Solar Energy
Solar Energy
• Perpetual/Continuous resource: remain
available in the same measure for an
indefinitely long time
• Origin: Thermonuclear fusion reactions
occurring in the sun
• 30 days of sunshine = the energy equivalent
of the total of all the planet’s fossil fuels
Advantages
• Radioactive byproducts remain behind on the
sun
• Running costs are low.
• No CO2 emissions- Reduced Greenhouse Effect
• No SO2 emissions to cause acid rain.
• Only pure radiant energy reaches the Earth
Disadvantages
• Solar energy is intermittent: dependent on
weather conditions and the time of day
• Solar energy is a diffuse source: Must
concentrate to harness.
• High initial cost of solar cells
Two Categories
Solar Thermal
Solar Photovoltaic (PV)
For Water Heating
For Electricity Production
Solar Thermal Energy
• Using solar thermal technologies for heating
fluids which can be used as a heat source or to
run turbines to generate electricity.
Solar thermal : How does it work?
Solar photovoltaics
• Solar Electric Systems
• Photovoltaic (PV) systems convert light
energy directly into electricity.
• Commonly known as “solar cells.”
• Simplest Ex: calculators
Semiconductors
• Conductivity can be readily modulated (by
doping or electrical potential) offering a
pathway to control electronic circuits.
• Elementary – Si, Ge.
• Compound – GaAs, InP, CdTe.
PV Cells – Basics
Band Diagram
Doping in Si
n-type
p-type
e- rich dopant (P, As)
e- deficient dopant (B, Ga)
5th valence e- - charge carrier
The hole acts as charge carrier
n-type doping
P-type doping
PV Cell
• A PV cell is a light illuminated p-n junction diode
• Converts solar energy into electricity via photovoltaic
effect.
• When sunlight strikes the surface of a PV cell,
photons with energy above the semiconductor bandgap impart enough energy to create electron-hole
pairs.
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• https://www.youtube.com/watch?v=xKxrkht7CpY&feat
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p-n junction
Major carriers : holes
Minor carriers : ens
Major carriers : ens
Minor carriers :holes
1. generation of electron-hole pair by absorption of photon
2. Combination of electron-hole pair
3. electron and hole separation
4. Electrons in external circuit
5. Recombination of electron-hole
Criteria for Materials to be Used in
Solar Cell
• Must have band gap from 1ev to 1.8ev.
• It must have high optical absorption.
• It must have high electrical conductivity.
• The raw material must be available in
abundance and the cost of the material must
be low.
Advantages of Solar Cell
• PV cells provide clean and green energy. No
harmful greenhouse gas emissions.
• Can be installed anywhere including rooftops
• suitable for smart energy networks with
distributed power generation
• Low operating and maintenance costs
• PV panels are totally silent
Disadvantages of Solar Cell
• Solar energy conversion is affected by
availability of light (night, cloudy days..)
• Need inverters to convert DC to AC
• Need to be connected to storage batteries for
continuous supply
• PV panels are fragile and can be damaged
relatively easily.
• High cost of installation.
• It has low efficiency.
Solar module and Arrays
• A solar cell has power output enough to operate
small devices like toys, pocket calculators etc.
• For energy intense applications many cells are
combined together.
• Solar cells when connected in series have
improved voltage output while connected in
parallel have better current output.
• Photovoltaic modules are formed by connecting
many PV cells. Many modules when connected
together form a panel and panels are connected
together to form an array.
Dye Sensitized Solar Cells
• Uses Photosensitive Dyes
• Some dyes when adsorbed on semiconductors
like TiO2, shifts spectral sensitivity towards
visible light
• Has 4 components
i) Semiconductor electrode (TiO2)
ii) Dye sensitizer
iii) Mediator ( Electrolyte) : I- or I3- complexes
iv) Counter electrode ( C or Pt based)
“Black Dye", an anionic Ru-terpyridine
complex
Working principle
 Photoexcitation of dye when exposed to light.
 The excited electron injected in the CB of TiO2
The oxidized form of the dye produced in this
process is subsequently reduced by the electrolyte.
The electrolyte is then regenerated by the
reduction at the counter-electrode.
The chemical electrolyte thus closes the circuit so
that the electrons are returned to the dye.
It is the movement of these electrons that creates
energy which can be harvested.
Advantages of DSSC
• Can perform well in a wide range of lighting
conditions
• Efficiency is not affected by high temperature.
• Its manufacturing process involves less
consumption of energy
• Sustainable and environment friendly
technology.