Renewable Energy Source SOLAR ENERGY

Solar Energy? Solar energy is quite simply the energy produced directly by the sun and collected elsewhere, normally the Earth. The sun creates its energy through a thermonuclear process that converts about 650,000,000 tons of hydrogen to helium every second. This process creates heat and electromagnetic radiation. The electromagnetic radiation (including visible light, infra-red light, and ultra-violet radiation) streams out into space in all directions.

The greatest advantage of solar energy as compared with other forms of energy is that it is clean and can be supplied without any environmental pollution.

Insolation Insolation is the amount of solar radiation reaching the earth. Also called Incident Solar Radiation. Maximum value is 1000 kW/m2. Components of Solar Radiation: Direct radiation Diffuse radiation Reflect radiation

Applications of Solar Energy Solar Thermal Energy Solar Heating – Solar Water Heating – Solar Space Heating – Solar Space Cooling Electricity Generation Using Solar Concentrators Photovoltaic Cells

Essential subsystems in a solar energy plant: 1. Solar collector or concentrator: This is a device which absorbs the incoming solar radiation, converts it into heat, and transfers this heat to a fluid (usually air, water, or oil) flowing through the collector. There are basically two types of solar collectors: 1.Non Concentrating or Flat Plate 2.Concentrating or Focusing

A Non Concentrating collector has the same area for intercepting and for absorbing solar radiation. A Concentrating solar collector usually has concave reflecting surfaces to intercept and focus the sun’s beam radiation to a smaller receiving area, thereby increasing the radiation flux.

Non concentrating collectors or Flat Plate In these collectors the area of collector to intercept the solar radiation is equal to the absorber plate and has concentration ratio of 1. Flat plate collector is most important part of any solar thermal energy system.

Non concentrating collectors or Flat Plate Working When solar radiation passes through a transparent cover and impinges on the blackened absorber surface of high absorptivity, a large portion of this energy is absorbed by the plate and then transferred to the transport medium in the fluid tubes to be carried away for storage or use. The underside of the absorber plate and the side of casing are well insulated to reduce conduction losses.

Non concentrating collectors or Flat Plate Working......... The liquid tubes can be welded to the absorbing plate, or they can be an integral part of the plate. The liquid tubes are connected at both ends by large diameter header tubes. It is simplest in design and both direct and diffuse radiations are absorbed by collector and converted into useful heat. These collectors are suitable for heating to temperature below 100ºC.

Non concentrating collectors or Flat Plate Construction The constructional details of flat plate collector is given below Insulated Box Transparent Cover Absorber Plate Tubes

Non concentrating collectors or Flat Plate Construction Insulated Box The rectangular box is made of thin G.I sheet and is insulated from sides and bottom using glass or mineral wool of thickness 5 to 8 cm to reduce losses from conduction to back and side wall. The box is tilted at due south and a tilt angle depends on the latitude of location. The face area of the collector box is kept between 1 to 2 m2.

Non concentrating collectors or Flat Plate Construction Transparent cover This allows solar energy to pass through and reduces the convective heat losses from the absorber plate through air space. The transparent tampered glass cover is placed on top of rectangular box to trap the solar energy and sealed by rubber gaskets to prevent the leakage of hot air.

Non concentrating collectors or Flat Plate Construction Transparent cover............ High transmittance and low surface degradation material is used as transparent cover. Generally Plastic glass is used because of low cost, light in weight and are suitable for low temperature application 70-120ºC. The temperature of glass cover is lower than the absorber plate and is a good absorber of thermal energy and reduces convective and radiative losses of sky.

Non concentrating collectors or Flat Plate Construction Absorber Plate It intercepts and absorbs the solar energy. The absorber plate is made of copper, aluminium or steel and is in the thickness of 1 to 2 mm. It is the most important part of collector along with the tubes products passing the liquid or air to be heated. The plate absorbs the maximum solar radiation incident on it through glazing (cover plate) and transfers the heat to the tubes in contact with minimum heat losses to atmosphere.

Non concentrating collectors or Flat Plate Construction Tubes The plate is attached to a series of parallel tubes through which water or other liquid passes. The tubes are made of copper, aluminium or steel in the diameter 1 to 1.5 cm and are brazed, soldered on top/bottom of the absorber water equally in all the tubes and collect it back from the other end.

Non concentrating collectors or Flat Plate Construction With increase in inlet temperature of working fluid, the losses increase to ambient. The high temperature fluid absorbed the less heat from absorber plate because of low temperature difference and increases the top loss coefficient. Therefore the efficiency of collector get reduced with rise in inlet temperature.

Concentrating Collectors or Focusing Collectors Concentrating collector is a device to collect solar energy with high intensity of solar radiation on the energy absorbing surface. Such collectors use optical system in the form of reflectors or refractors. These collectors are used for medium (100-300ºC) and high-temperature (above 300ºC) applications such as steam production for the generation of electricity. The area of the absorber is kept less than the aperture through which the radiation passes, to concentrate the solar flux.

The high temperature is achieved at absorber because of reflecting arrangement provided for concentrating the radiation at required location using mirrors and lenses.

Concentrating Collectors or Focusing Collectors These collectors require tracking to follow the sun because of optical system. The tracking rate depends on the degree of concentration ratio and needs frequent adjustment for system having high concentration ratio. The efficiency of these collectors lies between 50-70%.

Advantages of concentrating collector over flat collector The size of the absorber can be reduced that gives high concentration ratio. Thermal losses are less than FPC. However small losses occur in the concentrating collector because of its optical system as well as by reflection, absorption by mirrors and lenses. The efficiency increases at high temperatures.

Solar Thermal Energy Flat-plate collectors Solar thermal technologies involve harvesting energy from the sun for heating water or producing electrical power. Solar collectors are used for this purpose. Three Types: Flat-plate collectors Evacuated-tube collectors Integral collector-storage systems(Batch or Bread Box)

Flat plate collectors

Evacuated tube collecttors

Integral collector system

Water Heating Thermosyphon Collector storage systems Passive systems Thermosyphon Collector storage systems Active systems Direct circulation systems Indirect circulation systems Hot air systems. Thermosyphon

Space Heating Active Solar Heating System A system that uses water or air that the sun has heated and is then circulated by a fan or pump. Passive Solar Heating System The house itself acts as the solar collector and storage facility. No pumps or fans are used. This system makes use of the materials of the house to store and absorb heat.

Direct Indirect Greenhouse Passive Solar Heating System Three Types: Direct-Gain Indirect-Gain Attached Greenhouse Indirect Greenhouse

Space Cooling The heat from a solar collector can also be used to cool a building by using the solar heat as an energy source.

Electricity from Solar Energy Solar power is described as the conversion of sunlight into electricity. Sunlight could be changed into electricity with the use of : Directly using PV or photovoltaic or Indirectly by CSPs.

Concentrated Solar Power CSP is a power generation technology that uses mirrors or lenses to concentrate the sun’s rays and, That heat a fluid and produce steam. The steam drives a turbine and generates power in the same way as conventional power plants. Other concepts are being explored and not all future CSP plants will necessarily use a steam cycle.

Solar power is concentrated in various ways: There are now several devices and structures created which focus and concentrate solar power. Solar Parabolic Troughs Stirling Dish Solar Power Tower The Linear Fresnel Reflector

Photovoltaics Converting solar energy directly into electrical energy . Devices used are called solar panels. Solar panel is a group of solar cells. Solar cells work on the principle of photoelectric effect.

Structure of a Solar Cell A typical solar cell is a multi-layered unit consisting of a: Cover - a clear glass or plastic layer that provides outer protection from the elements. Transparent Adhesive - holds the glass to the rest of the solar cell. Anti-reflective Coating - this substance is designed to prevent the light that strikes the cell from bouncing off so that the maximum energy is absorbed into the cell. Front Contact - transmits the electric current. N-Type Semiconductor Layer - This is a thin layer of silicon which has been mixed (process called doping) with phosphorous. P-Type Semiconductor Layer - This is a thin layer of silicon which has been mixed or doped with boron. Back Contact - transmits the electric current.

Working of A solar cell Photoelectric effect When a light of certain frequency falls on the surface of a metal Electrons will absorb the energy If incident light energy is greater than the work function(minimum energy required to remove the loosely bound valence electrons)of the metal Then the photo electrons will be emitted and The excess energy is converted to the kinetic energy of electron.

When solar panels are placed in the sunlight , photons will strike the surface and emits electrons. As a result electron hole pair is created in the solar cell. When external circuit is connected to the solar cell , electrons flow in the circuit and the current is generated.

The Types of Solar Electric Systems The Stand Alone System Standalone, or off-grid, solar power systems consist of solar panels and a battery bank. Used in rural areas and regions where there is no access to the utility grid. Very good at giving economical electricity. Grid-Tie Solar System Very useful for homes that are already linked to the utility grid. Primary advantage is the cheap price of utility. The system needs to be wired with an inverter that creates ac electricity, which is needed for linking to the utility grid.

Stand Alone-off grid

Grid connected

USES OF SOLAR ENERGY Heaters Green houses Cars water pumps Lights Desalination Satellites Chilling Dryers Solar ponds Calculators Thermal Commercial use On an office building , roof areas can be covered with solar panels . Remote buildings such as schools , communities can make use of solar energy. In developing countries , this solar panels are very much useful. Even on the highways , for every five kilometres ,solar telephones are used.

Applications Solar car Solar heater Solar lights

Developing Solar Power In PAKISTAN In PAKISTAN, about 70% of the population lives in some 50,000 villages dispersed around the country. Many of these villages are far from the main transmission lines of the national grid because of their relatively small populations. It is not usually economically viable to connect these villages to the grid.

Solar energy has great potential in areas of PAKISTAN that receive high solar radiation throughout the year. For e.g. 19 mega Joules of solar energy per square meter is received everyday. The nation wide average is 5.5 kWh/mess/day. Enough energy potential for solar energy because there are 250-300 sunny days per year. Continuous cloudy days are rare.

Advantages of solar power development to PAKISTAN The power source of the sun is absolutely free. The production of solar energy produces no pollution. The technological advancements in solar energy systems have made them extremely cost effective. Most systems do not require any maintenance during their lifespan, which means you never have to put money into them.

Solar energy systems are now designed for particular needs Solar energy systems are now designed for particular needs. For instance, you can convert your outdoor lighting to solar. The solar cells are directly on the lights and can’t be seen by anyone. At the same time, you eliminate all costs associated with running your outdoor lighting. Solar energy can be used in remote areas where it is too expensive to extend the electricity power grid.  It is estimated that the worlds oil reserves will last for 30 to 40 years. On the other hand, solar energy is infinite (forever). Solar energy can be used in remote areas where it is too expensive to extend the electricity power grid.

Solar cells are long lasting sources of energy which can be used almost anywhere.  Solar cells are also totally silent

Disadvantages Of Solar Power Initial Cost : The initial cost of purchasing and installing solar panels always become the first disadvantage. Although subsidy programs, tax initiatives and rebate incentives are given by government to promote the use of solar panels we are still way behind in making full and efficient use of solar energy.

Location: The location of solar panels is of major importance in the generation of electricity. Areas which remains mostly cloudy and foggy will produce electricity but at a reduced rate and may require more panels to generate enough electricity homes. Houses which are covered by trees, landscapes or other buildings may not be suitable enough to produce solar power.

Pollution: Most of the photovoltaic panels are made up of silicon and other toxic metals like mercury, lead and cadmium. Pollution in the environment can also degrade the quality and efficiency of photovoltaic cells. New innovative technologies can overcome the worst of these effects. Reliability: Unlike other renewable source which can also be operated during night, solar panels prove to be useless during night which means you have to depend on the local utility grid to draw power in the night.

Inefficiency: Since not all the light from the sun is absorbed by the solar panels therefore most solar panels have a 40% efficiency rate which means 60% of the sunlight gets wasted and is not harnessed. Installation areas: For home users, a solar energy installation may not require huge space but for big companies, a large area is required for the system to be efficient in providing a source of electricity.

Current solar power plants functioning in PAKISTAN SOLAR ENERGY PAKISTAN LTD. (THATTA , SINDH) DACC LLC SOLAR (SINDH) WAH INDUSTRIES LIMITED SOLAR (TAXILA, PUNJAB) TEH ACCESS SOLAR (PUNJAB) CWE SOLAR (CHOLISTAN) BAKHSH ENERGY SOLAR (KASUR) ROSHAN POWER SOLAR

Future prospects Pakistan has a lot of potential especially in northern Baluchistan. It could also lead to development in that area. As well as a supply of electricity in Baluchistan which is presently lacking can be established. So the production of solar power is beneficial for Baluchistan. Recently the Punjab government has decided to allocate 5,000 acres of land for private solar power projects in the Cholistan which will be allotted to solar power sector investors at a nominal rate of one dollar per acre per year for a 20-year lease. This land is situated in Maroot, and Din Garh Road, Yazman, Bahawalpur.

Better ways of usage Government should take measures and see that solar lights are used as street lights in all the areas. We can place solar panels in the barren lands instead of keeping it away uselessly. We can also keep these solar panels in the deserts , where we can make use of this energy with the help of a rechargeable battery. Efficiency of solar panels depends on the range of frequencies of light that strikes the surface . So they can give higher efficiency if we split the light into different frequency ranges and direct the beams onto the cells tuned to these frequencies. Building a new home is the best time to design and orient the home to take the advantage of the sun’s rays.

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