High-
pressure steam is generated to produce electricity.
Figure 3.3.3 Power tower system with heliostats

18. Solar Photo-voltaic (PV) Systems

19. How electricity is generated through
Solar Energy?
 Solar photo voltaic (SPV). Can be used
to generate electricity form the sun.
 Silicon solar cells play an important role
in generation of electricity.

20. Photovoltaic cells
Sunlight falls on a semiconductor,
causing it to release electrons.
The electrons flow through a
circuit that is complete when
another semiconductor in the
solar cell absorbs electrons and
passes them on to the first
semiconductor.

21. How solar cells Generate electricity

22. 22
Absorption of Light by Atoms
Sources: http://members.aol.com/WSRNet/tut/absorbu.htm, http://csep10.phys.utk.edu/astr162/lect/light/absorption.html
Single electron
transition in an
isolated atom
• Absorption occurs only when the energy of
the light equals the energy of transition of
an electron
Light

23.  In dye-sensitized
solar cells…
 Talk about highest
occupied molecular
orbital (HOMO) and
lowest unoccupied
molecular orbital
(LUMO)
23
So What Does this Mean for Solar Cells?
Source: Original Images
• In single-crystal silicon
solar cells…
– Talk about “conduction
band” (excited states)
and “valence band”
(ground states)

24. 24
How a Silicon-Based Solar Cell
Works
Source: http://nanosense.org/activities/cleanenergy/solarcellanimation.html
• A positive “hole”
is left in the
electron’s place
• This separation of
electrons and holes
creates a voltage
and a current
• Light with energy greater than the band gap energy
of Si is absorbed
• Energy is given to an electron in the crystal lattice
• The energy excites the electron; it is free to move
Click image to launch animation
(requires web access)

25. Solar Cell Schematic
.
.
Protective Cover-Glass
Electrical Contact
Antireflective Layer
N
P-N Junction
P
Electrical Contact
Load
current
P

26.  Sunlight is made of photons, small particles of energy.
 These photons are absorbed by and pass through the material of a
solar cell or solar PV panel.
 The photons 'agitate' the electrons found in the material of the
photovoltaic cell.
 As they begin to move (or are dislodged), these are 'routed' into a
current.
 This, technically, is electricity - the movement of electrons along a
path.
The Process

27. Working Principle of Solar Cell
27
Source: https://www.youtube.com/watch?v=j1jF3in2JUE

28. From Cells to Modules
 The open circuit voltage of a single
solar solar cell is approx 0.5V.
 Much higher voltage voltage is
required for practical application.
 Solar cells are connected in series to
increase its open circuit voltage.

29. Groups of solar cells can be packaged into modules,
panels and arrays to provide useful output voltages and
currents to provide a specific power output.

30. 30

31. • Mono-crystalline solar panels,
silicon is formed into bars and
cut into wafers.
• These types of panels are called
“mono-crystalline” to indicate
that the silicon used is single-
crystal silicon.
• These cell is composed of a
single crystal, the electrons
that generate a flow of
electricity have more room to
move.
• As a result, monocrystalline

32.  Polycrystalline solar
panels are also made
from silicon.
 Polycrystalline solar
panels are also
referred to as “multi-
crystalline,” or many-
crystal silicon.
 There are many
crystals in each cell,
there is to less
freedom for the
electrons to move.
 As a result,
polycrystalline solar
panels have lower
efficiency ratings than
monocrystalline

33. pervoskite
solar cell
Advantages
 High power to weight ratio
 High power to cost ratio
 Minimum materials per Watt
 High absorption Capabilities
 Flexible and easy to install
 Simple manufacturing
 Convenience of shape and size
Fig: Flexible
Substrate

34. Solar Cell Efficiencies
1st Generation 2nd
Generation
3rd Generation
Mono Poly a-Si CdTe DSSC PSC
22-25% 14-
18%
6-
7.7%
9-
12.5%
13-14% 25%

35. Solar cell
 In principle, a solar cell is a junction device obtained
by placing two electronically dissimilar materials
together with a thin barrier.
 Solar cell works on the principle of photo-electric
effect i.e. the ejection of electrons from the metal
surface in response to incident light.
 The basic steps of photovoltaic energy conversion
 Light absorption
 Charge separation
 Charge collection.
35

36. Plasmonic Effect
 Surface plasmon resonance (SPR)
has the optical control ability to
trap light in solar cells.
 The metal NP boost the light
absorption capability of dye
molecules
 Core-Shell Ag@TiO2
Nanostructure avoid the metal
core from being degraded by dye
molecules and electrolyte 
Fig. Surface Plasmon Resonance
Fig. Core-Shell Nano particle Structure

37. Shell Thickness Effect
Fig. Illustration of LSPR and UV-VIS Absorption Spectra of Cu@TiO2 NS with Shell Thicknesses of 3, 5,
7, and 10 nm (blue, green, pink and red respectively)

38. Electric Field Intensity Distribution
Fig. EFI Distribution of Cu@TiO2 by FDTD Analysis at 520nm for Shell Thickness of (a) 3nm (b) 5nm (c)
7nm (d) 10nm

39. Results of Objectives-2
• The photo-anode based on Titanium Oxide, Graphene
Oxide, and their bilayer composite were modeled
using COMSOL Multiphysics
Figure: Photo-anode based on (a) Graphene oxide, (b) Titanium oxide
and (c) bilayer composite of Graphene oxide/Titanium oxide (GO/TiO2)

40. Absorption VS Wavelength
• DSSC based on bilayer
composite materials has
broadband absorption
(24.4%) as compared to
that based on pure TiO2
and GO layers.
• Bilayer structure that
resulted in a larger
surface area for dye
loading.
• As the coming light
trapped for a long time
so the photon interaction
with the dye molecules is
increased and produces
many excited electrons
that jump to the
conduction band of
GO/TiO .
Fig. 3 UV-Visible absorption spectrum of
oxides based photo-anode without silver
nanoparticles

41. Selected Figures from Paper 4
Fig. 1. various geometries of aluminum nanoparticles embedded in
SiO2
Fig. Schematic diagram of Composite bilayer structure of TiO2/SiO2
photoanode based on (a) spherical-shaped (b) nanorod/nanosphere (c)
nanosphere/nanorod

42. Conclusion from the
Characteristics.
 Power of the module has only single
maxima.
 Peak Power of the module changes
with the change in temperature.
 Need to track the peak power in
order to maximize the utilizations of
the solar module/array.

43. Photo-voltaic systems: Applications
Using the
sun to
generate
electricity

44. Solar Home Systems
Space
Water
Pumping
Telecom
Main Application Areas – Off-grid

45. Residential Home
Systems (2-8 kW)
PV Power Plants
( > 100 kW)
Commercial Building
Systems (50 kW)
Main Application Areas - Grid-connected