Index
Chapter No1:
Page No.
Introduction
2
(A) Need for sustainable energy sources
3-4
(B) Solar energy- a sustainable and clean energy
5-8
Chapter No 2: Solar Battery Charger-A solar powered device
9
(A) Details of the components used
10-20
(B) Circuit Diagram, block diagram, construction, layout
21-23
(C) Working and uses of solar battery charger
24-25
Conclusion
26
References
27
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Introduction: The world energy requirement is ever growing, particularly since the last few centuries. It is expected to grow in the future. There are two main drivers for increase in the energy demand: (a) growth in world’s population (b) the technoeconomical growth of the countries, particularly developing countries. As both of these grow, the energy demand grows. The total energy consumed in the form of coal, gas and oil, nuclear hydro and renewable energy sources is known as primary energy. As per International Energy Agency (IEA) the primary energy consumption has been grown by 5%. the world population increased 5%, annual CO2 emissions increased 10% and gross energy production increased 10%.Below is the energy consumption of the world as measured in 2010
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(A) Need for sustainable energy sources From the given data it is clear that the energy requirement of the world is ever increasing. The increasing energy demand put a lot of pressure on the conventional energy sources (oil, gas and coal). But the fossil fuel-based energy sources are limited in quantity and also cause environmental pollution. Therefore, there is a need for alternative energy sources which can provide us energy in sustainable manner. The problems of fossil fuel-based energy sources to become sustainable energy sources of the future are as follow. (i) Limited fossil fuels: Conventional energy sources are the one that have been using so far to fulfill most of our daily energy requirements of cooking, lighting, transportation, etc. these are based on fossil fuels like coal, petrol, diesel, kerosene, and natural gas. Fossil fuels are obtained from biologically degradable materials(such as plants & animals), but only after millions of
years of heat, pressure, chemical and
biological reactions. Thus, formation of these fuels takes a very very long time. After the industrial revolution, our energy demands have increased tremendously which results in the rate of consumption of fossil fuels at a much faster rate than their formation. As a result, the fossil fuel reserves of the world have become limited in quantity while our demands of these fuels are unlimited, clearly indicating a situation of imbalance. This imbalance implies that our activities on the earth (at current rate) cannot be sustained forever; at the most it can last only a century or two most with ever-increasing consumption of fossil fuels. Also, there is an imbalance in the distribution of fossil fuel reserves across the planet. This results in energy insecurity for the countries that are devoid of fossil fuels . Let us have a look at these fossil fuels and their reserves. Page | 3
Coal: It is the product of natural process of decomposition of organic matters buried in swamps & has been out of contact with oxygen. The world total estimated reserve of coal is about 984×10 9 tons. Oil: oil or crude oil occurs in the form of liquid. It is complex mixture of hydrocarbon and some amount of inorganic elements like sulphur, oxygen and nitrogen. The crude oil in itself is not useful for consumption in appliances. Crude oil is refined to get various products like petrol, diesel, kerosene and some solid materials such as nylon, paints, plastics, and so on. The world’s estimated reserve of crude oil is about thousand billion barrels. Natural gas: It comprises gases such as methane, ethane, propane, etc. with the principal component being methane. It is mainly found along with crude oil, but there are some reserves where it is obtained in the absence of crude oil. The worldwide reserve of the gas is in the range of 5500 trillion standard cubic feet. The current reserves and current production rate of coal, oil and gas are as follow.
Resource
Unit
Current
Current
Availability
reserves
production
(No. of years)
rate Oil
Billion barrels
1047.7
26
40.2
Gas
Trillion scf
5501.5
102.2
53.8
Coal
Billion tons
984
4.8
205
[Source: www.bp.com]
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(ii)Environmental Impact of Fossil Fuels: The fossil fuels are mainly carbon based. Fossil fuels are combusted (burned with oxygen) in order to derive useful energy, for instance, use of coal in power and use of petrol in automobiles. The combustion of fossil fuels result in the formation of carbon dioxide (CO2). After combustion of the fuels, CO2 is usually released in the atmosphere. This gas absorbs the infrared part of radiation from the earth and re-radiates it back to the earth, creating the effect of a ‘greenhouse’. The pre-historic concentration of CO2 was 280 ppm (parts per million) which has now increased to 377 ppm. The increased temperature of the earth due to the greenhouse effect will result in erratic weather patterns, folds, droughts and submerging of low-lying areas due to melting of ice at poles. (iii)Energy Security and Potential for Conflicts: The fossil fuel sources are not uniformly available in the world. This nonuniformity in the fossil fuel distribution could be a cause of international conflict. The countries, where these resources are not available in sufficient quantity, will always feel insecure in terms of their supply, as they will always be dependent on other countries. This dependency could result in conflicts and possibly war. So if the demand of these fossil fuels and their prices will increase decreasing their quantity, it is going to be very problematic for us. Isn’t it? Is there any alternative for it? The obvious choice of a clean energy source, which is abundant and could provide security for the future development and growth, is the sun’s energy-“The Solar Energy”, which has many advantages over the conventional sources.
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(B) Solar Energy- A Sustainable And Clean Energy Resource. The Sun, our nearest & the biggest star, is the biggest source of energy to us. The sun’s radiation arrives at no cost and is available during any clear day. In the broad sense of the term, solar energy also includes wind, wave, biomass, and fossil fuel energy as well. All these forms of energy originated as solar energy. The sun is an immense fusion reactor. "Fusion" simply means that hydrogen atoms are combined to make helium. In this reaction 4 hydrogen atoms (4 protons + 4 electrons) combine to form 1 helium atom (2 protons +2 neutrons+2electrons). Energy is produced due to difference between the mass of the four hydrogen atoms and the mass of hydrogen atom. Energy produced here is in the form of heat. That’s why sun is very hot. This reaction is going continuously. That is why fusion is called a chain reaction. The sun’s nuclear fusion process converts 508 million tons of hydrogen into 504 million tons of helium every second. The remaining 4 million tons of matter are converted to energy, making the core temperature of the sun extremely hot. As Albert Einstein found, a very small amount of matter converts to a very large amount of energy. In fact, one ounce of matter converted to energy by fusion could supply all the energy your home and car would need for a year -- plus five-thousand other people’s homes and cars as well. The energy the sun radiates is preferable to other sources of energy because solar radiation is abundant and will be for many more millions of years. Solar radiation cannot be cut off or made more costly, unlike other energy sources. Putting solar radiation to work does not directly pollute the environment. It is a clean, safe source of energy. The energy itself is free. Solar energy can be used in quite a few different ways. Page | 6
The solar energy reaching the periphery of the earth's atmosphere is considered to be constant for all practical purposes, and is known as the solar constant. Because of the difficulty in achieving accurate measurements, the exact value of the solar constant is not known with certainty but is believed to be between 1,353 and 1,395 W/m2 (approximately 1.4 kW/m2, or 2.0 cal/cm2/min). Below is the distribution of solar radiation on the surface of the earth.
[Source: www.inforse.org] This distribution gives an idea about solar energy distribution on earth. From this it is clear that solar energy is available everywhere on earth although not in same proportion. It is important to note that the majority of developing countries fall within the more favorable regions.
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Solar Energy: Advantages: Environmentally friendly: It is an everlasting, renewable energy source.It is a clean energy source, no potential damage to the environment. It is a very large source of energy. The power from the sun intercepted by the earth is about 1.8×1011 MW, which is many thousand times larger than our current power consumption from all sources. Saves your money: Solar energy is free and is available to all.Financial investments are available from the government that will reduce the cost. Because of the improvement in the technology, the solar equipments are getting cheaper Independency: Solar energy is available to all at fairly equal manner, unlike fossil fuel sources, which are concentrated at some locations only. This fact provides a chance that an individual can generate his/her own energy depending on the requirement, at his/her place of choice. Solar system therefore can be used in remote areas. Low/no maintenance: Solar energy systems are virtually maintenance free and will last for decades They operate with no moving parts, do not release offensive smell and do not require to add any fuel. Page | 8
Solar Battery Charger Solar battery charger is one of the examples of solar powered devices. In this kit, the solar energy is converted into electrical energy and is stored in the rechargeable batteries. When the batteries get discharged after the usage, they can be again charged by exposing the kit to the sun light. Here is how the kit actually looks.
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(A) Components used in Solar battery charger:
(a) 6 Volt solar panel. (b) LM317T regulator. (c) 10Ω resistor. (d) 4 rechargeable batteries.
(i) Solar Panel:
Solar panel is the packaged, connected assembly of solar cells. Solar panels use light energy from the sun to generate electricity. Solar panels are constructed as per the desired output.
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Solar cell: The solar cell is the basic building block of solar panel. The solar cell are made up of semiconducting material silicon.
Solar Cell Structure:
A. Encapsulate - The Encapsulate, made of glass or other clear material such clear plastic, seals the cell from the external environment. B. Contact Grid- The contact grid is made of a good conductor, such as a metal, and it serves as a collector of electrons. C. The Antireflective Coating (AR Coating)- Through a combination of a favorable refractive index, and thickness, this layer serves to guide light into the solar cell. Without this layer, much of the light would simply bounce off the surface. D. N-Type Silicon - N-type silicon is created by doping (contaminating) the Si with compounds that contain one more valence electrons than Si does, such as with either Phosphorus or Arsenic. Since only four electrons are required to bond with the four adjacent silicon atoms, the fifth valence electron is available for conduction. E. P-Type Silicon- P-type silicon is created by doping with compounds containing one less valence electrons than Si does, such as with Boron. Page | 11
When silicon (four valence electrons) is doped with atoms that have one less valence electrons (three valence electrons), only three electrons are available for bonding with four adjacent silicon atoms, therefore an incomplete bond (hole) exists which can attract an electron from a nearby atom. Filling one hole creates another hole in a different Si atom. This movement of holes is available for conduction. F. Back Contact - The back contact, made out of a metal, covers the entire back surface of the solar cell and acts as a conductor. Working of solar cell: A photon's path through the solar cell: After a photon makes its way through the encapsulate it encounters the antireflective layer. The antireflective layer channels the photon into the lower layers of the solar cell. Once the photon passes the antireflective layer, it will either hit the silicon surface of the solar cell or the contact grid metallization. The metallization, being opaque, lowers the number of photons reaching the Si surface. The contact grid must be large enough to collect electrons yet cover as little of the solar cell's surface, allowing more photons to penetrate. A Photon causes the Photoelectric Effect: Photoelectric Effect is emitting of electrons by a matter when hit by photons. The photon's energy transfers to the valence electron of an atom in the n-type Si layer. That energy allows the valence electron to escape its orbit leaving behind a hole. In the n-type silicon layer, the free electrons are called majority carriers whereas the holes are called minority carriers. As the term "carrier" implies, both are able to move throughout the silicon layer of the solar cell, and so are said to be
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mobile. Inversely, in the p-type silicon layer, electrons are termed minority carriers and holes are termed majority carriers, and of course are also mobile. The p-n junction: The region in the solar cell where the n-type and p-type Si layers meet is called the p-n junction. As you may have already guessed, the p-type silicon layer contains more positive charges, called holes, and the n-type silicon layer contains more negative charges, or electrons. When p-type and n-type materials are placed in contact with each other, current will flow readily in one direction (forward biased) but not in the other (reverse biased). An interesting interaction occurs at the p-n junction of a darkened solar cell. Extra valence electrons in the n-type layer move into the p-type layer filling the holes in the p-type layer forming what is called a depletion zone. The depletion zone does not contain any mobile positive or negative charges. Moreover, this zone keeps other charges from the p and n-type layers from moving across it.
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When photons hit the solar cell, freed electrons (-) attempt to unite with holes on the p-type layer. The p-n junction, a one-way road, only allows the electrons to move in one direction. If we provide an external conductive path, electrons will flow through this path to their original (p-type) side to unite with holes. The electron flow provides the current ( I ), and the cell's electric field causes a voltage ( V ). With both current and voltage, we have power ( P ), which is just the product of the two. Therefore, when an external load (such as an electric bulb) is connected between the front and back contacts, electricity flows in the cell
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(ii) LM317T –Voltage Regulator: Lm317T is a voltage regulator i.e. it is an electrical regulator designed to automatically maintain a constant voltage level. The solar energy is always fluctuating. So by using this regulator we can have a constant output. The LM317 is an adjustable three-terminal positive-voltage regulator capable of supplying more than 1.5 A over an output-voltage range of 1.25 V to 37 V. It is exceptionally easy to use and requires only two external resistors to set the output voltage. In addition to having higher performance than fixed regulators, this device includes on-chip current limiting, thermal overload protection, and safe operating-area protection. All overload protection remains fully functional, even if the Adjust terminal is disconnected.
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Pin diagram of LM317:
The resistance of the regulator varies in accordance with the load resulting in a constant output voltage A linear regulator employs an active pass device (series or shunt) controlled by a high gain differential amplifier. It compares the output voltage with a precise reference voltage and adjusts the pass device to maintain a constant output voltage. The regulating device is made to act like a variable resistor continuously adjusting a voltage divider network to maintain a constant output voltage. In this circuit the difference between the Vin and Volt cannot be more than 40.Thats why this circuit is used for charging.
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(iii) Resistor: A resistor is
a passive
two-terminal electrical
component that
implements electrical resistance as a circuit element. The current through a resistor is in direct proportion to the voltage across the resistor's terminals. Thus, the ratio of the voltage applied across a resistor's terminals to the intensity of current through the circuit is called resistance. The behavior of an ideal resistor is dictated by the relationship specified by Ohm's law:
Ohm's law states that the voltage (V) across a resistor is proportional to the current (I), where the constant of proportionality is the resistance (R).
Resistors determine the flow of current in an electrical circuit. Where there is high resistance in a circuit the flow of current is small, where the resistance is low, the flow of current is large. Resistors are used for regulating current and they resist the current flow and the extent to which they do this is measured in ohms (Ω).
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The temperature of a resistor also affects its resistivity. There will be more resistance to current flow when it is heated. Resistors are often compared to pipes, with the electric current inside it representing water. Just as a pipe's thickness can cause water to flow in a stream or trickle, thick resistors likewise allow more current flow than thin ones.
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(iv) Battery: An electrical battery is one or more electrochemical cells that convert stored chemical energy into electrical energy. It consists of a number of voltaic cells; each voltaic cell consists of two halfcells connected in series by a conductive electrolyte containing anions and cations. One half-cell includes electrolyte and the electrode to which anions (negatively charged ions) migrate, i.e., the anode or negative electrode; the other half-cell includes electrolyte and the electrode to which cations (positively charged ions) migrate, i.e., the cathode or positive electrode. In the redox reaction that powers the battery, cations are reduced (electrons are added) at the cathode, while anions are oxidized (electrons are removed) at the anode. The electrodes do not touch each other but are electrically connected by the electrolyte. Some cells use two half-cells with different electrolytes. A separator between half-cells allows ions to flow, but prevents mixing of the electrolytes. As the metal oxidizes, it gives off electrons; these electrons can also be transferred to another metal in the same electrolyte solution, resulting in electricity as they flow. The positive and negative sides of a battery connect to these two metals, but they are not directly connected to one another. Instead, electrons flow from the negatively charged side, through a device to positively charged side. Thus producing the current.
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Types of battery: (a) Primary battery (use and throw type): Primary batteries can produce current immediately on assembly. Disposable batteries are intended to be used once and discarded. These are most commonly used in portable devices that have low current drain, are used only intermittently, or are used well away from an alternative power source, such as in alarm and communication circuits where other electric power is only intermittently available. Disposable primary cells cannot be reliably recharged, since the chemical reactions are not easily reversible and active materials may not return to their original forms. Battery manufacturers recommend against attempting to recharge primary cells. Common types of disposable batteries include zinc–carbon batteries and alkaline batteries. In general, these have higher energy densities than rechargeable batteries.
(b) Secondary battery (rechargeable type): Secondary batteries have their electrochemical reactions electrically reversible . A normal battery (primary battery) produces electricity using an electrochemical reaction. This reaction causes electrons to flow from one electrode to another through an electrolyte (a liquid or solid chemical substance). The negative (-) and positive (+) terminals on a battery provide an outlet and inlet for the electrons to flow. In practice, electrical wires are connected to the terminals and electricity (in the form of electrons) flows through the wires, powering the device connected to the battery's terminals. Now reserve everything. In a rechargeable battery applying an electrical charge to the battery reverses the chemical reactions that take place. The reversed electron flow restores the chemical elements involved to their original form and the battery is ready to begin the process again. Page | 20
( B) Circuit diagram of Solar battery charger:
(C )Block Diagram of Solar battery charger:
Solar Pannel
Regulator
Resistor
Batteries
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(D) Constructing Solar Battery Charger:
Choosing solar panel: Common solar panels output are 3V and 6V which are perfect for charging for 2 and 4 batteries respectively. As per the output requirement the solar panel is to be selected. Regulating the input voltage : The intensity of the sun is not always constant so it is essential to regulate the input voltage. Here we are using LM317 regulator. Choosing the resistor: Resistors are only available in certain values - e.g. 5.6 Ohms and 6.8 Ohms, but not 6.2 Ohms. Below is a table of available resistor values together with the output current generated if each resistor is used in an LM317T current limiting circuit (R = resistance, I = current). R (Ohms) 3.9 4.7 5.6 6.8 8.2 10 I (mA)
12
15
18
22
27
33
321 266 223 184 152 125 104.2 83.3 69.4 56.8 46.3 37.9
Here we are going to charge 4 batteries of capacity 1.2V each. This gives us 4 x 1.2 = 4.8 Volts with a capacity of 800mah - therefore we want a charging current of around 80ma. According to the table above, a 15 Ohm resistor gives a fixed current of 83.3 milliamps which will be perfect. Rechargeable batteries: Here we are using 4 AA or AAA rechargeable batteries, which can be used to store electric energy.
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(E) Layout of Solar Battery Charger:
As show, the solar positive input is given to input of regulator, while the solar negative is directly provided as one of the final output terminal. The output of the regulator is given to resistor and the final positive output terminal is taken from the other end of the resistor.
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(F) Working of Solar battery charger: When the battery charger kit is exposed to sunlight, the photons are incident on the solar panel. These photons are absorbed by the solar panel. This absorbed light energy is converted into electrical energy by the solar panel, which is nothing but the photoelectric effect. We give the solar negative terminal as one of the final output terminal. The solar positive is given to the regulator input. Using theLM317 regulator the input is regulated. Now why to regulate this input? The sunlight which is incident on the panel is not always the same i.e. the intensity of the sun is always fluctuating. That’s why it becomes essential to regulate the input voltage. The regulator is made to act like a variable resistor continuously adjusting a voltage to maintain a constant output voltage. The voltage coming from the regulator is to be limited otherwise the batteries may be overcharged and may be damaged. We are using here a resistance of 15Ω.The signal from the regulator output is given to this 15Ω resistor and then it is given to final output. Now from the sunlight by taking the light energy and we can say processing it, we get electrical energy which now can be stored in rechargeable batteries that we have. When the batteries get discharged we can recharge them by exposing the kit to sunlight. (G) Uses: In our everyday life we use many devices working on batteries. Batteries can be used in remotes, toys, digital cameras, torches etc. Now this charger we made is of small capacity. If we want the charger for more applications obviously according to need we can design them using. Here are few solar powered chargers. Page | 24
Some solar powered chargers:
Solar iphone charger
Solar mobile charger
Solar laptop charger
Solar Battery charger
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Conclusion This solar battery charger is just one of the examples of solar powered devices. We are reusing these batteries by recharging them using solar energy. By doing so firstly we are saving the nonrenewable energy source and are avoiding electrical waste. Also without harming the environment we are using the natural energy sources for our energy needs. If everyone of us uses such more and more solar powered devices, the energy crisis can be minimized at a very great level. By using solar devices more we are directly reducing the rate of consumption of nonrenewable sources and are making these sources available to the upcoming generations.
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References 1. Solar Photovoltaics –by Chetan Singh Solanki 2. www.specmat.com 3. www.pvsolarchina.com 4. www.wikipedia.org 5. www.inforse.org 6. www.fairchildsemi.com 7. www.reuk.co.uk/Solar-Battery-Charger-With-LM317T
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