A report on SOLAR DEVICES

INTRODUCTION  Solar energy is the most readily available source of energy.  It is also the most important of the non-conventional sources of energy because it is non-polluting and, therefore, helps in lessening the greenhouse effect.  Solar energy can be put to great use in our day to day life vis-à-vis the use of solar devices.  This energy is used for: Cooking/Heating, Drying/Timber seasoning, Distillation, Electricity/Power generation, Cooling, Refrigeration, Cold storage

Various Types of Solar Devices: The various types of solar devices are:  Solar collectors  Solar cookers  Solar cells Apart from the above stated there exist solar heaters, solar dryers, solar timber kilns, solar air conditioners, solar invertors etc.

SOLAR COOKERS  As the supply of fossil fuels like coal, kerosene or cooking gas is deteriorating, more and more solar energy is harnessed for cooking purposes. THREE BASIC DESIGNS OF SOLAR COOKER:-  FLAT PLATE BOX TYPE SOLAR COOKER  MULTI REFLECTOR TYPE SOLAR OVEN  PARABOLIC DISC CONCENTRATOR TYPE SOLAR COOKER

FLAT PLATE BOX TYPE SOLAR COOKER –  It consists of a solar box of size usually 60 cm x 60 cm x 20 cm.  It is made up of inner and outer metal or wooden box with double glass sheet on it.  Absorber tray is painted black with dull color so that it can withstand maximum temperature attained inside the cooker as well as water vapour coming out of cooking utensils.  Top cover contains 2 plain glasses 3mm each, fixed in wooden frame with 20 mm distance between them.  Neoprene rubber sealing provided around contact surface of glass cover and cooker box. small vent is provided in sealing for vapour escape.  On one side of glass frame, plane reflecting mirror is hinged equal to size of box.

MULTI REFLECTOR TYPE SOLAR OVEN  The solar oven consists of a well insulated semi-cylindrical box made of aluminum sheet and wood.  Two shells are made and the space between them, 7.5 cms, is filled with fibre glass insulation.  The interior sheet is painted black.  A door of the same insulating material is also made for keeping and taking out food.  The window (40 X 40 cm) of the oven consists of two transparent glass sheet (3 mm thk) with a spacing of 2 cms.  Eight reflectors made of silvered glass mirrors, four of square shape and four of triangular shape have been used.  The oven can be manually tilted and oriented towards the sun.  With single reflector, temp attained reaches upto 160 deg and in multi- reflector temp reaches around 200 deg/c to 250 deg/c.

PARABOLIC DISC CONCENTRATOR TYPE SOLAR COOKER  Parabolic disc is used in this type of solar cooker.  Solar radiations are concentrated at a point, focus.  Cooking pot is placed at this point where a very high temperature is maintained, about 450 deg celcius. Wall Reflector Solar Cooker

Pictures Reflective Cooker Inclined box type cooker Box type solar cooker Inclined Solar Cooker

ADVANTAGES:  No attention is needed in cooking as in other devices.  No fuel is required.  Negligible maintenance cost.  No pollution.  Vitamins of food are not destroyed and food cooked is nutritive and delicious with natural taste.  No problem of charring of food and no over flowing. DISADVANTAGES:  One has to cook according to the sun shine.  One can not cook at short notice and food can not be cooked in the night or during cloudy days.  It takes comparatively more time.  Chapattis are not cooked because high temperature for baking is required and also needs manipulation at the time of baking.

Solar collector FLAT PLATE COLLECTORS:  The flat plate collector forms the heart of any solar energy collection system  Designed for operation in low temperature range from,ambient to 60 0 C, or the medium temperature range, from ambient to C. PRINCIPLE:  The principle behind a flat plate collector is that if a metal sheet is exposed to solar radiation, the temperature will rise, until the rate at which energy is received is equal to the rate at which heat is lost from the plate ( this temperature is termed as the ‘equilibrium temperature’.)  If the back of the plate is protected by a heat insulating material, and the exposed surface is painted black and is covered by one or two glass sheets, then the equilibrium temperature will be much higher than that for the simple exposed sheet.

Pictures Closed loop solar water heater Batch solar water heater Flat plate solar heater Flat plate over roof

ADVANTAGES:  absorb direct,diffused and reflected components of solar radiation  are fixed in tilt and orientation and, thus, there is no need of tracking the sun  are easy to make and are low in cost  have comparatively low maintenance cost and long life  operate at comparatively high efficiency. MATERIALS FOR FLAT PLATE COLLECTORS: Absorber plate: It should have:  high thermal conductivity  adequate tensile and compressive strength  good corrosion resistance.  Copper is generally preferred.  Other materials are aluminium, steel  and various thermoplastics

Insulation :  Several insulating materials which can be used to reduce the heat loses are available.  Desired characteristics of these insulating material are :-  Low thermal conductivity  Stability at high temperature ( upto 200degree Celsius)  No degassing upto around 200 degrees Celsius  Self supporting feature without any tendency to settle, ease of application  No contribution in corrosion. Cover plate :  Characteristics of cover plates through which solar energy is transmitted are extremely important in the functioning of a collector.  Functions of the cover plate are :-  To transmit maximum solar energy to absorber plate.  Minimize upward heat loss from the absorber plate to the environment.  To shield absorber plate from direct exposure to weathering.  Other factors such as strength, durability, non degradability are important.

THE LIQUID FLAT PLATE COLLECTOR:  It consists of several basic elements:  flat absorbing plate, normally  metallic upon which the short wave  solar radiation falls and is absorbed  tubes, channels or passages  attached to the absorber plate to FLAT PLATE COLLECTOR  circulate the liquid required to remove the thermal energy from the plate  thermal insulation provided at the back and sides of the absorber plate to minimize the heat losses  a transparent cover of glass or transparent plastic to reduce the upward heat loss from the absorber plate  a weather-tight container to enclose the above components.

Flat plate collectors are classified into three groups depending on the applications:  simple and low cost collectors with no cover and insulation.  e.g. for heating swimming pools where less heat is required.  Collectors with low cost insulation and one transparent cover e.g. in areas requiring domestic water heating.  Well engineered and sophisticated flat plate collectors for process heating or small-power production. The absorber plates can broadly be divided into three basic types:  Pipe and fin type, in which the liquid flows only in the pipe, and hence has comparatively low wetted area and liquid capacity.  Rectangular or cylindrical full sandwich type in which both the wetted area and the water capacity are high.  Roll bond type or semi-sandwich type, intermediate between type I and II.

Pictures Basic collector absorber plate types Flat plate solar heater for swimming pools

Solar panels  The fundamental power unit of a pv system is a solar cell.  It is a semi conductor generally made of silicon.  A solar cell is a thin wafer, which is chemically treated and processed at high temperature.  Many such wafers are joined together to create a p-n junction, across which voltage develops when sunlight falls on these cells.  There are four common types of silicon photo voltaic cell :-  Single crystalline silicon  Poly crystalline silicon  Ribbon silicon  Amorphous silicon

 Solar photovoltaic panel :- when many cells are connected in series to increase the voltage.  Several series of cells cen be interconnected in parallels to increase the power output.  Solar cells are extremely fragile, so to protect them from damage, they are sealed on the top by a layer of glass and bottom with a layer of plastic or a metal or a combination of the two.  The spv panels are rated in terms of peak watt units – which means minimum no. of hours of sunlight required to produce a desirable amount of electricity daily.

Solar lantern  Solar lantern is a single light point portable system.  Apart from the pv panel, it consists of  Lamp  Battery  Electronic components  All placed in a casing, either made of metal plasticor fibre glass.  Because of the portability, it is found in both indoors and outdoors applications.

Battery  A sealed maintenance free, lead –acid battery or a tubular plate lead acid battery with spill proof feature is used. PV panel  This PV panel has a power rating of 12 volts. Electronic component  Invertors with atleast 80 percent efficiency is provided with system.  Solar lantern are also provided with two led indicators to indicate charging and deep discharge state.

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