Download File - Ashvin Patel

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Properties of silicon
• A pure commercially available silicon containing impurity atoms
with concentration of the less the 1018 per m3 and electrical
resistance of 2500 ohms/meter with four valance electrons
which are shared with adjacent silicon atoms with covalent
bonding.
• It can be doped by Boron, Arsenic, Copper, Cadmium etc.
• It can be divided in very thin slices called wafers required for
constructing the solar cells.
• It can withstand high temperature, has high boiling point.
• Its resistance decreases with increase in temperature.
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Photovolatic Applications:
• Industrial : In field of telecommunication, transmitters
and relay towers can be operated by PV cells, cathodic
protection of structures like pipe lines, well heads and
bridges etc by introducing small dc current to prevent
corrosion, alarm systems, automatic meteorological
stations and emergency equipments.
• Social : A small PV power supply system can be used to
provide electricity in remote houses for light, fans and
refrigerator. PV water pumps can be installed for domestic
water supply and irrigation.
• Consumer : The solar PV has very large application in
consumer articles such as pocket calculators, watches,
clocks, torches, lanterns, garden lights, radios. portable
fans, toys etc.
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Solar Pond:
• The solar radiation is transmitted through the water layer up to
the bottom layer which is heated up.
• The heated water layer of the bottom layer rises up. The bottom
of the pond is painted black for heat absorption.
• The warm water from bottom is prevented from rising up to the
top.
• This is achieved by dissolving salt in high concentration near
bottom, with decreasing salt concentration toward the surface.
• The most commonly used salts are sodium chloride and
magnesium chloride.
• The bottom layer is convective one with constant salt level and
acts as storage of thermal energy.
• Hot water from lower layer goes into the heat exchanger where
working fluid absorbs heart from hot water.
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Cont…
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Solar Pond Power Plant:
• Hot water from the bottom level of the pond is pumped to the heat
exchanger, where working fluid is vaporized.
• The working fluid is allow to pass through turbine blades where heat
energy is converted into mechanical energy.
• Vapour goes to condenser where cold water from upper layer of solar
pond condenses the vapour back to a liquid state. The liquid is pump back
to the evaporator where the cycle is repeated.
• A 2000 Sq-m solar point equipped with a 20 kW Rankine cycle heat
engine solar pond power plant has been constructed at Australia.
Binary Cycle Solar Thermal Power Plant:
• Binary cycle has two cycles:
(i)Water cycle (ii)Gas cycle
• Solar thermal collectors collect the solar energy and heat-up the
heat transport fluid (water).
• In heat exchanger heat exchange takes place between water and
working fluid(ammonia)
• The ammonia gets vaporized and hot ammonia vapour drives the
turbine rotor.
• The exhaust ammonia condenses in condenser. The condensate is
pump back to heat exchanger.
Cont…
Solar Power Generation:
• A generating station which utilized the solar (heat) energy of sun,
this heat can be used to rise steam and electrical energy can be
produced with the help of turbine- Generator set is called solar
thermal power generation.
• The solar power generation system is the conversion of solar
energy to electrical energy by suitable cycle.
• The system can be broadly divided into three categories.
a) Low temperature Power Generation system (the maximum
temperature of about 100° C.)
b) Medium temperature Power Generation system (the maximum
temperature of about 400° C.)
c) High temperature Power Generation system (the temperature above
400° C.)
(a)Low Temp. Power Gen. System
• The water is heated by an array of flat-plate collectors.
• To obtain the maximum temperature, boosting mirrors
(reflectors) are used.
• The hot water at the temperature of about 100° C is stored in a
thermal storage tank which is well insulated.
• The heated water flows to the vapour generator through which
the working fluid of Rankine cycle is also passed.
• The fluid has low boiling point and it is vaporized at about 90°C
and has pressure of few atmospheres.
• This vapour leaves the generator and executes the regular
Rankine cycle by flowing through a prime mover, condenser and
pump.
• The working fluids normally used are methyl chloride and
toluene.
• The efficiency of this system is very low because the
temperature difference between the vapour leaving the
generator and the condensed liquid from the condenser is very
small.
• For the layout shown, the temperature difference is about 55° C
and thus the Rankine cycle efficiency is about 8%. The efficiency
of the collector system is around 25%, giving overall efficiency of
about 2%.
• For cost effectiveness the use of solar pond instead of flat-plate
collector is recommended.
(b)Medium Temperature System
● The system operates at a temperature of about 4000C. To
achieve this temperature, the line focusing parabolic collector is
employed.
● The efficiency of such a collector system is around 0.7. The
Rankine cycle efficiency is about 0.38 giving an overall efficiency of
about 0.25.
(c)High Temperature System
1) Parabolic dish
2) Central receiver
1) Parabolic dish:
● The sun's radiation is brought to a point focus by using
parabolic dish as a collector.
● A fluid passing through the receiver is heated up and is used to
drive the prime mover.
● Sterling engines are favored as prime movers. The system has
efficiency of about 0.3.
2) Central Receiver System:
● The solar radiation reflected from the mirrors called heliostats
is concentrated on the receiver provided on the tower top.
● A fluid flowing through the receiver absorbs heat of the
concentrated radiation and transports to the ground where it is
used to the Rankine power cycle.
● Alternately the receiver is used to heat a liquid metal or a
molten salt and this fluid is generated.
● The steam is used in power cycle passed through a heat
exchanger where steam is
Central Receiver System:
Solar PV Power Generating System:
• The main important components in PV system which include
(1) Structure and installation.
(2) Power conditioning and control.
(3) Storage batteries.
Cont…
• There are two broad categories of PV power system.
(a) Stand-alone system
(b) Grid connected system
(a)Stand-alone system:
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Cont…
• The solar cell array consists of an appropriate number of cells
connected in series and/or parallel to produce the required
voltage and current.
• The array is oriented to collect maximum solar radiation round
the year.
• The power conditioners regulate the output of the array, protect
batteries and provides interface between the load and array.
• An inverter is a device to convert DC from the array or battery to
single or three phase A.C.
• Storage batteries with charge regulators are used to provide a
back-up power source during periods of low solar radiation and
night.
• This PV power system is used to supply power to light houses,
meteorological stations radio/TV relay stations and remote areas.
(b) Grid connected system:
• A grid-connected PV system is connected to the commercial grid.
• These systems are small to medium size systems providing about
3 kW for private residence, 20 kW for housing colony and 100200 kW for schools and factories.
• The system operates on the principle of feeding power into grid
when solar generation exceeds local demand and taking energy
from the grid when required.
• There is no storage of energy but needs components to regulate
voltage, frequency and waveform.