CHAPTER ONE INTRODUCTION 1.1 BACKGROUND OF STUDY We are like tenant farmers chopping down the fence around our house for fuel when we should be using nature's inexhaustible sources of energy -- sun, wind and tide (Edison, 1931) In 1931, not long before he died, the inventor told his friends Henry Ford and Harvey Firestone: ‘I’d put my money on the sun and solar energy. what a source of power! I hope we don't have to wait until oil and coal run out before we tackle that.’ Solar power is a big idea, whose time has come. And, like the space program, solar is an idea that can shape our nation in significant and positive ways. In the coming months, in the coming years, we will face critical decisions on how to address climate change, reduce our dependence on foreign energy, and boost our economic competitiveness. The beauty of solar power is that it offers an elegant solution to all three of these challenges. Imagine what it would be like if every time that it rained it rained oil, big black drops falling from the sky. Don't you think that we would find some way to run around with a big bucket and collect all of that energy that was falling from the sky? I know this sounds like an absurd picture, but the reality is that what we have outside today is something very comparable to that. (Gifford, 2008) Solar energy is quite simply the energy produced directly by the sun and collected elsewhere, normally the Earth. The sun creates its energy through a thermonuclear process that converts about 650,000,000tons of hydrogen to helium every second. The process creates heat and electromagnetic radiation. The heat remains in the sun and is instrumental in maintaining the thermonuclear reaction. The electromagnetic radiation (including visible light, infra-red light, and ultra-violet radiation) streams out into space in all directions. Only a very small fraction of the total radiation produced reaches the Earth. The radiation that does reach the Earth is the indirect source of nearly every type of energy used today. The exceptions are geothermal energy, and nuclear fission and fusion. Even fossil fuels owe their origins to the sun; they were once living plants and animals whose life was dependent upon the sun. Solar power is a safe form of nuclear energy. We are using fusion reactions that are 93 million miles away to make light that we then convert to electricity with photovoltaic modules (White, 2014). Solar energy can be utilized to produce electric power by a solar inverter. A solar power inverter is similar to a normal electric inverter but uses the energy of the sun The need of running AC Loads on solar energy leads us to the design of Solar Power Inverter. Since the majority of modern conveniences all run on 240 volts AC, the Power Inverter will be the heart of the Solar Energy System. It not only converts the low voltage 12 volts DC to the 240 volts AC that runs most appliances, but also can charge the batteries. A solar inverter or PV (photovoltaic) inverter, is a type of electrical converter which converts the variable direct current (DC) output of a photovoltaic (PV) solar panel into a utility frequency alternating current (AC) that can be fed into a commercial electrical grid or used by a local, offgrid electrical network. It is a critical balance of system (BOS)–component in a photovoltaic system, allowing the use of ordinary AC-powered equipment. Solar power inverters have special functions adapted for use with photovoltaic arrays, including maximum power point tracking and anti-islanding protect (Wikipedia, 2014) The solar inverter is a critical component in a solar energy system. It performs the conversion of the variable DC output of the Photovoltaic (PV) module(s) into a clean sinusoidal 50 or 60 Hz AC current that is then applied directly to the commercial electrical grid or to a local, off-grid electrical network 1.2 PROBLEM STATEMENT 1.3 AIM AND OBJECTIVES 1.3.1 AIM The main aim of this project is to design and construct a 2KVA solar power inverter 1.3.2 OBJECTIVES The objectives are; Review of the project Design of a 2KVA solar power inverter Construction of a 2KVA solar power inverter Test 1.4 SCOPE OF STUDY Solar energy makes it possible to provide a clean reliable supply of alternative electricity free of sags or surges which could be found in the line voltage frequency. This project design aims at creating a 2KVA power source which can be utilized as a regular power source by individuals at home or in the office This project covers the design and construction of a 2KVA Solar Power inverter which involves a solar panel, battery and an inverter. .1.5 SIGNIFICANCE OF PROJECT The major problem solved by this design is regularity of electricity supply at all times, as the battery will be constantly charged during day periods without affecting the integrity of the battery during night periods when it will be used as an alternate source if supply from the national grid fails The projects seek to improve solar power inverters and bring innovative features such as Availability of a low-cost power source An ecofriendly backup power supply Low maintenance cost The use of solar power has many advantages. First, the energy from the sun is free and readily accessible in most parts of the world. Moreover, the sun will keep shining until the world's end. Also, silicon from which most photovoltaic cells are made is an abundant and nontoxic element (the second most abundant material in the earth's crust). Second, the whole energy conversion process is environmentally friendly. It produces no noise, harmful emissions or polluting gases. The burning of natural resources for energy can create smoke, cause acid rain and pollute water and air. Carbon dioxide, CO2, a leading greenhouse gas, is also produced in the case of burning fuels. Solar power uses only the power of the sun as its fuel. It creates no harmful by-product and contributes actively to the reduction of global warming. 1.6 ORGANISATION OF CHARTS There are two chapters in all Chapter 1 explains the background of the project, statement of problem, aims and objectives of the project, significance of project and limitations Chapter 2 talks of the literature review which entails the introduction to solar energy, solar cells, how solar cells work, inverters, types of inverter and battery 1.7 LIMITATONS The major limitation of this project is the dependence on a battery source to operate at night and dc energy from solar panel to operate in the day. This means the possibility and duration of operation is dependent on the availability of a DC source (battery or solar panel) to operate. CHAPTER TWO LITERATURE REVIEW 2.1 INTRODUCTION TO SOLAR ENERY In today's climate of growing energy needs and increasing environmental concern, alternatives to the use of non-renewable and polluting fossil fuels have to be investigated. One such alternative is solar energy. Solar energy is quite simply the energy produced directly by the sun and collected elsewhere, normally the Earth. The sun creates its energy through a thermonuclear process that converts about 650,000,000 tons of hydrogen to helium every second. The process creates heat and electromagnetic radiation. The heat remains in the sun and is instrumental in maintaining the thermonuclear reaction. The electromagnetic radiation (including visible light, infra-red light, and ultra-violet radiation) streams out into space in all directions. Only a very small fraction of the total radiation produced reaches the Earth. The radiation that does reach the Earth is the indirect source of nearly every type of energy used today. The exceptions are geothermal energy, and nuclear fission and fusion. Even fossil fuels owe their origins to the sun; they were once living plants and animals whose life was dependent upon the sun. Much of the world's required energy can be supplied directly by solar power. More still can be provided indirectly 2.2 SOLAR PANELS A solar panel is a device that collects and converts solar energy into electricity or heat. Solar photovoltaic panels can be made so that the sun's energy excites the atoms in a silicon layer between two protector panels. Electrons from these excited atoms form an electric current, which can be used by external devices. Solar panels were in use over one hundred years ago for water heating in homes. Solar panels can also be made with a specially shaped mirror that concentrates light onto a tube of oil. The oil then heats up, and travels through a vat of water, instantly boiling it. The steam is created and then it turns a turbine for power. Some materials are able to absorb photons of light and release electron, this phenomenon is called photoelectric effect. Photovoltaic cells convert sunlight directly into electrical energy without using any mechanical or chemical mechanism. Photovoltaic cell operation is based on the principal of semiconductor technology. When two semiconductors, such as silicon and gallium arsenide, are put into contact with each other and exposed to light, electricity will flow between them. This was first noted by Edmund Becquerel in 1839 (SEIA). Actual development of PV technology began in the 1950s and gained greater impetus through the National Aeronautics and Space Administration (NASA) space program during the 1960s (NASA). Now researchers are trying to increase conversion efficiencies and mass production strategies in order to cost down the producing of PV modules. Solar energy offers several advantages over other energy sources It consumes no conventional fossil fuels, Creates no pollution Is a widely available and reliable source of energy- Has no associated storage or transportation difficulties Is eminently reliable and practicable for wide scale power production However, this technology can be limited because of the movement of the sun, especially in extreme latitudes. A variety of materials may be used in the manufacture of solar cells, each of which has different cost efficiency. In fact, PV cells must be designed to convert different wave lengths of sunlight that reaches the earth's surface into useful energy with high efficiency. The materials used to make solar cells can be classified into three generations: The first generation of PV technologies: crystalline silicon cells. Silicon is one of the most abundant elements on the earth and it is very suitable for use in photovoltaic systems. Depending on how silicon wafers are made, crystalline silicon cells are divided into two general categories: mono-crystalline silicon and poly-crystalline silicon. Other crystalline categories include gallium arsenide cells. Second generation of PV technologies: Thin film solar cells. After more than 20 years of research and development, thin film solar cells have started to spread. Compared to silicon wafers, thin films reduced the cost of electricity quite significant. Three main types of thin film solar cells, which have already been commercialized, are: Amorphous silicon (aSi/µc-Si) Cadmium telluride (Cd-Te) Copper–indium–selenide (CIS) and Copper- indium –gallium- selenide (CIGS) The third generation of PV technologies: In development. These technologies are still and still being developed and tested. They include: Concentrated photovoltaic (CPV) Organic solar cells Dye-sensitized solar cell Polymer solar cells Liquid-crystal solar cells Crystalline Silicon Cell Structure (Four Peaks Technologies, 2011) Layers of a Solar Cell Dako Power, cc 2008 2.3 HISTORY OF SOLAR CELL The history of solar cells started way back in 1876. William Grylls Adams along with a student of his, Richard Day, discovered that when selenium was exposed to light, it produced electricity. An electricity expert, Werner von Siemens, stated that the discovery was “scientifically of the most far-reaching importance”. The selenium cells were not efficient, but it was proved that light, without heat or moving parts, could be converted into electricity. In 1953, Calvin Fuller, Gerald Pearson, and Daryl Chapin, discovered the silicon solar cell. This cell actually produced enough electricity and was efficient enough to run small electrical devices. The New York Times stated that this discovery was “the beginning of a new era, leading eventually to the realization of harnessing the almost limitless energy of the sun for the uses of civilization.” The year is 1956, and the first solar cells are available commercially. The cost however is far from the reach of everyday people. At $300 for a 1-watt solar cell, the expense was far beyond anyone’s means. 1956 started showing us the first solar cells used in toys and radios. These novelty items were the first item to have solar cells available to consumers. In the late 1950’s and early 1960’s satellites in the USA’s and Soviet’s space program were powered by solar cells and in the late 1960’s solar power was basically the standard for powering space bound satellites. In the early 1970’s a way to lower to cost of solar cells was discovered. This brought the price down from $100 per watt to around $20 per watt. This research was spearheaded by Exxon. Most off-shore oil rigs used the solar cells to power the waning lights on the top of the rigs. The period from the 1970’s to the 1990’s saw quite a change in the usage of solar cells. They began showing up on railroad crossings, in remote places to power homes, Australia used solar cells in their microwave towers to expand their telecommunication capabilities. Even desert regions saw solar power bring water to the soil where line fed power was not an option! Today we see solar cells in a wide variety of places. You may see solar powered cars. There is even a solar powered aircraft that has flown higher than any other aircraft with the exception of the Blackbird. With the cost of solar cells well within everyone’s budget, solar power has never looked so tempting. Recently new technology has given us screen printed solar cells, and a solar fabric that can be used to side a house, even solar shingles that install on our roofs. International markets have opened up and solar panel manufacturers are now playing a key role in the solar power industry. 2.4 HOW SOLAR PANELS WORK The basic element of solar panels is pure silicon. When stripped of impurities, silicon makes an ideal neutral platform for transmission of electrons. In silicon’s natural state, it carries four electrons, but has room for eight. Therefore, silicon has room for four more electrons. If a silicon atom comes in contact with another silicon atom, each receives the other atom's four electrons. Eight electrons satisfy the atoms' needs, this creates a strong bond, but there is no positive or negative charge. This material is used on the plates of solar panels. Combining silicon with other elements that have a positive or negative charge can also create solar panels. For example, phosphorus has five electrons to offer to other atoms. If silicon and phosphorus are combined chemically, the results are a stable eight electrons with an additional free electron. The silicon does not need the free electron, but it cannot leave because it is bonded to the other phosphorous atom. Therefore, this silicon and phosphorus plate is considered to be negatively charged. A positive charge must also be created in order for electricity to flow. Combining silicon with an element such as boron, which only has three electrons to offer, creates a positive charge. A silicon and boron plate still have one spot available for another electron. Therefore, the plate has a positive charge. The two plates are sandwiched together to make solar panels, with conductive wires running between them. Photons bombard the silicon/phosphorus atoms when the negative plates of solar cells are pointed at the sun. Eventually, the 9th electron is knocked off the outer ring. Since the positive silicon/boron plate draws it into the open spot on its own outer band, this electron does not remain free for long. As the sun's photons break off more electrons, electricity is then generated. When all of the conductive wires draw the free electrons away from the plates, there is enough electricity to power low amperage motors or other electronics, although the electricity generated by one solar cell is not very impressive by itself. When electrons are not used or lost to the air they are returned to the negative plate and the entire process begins again 2.5 METHODS FOR USING SOLAR ENERGY Photovoltaic systems are applicable for public consumption and agriculture. It can be connected to the power grid or works as stand-alone systems (autonomous) with the fixed or mobile structure in small or large scale from providing energy required for small calculators to large power plant. Possibility to track the sun and maximizing electricity generation from the sun light during the day are the key advantages of using mobile system however due to the high risk of failures in mechanical systems, using this technology for small and sporadic scale are not recommended. This technology has been used only in few PV power plants around the worlds. 2.5.1 GRID CONNECTED In this method, electrical energy from photovoltaic systems is transferred directly to the national power grid. Voltage and frequency of the electrical energy produced by the photovoltaic system can be adjusted to meet the voltage, frequency and phase characteristic of the national power grid using electrical equipment to convert direct current (DC) to alternating current (AC), such as inverters connected to the network and etc.) Centralize/decentralize form of grid connected PV system boosts energy power of distribution network (injected voltage and current prevents voltage drop of power distribution network during the day.) By implementing grid connected PV system, each member of national power grid represents as a small distributed generation (DG). In addition to providing enough supply of electrical energy required by the consumer; a consumer surplus can be injected to distributed network grid Grid-Connected Small Solar Electric Systems (Encyclopedia of Science) 2.5.2 STAND-ALONE PV SYSTEM A stand-alone system provides energy for telecommunications, residential house, nomadic tents and rural cottages needs, in general areas lacking electricity network. These systems produce a high proportion of the world’s off-grid power generation. In many countries without electricity (especially developing countries) these systems can be used to provide electrical energy requirements of villages, for example, Indonesia has been providing electricity for rural households in this way, since 2007. (RENDEV, 2009) The major benefits of these systems, particularly in deprived and rural areas are: No need for fuel and problems to providing it, especially in hard to reach areas. No need for constant repair and maintenance with proper lifetime. 2.6 INVERTERS The inverter takes DC power from the charged battery bank and converts it to AC power for the typical household lights and appliances. Once the number of watt-hours required for a day is determined, the peak loads need to be ascertained to properly size the inverter. This is the number of watts used based on all appliances and loads that will be running at one time. A water pump and washing machine motor is an example of what may be the peak load requirements. A 1/2 HP (horse power) pump and washing machine will use about 1875 (adjusted) watts per hour. If this represents the total peak loads, an inverter that will be able to supply at least 1875 watts of continuous power from the battery bank; say one in the 2000-watt range will be needed. It's a good idea to start out the system with the size of inverter you plan to grow into, as upgrading to newer, larger models is costly. (Pure Energies 2014) 2.7 TYPES OF INVERTERS There are two basic types of inverters. 2.7.1 CENTRAL INVERTERS Central inverters are well-tested and reliable systems that have been around for decades. These are the most common types of inverters. With central inverters, every solar panel is wired in a “string” to the inverter box. The conversion from DC to AC occurs at one central location, such as a garage. Because the solar panels are wired in “series,” each panel’s power output depends on all of the panels working. For example, In a string of Christmas tree lights. If one bulb goes out, the whole string of lights go out until the bad bulb is replaced. So, if shade from a tree covers one panel, it can seriously diminish the power produced by the whole solar system until the shade clears. This is why an accurate shade analysis is so important. 2.7.2 MICRO INVERTERS Micro inverters are relatively new to solar. Instead of converting the DC to AC power at a central location, micro inverters are installed right under each solar panel. The main advantage to micro inverters is the ability for each solar panel to transmit power into the house. In other words, each panel produces its own solar power and keeps producing out solar watts regardless of what happening to the panel beside it. The down side of micro inverters is that they can be more expensive and take more labor cost to replace each inverter. Also, because they are so new, micro inverter reliability is unproven outside of lab testing. (Pure Energies 2014) 2.8 HARDWARE REQUIREMENT FOR INVERTERS Battery PWM Inverter MOSFET Photovoltaic cells/solar cells Resistor Capacitor 2.8.1 BATTERY An electrical battery is a combination of one or more electrochemical cells, used to convert stored chemical energy into electrical energy. The battery has become a common power source for many household, robotics and industrial applications. Larger batteries provide standby power for telephone exchanges or computer data centers. 2.8.2 PWM (Pulse Wave Modulation) INVERTER IC The PWM Inverter is used to develop the PWM pulses based on a fixed frequency using a common oscillator The IC SG3524 operates at a fixed frequency, the oscillation frequency is determined by one timing resistor RT and one timing capacitor CT. The SG3524 contains an inbuilt 5V regulator that supplies as a reference voltage, also providing the SG3524 internal regulator control circuitry. Comparator provides a linear control of the output pulse width (duration) by the error amplifier. The resultant PWM pulse from the comparator is passed to the corresponding output pass transistor (Q1, Q2 refers block diagram) using the pulse steering flip flop, which is synchronously toggled by the oscillator output. 2.8.3 MOSFET (IRF 510) The metal–oxide–semiconductor field-effect transistor (MOSFET, MOS-FET, or MOS FET) is a device used for amplifying or switching electronic signalsThe basic principle of the device a voltage on the oxide-insulated gate electrode can induce a conducting channel between the two other contacts called the source and drainIt is by far the most common transistor in both digital and analog circuits, though the bipolar junction transistor was at one time much more common. 2.8.4 BC547 (NPN –Transistor) The BC547 transistor is an NPN Epitaxial Silicon Transistor. It is used in general-purpose switching and amplification BC847/BC547 series 45 V, 100 mA NPN general-purpose transistors. The ratio of two currents (Ic/Ib) is called the DC Current Gain of the device and is given the symbol of hfe or nowadays Beta, (β). The current gain from the emitter to the collector terminal, Ic/Ie, is called Alpha, (α), and is a function of the transistor itself. 2.8.5 1N4148 The 1N4148 is a standard small signal silicon diode used in signal processing. The 1N4148 is generally available in a DO-35 glass package and is very useful at high frequencies with a reverse recovery time of no more than 4ns. This permits rectification and detection of radio frequency signals very effectively, as long as their amplitude is above the forward conduction threshold of silicon (around 0.7V) or the diode is biased.