Abstract

Renewable energy is rapidly gaining importance as an energy resource as fossil fuel prices fluctuate. At the educational level, it is therefore critical for engineering and technology students to have an understanding and appreciation of the technologies associated with renewable energy. One of the most popular renewable energy sources is solar energy. This paper describes a capstone design project where a student in electronics engineering technology designed and built a microcontroller – based solar panel tracking system. Solar tracking enables more energy to be generated because the solar panel is able to maintain a perpendicular profile to the sun’s rays. This system builds upon a prior senior design project where students built a solar- powered battery charger, thus making this system ideally self-contained. The student was able to demonstrate a working system, thus validating the design. Potential improvements to the system are presented.

ABSTRACTIn this project we design the system for tracking the solar panel automatically. It ismicrocontroller based system . we have used the microcontroller 89C51 for automatic tracking operation. Twophotodiodes are fixed in such a way that one of them faces the east side(P1) and other face the west side(P2). Whensun rays falls on P1 Solar panel moves towards east side and when sun rays are falls on P2 solar panel movestowards west sides. The solar pannel converts the incident light of sun into electric signals and then the electricityproduced is stored in the 6v rechargable battery. This stored electricity can be used to glow light or to work any 6velectronic/electric device. Electricity produced from photovoltaic cells does not result in air or water pollution,deplete natural resources, or endanger animal or human health. The only potential negative impacts are associatedwith some toxic chemicals, like cadmium and arsenic, that are used in the production process. These environmentalimpacts are minor and can be easily controlled through recycling and proper disposal.

AbstractNowadays electricity is one of the basic necessities of mankind. As the demand of electricity isincreasing day by day, there is need to exploit renewable sources of energy. In the current era of

power shortage in Pakistan, the use of solar energy could be beneficial to great extent. Consideringthe high cost of solar panels, our project addresses to analyze, design and implement an efficientalgorithm for power extraction from solar panel using dc-dc converter and then utilizing that powerfor the electricity requirement of off-grid system. Moreover this project also address to the study of

boosting efficiency of solar system by two dimensional sun tracking.

Acknowledgements

In the name of ALLAH, who is the most merciful, the most compassionate; the one and onlysupreme power, the one whose will makes everything possible, and the one without whose will thesimplest is impossible.All thanks to our beloved Family members for their prayers, guidance, support and care. Theydreamed for our future and advised us to work hard to fulfill their dreams. Without their moral andfinancial support it would not have been possible for us to become supreme professionals.We are really thankful to Dr. Mian Muhammad Saleem, our project supervisor for his kind supportand guidance during each and every phase of this project.We also thank to Babar Bhai who helped us a lot in design and manufacturing of sun trackingstructure.Finally, we are also indebted to the University of Engineering & Technology, Lahore whichsupported us throughout our stay by providing their best teachers, equipped labs and with suitable

conditions for us to work on the project.

Dedications

Dedicated to Our Beloved Parents & Family Who Provided Us Every Opportunity to Achieve OurGoals and to Our Teachers Who Tried Their Level Best to Convey Us the Knowledge They Had.

DEDICATIONS ..........................................................................................................................................................3ACKNOWLEDGEMENTS ........................................................................................................................................4ABSTRACT ................................................................................................................................................................5TABLE OF CONTENT ..............................................................................................................................................61. ENERGY ............................................................................................................................................................81.1 INTRODUCTION

........................................................................................................................................

........81.2 ENERGY CRISIS IN PAKISTAN

.............................................................................................................................81.3 SOURCES OF ENERGY

.......................................................................................................................................91.4 WHY EVERY KIND OF ENERGY IS CONVERTED INTO ELECTRIC ENERGY

............................................................ 131.5 METHODS TO GENERATE ELECTRIC ENERGY

.................................................................................................... 132. SOLAR ENERGY ............................................................................................................................................ 152.1 AVERAGE ENERGY OVER THE YEARS

......................................................................................................................... 152.2 HOW SOLAR ENERGY IS

USED? ............................................................................................................................... 162.3 SOLAR CELLS

........................................................................................................................................

............. 162.4 CONSTRUCTION

........................................................................................................................................

......... 202.5 SOLAR MODULE AND ARRAY

................................................................................................................................. 212.6 THEORY OF SOLAR CELLS

...................................................................................................................................... 223. ELECTRICAL CHARACTERISTICS OF SOLAR CELLS AND MAXIMUM POWER POINT ................ 253.1 EQUIVALENT CIRCUIT OF A SOLAR CELL

........................................................................................................... 253.2 CHARACTERISTIC EQUATION

............................................................................................................................ 26

3.3 I-V CURVE OF SOLAR CELL

............................................................................................................................. 284. DC-DC CONVERTERS AND IMPLEMENTATION OF MPPT ................................................................... 304.1 DC-DC CONVERTER TYPES

............................................................................................................................. 304.2 BUCK CONVERTER

........................................................................................................................................

. 314.3 OUR IMPLEMENTATION OF MPPT .................................................................................................................... 325. SUN TRACKING ............................................................................................................................................. 335.1 NEED OF SUN TRACKING

................................................................................................................................ 335.2 HOW TO TRACK

........................................................................................................................................

..... 355.3 ALGORITHMS FOR SUN TRACKING

................................................................................................................... 375.4 SENSORS

........................................................................................................................................

................ 385.5 OUR STRUCTURE FOR SOLAR TRACKING

.......................................................................................................... 396. INVERTERS .................................................................................................................................................... 416.1 CIRCUIT TOPOLOGIES USED IN INVERTERS

........................................................................................................ 416.2 OUTPUT WAVEFORM

...................................................................................................................................... 426.3 THREE-PHASE INVERTERS

............................................................................................................................... 436.4 CONTROL SIGNALS

........................................................................................................................................

. 437. COMMERCIAL IMPLEMENTATION OF SOLAR SYSTEM...................................................................... 447.1 GRID-TIED SYSTEMS

...................................................................................................................................... 447.2 OFF-GRID SOLAR SYSTEMS

.............................................................................................................................. 467.3 SOLAR BATTERY BACKUP - THE PROS AND CONS OF SOLAR BATTERY SYSTEMS

............................................... 468. FINAL IMPLEMENTATION OF OUR SYSTEM .......................................................................................... 478.1 SOLAR PANEL

........................................................................................................................................

........ 47

8.2 DC-DC CONVERTER

...................................................................................................................................... 498.3 SUN

TRACKING............................................................................................................................................... 498.4 CONTROL PART

........................................................................................................................................

...... 498.5 TRANSFORMER

........................................................................................................................................

....... 508.6 BATTERY

........................................................................................................................................

............... 518.7 INVERTER

........................................................................................................................................

.............. 528.8 SCHEMATICS

........................................................................................................................................

.......... 538.9 PCB LAYOUT

........................................................................................................................................

......... 56A. BATTERIES .................................................................................................................................................... 58A.1 INTRODUCTION

........................................................................................................................................

............ 58A.2 CATEGORIES OF BATTERIES

...................................................................................................................................... 59B. TRANSFORMER DESIGN .............................................................................................................................. 62C. INDUCTOR DESIGN ...................................................................................................................................... 63D. SOURCE CODE.................................................................................................................................................... 64D.1 16F877A_MODIFIED.H

........................................................................................................................................

.. 64D.2 ALLOCATIONS.H

........................................................................................................................................

............ 79D.3 SPECSANDDEFS.H

........................................................................................................................................

......... 83D.4 MAIN.C

........................................................................................................................................

...................... 85

D.5 MPPT.C

........................................................................................................................................

..................... 88D.6 SUNTRACK.C

........................................................................................................................................

................ 95D.7 LCD.C

........................................................................................................................................

........................ 99D.8 MISC.C

........................................................................................................................................

..................... 104REFERENCES .............................................................................................

........................................................... 106

1. Energy

1.1 IntroductionEnergy is fundamental to the quality of our lives. Nowadays, we are totally dependent on anabundant and uninterrupted supply of energy for living and working. It is a key ingredient inall sectors of modern economies. We use it constantly at home, at work and for leisure.Energy maintains our standard of living and economy. From the time you wake up to the time

you go to sleep at night, energy has affected your life. Energy is important in everyone’s life,whether you notice it or not. Without it people would have a harder time waking up and aneven harder time getting anywhere. Energy is important in many ways like. You wake up tothe sound of your alarm clock, in a nice warm home. Energy is important to heat our homes,and most houses have gas, oil or electric heaters. The mechanical energy in a wind up alarmor electric energy in a battery or plug in alarm is important to wake you up. Energy is neededto heat water, which is used when you take a shower or wash your face in the morning.Energy even effects when you put on fresh clothes in the morning. Your clothing wereprobably made in a factory, which was powered by electricity. Now a days energy hasbecome more important for the collective good than individual’s need. Electricity runs likeblood through the veins of economy without it the economy will tremble and it will bedifficult for it to survive. Taking in account the diminishing natural resource known tomankind it the need of the hour, that someone stood up and discover new horizons exploremore possibilities and bring forward new ideas to fulfill the exponentially increasing energy

needs of the world’s population.

1.2 Energy Crisis in Pakistan

Energy is one of the most problematic issues in the world. Whereas oil prices are steadilyrising and no stability is seen in near future. Demands of energy from the emerging marketslike China and India growing day by day. Pakistan with official figures of growth rate of 8%will have a definite rise in demand of energy for minimum 3% In USA the Gulf of Mexico isfamous for oil producing and refining facilities. The prosperity of Houston is only due to oilindustry being flourished. However the weather is not so kind on this area and hurricanes and

tornadoes commonly hit the southern part of USA and Caribbean. Such is the volatility offuel market now that just news of one hurricane developing in Caribbean shoots the oil pricesin the world. A few years before oil was being traded on 20$ and nobody ever thought thatthe weather conditions in the gulf can affect the oil market. Politically the Iran situation isdeteriorating day by day where as Iraq condition is not stabilizing. Oil today is being tradedaround 65 $/, and the most vital question now is what will happen if the prices rises to 75 $ oreven one hundred $/barrel. Pakistan with small manufacturing market, surrounded by major

emerging economies like China, India, Malaysia, Indonesia, Philippines and Bangladesh willbe worst effected with the rise of energy prices. As a rule of thumb modern daymanufacturing industries utilize at least 33% production cost in terms of energy prices. Anincrease of energy cost will affect their production cost and will force the manufacturers thateither to reduce the labor cost or to remain competitive in market by improving the qualitystandards. Major giants China and India will benefit with this condition and smallereconomies will suffer badly. Are our policy makers in Islamabad thinking for the gravity ofproblem which is now just standing on our door step? On famous oil embargo days a lot ofresearch in Europe was carried out to find the alternate source of energy. However with thedrop of oil prices such alternatives were uneconomical and therefore shelved. This is the timethat Pakistan now asses very carefully that in case of oil prices rising to 75 $ what actions itshould take to conserve energy and to find the alternate source of energy. A volunteer optionfor all energy users is to conserve energy. To make the plants more efficient and to see thateach drop of petrol is saved .If we make serious study on this subject then we may achieve upto 20% saving in energy ,hence saving in our production cost and making our products more

attractive in international market. Of course the energy conservation programs cost money.However the investment will be rewarding and will be beneficial in long terms. Pakistan’sthermal units are day by day become aging, reducing their output power. With the rise ofdemand we are seeing an acute shortage of energy and hence load shedding and shutting ofthe industrial units. This will seriously affect our competitiveness in the international market.This is the responsibility of government to look for the alternate options for finding theenergy resources. This investment can only be made by the federal government. This is thetime of survival. Only the countries which are prepared for the worst will have a prosperousfuture. But it is extremely difficult for the government with the current economy to blindlyinvest a large amount in alternate energy projects. In light of above facts we volunteer toanalyze, study and implement Alternate energy project and to see the difficulties and it’s costcomparison.

1.3 Sources of EnergyNonrenewableNon-renewable energy is energy, taken from "finite resources that will eventually dwindle,becoming too expensive or too environmentally damaging to retrieve", as opposed torenewable energy sources, which "are naturally replenished in a relatively short period oftime.Following are the details of some Non-renewable energy sources know to man from at leasttwo centuries.

CoalCoal, a fossil fuel, is the largest source of energy for the generation of electricity worldwide,as well as one of the largest worldwide anthropogenic sources of carbon dioxide emissions.Gross carbon dioxide emissions from coal usage are slightly more than those from petroleumand about double the amount from natural gas. Coal is extracted from the ground by mining,

either underground or in open pits.Petroleum OilPetroleum or crude oil is a naturally occurring, flammable liquid found in rock formations inthe Earth consisting of a complex mixture of hydrocarbons of various molecular weights, plusother organic compounds. Petroleum, in one form or another, is not a recent discovery but isnow an important part of politics society and technology. The invention of the internalcombustion engine was the major influence in the rise in the importance of petroleum. In themodern world petroleum has an influence across society, including geopolitics.Natural GasNatural gas is a gas consisting primarily of methane. It is found associated with fossil fuels,in coal beds, as methane catharses, and is created by methanogenic organisms in marshes,bogs, and landfills. It is an important fuel source, a major feedstock for fertilizers, and apotent greenhouse gas.Natural gas is often informally referred to as simply gas, especially when compared to otherenergy sources such as electricity. Before natural gas can be used as a fuel, it must undergoextensive processing to remove almost all materials other than methane. The by-products ofthat processing include ethane, propane, butanes, pentanes and higher molecular weighthydrocarbons, elemental sulfur, and sometimes helium and nitrogen.NuclearNuclear power is any nuclear technology designed to extract usable energy from atomicnuclei via controlled nuclear reactions. The only method in use today is through nuclearfission, though other methods might one day include nuclear fusion and radioactive decay(see below). All utility-scale reactors heat water to produce steam, which is then convertedinto mechanical work for the purpose of generating electricity or propulsion. In 2007, 14% ofthe world's electricity came from nuclear power. Also, more than 150 nuclear-powered navalvessels have been built, and a few radioisotope rockets have been produced. Nuclear power is

a low carbon power source.

RenewableRenewable energy is energy generated from natural resources—such as sunlight, wind, rain,tides, and geothermal heat—which are renewable (naturally replenished). In 2006, about 18%of global final energy consumption came from renewable, with 13% coming from traditionalbiomass, such as wood-burning. Hydroelectricity was the next largest renewable source,providing 3% of global energy consumption and 15% of global electricity generation.Wind power is growing at the rate of 30 percent annually, with a worldwide installed capacityof 121,000 megawatts (MW) in 2008. The annual manufacturing output of the photovoltaic’sindustry reached 6,900 MW in 2008, The world's largest geothermal power installation is TheGeysers in California, with a rated capacity of 750 MW.[8] Brazil has one of the largestrenewable energy programs in the world, involving production of ethanol fuel from sugarcane, and ethanol now provides 18 percent of the country's automotive fuel. Ethanol fuel isalso widely available in the USA. While most renewable energy projects and production islarge-scale, renewable technologies are also suited to small off-grid applications, sometimesin rural and remote areas, where energy is often crucial in human development. Kenya hasthe world's highest household solar ownership rate with roughly 30,000 small (20–100 watt)solar power systems sold per year.Some renewable-energy technologies are criticized for being intermittent or unsightly, yet therenewable-energy market continues to grow. Climate-change concerns, coupled with high oilprices, peak oil, and increasing government support, are driving increasing renewable-energylegislation, incentives and commercialization. New government spending, regulation andpolicies should help the industry weather the 2009 economic crisis better than many othersectors.

SunThe majority of renewable energy technologies are powered by the sun. The Earth-Atmosphere system is in equilibrium such that heat radiation into space is equal to incomingsolar radiation, the resulting level of energy within the Earth-Atmosphere system can roughlybe described as the Earth's "climate." The hydrosphere (water) absorbs a major fraction of theincoming radiation. Most radiation is absorbed at low latitudes around the equator, but thisenergy is dissipated around the globe in the form of winds and ocean currents. Wave motionmay play a role in the process of transferring mechanical energy between the atmosphere andthe ocean through wind stress. Solar energy is also responsible for the distribution ofprecipitation which is tapped by hydroelectric projects, and for the growth of plants used tocreate biofuels.

Renewable energy is derived from natural processes that are replenished constantly. In itsvarious forms, it derives directly from the sun, or from heat generated deep within the earth.

WindAirflows can be used to run wind turbines. Modern wind turbines range from around 600 kWto 5 MW of rated power, although turbines with rated output of 1.5–3 MW have become themost common for commercial use; the power output of a turbine is a function of the cube ofthe wind speed, so as wind speed increases, power output increases dramatically.Areas where winds are stronger and more constant, such as offshore and high altitude sitesare preferred locations for wind farms.Geo ThermalGeothermal energy is energy obtained by tapping the heat of the earth itself, both fromkilometers deep into the Earth's crust in some places of the globe or from some meters ingeothermal heat pump in all the places of the planet. It is expensive to build a power station

but operating costs are low resulting in low energy costs for suitable sites. Ultimately, thisenergy derives from heat in the Earth's core.Three types of power plants are used to generate power from geothermal energy: dry steam,flash, and binary. Dry steam plants take steam out of fractures in the ground and use it todirectly drive a turbine that spins a generator. Flash plants take hot water, usually attemperatures over 200 °C, out of the ground, and allows it to boil as it rises to the surfacethen separates the steam phase in steam/water separators and then runs the steam through aturbine. In binary plants, the hot water flows through heat exchangers, boiling an organicfluid that spins the turbine. The condensed steam and remaining geothermal fluid from allthree types of plants are injected back into the hot rock to pick up more heat.The geothermal energy from the core of the Earth is closer to the surface in some areas thanin others. Where hot underground steam or water can be tapped and brought to the surface itmay be used to generate electricity.There is also the potential to generate geothermal energy from hot dry rocks. Holes at least3 km deep are drilled into the earth. Some of these holes pump water into the earth, whileother holes pump hot water out. The heat resource consists of hot underground radiogenicgranite rocks, which heat up when there is enough sediment between the rock and the earth’ssurface. Several companies in Australia are exploring this technology.

WeatherPower can also be obtained from sewage water. The technique used therefore is Microbialfuel cells. Also using the same microbial fuel cells, instead of from wastewater, energy mayalso be obtained directly from (certain) aquatic plants. These include reed sweet grass, cordgrass, rice, tomatoes, lupines, alga.Bio MassPlants use photosynthesis to grow and produce biomass. Also known as biomaterial, biomasscan be used directly as fuel or to produce biofuels. Agriculturally produced biomass fuels,

such as biodiesel, ethanol and bagasse (often a by-product of sugar cane cultivation) can beburned in internal combustion engines or boilers. Typically biofuel is burned to release itsstored chemical energy. Research into more efficient methods of converting biofuels andother fuels into electricity utilizing fuel cells is an area of very active work.

1.4 Why Every Kind of Energy is Converted into Electric EnergyEvery kind of energy is preferably converted into electrical energy because: It is easy to store electric energy. In this era there many devices that can convert electrical energy into anyother form of energy. It is easy to transport electric energy.1.5 Methods to Generate Electric EnergyThere are seven fundamental methods of directly transforming other forms of energy intoelectrical energy:A.1 Static electricity, from the physical separation and transport of charge(examples: turboelectric effect and lightning)

A.2 Electromagnetic induction, where an electrical generator, dynamo oralternator transforms kinetic energy (energy of motion) into electricityA.3 Electrochemistry, the direct transformation of chemical energy intoelectricity, as in a battery, fuel cell or nerve impulseA.4 Photoelectric effect, the transformation of light into electrical energy, as insolar cellsA.5 Thermoelectric effect, direct conversion of temperature differences toelectricity, as in thermocouples and thermopilesA.6 Piezoelectric effect, from the mechanical strain of electrically anisotropicmolecules or crystalsA.7 Nuclear transformation, the creation and acceleration of charged particles(examples: betavoltaics or alpha particle emission)

Almost all commercial electrical generation is done using electromagnetic induction, inwhich mechanical energy forces an electrical generator to rotate. There are many differentmethods of developing the mechanical energy, including heat engines, hydro, wind and tidalpower.

2. Solar Energy

Solar energy is the radiant light and heat from the Sun that has been exploiting by humanssince ancient times using a range of ever-evolving technologies. Solar radiation along withsecondary solar resources such as wind and wave power, hydroelectricity and biomassaccount for most of the available renewable energy on Earth. Only a little fraction of theavailable solar energy is used.Solar energy refers primarily to the use of solar radiation for practical ends. However, allrenewable energies, other than geothermal and tidal, derive their energy from the sun.Solar technologies are broadly characterized as either passive or active depending on the waythey capture, convert and distribute sunlight. Active solar techniques use photovoltaic panels,pumps, and fans to convert sunlight into useful outputs. Passive solar techniques includeselecting materials with favorable thermal properties, designing spaces that naturally circulateair, and referencing the position of a building to the Sun. Active solar technologies increasethe supply of energy and are considered supply side technologies, while passive solartechnologies reduce the need for alternate resources and are generally considered demand

side technologies.

2.1 Average Energy over the YearsThe Earth receives 174 pet watts (PW) of incoming solar radiation at the upper atmosphere.Approximately 30% is reflected back to space while the rest is absorbed by clouds, oceansand land masses. The spectrum of solar light at the Earth's surface is mostly spread across the

visible and near-infrared ranges with a small part in the near-ultraviolet.The total solar energy absorbed by Earth's atmosphere, oceans and land masses isapproximately 3,850,000 exajoules (EJ) per year. In 2002, this was more energy in one hourthan the world used in one year. Photosynthesis captures approximately 3,000 EJ per year inbiomass. The amount of solar energy reaching the surface of the planet is so vast that in oneyear it is about twice as much as will ever be obtained from all of the Earth's non-renewable

resources of coal, oil, natural gas, and mined uranium combined.

2.2 How Solar Energy is used?

Generate electricity using photovoltaic solar cells. Generate electricity using concentrated solar power. Generate electricity by heating trapped air which rotates turbines in a solarupdraft tower. Generate hydrogen using photo electrochemical cells. Heat and cool air through use of solar chimneys. Heat buildings, directly, through passive solar building design. Heat foodstuffs, through solar ovens. Heat water or air for domestic hot water and space heating needs using solarthermalpanels.

Solar air conditioning

2.3 Solar CellsA solar cell or photovoltaic cell is a device that converts light directly into electricity by the

photovoltaic effect. Sometimes the term solar cell is reserved for devices intendedspecifically to capture energy from sunlight, while the term photovoltaic cell is used when thelight source is unspecified. Assemblies of cells are used to make solar panels, solar modules,or photovoltaic arrays.Types of Solar CellsCrystallineHistorically, crystalline silicon (c-Si) has been used as the lightabsorbingsemiconductor in most solar cells, even though it is arelatively poor absorber of light and requires a considerable

thickness (several hundred microns) of material. Nevertheless, it

has proved convenient because it yields stable solar cells with good efficiencies (11-16%,half to two-thirds of the theoretical maximum) and uses process technology developed fromthe huge knowledge base of the microelectronics industry.Two types of crystalline silicon are used in the industry. The first is monocrystalline,produced by slicing wafers (up to 150mm diameter and 350 microns thick) from a high-puritysingle crystal boule. The second is multicrystalline silicon, made by sawing a cast block ofsilicon first into bars and then wafers. The main trend in crystalline silicon cell manufactureis toward multicrystalline technology.For both mono- and multicrystalline Si, a semiconductor homojunction is formed bydiffusing phosphorus (an n-type dopant) into the top surface of the boron doped (p-type) Siwafer. Screen-printed contacts are applied to the front and rear of the cell, with the front

contact pattern specially designed to allow maximum light exposure of the Si material withminimum electrical (resistive) losses in the cell.AmorphousAn amorphous solar cell is a type of solar cell that is relatively cheap to produce and widelyavailable. They are named so because of their composition at the microscopic scale.Amorphous means "without shape". When the term is applied to solar cells it means that thesilicon material that makes up the cell is not highly structured or crystallized.Amorphous solar cells are usually created by applying doped silicon material to the back of aplate of glass. The cells usually appear dark brown on the sun-facing side and silvery on theconductive side. When produced as a solar panel (a collection of many solar cells) it willappear to have several thin parallel lines running across its surface. These thin lines areactually breaks in the N and P layers of the silicon substrate and they create the boundaries ofindividual cells in the panel. Amorphous solar panels usually come without any obvious

hook-up points or wires. It can be very puzzling to figure out how to use them!

CIGSCopper indium gallium (di)selenide (CIGS) is a I-III-VI2 compound semiconductor materialcomposed of copper, indium, gallium, and selenium. The material is a solid solution ofcopper indium selenide (often abbreviated "CIS") and copper gallium selenide, with achemical formula of CuInxGa(1-x)Se2, where the value of x can vary from 1 (pure copperindium selenide) to 0 (pure copper gallium selenide). It is a tetrahedrally-bondedsemiconductor, with the chalcopyrite crystal structure, and a bandgap varying continuouslywith x from about 1.0eV (for copper indium selenide) to about 1.7eV (for copper galliumselenide). It is used as light absorber material for thin-film solar cells.CIGS is mainly used in photovoltaic cells (CIGS cells), in the form of polycrystalline thin

films. Unlike the silicon cells based on a homojunction p-n junction, the structure of CIGScells is a more complex heterojunction system. The best efficiency achieved as of December2005 was 19.5% reported by Contreras et al. A team at the National Renewable EnergyLaboratory achieved 19.9% new world record efficiency by modifying the CIGS surface andmaking it look like CIS. This idea was first introduced in the IEEE conference in 2005. The19.9% efficiency is by far the highest compared with those achieved by other thin filmtechnologies such as Cadmium Telluride (CdTe) or amorphous silicon (a-Si). . As for CIS,and CGS solar cells, the world record total area efficiencies are 15.0% and 10.2%respectively.CIGS solar cells are not as efficient as crystalline silicon solar cells, for which the recordefficiency lies at 24.7%, but they are expected to be substantially cheaper. CIGS can bedeposited directly onto molybdenum coated glass sheets in a polycrystalline form, saving the(energy) expensive step of growing large crystals, as necessary for solar cells made fromcrystalline silicon. The latter are made of slices of solid silicon and require therefore moreexpensive semiconductor material.

Cross-section of Cu(In,Ga)Se2 solar cell

Three generation of Solar CellsSolar Cells are classified into three generations which indicates the order of which eachbecame important. At present there is concurrent research into all three generations while thefirst generation technologies are most highly represented in commercial production,accounting for 89.6% of 2007 production.First generationFirst generation cells consist of large-area, high quality and single junction devices. FirstGeneration technologies involve high energy and labor inputs which prevent any significantprogress in reducing production costs. Single junction silicon devices are approaching thetheoretical limiting efficiency of 31% and achieve cost parity with fossil fuel energygeneration after a payback period of 5–7 years.Second generationSecond generation materials have been developed to address energy requirements andproduction costs of solar cells. Alternative manufacturing techniques such as vapordeposition, electroplating, and use of Ultrasonic Nozzles are advantageous as they reducehigh temperature processing significantly. It is commonly accepted that as manufacturingtechniques evolve production costs will be dominated by constituent material requirements,whether this be a silicon substrate, or glass cover.The most successful second generation materials have been cadmium telluride (CdTe),copper indium gallium selenide, amorphous silicon and micromorphous silicon. Thesematerials are applied in a thin film to a supporting substrate such as glass or ceramics,reducing material mass and therefore costs. These technologies do hold promise of higherconversion efficiencies, particularly CIGS-CIS, DSC and CdTe offers significantly cheaper

production costs.Among major manufacturers there is certainly a trend toward second generation technologies;however commercialization of these technologies has proven difficult. In 2007 First Solarproduced 200 MW of CdTe solar cells making it the fifth largest producer of solar cells in2007 and the first ever to reach the top 10 from production of second generation technologiesalone. Wurth Solar commercialized its CIGS technology in 2007 producing 15 MW.Nanosolar commercialized its CIGS technology in 2007 with a production capacity of430 MW for 2008 in the USA and Germany.Third generationThird generation technologies aim to enhance poor electrical performance of secondgeneration (thin-film technologies) while maintaining very low production costs.Current research is targeting conversion efficiencies of 30-60% while retaining low costmaterials and manufacturing techniques. They can exceed the theoretical solar conversionefficiency limit for a single energy threshold material, that was calculated in 1961 by

Shockley and Queisser as 31% under 1 sun illumination and 40.8% under the maximal

artificial concentration of sunlight (46,200 suns, which makes the latter limit more difficult toapproach than the former).There are a few approaches to achieving these high efficiencies including the use ofMultijunction photovoltaic cells, concentration of the incident spectrum, the use of thermalgeneration by UV light to enhance voltage or carrier collection, or the use of the infraredspectrum for night-time operation.High efficiency cellsHigh efficiency solar cells are a class of solar cell that can generate more electricity perincident solar power unit (watt/watt). Much of the industry is focused on the most costefficient technologies in terms of cost per generated power. The two main strategies to bring

down the cost of photovoltaic electricity are increasing the efficiency (as many of the costsscale with the area occupied per unit of generated power), and decreasing the cost of the solarcells per generated unit of power. The later approach might come at the expense of reducedefficiency, so the overall cost of the photovoltaic electricity does not necessarily decrease bydecreasing the cost of the solar cells. The challenge of increasing the photovoltaic efficiencyis thus of great interest, both from the academic and economic points of view.2.4 ConstructionSilicon solar cells have been available for a relatively long period of time. In order to increasethe output from such solar cells it has been conventional to provide a single layer antireflectioncoating overlaying the solar cell. Typically these single layer anti-reflectioncoatings have been formed of silicon monoxide, a titanium oxide such as titanium dioxide orgas reacted titanium monoxide as well as tantalum pentoxide. Since the tantalum pentoxideand the titanium oxide have an index of refraction which is greater than that of siliconmonoxide, they form a better anti-reflection coating between the silicon solar cell and theglass cover which conventionally covers such a solar cell.The silicon solar cell construction consists of a body formed essentially of silicon and havinga surface with a photovoltaic junction formed thereon. First and second layers are formed onthe surface of the solar cell and serve to provide an anti-reflection coating which is effectivewithin the spectral range of 400 to 1200 nanometers. A glass solar cell cover is providedwhich is secured to the body having the first and second layers thereon by a cement. The firstlayer is, counting from the body, formed of material that has an index of refraction which isless than that of the body and which is greater than that of the glass cover. The second layer isformed of a material that has an index of refraction which is greater than that of the glass

cover but which is less than that of the first layer.

Solar cells are in fact large area semiconductor diodes. Due to photovoltaic effect energy oflight (energy of photons) converts into electrical current. At p-n junction, an electric field isbuilt up which leads to the separation of the charge carriers (electrons and holes). Atincidence of photon stream onto semiconductor material the electrons are released, if theenergy of photons is sufficient. Contact to a solar cell is realised due to metal contacts. If thecircuit is closed, meaning an electrical load is connected, then direct current flows.2.5 Solar Module and ArrayRegardless of size, a typical silicon PV cell produces about 0.5 – 0.6 volt DC under opencircuit,no-load conditions. The current (and power) output of a PV cell depends on itsefficiency and size (surface area), and is proportional the intensity of sunlight striking thesurface of the cell. For example, under peak sunlight conditions, a typical commercial PV cellwith a surface area of 160 cm^2 (~25 in^2) will produce about 2 watts peak power. If thesunlight intensity were 40 percent of peak, this cell would produce about 0.8 watts.PV cells can be arranged in a series configuration to form a module, and modules can then beconnected in parallel-series configurations to form arrays. When connecting cells or modulesin series, they must have the same current rating to produce an additive voltage output, and

similarly, modules must have the same voltage rating when connected in parallel to produce

larger currents.

Solar cells are typically combined into modules that hold about 40 cells; about 10 of thesemodules are mounted in PV arrays (Array: A collection of photovoltaic modules electricallywired together in one structure to produce a specific amount of power) that can measure up toseveral meters on a side. These flat-plate PV arrays can be mounted at a fixed angle facingsouth, or they can be mounted on a tracking device that follows the sun, allowing them tocapture the most sunlight over the course of a day. About 10 to 20 PV arrays can provideenough power for a household; for large electric utility or industrial applications, hundreds of

arrays can be interconnected to form a single, large PV system.

2.6 Theory of Solar cells

Simple explanation1. Photons in sunlight hit the solar panel and are absorbed by semiconducting materials,such as silicon.2. Electrons (negatively charged) are knocked loose from their atoms, allowing them toflow through the material to produce electricity. Due to the special composition ofsolar cells, the electrons are only allowed to move in a single direction. Thecomplementary positive charges that are also created (like bubbles) are called holesand flow in the direction opposite of the electrons in a silicon solar panel.3. An array of solar cells converts solar energy into a usable amount of direct current

(DC) electricity.

Photo generation of charge carriersWhen a photon hits a piece of silicon, one of three things can happen:1. the photon can pass straight through the silicon — this (generally) happens for lowerenergy photons,2. the photon can reflect off the surface,3. The photon can be absorbed by the silicon, if the photon energy is higher than thesilicon band gap value. This generates an electron-hole pair and sometimes heat,depending on the band structure.When a photon is absorbed, its energy is given to an electron in the crystal lattice. Usuallythis electron is in the valence band, and is tightly bound in covalent bonds betweenneighboring atoms, and hence unable to move far. The energy given to it by the photon"excites" it into the conduction band, where it is free to move around within thesemiconductor. The covalent bond that the electron was previously a part of now has onefewer electron — this is known as a hole. The presence of a missing covalent bond allows thebonded electrons of neighboring atoms to move into the "hole," leaving another hole behind,and in this way a hole can move through the lattice. Thus, it can be said that photons

absorbed in the semiconductor create mobile electron-hole pairs.A

A photon need only have greater energy than that of the band gap in order to excite anelectron from the valence band into the conduction band. However, the solar frequencyspectrum approximates a black body spectrum at ~6000 K, and as such, much of the solarradiation reaching the Earth is composed of photons with energies greater than the band gapof silicon. These higher energy photons will be absorbed by the solar cell, but the differencein energy between these photons and the silicon band gap is converted into heat (via latticevibrations — called phonons) rather than into usable electrical energy.

Charge Carrier SeparationThere are two main modes for charge carrier separation in a solar cell:1. Drift of carriers, driven by an electrostatic field established across the device2. Diffusion of carriers from zones of high carrier concentration to zones of low carrierconcentration (following a gradient of electrochemical potential).In the widely used p-n junction solar cells, the dominant mode of charge carrier separation isby drift. However, in non-p-n-junction solar cells (typical of the third generation solar cell

research such as dye and polymer solar cells), a general electrostatic field has been confirmedto be absent, and the dominant mode of separation is via charge carrier diffusion.The p-n JunctionThe most commonly known solar cell is configured as a large-area p-n junction made fromsilicon. As a simplification, one can imagine bringing a layer of n-type silicon into directcontact with a layer of p-type silicon. In practice, p-n junctions of silicon solar cells are notmade in this way, but rather, by diffusing an n-type dopant into one side of a p-type wafer (orvice versa).If a piece of p-type silicon is placed in intimate contact with a piece of n-type silicon, then adiffusion of electrons occurs from the region of high electron concentration (the n-type sideof the junction) into the region of low electron concentration (p-type side of the junction).When the electrons diffuse across the p-n junction, they recombine with holes on the p-typeside. The diffusion of carriers does not happen indefinitely however, because of an electrifield which is created by the imbalance of charge immediately on either side of the junctionwhich this diffusion creates. The electric field established across the p-n junction creates adiode that promotes charge flow, known as drift current, that opposes and eventually balancesout the diffusion of electron and holes. This region where electrons and holes have diffusedacross the junction is called the depletion region because it no longer contains any mobilecharge carriers. It is also known as the "space charge region".Connection to an External LoadOhmic metal-semiconductor contacts are made to both the n-type and p-type sides of thesolar cell, and the electrodes connected to an external load. Electrons that are created on then-type side, or have been "collected" by the junction and swept onto the n-type side, maytravel through the wire, power the load, and continue through the wire until they reach the ptypesemiconductor-metal contact. Here, they recombine with a hole that was either created

as an electron-hole pair on the p-type side of the solar cell, or are swept across the junctionfrom the n-type side after being created there.The voltage measured is equal to the difference in the quasi Fermi levels of the minority

carriers i.e. electrons in the p-type portion, and holes in the n-type portion.

Electrical Characteristics of SolarCells and Maximum Power Point

3.1 Equivalent circuit of a solar cellTo understand the electronic behavior of a solar cell, it is useful to create a model which iselectrically equivalent, and is based on discrete electrical components whose behavior is well

known

The equivalent circuit of a solar cell

The schematic symbol of a solar cell

An ideal solar cell may be modeled by a current source in parallel with a diode; in practiceno solar cell is ideal, so a shunt resistance and a series resistance component are added to themodel. The resulting equivalent circuit of a solar cell is shown on the FIGURE NUMBER.Also shown, on the FIGURE NUMBER, is the schematic representation of a solar cell for use

in circuit diagrams.

3.2 Characteristic equationFrom the equivalent circuit it is evident that the current produced by the solar cell is equal tothat produced by the current source, minus that which flows through the diode, minus thatwhich flows through the shunt resistor.I = IL − ID − ISH

Where I = output current (amperes) IL = photo generated current (amperes) ID = diode current (amperes) ISH = shunt current (amperes)The current through these elements is governed by the voltage across them:

Vj = V + IRS

Where Vj = voltage across both diode and resistor RSH (volts) V = voltage across the output terminals (volts) I = output current (amperes) RS = series resistance (Ω)By the Shockley diode equation, the current diverted through the diode

is:

where I0 = reverse saturation current(amperes) n = diode ideality factor (1 for an ideal diode) q = elementary charge k = Boltzmann's constant T = absolute temperature

For silicon at 25°C

volts

By Ohm's law, the current diverted through the shunt resistor is:

where7.1 RSH = shunt resistance (Ω)Substituting these into the first equation produces the characteristic equation of a solar cell,which relates solar cell parameters to the output current and voltage:

An alternative derivation produces an equation similar in appearance, but with V on the lefthandside. The two alternatives are identities; that is, they yield precisely the same results.In principle, given a particular operating voltage V the equation may be solved to determinethe operating current I at that voltage. However, because the equation involves I on both sidesin a transcendental function the equation has no general analytical solution. However, evenwithout a solution it is physically instructive. Furthermore, it is easily solved using numericalmethods. (A general analytical solution to the equation is possible using Lambert's Wfunction, but since Lambert's W generally itself must be solved numerically this is atechnicality.)Since the parameters I0, n, RS, and RSH cannot be measured directly, the most commonapplication of the characteristic equation is nonlinear regression to extract the values of theseparameters on the basis of their combined effect on solar cell behavior.

Open-circuit voltage and short-circuit current

When the cell is operated at open circuit, I = 0 and the voltage across the output terminals isdefined as the open-circuit voltage. Assuming the shunt resistance is high enough to neglect

the final term of the characteristic equation, the open-circuit voltage VOC is:

Similarly, when the cell is operated at short circuit, V = 0 and the current I through theterminals is defined as the short-circuit current. It can be shown that for a high-quality solar

cell (low RS and I0, and high RSH) the short-circuit current ISC is:

The values of I0, RS, and RSH are dependent upon the physical size of the solar cell. Incomparing otherwise identical cells, a cell with twice the surface area

of another will, in

principle, have double the I0 because it has twice the junction area across which current canleak. It will also have half the RS and RSH because it has twice the cross-sectional areathrough which current can flow. For this reason, the characteristic equation is frequently

written in terms of current density, or current produced per unit cell area:

Where J = current density (amperes/cm2) JL = photo generated current density (amperes/cm2) Jo= reverse saturation current density (amperes/cm2) rS = specific series resistance (Ω-cm2) rSH = specific shunt resistance (Ω-cm2)This formulation has several advantages. One is that since cell characteristics are referencedto a common cross-sectional area they may be compared for cells of different physicaldimensions. While this is of limited benefit in a manufacturing setting, where all cells tend tobe the same size, it is useful in research and in comparing cells between manufacturers.Another advantage is that the density equation naturally scales the parameter values to similar

orders of magnitude, which can make numerical extraction of them simpler and moreaccurate even with naive solution methods.A practical limitation of this formulation is that as cell sizes shrink, certain parasitic effectsgrow in importance and can affect the extracted parameter values. For example,recombination and contamination of the junction tend to be greatest at the perimeter of thecell, so very small cells may exhibit higher values of J0 or lower values of rSH than largercells that are otherwise identical. In such cases, comparisons between cells must be madecautiously and with these effects in mind.3.3 I-V Curve of Solar CellPV cells can be modeled as a current source in parallel with a diode. When there is no lightpresent to generate any current, the PV cell behaves like a diode. As the intensity of incident

light increases, current is generated by the PV cell, as illustrated in Figure.

Curve of PV Cell and Associated Electrical Diagram

In an ideal cell, the total current I is equal to the current Iℓ generated by the photoelectric

effect minus the diode current ID, according to the equation:

where I0 is the saturation current of the diode, q is the elementary charge 1.6x10-19 Coulombs,k is a constant of value 1.38x10-23J/K, T is the cell temperature in Kelvin, and V is themeasured cell voltage that is either produced (power quadrant) or applied (voltage bias).The I-V curve of an illuminated PV cell has the shape shown in Figure as the voltage across

the measuring load is swept from zero to VOC..

5. Sun TrackingA sun tracker or solar tracker is a device for orienting a day lighting reflector, solarphotovoltaic panel or concentrating solar reflector or lens toward the sun.5.1 Need of Sun TrackingA solar tracker is a device for orienting a day lighting reflector, solar photovoltaic panel orconcentrating solar reflector or lens toward the sun. The sun's position in the sky varies bothwith the seasons and time of day as the sun moves across the sky. Solar powered equipmentworks best when pointed at or near the sun, so a solar tracker can increase the effectiveness ofsuch equipment over any fixed position, at the cost of additional system complexity. Thereare many types of solar trackers, of varying costs, sophistication, and performance. One wellknowntype of solar tracker is the heliostat, a movable mirror that reflects the moving sun to afixed location, but many other approaches are used as well.Tracker mount typesSolar trackers may be active or passive and may be single axis or dual axis. Single axistrackers usually use a polar mount for maximum solar efficiency. Single axis trackers willusually have a manual elevation (axis tilt) adjustment on a second axis which is adjusted onregular intervals throughout the year. Compared to a fixed mount, a single axis trackerincreases annual output by approximately 30%, and a dual axis tracker an additional 6%.There are two types of dual axis trackers, polar and altitude-azimuth.PolarPolar trackers have one axis aligned to be roughly parallel to the axis of rotation of the earth

around the north and south poles—hence the name polar. (With telescopes, this is called

equatorial mount.)

Single axis tracking is often used when combined with time-of-use metering, since strongafternoon performance is particularly desirable for grid-tied photovoltaic systems, asproduction at this time will match the peak demand time for summer season air-conditioning.A fixed system oriented to optimize this limited time performance will have a relatively low annual production. The polar axis should be angled towards due north, and the angle betweenthis axis and the vertical should be equal to your latitude.Simple polar trackers with single axis tracking may also have an adjustment along a secondaxis: the angle of declination. This allows you to angle the panel to face the sun when it ishigher in the sky (and further northward) in the summer, and to face it lower in the sky (andfurther southward) in the winter. It might be set with manual or automated adjustments,depending on your polar-tracking device. If one is not planning on adjusting this angle of

declination at all during the year, it is normally set to zero degrees, facing your panel straightout perpendicular to the polar axis, as that is where the mean path of the sun is found.Occasional or continuous adjustments to the declination compensate for the northward andsouthward shift in the sun's path through the sky as it moves through the seasons (and aroundthe ecliptic) over the course of the year.When the manual method is used for adjustment of the declination, it should be done at leasttwice a year: Once at the autumnal equinox to establish the best position for the winter, and asecond adjustment on the vernal equinox, to optimize it for the summer. The sun's declinationat the spring equinox is 0o. It moves up to 22.5o in the summer, then drifts back down through0o at fall equinox, and down to -22.5o in the winter. So, for example, you might choose to setthe declination at 15o or 20o as a reasonably optimal position for the summer months.Horizontal axleSeveral manufacturers can deliver single axis horizontal trackers which may be oriented byeither passive or active mechanisms, depending upon manufacturer. In these, a longhorizontal tube is supported on bearings mounted upon pylons or frames. The axis of the tubeis on a North-South line. Panels are mounted upon the tube, and the tube will rotate on itsaxis to track the apparent motion of the sun through the day. Since these do not tilt toward theequator they are not especially effective during winter mid day (unless located near the

equator), but add a substantial amount of productivity during the spring and summer seasons

When the solar path is high in the sky. These devices are less effective at higher latitudes.The principal advantage is the inherent robustness of the supporting structure and thesimplicity of the mechanism. Since the panels are horizontal, they can be compactly placed

on the axle tube without danger of self-shading and are also readily accessible for cleaning.

For active mechanisms, a single control and motor may be used to actuate multiple rows ofpanels.Vertical axleA single axis tracker may be constructed that pivots only about a vertical axle, with thepanels either vertical, at a fixed, adjustable, or tracked elevation angle. Such trackers withfixed or (seasonably) adjustable angles are suitable for high latitudes, where the apparentsolar path is not especially high, but which leads to long days in Summer, with the suntraveling through a long arc. This method has been used in the construction of a cylindrical

house in Austria (latitude above 45 degrees north) that rotates in its entirety to track the sun,with vertical panels mounted on one side of the building.Altitude-azimuthA type of mounting that supports the weight of the solar tracker and allows it to move in twodirections to locate a specific target. One axis of support is horizontal (called the altitude) andallows the telescope to move up and down. The other axis is vertical (called the azimuth) andallows the telescope to swing in a circle parallel to the ground. This makes it easy to positionthe telescope: swing it around in a circle and then lift it to the target. However, tracking anobject as the Earth turns is more complicated. The telescope needs to be adjusted in both

directions while tracking, which requires a computer to control the telescope.

5.2 How to Track

Drive TypesActive trackerActive trackers use motors and gear trains to direct the tracker as commanded by a controller

responding to the solar direction.

Active two-axis trackers are also used to orient heliostats - movable mirrors that reflectsunlight toward the absorber of a central power station. As each mirror in a large field willhave an individual orientation these are controlled programmatically through a centralcomputer system, which also allows the system to be shut down when necessary.Light-sensing trackers typically have two photo sensors, such as photodiodes, configureddifferentially so that they output a null when receiving the same light flux. Mechanically,they should be Omni directional (i.e. flat) and are aimed 90 degrees apart. This will cause thesteepest part of their cosine transfer functions to balance at the steepest part, which translatesinto maximum sensitivity.

Since the motors consume energy, one wants to use them only as necessary. So instead of acontinuous motion, the heliostat is moved in discrete steps. Also, if the light is below somethreshold there would not be enough power generated to warrant reorientation. This is alsotrue when there is not enough difference in light level from one direction to another, such aswhen clouds are passing overhead. Consideration must be made to keep the tracker fromwasting energy during cloudy periods.Passive trackerPassive trackers use a low boiling point compressed gas fluid that is driven to one side or theother (by solar heat creating gas pressure) to cause the tracker to move in response to animbalance. As this is a non-precision orientation it is unsuitable for certain types ofconcentrating photovoltaic collectors but works fine for common PV panel types. These willhave viscous dampers to prevent excessive motion in response to wind gusts.Shader/reflectors are used to reflect early morning sunlight to "wake up" the panel and tilt ittoward the sun, which can take nearly an hour. The time to do this can be greatly reduced byadding a self-releasing tie down that positions the panel slightly past the zenith (so that thefluid does not have to overcome gravity) and using the tie down in the evening. (A slackpullingspring will prevent release in windy overnight conditions.)The term "passive tracker" is also used for photovoltaic modules that include a hologrambehind stripes of photovoltaic cells. That way, sunlight passes through the transparent part ofthe module and reflects on the hologram. This allows sunlight to hit the cell from behind,thereby increasing the module's efficiency. Also, the module does not have to move since thehologram always reflects sunlight from the correct angle towards the cells.Chronological trackerA chronological tracker counteracts the Earth's rotation by turning at an equal rate as theearth, but in the opposite direction. Actually the rates aren't quite equal, because as the earth

goes around the sun, the position of the sun changes with respect to the earth by 360° everyyear or 365.24 days. A chronological tracker is a very simple yet potentially a very accuratesolar tracker specifically for use with a polar mount (see above). The drive method may be assimple as a gear motor that rotates at a very slow average rate of one revolution per day (15degrees per hour). In theory the tracker may rotate completely, assuming there is enoughclearance for a complete rotation, and assuming that twisting wires are not an issue, such aswith a solar concentrator, or the tracker may be reset each day to avoid these issues.

Alternatively, an electronic controller may be used, with a real time clock that is used to infer

the "solar time" (hour angle). Tracking adjustments can be made incrementally or

continuously.

5.4 Sensors

LDRA photo resistor or light dependent resistor or cadmium sulfide (CdS) cell is a resistor whoseresistance decreases with increasing incident light intensity. It can also be referenced as aphotoconductor.A photo resistor is made of a high resistance semiconductor. If light falling on the device is ofhigh enough frequency, photons absorbed by the semiconductor give bound electrons enoughenergy to jump into the conduction band. The resulting free electron (and its hole partner)conduct electricity, thereby lowering resistance.A photoelectric device can be either intrinsic or extrinsic. An intrinsic semiconductor has itsown charge carriers and is not an efficient semiconductor, e.g. silicon. In intrinsic devices theonly available electrons are in the valence band, and hence the photon must have enough

energy to excite the electron across the entire band gap. Extrinsic devices have impurities,also called dopants, added whose ground state energy is closer to the conduction band; sincethe electrons do not have as far to jump, lower energy photons (i.e., longer wavelengths andlower frequencies) are sufficient to trigger the device. If a sample of silicon has some of itsatoms replaced by phosphorus atoms (impurities), there will be extra electrons available forconduction. This is an example of an extrinsic semiconductor.Photo DiodesA photodiode is a type of photo detector capable of converting light into either current orvoltage, depending upon the mode of operation.Photodiodes are similar to regular semiconductor diodes except that they may be eitherexposed (to detect vacuum UV or X-rays) or packaged with a window or optical fiberconnection to allow light to reach the sensitive part of the device. Many diodes designed foruse specifically as a photodiode will also use a PIN junction rather than the typical PNjunction.A photodiode is a PN junction or PIN structure. When a photon of sufficient energy strikesthe diode, it excites an electron, thereby creating a mobile electron and a positively chargedelectron hole. If the absorption occurs in the junction's depletion region, or one diffusionlength away from it, these carriers are swept from the junction by the built-in field of thedepletion region. Thus holes move toward the anode, and electrons toward the cathode, and a

photocurrent is produced.

PV CellsA solar cell or photovoltaic cell is a device that converts light directly into electricity by thephotovoltaic effect. Sometimes the term solar cell is reserved for devices intendedspecifically to capture energy from sunlight, while the term photovoltaic cell is used when thelight source is unspecified. Assemblies of cells are used to make solar panels, solar modules,

or photovoltaic arrays. Photovoltaic is the field of technology and research related to theapplication of solar cells in producing electricity for practical use. The energy generated this

way is an example of solar energy

Chapter - 1

Introduction

There are three ways to increase the efficiency of a photovoltaic (PV) system1. The first is to increase the efficiency of the solar cell. The second is to maximize the energy conversion from the solar panel. To better explain this, please refer to Figure 1. A solar panel under an open circuit is able to supply a maximum voltage with no current, while under a short circuit is able to supply a maximum current with no voltage. In either case, the amount of power supplied by the solar panel is zero. The key is to develop a method whereby maximum power can be obtained from the voltage and current multiplied together. This “maximum power point” is illustrated by looking at a voltage-current (VI) curve in Figure 1, and finding the “knee” of the curve. A number of maximum power point tracking (MPPT) algorithms have been developed andemployed.2

Figure 1. Illustration of a V-I Curve for a Solar Panel

The third method to increase the efficiency of a PV system is to employ a solar panel tracking system. Development of solar panel tracking systems has been ongoing for several years now.

As the sun moves across the sky during the day, it is advantageous to have the solar panels track the location of the sun, such that the panels are always perpendicular to the solar energy radiated by the sun. This will tend to maximize the amount of power radiated by the sun. It has been estimated that the use of a tracking system, over a fixed system, can increase the power output by 30% - 60%3. When tracking the sun, it is noted that the direction of the sun, as seen by the solar panel, will vary in two directions. The azimuth angle is the horizontal direction from the observer to the sun4. There is also an altitude angle, representing the vertical direction from the observer to the sun. More effective solar panel trackers are two-axis in nature5,6,7 and have been demonstrated,for example, in the use of a solar oven concentrator8.

The purpose of this paper is to present the results of a project whereby an Electronics

Engineering Technology student developed a one-axis (azimuth) solar panel tracking

system to satisfy the requirements for his capstone senior project. The capstone design

project covers two semesters. In the first (fall) semester, requirements for the project are

identified and long lead materials are ordered. A schedule (Gantt chart) is developed by

the student to ensure that steady progress occurs. During the second (spring) semester,

the project is designed, built and tested to ensure specification compliance. At the end of

the second semester, each project is presented to thefaculty, other students, and to the

community at large as part of a senior design day

Chapter-2

OVERVIEW OF MICROCONTROLLER (AT89C51)

2.1 MICROPROCESSOR AND MICROCONTROLLER BASICS

The past two decades have seen the introduction of a technology that has radically

changed the way in which we analyze and control the world around us. Born of parallel

development in computer architecture and integrated circuit fabrication, the

microprocessor, or “computer on a chip,” first become a commercial reality in 1971 with

the introduction of 4-bit 4004 by a small, unknown company by the name of Intel

Corporation. Other better established, semiconductor firms soon follow Intel’s pioneering

technology so that by the late 1970s one could choose from a half dozen or so

microprocessor types.

The microprocessor[1] has been with us for some 15-years now growing from an

awkward 4-bit chip to a robust 32-bit adult. Soon 64 and 128-bit wizards will appear to

crunch numbers, spreadsheets, and CAD CAM. The engineering community became

aware of, enamored with, the 8-bit microprocessor of the middle to late 1970’s.

The 1970s also saw the growth of the number of personal computer users from a

handful of hobbyists and “hackers” to millions of business, industrial, governmental,

defense, educational, and private users now enjoying the advantages of inexpensive

computing.

New technology makes possible, however, a better type of small computer-one

with not only the CPU on the chip, but RAM, ROM, Timer, UARTS, Ports, and other

common peripheral I/O functions also. The microprocessor has become the

microcontroller[4]. A by-product of microprocessor development was the microcontroller.

The same fabrication techniques and programming concepts that make possible the

general purpose microprocessor also yielded the microcontroller.

Microcontrollers are not as well known to the general public, or even the technical

community, as are the more glamorous microprocessor. The public is, however, very well

aware that “something” is responsible for all of the smart VCRs, clock radios washers,

and dryers, video games, telephones, microwaves, TVs, automobiles, toys, Vending

machines, copiers, elevators, irons, and a myriad of other articles that have suddenly

become intelligent and “programmable.” Companies are also aware that being

competitive in this age of microchip requires their products, or the machinery they use to

make those products, to have some “smarts.”

Some manufacturers, hoping to capitalize on our software investment, have

brought our families of microcontrollers that are software compatible with the older

microprocessor. Other, wishing to optimize the instruction set and architecture to improve

speed and reduce code size, produce totally new designs that had little in common with

their earlier microprocessors. Both of these trend continue.

Microprocessor:

A Microprocessor[4], as the term has come to be known is a general purpose

digital computer central processing unit (CPU). Although popularly known as a

“computer on a chip,” the microprocessor is in no sense a complete digital computer.

Figure 1 shows a block diagram of a microprocessor CPU, which contains

arithmetic and logic unit (ALU), a program counter (PC), a stack pointer (SP), some

working registers, a clock timing circuit and interrupt circuits. The microprocessor

contains no RAM, no ROM, and no I/O ports on the chip itself.

The key term in describing the design of microprocessor is “general purpose.”

The hardware design of a microprocessor CPU is arrange so that a small or very large

system can be configured around the CPU as the application demands. The internal CPU

architecture, as well as the resultant machine level code that operates that architecture, is

comprehensive but as flexible as possible.

Although the addition of external RAM, ROM, and I/O ports make these systems

bulkier and much more expensive, they have the advantage of versatility such that the

designer can decide on the amount of RAM, ROM, and I/O ports needed to fit the task at

hand

Accumulator

Working Register(s)

Interrupt Circuit

Clock Circuit

Program Counter Stack Pointer

Arithmetic and

logic unit

Figure 2.1: A Block Diagram of a Microprocessor

Microcontroller:

A microcontroller[5] has a CPU (a microprocessor) in addition to a fix amount of

RAM, ROM, I/O ports, and a timer all on a single chip. In other words, the processor,

RAM, ROM, I/O ports, and timer are all embedded together on one chip; therefore,

the designer cannot add any external memory, I/O, or timer to it.

Figure 2 shows the block diagram of a typical microcontroller which is a true

computer on a chip. The design incorporates all of the features found in a

microprocessor CPU: ALU, PC, SP, and registers. It also has added the others

features needed to make a complete computer: RAM, ROM, parallel I/O, serial I/O,

counters, and a clock circuit.

Internal ROM

AccumulatorI/O Ports

Interrupt Circuits

Registers

Timer/Counter I/O Ports

Clock Circuit

ALU

Program Counter

Stack Pointer

Internal RAM

Figure 2.2: A block diagram of a Microcontroller

Like the microprocessor, a microcontroller is a general purpose device, but one

which is meant to fetch data, perform limited calculations on that data and control it

environment based on those calculations. The prime use of a microcontroller is to

control the operation of machine using a fixed program that is stored in ROM and that

does not change over the life time of the system.

2.2 CHARACTERISTICS FEATURES OF AT89C51

AT89C51 is an 8-bit microcontroller from Atmel Corporation.

Features

• Compatible with MCS-51™ Products

• 4K Bytes of In-System Reprogrammable Flash Memory

– Endurance: 1,000 Write/Erase Cycles

• Fully Static Operation: 0 Hz to 24 MHz

• Three-level Program Memory Lock

• 128 x 8-bit Internal RAM

• 32 Programmable I/O Lines

• Two 16-bit Timer/Counters

• Six Interrupt Sources

• Programmable Serial Channel

• Low-power Idle and Power-down Modes

2.3 BLOCK DIAGRAM OF AT89C51

The AT89C51[6] is a low-power, high-performance CMOS 8-bit microcomputer

with 4K bytes of Flash programmable and erasable read only memory (PEROM). The

device is manufactured using Atmel’s high-density nonvolatile memory technology and

is compatible with the industry-standard MCS-51 instruction set and pinout. The on-chip

Flash allows the program memory to be reprogrammed in-system or by a conventional

nonvolatile memory programmer. By combining a versatile 8-bit CPU with Flash on a

monolithic chip, the Atmel AT89C51 is a powerful microcomputer which provides a

highly-flexible and cost-effective solution to many embedded control applications.

The AT89C51 provides the following standard features: 4K bytes of Flash, 128

bytes of RAM, 32 I/O lines, two 16-bit timer/counters, a five vector two-level interrupt

architecture, full duplex serial port, on-chip oscillator and clock circuitry. In addition, the

AT89C51 is designed with static logic for operation down to zero frequency and supports

two software selectable power saving modes. The Idle Mode stops the CPU while

allowing the RAM, timer/counters, serial port and interrupt system to continue

functioning. The Power-down Mode saves the RAM contents but freezes the oscillator

disabling all other chip functions until the next hardware reset.

Figure 2.3: Block Diagram of AT89C512.4 PIN DESCRIPTION OF AT89C51:

PDIP: Plastic Dual Inline Package.

Figure 2.4: Pin diagram of AT89C51

Pin description:

In the AT89C51 there are a total of four ports for I/O operations.

Examining Figure 5, note that of the 40 pins, a total of 32 pins are set aside for the

four ports P0, P1, P2, and P3, where each port takes 8 pins. The rest of the pins

are designated as Vcc, GND, XTAL1, XTAL2, RST, EA, ALE/PEOG, and

PSEN.

GND

VCC

PO.O(AD 0)

PO.1(AD 1)

PO.3(AD 3)PO.4(AD 4)

PO.5(AD 5)

PO.6(AD 6)

PO.7(AD 7)

PO.2(AD 2)

EA/VPP

P2.7(AD 15)

P2.6(AD 14)

P2.5(AD 13)

P2.4(AD 12)

ALE/PROGPSEN

P2.3(AD 11)

P2.2(AD 10)

P2.1(AD 9)

P2.0(AD 8)

P1.0

P1.2

P1.3

P1.4P1.5

P1.6

P1.7

P1.1

RST

XTAL2

XTAL1

(RXD) P3.O

(TXD) P3.O

(INT0) P3.2 (INT1) P3.3

(T0) P3.4 (T1) P3.5

(WR) P3.6

(RD) P3.7

VCC:

Supply voltage.

GND:

Ground.

I/O port pins and there functions:

The four ports P0, P1, P2, and P3 each use 8 pins, making them 8 bit

ports. All the ports upon RESET are configured as inputs, ready to be used as

input ports. When the first 0 is written to a port, it becomes an output. To

reconfigure it as an input, a 1 must be sent to the port.

Port 0:

Port 0 is an 8-bit open drain bidirectional I/O port. As an output port each

pin can sink eight TTL inputs. When 1s are written to port 0 pins, the pins can be

used as high-impedance inputs. Port 0 may also be configured to be the

multiplexed low order address/data bus during accesses to external program and

data memory. In this mode P0 has internal pullups. Port 0 also receives the code

bytes during Flash programming, and outputs the code bytes during program

verification. External pullups are required during program verification.

Port 1:

Port 1 is an 8-bit bidirectional I/O port with internal pullups. The Port 1 output

buffers can sink/source four TTL inputs. When 1s are written to Port 1 pins they

are pulled high by the internal pullups and can be used as inputs. As inputs, Port 1

pins that are externally being pulled low will source current (IIL) because of the

internal pullups. Port 1 also receives the low-order address bytes during Flash

programming and program verification.

Port 2:

Port 2 is an 8-bit bi-directional I/O port with internal pullups. The Port 2 output

buffers can sink/source four TTL inputs. When 1s are written to Port 2 pins they

are pulled high by the internal pullups and can be used as inputs. As inputs, Port 2

pins that are externally being pulled low will source current (IIL) because of the

internal pullups. Port 2 emits the high-order address byte during fetches from

external program memory and during accesses to external data memory that use

16-bit addresses (MOVX @ DPTR). In this application, it uses strong internal

pull-ups when emitting 1s. During accesses to external data memory that use 8-bit

addresses (MOVX @ RI), Port 2 emits the contents of the P2 Special Function

Register. Port 2 also receives the high-order address bits and some control signals

during Flash programming and verification.

Port 3:

Port 3 is an 8-bit bi-directional I/O port with internal pullups. The Port 3

output buffers can sink/source four TTL inputs. When 1s are written to Port 3 pins

they are pulled high by the internal pullups and can be used as inputs. As inputs,

Port 3 pins that are externally being pulled low will source current (IIL) because

of the pullups. Port 3 also serves the functions of various special features of the

AT89C51 as listed below:

Table 2.1

Port 3 also receives some control signals for Flash programming and verification.

RST:

Reset input. A high on this pin for two machine cycles while the oscillator

is running resets the device.

ALE/PROG:

Address Latch Enable output pulse for latching the low byte of the address

during accesses to external memory. This pin is also the program pulse input

(PROG) during Flash programming.

In normal operation ALE is emitted at a constant rate of 1/6 the oscillator

frequency, and may be used for external timing or clocking purposes. Note,

however, that one ALE pulse is skipped during each access to external Data

Memory.

If desired, ALE operation can be disabled by setting bit 0 of SFR location 8EH.

With the bit set, ALE is active only during a MOVX or MOVC instruction.

Otherwise, the pin is weakly pulled high. Setting the ALE-disable bit has no

effect if the microcontroller is in external execution mode.

PSEN:

Program Store Enable is the read strobe to external program memory.

When the AT89C51 is executing code from external program memory, PSEN is

activated twice each machine cycle, except that two PSEN activations are skipped

during each access to external data memory.

EA/VPP:

External Access Enable. EA must be strapped to GND in order to enable

the device to fetch code from external program memory locations starting at

0000H up to FFFFH. Note, however, that if lock bit 1 is programmed, EA will be

internally latched on reset. EA should be strapped to VCC for internal program

executions. This pin also receives the 12-volt programming enable voltage (VPP)

during Flash programming, for parts that require 12-volt VPP.

XTAL1:

Input to the inverting oscillator amplifier and input to the internal clock

operating circuit.

XTAL2:

Output from the inverting oscillator amplifier.

Oscillator Characteristics:

XTAL1 and XTAL2 are the input and output, respectively, of an inverting

amplifier which can be configured for use as an on-chip oscillator, as shown in

Figure 6. Either a quartz crystal or ceramic resonator may be used. To drive the

device from an external clock source, XTAL2 should be left unconnected while

XTAL1 is driven as shown in Figure 7.

There are no requirements on the duty cycle of the external clock signal,

since the input to the internal clocking circuitry is through a divide-by-two flip

flop, but minimum and maximum voltage high and low time specifications must

be observed.

Figure 2.5: Oscillator Connections Figure 2.6: External Clock Drive Configurations

Idle Mode:

In idle mode, the CPU puts itself to sleep while all the on-chip peripherals

remain active. The mode is invoked by software. The content of the on-chip RAM

and all the special functions registers remain unchanged during this mode.

The idle mode can be terminated by any enabled interrupt or by a

hardware reset. It should be noted that when idle is terminated by a hard ware

reset, the device normally resumes program execution, from where it left off, up

to two machine cycles before the internal reset algorithm takes control.

On-chip hardware inhibits access to internal RAM in this event, but

access to the port pins is not inhibited. To eliminate the possibility of an

unexpected write to a port pin when Idle is terminated by reset, the instruction

following the one that invokes Idle should not be one that writes to a port pin or to

external memory.

Power-down Mode:

In the power-down mode, the oscillator is stopped, and the instruction that

invokes power-down is the last instruction executed. The on-chip RAM and

Special Function Registers retain their values until the power-down mode is

terminated. The only exit from power-down is a hardware reset. Reset redefines

the SFRs but does not change the on-chip RAM. The reset should not be activated

before VCC is restored to its normal operating level and must be held active long

enough to allow the oscillator to restart and stabilize.

Status of External Pins during Idle and Power-down Modes:

Table 2.2

Other Pin Configurations:

PQFP/TQFP:

PQFP: Plastic Gull Wing Quad Flatpack.

TQFP: Thin Plastic Gull Wing Quad Flatpack.

2.5 8051 ADDRESSING MODES:

An “addressing mode “refers to how you are addressing a given memory

location. The addressing modes are as follows.

With an example of each:

Immediate Addressing MOV A, #20h

Direct Addressing MOV A, 30h

Indirect Addressing MOV A,@R0

External Direct MOV A,@DPTR

Code Indirect MOV A,@+DPTR

Immediate Addressing:

Immediate addressing is so-named because the value to be stored in memory

immediately follows the operation code in memory. That is to say , the instruction

itself dictates what value will be stored in memory.

For example the instruction:

MOV A, #20h

This instruction uses immediate addressing because the Accumulator will

be loaded with the value that immediately follows, in this case 20 (hexadecimal).

Direct Addressing:

Direct addressing is so-named because the value to be stored in memory is

obtained by directly retrieving it from another memory location. For example:

MOV A, 30h

This instruction will read the date out of Internal RAM address30

(hexadecimal) and store it in the Accumulator. Direct addressing is generally fast

since, although the value to be loaded isn’t included in the instruction, it is

quickly accessible since it is stored in the 8051’s Internal RAM. It is also much

more flexible than Immediate Addressing since the value to be loaded is whatever

is found at the given address-which may be variable.

The obvious question that may arise is, “If direct addressing an address

from 80h through FFh refers to SFRs, how can I access the upper 128 bytes of

Internal RAM that are available on the 8052?” The answer is:

You can’t access them using direct addressing. As stated, if you directly refer to

an address of 80h through FFh you will be referring to an SFR. However, you

may access the 8052’s upper 128 bytes of RAM by using the next addressing

mode, “indirect addressing.”

Indirect Addressing:

Indirect addressing is a very powerful addressing mode which in many

cases provides an exceptional level of flexibility. Indirect addressing is also the

only way to access the extra 128 bytes of Internal RAM found on an 8052.

Indirect addressing appears as follows:

MOV A,@R0

This instructing causes the 8051 to analyze the value of the R0 register.

The 8051 will then load the accumulator with the value from Internal RAM which

is found at address indicated by R0. For example, let’s say R0 holds the value 40h

and Internal RAM address 40h holds the value 67h. When the above instruction is

executed the 8051 will check the value of R0. Since R0 holds 40h the 8051 will

get the value out of Internal RAM address 40h (which holds 67h) and store it in

the Accumulator. Thus, the Accumulator ends up holding 67h. Indirect never

refers to Internal RAM; it never refers to an SFR. Thus, in a prior example we

mentioned that SFr 99h can be used to write a value to the serial port. Thus one

may think that the following would be a valid solution to write the value’1’ to the

serial port:

MOV R0,#99h ; Load the address of the serial port

MOV @R0,#01h; Send 01 to the serial port—WRONG!!

This is not valid. Since indirect addressing always refers to Internal RAM

these two instructions would write the value 01h to Internal RAM address 99h on

an 8052. On an 8051 these two instructions would produce an undefined result

since the 8051 only has 128 btes of Internal RAM.

External Direct:

It is used to access external memory rather than internal memory. There

are only two commands that use External Direct addressing mode:

MOVXA,@DPTR

MOVX@DPTR,A

As you can see, both commands utilize DPTR. In these instructions,

DPTR must first be loaded with the address of external memory that you wish to

read or write. Once DPTR holds the correct external memory address, the first

command will move the contents of the external memory address into the

Accumulator. The second command will do the opposite: it will allow you to

write the value of the Accumulator to the external memory address pointed to by

DPTR.

External Indirect:

This form of addressing is usually only used in relatively small projects

that have a very small amount of external RAM. An example of this addressing

mode is:

MOVX@R0,A

Once again, the value of R0 is first read and the value of the Accumulator

is written to that address in External RAM. Since the value of @R0 can only be

00h through FFh the project would effectively be limited to 256 bytes of External

RAM.

Chapter –

Conclusion

In this paper a solar panel tracker has been developed to increase the amount of power

generated by the solar panel as the sun traverses across the sky. An 8051 microcontroller

was used to control the movement of the solar panel. The system was designed to be

autonomous, such that energy generated by the solar panel would be used to charge two

lead acid batteries. The system was successfully demonstrated during a senior design day

presentation, although later subsequent testing yielded system design and /or

implementation flaws. Overall, the system was a positive learning experience for the

student , and allowed him to both maximize his creative potential as well as utilize many

different technologies in the electronics engineering discipline.

CONCLUSIONSolar energy is the main renewable source of energy . But it have many disadvantages whichare harmful for human beings. So the detecting and recording of solar energy have a great importance incoming years to control use and handle the solar radiation (solar energy). This system is easy to implementand have a wide range of applications.This system provide accurate output values for a wide range of environmental conditions..this makesolar recorder to use in areas where human can’t directly reach. This make this embedded system as one ofthe best human friend.

Solar Panel

Solar photo voltaic (SPV). Can be used to generate electricity form the sun.

Silicon solar cells play an important role in generation of electricity.

Solar cells Characteristics. Isc-short circuit current. Voc-open circuit voltage. Peak power.

How solar cells Generate electricity

From Cells to Modules

The open circuit voltage of a single solar cell is approx 0.5V.

Much higher voltage is required for practical application.

Solar cells are connected in series to increase its open circuit voltage.

Advantages The advantage of this unit is that to run the system it does not

need computer Solar cells directly convert the solar radiation into electricity

using photovoltaic effect without going through a thermal process.

During the winter the sun has a low position , tracking angle from sunrise to sunset is shortened.

The plant will not driven up to the final position but just to that position at which really sets, therefore saving of power.

Depending on the radiation intensity, it may sinks under a predefined value for instance at dusk , when the sky is cloudy, tracking is interrupted.

Limitations Using this system at a time we can controls only one solar panel.

Higher hardware expenditure

ObjectiveBy using solar photovoltaics, to harnessthe solar energy and turn it to electricitythat can be stored in batteries which canbe used to power the street light.

APPLICATIONS1. The solar recorder can be used as a intensity meter for light intensity measurements with high accuracy2. It can be used as a digital thermometer for high accuracy temperature measurements3.It can be used as an intensity recorder for long range measurements upto 6 months. The data can besecured for ten years4.It can be used as a temperature recording instrument and the data can be stored upto ten years.5. By measuring and recording the temperature and intensity of light for long periods we can analyze that,that particular place can be used for solar electric power generating station..6.The solar recorders can be interfaced with computers and can be controlled by them. So we can extendthe storage memory and can be interfaced with a network.7. By measuring the temperature and intensity we can maintain the necessary atmospheric conditions for theagricultural field ,medical field ,film industry etc.8.The peripherals of the circuit have a wide range of operating temperature. So we can sense the intensity

and temperature in places where human cannot reach9.By including a few multiplication step we can convert this device into solar power recorder for powermeasurement.10.By measuring the continuous temperature values for a long period we can easily get an idea about theglobal warming rate by plotting a graph.11.It can be used for the study of any radiation which can produce photoelectric effect and/or temperaturevariation.12. It is a real time embedded system so it can be used for real time controlling.

5 ADVANTAGES1. Solar recorders are very cheap as compare with other solar recorders which using pyranometer asintensity sensors.2. LM35 is used in this circuit which is more linear than thermistor which increase accuracy of this circuit.3. This circuit use pic16f877a as microcontroller which has internal ADC, port for serial communication andmore protection circuits as compared to other microcontrollers (8051) which reduces the number of externalperipherals and hence reduces the size of the circuit4.Microcontroller, the other peripherals required only +5v power supply this reduces the power usage sothis circuit require battery (9-30v) for driving the circuit this again reduces the cost.5. Microcontroller has 8kb of internal program memory so there is no need for external memory.6. Solar recorder has external flash memory of 512kb which can be extended up to 1MB of permanentstorage of data this help to increase the continuous working up to 1 year.7. By interfacing with computer, we can extend storage space into a large extend

8. Small size of the embedded system made it more reliable , it is very easy to handle9.Display unit (LCD display) need only low power and it have an internal light source which make it to usein low light area.10. Using a computer interface through USART software of solar recorder can be modified to addadditional functions.11. The solar recorder only using bellow 50% of output port so hardware modification of solar recorder ispossible12. The wide range of operating range of sensors (LM35 (-55 to+155c) make it possible to operate in widerange of environment parameters.

PRECAUTIONS1. Temperature to be measured should be lies between -55 & 155 for accurate measurement andfor the safety of temperature sensor (LM35)2. Use of reset switch should be minimize to minimize the power usage.3. Power supply applied should be between 9V and 100v for safety operation of solar recorder(flash memory chip & microcontroller). So battery checking and replacing should be done atregular intervals. if input voltage is more than 100V it should destroy the capacitors of circuit.If the input voltage is bellow 9V the voltage regulator unable to produce +5V.That create errorsin operation of device.4. The memory chip have a maximum capacity to store upto 6 months, so it should be replaced ordata should saved to computer and clear the memory to avoid the erroneous recording of data.5. There is no protection is provided for the safety of sensor unit for maximum accuratemeasurement. So special care should be taken for the safety of sensors (solar panel & LM35).6. In modification of software some precautions are to be taken, that is the modification not affectthe booting program and the main part of the program.7. There is no switch provided to control the power supply. So external switch is connected forsafety turn of and turn on.8. There is a time delay is provided between power supply on and turn on of individualcomponents of solar recorder for safety and accurate operation of device. So key press and

controlling through serial port should be given only after the display unit display the currentvalue that the sensor measured.

Referencea. Microchip reference manual DS30292B from www.Microchip.comb. Fairchild reference manual KA78XX/KA78XXA from www.fairchildsemi.comc. Atmel reference manual 5297A from www.atmel.comd. National semiconductor reference manual DS005516 from www.national.come. Microchip reference manual DS00826A from www.microchip.comf. www.atmel.comg. Microchip reference manual DS30292C from www.microchip.comh. Microchip reference manual DS41159Cfrom www.microchip.comi. Reference manual AXE033 from www.rev-ed.co.uk.

SUNTRACKER

Even after all this time, the sun never says to the earth, "You owe Me." - From The Gift by Hafiz

A day will come when all the fossil fuels will get exhausted. With rising fuel costs, climate change concerns and a growing demand for electricity, renewable energy resources such as solar power and wind power are becoming an increasingly valuable part of the world's energy mix. Around the globe, businesses and homeowners are harnessing the power of the earth's most abundant natural resource - sunlight - to provide energy using solar power. Most widely used solar energy harnessing is done through solar panels. If we are able to make a solar panel to turn according to the movement of sun from morning to evening, obviously with little thinking we find that efficiency of the solar panel can be increased. What we need is an automated tracking mechanism that keeps the panel perpendicular to sun all the day. ARENA For the current event you are asked to design a control system for the panel and frame arrangement that you will be given at the venue. The frame consists of a base to hold the solar panel. The frame is allowed is rotate in one axis for tracking. The frame can be driven by an

electric motor whose motion has to be controlled autonomously with the control system that you have designed. The event will be held in a dark room, where your design will be tested against a moving sodium vapour lamp. INTRODUCTION TO TRACKING For participating in this event all that you need to have is a little knowledge on sensors and motors. The control system can be made out of discrete electronic components or can use a microcontroller. The one using microcontroller though may seem to be complicated for a beginner but when done properly can make it a good reliable one. Different Approaches to the control system design: 1: Using discrete components: Here sensors and associated electronic circuits are the basic requirements. First about choosing the sensors. This can be decided based on the electronics circuit you are going to use/design for the present problem. There are a large number of electronic circuits which can be designed for this. You can design

your own circuit with the easily available cheap components such as transistors, op‐amps etc. The basic idea behind all such circuit is that the motor should start rotating when the panel is not facing the sun in the expected manner and stops when the desired position is achieved. This can be easily designed using transistors/ Darlington pairs and LDRs as biasing resistors in suitable places such that if the output is ON, motor will be ON and OFF in the other cases. For the sensor, LDR is the cheapest and better sensible to visible light. Photo diode and phototransistor are other options, but are very costly. Another choice for the design is by using opamps and comparators with the above mentioned basic principle. For more information relating to such circuits, you can refer ‘Encyclopedia of electronic circuits’ by Rudolf F Graf and the eBook ‘My experience in autonomous robotics by Bibin John. http://www.geocities.com/njbibin/robobook.html 2: Using Microcontrollers: The main advantage in going for a microcontroller controlled system is its reliability. Once calibrated properly with the sensors, the circuit will be smooth to operate. The same microcontroller can be programmed for any other system to suit your needs. Assume you are using two LDR’s, and you have connected to MC through two pins. All you have to do is to program the MC such that it continuously checks the input from those two pins, and check the one in darker region and the one illuminated brightly. The MC will then drive the motor connected to it and aligns the solar panel such that all the sensors are illuminated equally thus keeping the panel to our desired position of maximum intensity. However you can increase the number of sensors used and thus making the system more accurate and reliable. For further details on microcontroller based solar trackers, you can visit the website http://www.8051projects.info. which can give you a detailed idea of a simple solar tracker. For those who are beginner to the world of microcontrollers and stepper motors, here is the link

http://www.societyofrobots.com. SENSOR LDR (Light dependent resistor) is the most reliable and cheapest sensor that can be used for light sensing (Visible range). LDR is basically a resistor whose resistance varies with intensity of light. More intensity less its resistance (i.e., in black it offers high resistance and in white it offers less resistance). LDR connection: The basic circuit for connecting an LDR is shown in the figure. Vo is fed in to the microcontroller. When under bright light, the resistance of the LDR is very low

and vice versa. So the Vo input voltage to the MC will be small for the LDR exposed to lesser intensity. This magnitude of this voltage will be realised by the MC through ADC (Analogue to digital) conversion.

Different LDR sensors available in the market are shown below:

These sensors are made of Cadmium Sulphide. More the area of the sensor, more its sensitivity.

Position the sensors For a one dimensional tracking, either of the two methods are recommended,

1.) Direct sensing: This employs the conventional method of placing sensors (LDR suggested) at different positions of the panel to get a clear idea of the distribution of energy on the surface of the solar panel. But the major disadvantage in this scenario is the proper calibration of the sensors. Sometimes it is even necessary to calibrate each sensor individually.

2.) Move out of Shadow: In this method raise a pillar and arrange the sensors around it and try to get the shadow properly on all sensors. If there is any inclination of the panel with the light source, at least one sensor will give the signal to MC. Simultaneously the MC can make the motors aligned to the light source. An easy to make and calibrate method.

Selection of motors Any type of DC motors can be used for the suntracker. But we suggest using high torque geared DC motors or Servo type motors. Since the solar panel arrangement is heavy and so the motor requires a high holding torque for keeping the panel at a particular position. Stepper motors can also be used, but since most common stepper motors available does not give enough dynamic torque, these motors if used have to be selected properly. All these selections are to be based on the criteria of producing torque to

move the heavy solar panel (1.960kg). MICROCONTROLLER

This is the decision making part of the control system. Microcontrollers are programmable ICs whose output varies according to its input and according to the program that we write inside it. Our task is to make the program in C(& many other programming languages are possible) and compile it and write its machine code into the microcontroller memory, there are many microcontroller available in the market you may use any of them. Like AtMega, PIC etc

Power Supply There should be sufficient power to drive both the circuit and the motors. Ordinary AAA cells would be sufficient. It would be better if you could use separate power supplies for the circuit and motors.