Solar Energy Presented By Ashvin G. Patel Asst. Prof. (E.E.) GPERI, Mehsana
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.
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.
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.
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.
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. • Low temperature Power Generation system (the maximum temperature of about 100° C.) • Medium temperature Power Generation system (the maximum temperature of about 400° 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: Parabolic dish Central receiver • 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
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 twobroad categories of PV power system. • Stand-alone system • Grid connected system (a)Stand-alone system:
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 100-200 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.