SOLAR ENERG

Y

The sun is the source of all energy. The sun provides us heat and light energy free of cost! The energy obtained from sun is called solar energy. The nuclear fusion reactions taking place inside the sun keep on liberating enormous amounts of heat and light energy. This heat and light energy is radiated by the sun in all directions in the form of solar energy. The sun has been radiating an enormous amount of energy at the present rate for nearly 5 billion years(5×109 years) and will continue radiating energy at that rate for about 5 billion years more.

India is fortunate to receive solar energy for greater part of the year. It has been estimated that India receives solar energy equivalent to more than 5000 trillion kWh (5000×1018 kWh) during the year. Under clear sky conditions, the daily average of solar energy varies from 4 to 7 kWh/m2 in our country.

INTTRODUCTION

SOLAR CONSTANTThe energy that the near earth space receives from the

sun is about 1.4 kilojoules per second per square meter and this quantity is called the solar constant. We can define the solar constant as follows: The amount of solar energy received per second by one square meter area of the near earth space (exposed perpendicularly to the rays of the sun) at an average distance between the sun and the earth, is called solar constant. Thus, the solar constant tells us the amount of energy which falls in 1 second on a 1m2 area of the near earth space at an average distance between the sun and the earth. The value of solar constant is 1.4 kJ/s/m2 or 1.4kW/m2 .

A device which gets heated by using sun’s heat energy is called a solar heating device.

EXAMPLES:

Solar air conditioning, Solar balloon, Solar charger, Solar backpack, Solar cell phone charger, Strawberry Tree (solar energy device), Solar chimney, Solar calculator, Solar powered compacting trash can, Solar cooker, Solar dryer, Solar fan, Solar furnace, Solar inverter, Solar keyboard, Solar lamp, Solar pond, Solar road stud ,Solar street light, Solar traffic light, Solar Tuki, Solar powered flashlight, Solar notebook, Solar powered calculator, Solar powered desalination unit, Solar-powered pump, Solar powered fountain, Solar powered radio, Solar powered refrigerator, Solar Powered Stirling Engines, Solar powered watch, Solar-pumped laser, Solar roadway, Solar Spark Lighter, Solar still, Solar tree, Solar vehicle, Solar balloon, Solar boat, Tûranor PlanetSolar, Solar bus, Solar car, Solar golf cart, Solar panels on spacecraft, Solar sail, Solar thermal rocket

SOLAR ENERGY DEVICES

LET US TAKE THE EXAMPLE OF SOLAR COOKER

PRINCIPLES1) Concentrating sunlight: A mirrored surface with high specular reflectivity is used to concentrate light from the sun onto a small cooking area. Depending on the geometry of the surface, sunlight can be concentrated by several orders of magnitude producing temperatures high enough to melt salt and smelt metal. For most household solar cooking applications, such high temperatures are not required. Solar cooking products, thus, are typically designed to achieve temperatures of 150°F (65°C) (baking temperatures) to 750°F (400°C) (grilling/searing temperatures) on a sunny day.2) Converting light energy to heat energy: Solar cookers concentrate sunlight onto a receiver such as a cooking pan. The interaction between the light energy and the receiver material converts light to heat. This conversion is maximized by using materials that conduct and retain heat. Pots and pans used on solar cookers should be matte black in color to maximize the absorption.3) Trapping heat energy: It is important to reduce convection by isolating the air inside the cooker from the air outside the cooker. Simply using a glass lid on your pot enhances light absorption from the top of the pan and provides a greenhouse effect that improves heat retention and minimizes convection loss. This "glazing" transmits incoming visible sunlight but is opaque to escaping infrared thermal radiation. In resource constrained settings, a high-temperature plastic bag can serve a similar function, trapping air inside and making it possible to reach temperatures on cold and windy days similar to those possible on hot days.[citation needed]

OPERATION:Different kinds of solar cookers use somewhat different methods of cooking, but most follow the same basic principles.Food is prepared as if for an oven or stove top. However, because food cooks faster when it is in smaller pieces, food placed inside a solar cooker is usually cut into smaller pieces than it might otherwise be.[4] For example, potatoes are usually cut into bite-sized pieces rather than roasted whole.[5] For very simple cooking, such as melting butter or cheese, a lid may not be needed and the food may be placed on an uncovered tray or in a bowl. If several foods are to be cooked separately, then they are placed in different containers.The container of food is placed inside the solar cooker, which may be elevated on abrick, rock, metal trivet, or other heat sink, and the solar cooker is placed in direct sunlight.[4] If the solar cooker is entirely in direct sunlight, then the shadow of the solar cooker will not overlap with the shadow of any nearby object. Foods that cook quickly may be added to the solar cooker later. Rice for a mid-day meal might be started early in the morning, with vegetables, cheese, or soup added to the solar cooker in the middle of the morning. Unlike cooking on a stove or over a fire, which may require more than an hour of constant supervision, food in a solar oven is generally not stirred or turned over, both because it is unnecessary and because opening the solar oven allows the trapped heat to escape and thereby slows the cooking process. If wanted, the solar oven may be checked every one to two hours, to turn the oven to face the sun more precisely and to ensure that shadows from nearby buildings or plants have not blocked the sunlight. If the food is to be left untended for many hours during the day, then the solar oven is often turned to face the point where the sun will be when it is highest in the sky, instead of towards its current position.[6]

The cooking time depends primarily on the equipment being used, the amount of sunlight at the time, and the quantity of food that needs to be cooked.. 

WORKING OF SOLAR CELLS

A solar cell, or photovoltaic cell, is an electrical device that converts the energy of light directly into electricity by the photovoltaic effect, which is a physical and chemical phenomenon. It is a form of photoelectric cell, defined as a device whose electrical characteristics, such as current, voltage, or resistance, vary when exposed to light. Solar cells are the building blocks of  solar panels.

Under the sun, a photovoltaic cell acts as a photosensitive diode that instantaneously converts light – but not heat – into electricity. A top, phosphorus-diffused silicon layer carries free electrons – un-anchored particles with negative charges. A thicker, boron doped bottom layer contains holes, or absences of electrons, that also can move freely. In effect, precise manufacturing has instilled an electronic imbalance between the two layers.

Sun Activation Photons bombard and penetrate the cell. They activate electrons, knocking them loose in both silicon layers. Some electrons in the bottom layer sling-shot to the top of the cell. These electrons flow into metal contacts as electricity, moving into

a circuit throughout a 60-cell module. Electrons flow back into the cell via a solid contact layer at the

bottom, creating a closed loop or circuit.Powering Homes and Businesses with Solar Current leaving a module, or array of modules, passes through a

wire conduit leading to an inverter. This device, about the shape of a waffle iron, inverts direct current, which flows with a fixed current and voltage, into alternating current, which flows with oscillating current and voltage. Appliances worldwide operate on AC. From the inverter, the solar-generated power feeds into circuitry of a household, business or power plant and onto the region’s electrical grid. A remote, or independent, power system also can form a self-contained circuit without connecting to the grid. The off-grid system, however, requires batteries to store power for times, such as night, when modules do not capture enough light energy from the sun.

USES OF SOLAR CELLS Solar cells are used for providing electricity in

artificial satellites and space probes. Solar cells are used for providing electricity to

remote, inaccessible and isolated places where normal electricity transmission lines do not exist.

Solar cells are used for the transmission of radio and television programmes in remote areas.

Solar are used for providing electricity to ‘ light houses’ situated in the sea and to off-shores oil drilling platforms.

Solar cells are used for operating traffic signals, watches, calculators and toys.

Solar cells are typically combined into modules that hold about 40 cells; about 10 of these modules are mounted in PV arrays that can measure up to several meters on a side. These flat-plate PV arrays can be mounted at a fixed angle facing south, or they can be mounted on a tracking device that follows the sun, allowing them to capture the most sunlight over the course of a day. About 10 to 20 PV arrays can provide enough power for a household; for large electric utility or industrial applications, hundreds of arrays can be interconnected to form a single, large PV system.

Some solar cells are designed to operate with concentrated sunlight. These cells are built into concentrating collectors that use a lens to focus the sunlight onto the cells. This approach has both advantages and disadvantages compared with flat-plate PV arrays. The main idea is to use very little of the expensive semiconducting PV material while collecting as much sunlight as possible. But because the lenses must be pointed at the sun, the use of concentrating collectors is limited to the sunniest parts of the country.

SOLAR CELLS AND ARRAYS

HOW IS SOLAR ENERGY CONVERTED TO ELECTRICAL ENERGY:

The sun's energy can be harnessed as either light or heat. The process of converting light (photons) to electricity (voltage) is called the photovoltaic (PV) effect. The PV effect was first discovered by the French physicist Edmund Becquerel in 1839 using copper oxide in an electrolyte. We'll go into more detail about the current materials for PV further down the page.

To create the PV effect, radiation from the sun ('sunlight') hits a photovoltaic cell. These cells are made up of two layers of semi-conducting material, typically silicon, that have been chemically treated. The industry refers to these layers as P and N. The boundary between P and N acts as a diode allowing electrons to move from N to P, but not from P to N. When photons with sufficient energy hit the cell, they cause electrons to move (from N to P only) causing excess electrons in the N-layer and a shortage in the P layer.

This voltage difference is typically in the range of 0.5V for as long as the cell is in sunlight. If you short-circuit the upper and lower layer a current runs of about 3 Amps. If you arrange sufficient cells in series, the result is a PV module or PV panel. Let's say 36 cells in series produce 36 x 0.5V = 18V at 3 Amps = 54Watts.

  The following graphic sets out the layers within the cell. The top layer is an Anti-Reflective-

Coating (ARC) that enhances the light effect of the sun. The N layer is typically semi-conducting silicon doped with phosphorus that creates the free flow of electrons. The P layer is again typically semi-conducting silicon, but this time doped with boron which creates the free flow of positive charges called “holes”. As the holes and electrons are attracted and move towards each other, they create an electrical field across the P-N junction. Sunlight striking this electrical field separates the electrons and holes, creating the voltage.

The voltage pushes the flow of electrons or 'DC current' to contacts at the front and back of the cell where it is conducted away along the wiring circuitry that connects the cells together.

ARRANGEMENT OF SOLAR CELLS

Advantages of solar cells: Site Access - A well-designed solar cell system will operate

unattended and requires minimum periodic maintenance. The savings in labor costs and travel expenses can be significant.

Modularity - A solar cell system can be designed for easy expansion. If your power demand could increase in future years, the ease and cost of increasing the solar cell power supply should be considered.

Fuel Supply - Supplying conventional fuel to the site and storing it can be much more expensive than the fuel itself. Solar energy is delivered free of charge.

Environment - Solar cells create no pollution and generate no waste products when operating.

Maintenance - Solar cells have no moving parts and require no maintenance other than to be regularly cleaned.

Durability - Most of today's solar cells are based on proven technology that has experienced little degradation in more than 15 years of operation.

Cost - For many applications, the advantages of solar cells offset their relatively high initial cost.  Federal energy tax credits, new feed-in tariffs, net metering and lower prices are combining to make solar cells and solar panels an attractive energy alternative.

Solar energy is not only sustainable, it is renewable and this means that we will never run out of it. It is about as natural a source of power as it is possible to generate electricity.

The creation of solar energy requires little maintenance. Once the solar panels have been installed and are working at maximum efficiency there is only a small amount of maintenance required each year to ensure they are in working order.

They are a silent producer of energy. There is absolutely no noise made from photovoltaic panels as they convert sunlight into usable electricity.

There are continual advancements in solar panel technology which are increasing the efficiency and lowering the cost of production, thus making it even more cost effective.

During operation solar electricity power plants produce zero emissions.

MERITS OF SOLAR ENERGY:

DEMERITS OF SOLAR ENERGY:

1. Initial Cost : The initial cost of purchasing and installing solar panels always become the first disadvantage when the subject of comes up. 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. As new technologies emerge, the cost of solar panels is likely to decrease and then we can see an increase in the use of solar cells to generate electricity.

2. 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 for your home. Houses which are covered by trees, landscapes or other buildings may not be suitable enough to produce solar power.

3. 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.

4. 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. New emerging technologies however have increased the rate of efficiency of solar panels from 40 to 80% and on the downside have increased the cost of solar panels as well.

5. 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. Else you can buy solar batteries to store excess power which you can later utilize in the night.

6. Installation area : 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.

Above disadvantages makes it quite obvious that one has to shell out good amount of money to harness solar energy that is available free but before you reach any further conclusion lets go through the advantages of solar power which will make you think that it would be wise to make this investment once and then reap its benefits later.

COMPARISON OF FOSSIL FUELS AND SUN AS SOURCES OF ENERGY:

i. The sun is a renewable source of energy but fossil fuels are a non-renewable source of energy.

ii. The sun’s energy does not cause any pollution but burning of fossil fuels causes a lot of pollution.

iii. The sun’s energy is available in diffused form but fossil fuels provide energy in concentrated form.

iv. A special device is always needed to utilise sun’s energy but this is not so in the case of fossil fuels.

v. the sun’s energy is available only during the day time when the sun shines but energy of fossil fuels can be used all the time

SOME QUESTIONS TO TEST WHAT HAVE YOU LEARNT:

1) WHAT IS SOLAR CONSTANT?2) WHICH TYPE OF LENS/MIRROR IS USED IN SOLAR

COOKER?3) GIVE TWO MERITS OF USING SOLAR ENERGY?4) GIVE TWO DEMERITS OF USING SOLAR ENERGY?5) COMPARE AND CONTRAST FOSSIL FUELS AND THE

SUN AS DIRECT SOURCES OF ENERGY?6) GIVE FIVE EXAMPLES OF DEVICES WHICH USE

SOLAR ENERGY TO POWER THEM?

ALWAYS TRY TO USE CLEANER FUELS BUT ALSO KEEP IN MIND THAT IN REALITY NO

SOURCE OF ENERGY IS SAID TO BE POLLUTION FREE

THANK YOU

BY SOUMYA AND GROUP