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Sola Photovoltaics
Solar Photovoltaics
Phenomenal Price Reduction of Solar
Photovoltaics
Phenomenal growth of installation of
Solar Photovoltaics
Mainly Due to massive production of
SPV in China
Basic Features of Solar pV
 pV systems have no fuel requirement in
remote areas diesel or kerosene fuel supplies
are erratic and often very expensive. The
recurrent costs of operating and maintaining
pV systems are small.
 pV systems are modular – A solar array is
composed of individual pV moduels so each
system can be sized to meet the particular
demand.
 pV systems can be used to improve quality
of life - for example the provision of lighting in a
rural school allows evening educational or
community activities. Refrigeration at a health
centre improves effectiveness of immunization
programmes.
 pV Systems are highly reliable – the
reliability of pV systems are significantly higher
that of diesel or any similar generators
 pV Systems are easy to maintain –
Operation and routing maintenance
requirements are simple.
 pV modules have long life – There is little
degradation in performance of over 15 yrs.
 pV systems provide national economic
benefits – Reliance on imported fuel such
as coal and oil is reduced.
 pV systems are environmentally begin –
There is no harmful pollution through the use
of a pV system.
 Pv systems are economically viable – On a
life cycle cost basis and taking into
consideration the higher reliability of PV
many small scale applications can be more
economically powered by PV than with
diesel systems or some other small
systems.
Applications of Photovoltaics
 RURAL ELECTRIFICATION(EITHER GRID
CONNECTED OR OFF GRID)
 SOLAR HOME SYSTEMS (SHS)
 WATER PUMPING AND TREATMENT
SYSTEMS
 HEALTH CARE SYSTEMS
 COMMUNICATIONS
 MID SEA BUOYS
 CATHODIC PROTECTION
Stationary power station (Off grid or mini grid)
• grid )
Solar cell capacity:
3.4kW
Wind Power capacity: 1.8kW
Inverter capacity:
5kVA
11
• Stationary power station (Grid connected )
Site:
Installation:
Capacity:
Purpose:
12
Funafuti Tuvalu
Feb. in 2008
40kW
Grid connected power supply for fuel conservation
and CO2 reduction.
Solar array
Solar array
Solar array
Controller
Light
Solar array
Storage battery
• Roof top of school ,community-center building.
(For education and emergency power)
14
Roof top of residence ( Grid connected )
Owner can sell excess power to
power utility.
Most popular installation style
in Japan.
(Almost 85% PV in Japan )
15
Distant and independent power
supply ( Off grid )
Advertising sign beside highway
Relay station on top of mountain
16
Solar Home Systems in remote locations
• Mountain lodge ( Off grid )
Inverter and controller
1.2kW system
17
Technical Comparison of
off grid energy System
Off Grid Systems – Diesel Generators
Advantages
 Widespread Operating and maintenance
experience
 Moderate capital cost
 Easy to install
 Can be a combined power supply for additional
uses
Disadvantages
 Creates noise and fume pollution
 Requires a reliable fuel supply
 High running costs
 High maint. Costs
 Low operating efficiency
Automotive Battery Recharging
Advantages
 Low capital cost
 Easy to install
 Batteries locally available
Disadvantages
 Relies on transportation to charging
centres
 High charging fees often apply
 Short battery life times
Photo – Voltaics
 High reliability
 Low maintenance requirements
 Low running costs
 Suited to most locations
 Long life expectancy for main components
 Involves the introduction of a new and
poorly understood technology
 High capital cost
 Not physically robust so vulnerable to
damage
 Specialized batteries not widely available
Micro Hydro Systems
 Uses simple engineering principles hence widely
accepted technology
 Locally available skills only required for most
applications
 Robust machinery used
 Most village level and local technicians can do
maintenance
 Relatively high capital cost
 Generation depends on availability of water
 Control gear may require sophisticated components
 Conflicting water users may hinder total potential
unlisation
Solar PV is a
very good substitute
for Kerosene lighting !
Solar Phtovoltaic Technology
Semi-conductor Physics
• In an intrinsic semi-conductor valance band has four
electrons and hence only very few electrons can escape
to conduction band. EG = Energy gap energy required
for an electron to jump from
the valance band to conduction
band ~ 0.5 eV to 2.5 eV.
Solar light wave length~ 0.3 μmto2.5μm
This corresponds to photon energy
range of 0.5 eV to 4.0 eV
1 eV= 1.6x10-19 J
E= hν Where ν=c/λ
h= 6.626x10-34 J-s Plank’s Constant
Fermi Level
• Fermi Level Ef is the energy level at which an
electron has an equal probability of being either in
the valance band or the conduction band
• Hence in an intrinsic semiconductor
Fermi level lies exactly at the mid point
of the forbidden zone or the energy gap.
Fermi Level in a n type semi conductor
• Fermi level lies close to conduction band
Fermi Level in a p type semi conductor
• Fermi Level lies close to valance band
When a n type and p type junction is
created in a semiconductor
• The energy level at each end of the
semiconductor and at the junction appears
like this:
Initially electrons diffuse to p type and
holes diffuse to n type at the junction
This diffusion creates an electric field that
leads to a drift current Ie while the movement
of holes from p type and
electrons from n type
creates a current known
as the diffusion current Id
Due to the electric field at
thermal equilibrium Ie = Id
Behavior under forward bias of a Diode
• When a diode if forward biased , an electric current
flows in the forward direction of the diode i.e. a
current pass through the diode from p type to n type
in the semiconductor
When a Diode if forward biased
E decreases Hence Ie decreases
Vb increases Id increases
When a Diode if forward biased
• Vb Increases causing Id to increase and E decreases causing Ie to decrease hence
when a diode is forward biased a current passes through the diode
Characteristic curve of a Diode
• I increases rapidly when a diode is forward
biased caused by excitation of electrons across
the n-p junction to gain enough energy from
the battery to jump to the valance band
n-p junction under solar Insolation
• With the absorption of photon energy from the
light more electron – hole pairs are created in the
solar cell (n-p junction)
What happens when a solar cell exposed to
light is connected externally
With the solar insolation a current flows from the solar cell depicting
I = IL-Id where IL is the current created by excitation of electrons in the
junction to flow out of the n side in the external circuit to combine
with holes created in the p type thus a current flows in the external
circuit from the p side to the n side. Due to this current , a
voltage is built up in the external
circuit forward biasing the diode
hence the ‘drift current flows in the
opposite direction of the current
created by solar light
What Happens When the Solar Cell is Short
Circuited
Under Short Circuit conditions V=0 hence diffusion current Id becomes
zero. Hence the current flowing in the external circuit is the same current
produced in the solar cell due to solar light equal to the drift current
Characteristic Curve of a solar cell
• At Short circuit V = 0 hence I = IL
• At Open Circuit No external current flows hence
Ie= Id
The Equivalent circuit of a solar cell
• This is the simplified equivalent circuit of a solar cell however
the real solar cell should comprise of a series resistance
depicting the internal resistance of the cell and the contact
resistance and also a parallel resistance depicting the reverse
saturation current of the diode.