Application Of Solar Energy In Street Lamp Using Dual Mode Switching Operation Based On Microcontrol

Application Of Solar Energy In Street Lamp Using Dual Mode Switching Operation Based On Microcontroller Chapter 1 1.0 Introduction This chapter describes about the thesis introduction. It consists of overview Of the project base thesis, the thesis aim, objectives and scopes of the project.

1.1 Thesis Overview This project proposes an idea about to develop solar photovoltaic (PV) system and fabricate the circuit that can operates the dual mode operation in street lamps when solar power is active as the power source then grid power is off otherwise it turns on. To control the operation of system, we used the control circuit base on microcontroller that can implement the Dual mode operation. For the switching to the load, we used microcontroller (ATMEGA8) to switch on the lamp, by using the photocell sensor and relay 220V AC. When charging of battery reach the sufficient charge by source of solar power then is the switching to the load. Photo diode will determine whether is in daylight or in night by determination by the photocell sensor. The value to determine the intensity of the light we had set up it into the coding of the Microcontroller.

To control the intensity of the light, we need the other input from sensor. When light sensor detect that have some wave from the road, Microcontroller will give the output to switch on for the light. So the intensity of the light will increase and the timing will start counter. After finish the counter, Microcontroller will automatically switch off the light. By using this method, its can save the energy that we using from the battery. When night change to day, photocell sensor detect the ray from the sun, Microcontroller will give the output to switch off the lamp and the charging circuit will continue charge the battery for the day.

1.2 Project Aim To develop the structure of solar PV system and the solar street lamp is designed specifically for using in two methods like solar and grid power. It’s also as the new way to save the energy and use it more efficiently.

1.3 Objective The main objective of this project is to develop the solar system and solar street lamp that is also operated by grid power.

There are two secondary objectives to be achieved in order to achieve the main objective stated above. The two secondary objectives were discussed in the following paragraph.

The first objective is to develop the charging circuit that can charge 12V lead acid battery by using the solar panel as the DC source. The charging of battery is control by charge controller. The charge controller controls overcharging and over discharging by set points. This DC current converted into AC current by inverter.

The second objective is to design and program the control circuit by that contain of Microcontroller,LED,Relay to control the circuit to switch on and off the lamp when the situation change like from the day to night. This circuit also to control the intensity of the light and charge amount of battery. That can improve the efficiency of using energy that only use when need.

1.4 Scope Of The thesis The scope of this project base thesis includes theoretical argument and construct solar system like (charging circuit,charge crontroller ,inverter) in order to AC current application. Inverter will supply power to switch the lamp when there is no light or night condition. The supply power of solar is not enough then the supply power swishing into grid power in order to control circuit by coding of microcontroller.

Finally, the system was combined together to complete the development of the system 1.5 Flowchart of supply power of our system: Solar System

Charging Circuit

Charge Controller

Battery (DC)

Power (Grid) Supply

Solar System

Power (Grid) Supply

Inverter (AC)

Deactivate (off)

Load

off

on

Load

Fig.1: Street lamp turns on by main source system

Fig.2: Street lamp turns on by power during disturbing solar CHAPTER 2 Form of Energy and Power condition of Bangladesh

2.0 Introduction Electrical energy could be considered as the most convenient form of energy. An important aspect of electricity is the flexibility; it is very easy to carry electricity from one place to other by using conductors. Electrical energy is much cheaper compared to other forms of energy. It is an inevitable component in all sectors of the modem world. Fossil fuels provide around 66% of the world’s electrical power, and 95% of the world’s total energy demands (including heating, transport, electricity generation and other uses). Coal provides around 28% of energy, oil provides 40% and natural gases provide about 20%. A concern is that the fossil fuels are being used up at an increasing rate, and they will soon run out. If these fossil fuels were to run out now there would not be a suitable replacement for them that is equally as efficient at producing the same amount of energy. Storage of renewable electrical energy is also a matter of great importance. Electrical energy storage in batteries and electrochemical capacitors will be vital for any future success in the global effort to shift energy usage away from fossil fuels. Fossil fuels are the main sources that are being used to produce energy today. They are not only being depleted, but also polluting the environment, and affecting our economical stability. Solar hydrogen and fuel cell systems when integrated together represent a new approach that promises clean and friendly energy production.

2.2.1

Solar Energy

At the present moment two methods exist by which sunlight can be converted into directly usable energy: conversion to warmth (thermal energy) and conversion to electricity (photovoltaic energy). In the first method, for example, sunlight is absorbed by a blackened surface, which then warms up. If air or water is passed alongside or through this warmed surface, it too will be warmed. In this way the warmth can be transported to wherever it is

needed. For storage, an insulated chamber is usually employed, from which, for example, hot water can be drawn. This, in brief, is a principle of thermal conversion. In photovoltaic conversion, sunlight falling onto a ‘solar cell’ induces an electrical tension; a number of cells combined in a panel are capable of generating electric current.

2.2.2 Solar Electricity Solar energy technology is used on both small and large scales to produce electricity. A unique advantage of small-scale solar energy systems is that, if they include storage devices, they may eliminate the need to connect to the electric grid.

2.2.3 Uses Solar energy has many uses. It can be used to provide heat, light or to generate electricity.

Passive solar energy refers to the collection of heat and light; passive solar design, for instance, uses the sun’s energy to make homes and buildings more energy-efficient by eliminating the need for daytime lighting and reducing the amount of energy needed for heating and cooling. Active solar energy refers to storing and converting this energy for other uses, either as photovoltaic (PV) electricity or thermal energy.

There are many reasons of solar power being an important addition in solar panel history to any household. It helps in fighting environment and climate change as well as helping in saving the traditional sources of energy. Installing solar panels will give a significant boost to our electricity supply. The electricity bill will be reduced significantly and the cost of initial installation of a solar energy system will pay itself off over time.

Home solar power systems can be added be households and it can be used to use solar energy to heat our water supply. It is very viable natural energy technology to use if we are seeking a significant reduction to our electricity bill proven in solar panel history. It will dramatically reduce the price of heating based on the capacity and technologies used in the systems. We can install a lower capacity system. We can make use of solar power panels that can be found in a variety of shapes, sizes, formats and integrated technologies.

The solar power cells are dependent on the output of energy we require. It can also provide lighting in remote locations to our power supply, like our garden or a shed. It will remove the hassle of digging up the ground and laying the appropriate cable. We can also install lights in the garden with the help of solar panels.

2.3 Introduction to Street Light or Lamp 2.3.1 What is Street Light or Lamp A Street light or Lamp is a raised source of light on the edge of a road or walkway, which is turned on or lit at a certain time every night. Modern lamps may also have lightsensitive photocells to turn them on at dusk off at down or activate automatically in dark whether.

2.3.2 Why Using Street Lamp The well known photo of the Earth’s city lights at night, shown in Figure 1 illustrates the urbanization present on the planet as well as the tremendous use of lights. The contribution to the illumination of the world can be attributed to the central role that streetlights play in the urban environment. Street lighting contributes to a belief in the reduction of crime. Though the research does not show a direct correlation between street lighting and crime reduction, the presence of the belief is important in contributing to a sense of community. The presence of adequate lighting is also seen as a key factor for the promotion of cycling and walking within cities. Street lighting also reduces stress for drivers by increasing visibility of motorways and pedestrians, making roads safer for all users. These factors highlight the central role street lighting plays in urban environments and in the communities which they encompass.

Figure 1 City Lights of Earth

Ubiquitous nature of street lights allows them to fulfill their role for vehicle, cycling and pedestrian uses. Additionally, it also makes them an excellent candidate to leverage in addressing issues of distributed power generation through the integration of solar photovoltaic (PV) cells in their masts, representing a form of distributed generation referred to as electricity generated from renewable sources (RES-E). Renewable sources of electricity are essential for two reasons: 1) electricity is one of the most valuable forms of energy; and 2) there is a reduction in the environmental harm typically associated with generation.

Historically much of our energy has come from the burning of fossil fuels, resulting in water pollution, air pollution and an increased concentration of greenhouse gas (GHG) emissions, thus contributing to climate change.

2.4.1 Electrical Energy Electrical energy is the scientific form of electricity, and refers to the flow of power or the flow of charges along a conductor to create energy. Electrical energy is known to be a secondary source of energy, which means that we obtain electrical energy through the conversion of other forms of energy. These other forms of energy are known as the primary sources of energy and can be used from coal, nuclear energy, natural gas, or oil. The primary sources from which we create electrical energy can be either non-renewable forms of energy or renewable forms of energy. Electrical energy however is neither non-renewable nor renewable.

The electrical energy that an appliance or device consumes can be determined only if we know how long (time) it consumes electrical power at a specific rate (power). To find the amount of energy consumed, we multiply the rate of energy consumption (measured in watts) by the amount of time (measured in hours) that it is being consumed. Electrical energy is measured in watt-hours (Wh).

Energy = power x time E = P x t or E = W x h = Wh Electrical energy is a standard part of nature, and today it is our most widely used form of energy. Many towns and cities were developed beside waterfalls which are known to be primary sources of mechanical energy. Wheels would be built in the waterfalls and the falls would turn the wheels in order to create energy that fueled the cities and towns. Before this type of electrical energy generation was developed, homes would be lit with candles and kerosene lamps, and would be warmed with coal or wood-burning stoves.

It is important to understand that electrical energy is not a kind of energy in and of itself, but it is rather a form of transferring energy from one object or element to another. The energy that is being transferred is the electrical energy. In order for electrical energy to transfer at all, it must have a conductor or a circuit that will enable the transfer of the energy. Electrical energy will occur when electric charges are moving or changing position from one element object to another.

When the electrical energy is moved, it is frequently stored in what we know of today as batteries or energy cells.

2.4.2 Electrical Power Power (P) is a measure of the rate of doing work or the rate at which energy is converted.

Electrical power is the rate at which electricity is produced or consumed. Using the water analogy, electric power is the combination of the water pressure (voltage) and the rate of flow (current) that results in the ability to do work.

Electrical power is defined as the amount of electric current flowing due to an applied voltage. It is the amount of electricity required to start or operate a load for one second.

Electrical power is measured in watts (W). The formula is: Power = voltage x current P=V x I Or, W = V x A 2.5 Dual mode running condition of Street Lamp It is the concept of an on-off Grid system in which a DC battery is charged by solar energy and it’s converted into AC current by Inverter. The charge controller control the flow of electricity in this proper way a street Lamp is turn on and is given light on the road or space.

Solar energy is acting as a regular source. But in sometimes solar energy don’t work properly due to bad weather and others like cloudy, rainy season, dark, heavy rainfall, instruments faults etc. In this situation grid power is used for emergency supply otherwise grid power is off. Due to utilizing this dual mode system that makes positive influence on the power crisis in Bangladesh.

2.6 Power Status in Bangladesh After the independence of Bangladesh in 1971, in 1972 Bangladesh Power Development Board (BPDB) was created to look after the same function. Dhaka Electric Supply, headed by

a Chief Engineer under BPDB used to control the electricity distribution and sales in Greater Dhaka District area up to September 1991.

To improve services to the consumers and to enhance revenue collection by reducing the prevailing high system loss, Dhaka Electric Supply Authority (DESA) was created by an ordinance promulgated by the President of the Peoples Republic of Bangladesh in 1990.The President of the Govt. of Peoples Republic of Bangladesh ordered for establishment of The Dhaka Electric Supply Authority (DESA) by promulgation of ordinance No. 6 of 1990 on 6th March. ( Published in the Bangladesh Gazette, Additional issue on 14th March, 1990 ). Act No. 36 of 1990 for establishment of the Dhaka Electric Supply Authority (DESA) was issued (published in Bangladesh Gazette, Additional issue, 23rd June 1990) in super ceding the ordinance no. 6 of I 990.

2.6.1 Effect of Current Shortage of Electricity in Bangladesh Bangladesh is losing at least 3.5% of Gross Domestic product (GDP) due to the shortage of Power supply. Total losses reach to Taka 130000 Million in this year. If the government fails to increase the capacity of power supply by new production, the loss of economy will grow up day by day.

According to a research report of Centre for Policy Dialogue (CPD, A civil society think tank, the size of GDP would be enlarge 3.5% compare to current status. The loss of past year GDP was Takal2, 000 crore, equal to 3.2% of GDP, due to power crisis. It will reach 3.5 % of GDP in this year, which is more than Taka 13, 000 crore.

The main victim of power shortage is commercial activities of the country. Business and Commercial activities of the country is boosting every year. But power crisis is hampering the growth of this sector. Total toss of this sector has reached to Taka 7,000 crore in this year.

Impacts of power shortage in industrial sector reach to double by only two years. In 2008-09 total loss of this sector was Taka 4,000 crore. It will be reached to Taka 5,000 crore this year.

In addition Export oriented industry of the country is fighting with power crisis. Factories all over the country do not get power supply minimum 4 hours in production time. 3O% of production of Readymade garment (RMG), 76% export earning sector of the country, has decreased lack of power supply. Production cost of RMG also increasing and Bangladesh loosing competitiveness in world market according to statistics of Bangladesh Knitwear

Manufacturers and Exporters Association (BKMEA).

CPD statistics shows, Total lost in agriculture sector reached to Taka 950 crore in this year. It was Taka 518 crore in previous year. 625 irrigation pumps has damaged in northern area of the country last year due to load shading.

2.6.2 Load Shedding When the supplying company receives more demand for electrical power than its generating or transmission or installed capacity can deliver, the company has to resort to rationing of the available electricity to its customers. This act is called load shedding.

2.6.3 Load Shedding Perspective of Bangladesh Shortage of Electricity shortage of electricity may be considered in two forms. Firstly, reviewing the scenario of per ~pita electricity consumption and percentage of population having access to electricity in Bangladesh compared to other countries and secondly, determining gap between demand and supply of electricity m perspective of country’s economic situation and GDP growth.

Demand for electricity is increasing with the improvement of living standard, increase of agricultural production, development of industries as well as overall development of the country; but due to the failure in the last few years to increase electricity generation capacity proportionately to the demand, there exists 1500-1800 Megawatt electricity shortage at present. Especially a huge shortage exists during the evening peak demand. Due to the crisis of gas supply, lack of necessary maintenance and rehabilitation of old power plants, it is not possible to utilize the total installed capacity. The shortage of electricity can be from the loadshedding made during the peak demand (6500 MW) of summer which is about 1800 Megawatt each day.

Power Sector: An update (April 2011) Installed Capacity

7,500 MW

Rerated Capacity

6,225 MW

Production

4500-5025 MW

Electricity Demand (Peak Demand) Access to electricity Per capita electricity consumption 2.6.4 How to Overcome Load Shedding

6,250 MW 63 percent 240 KWh

We can temporally overcome from the situation by using •

Generator

•

IPS

•

UPS

We can also permanently overcome the situation by using renewable energy, like • Solar energy • Wind energy 2.7

Way of Our Thesis/project

To establish our concept we need following basic structure Solar energy Supply electricity Charging DC battery Design of DC to AC inverter Charge controller Switching circuit base on microcontroller Dual mode operation 2.8 Organization of Thesis Every day we face load shedding in Bangladesh due to shortage of electricity. Street lamps are available in almost every big and district city in Bangladesh. For this purpose huge electricity uses every day. After facing the problem of shortage of electricity, we come to enlarge our idea about a solar energy that will provide continuous power supply and minimize the crisis of shortage of electricity. Here we proposed a concept of building a system that will store electrical energy using solar energy and system supply. During unable to solar energy, battery will be charged by grid power through connecting wire as well as an emergency power supply. For grid connection, we have no need any investment because of almost all street Lamps already connected by grid. Implementation of such solar energy will decline the consumption of electricity from national grid and also it effectively utilizes a renewable source which is free of cost and available everywhere.

CHAPTER 3 ELECTRICITY FROM THE SUNLIGHT AND STREET LAMP 3.0 Introduction

In a solar cell light is converted into electricity by means of the so called photovoltaic (PV) effect. PV is still enjoying large research and development efforts in order to produce more efficient and cheaper solar cells. But solar electricity is already economically feasible compared to other energy sources for a number of applications. In the past, inadequate system design and sizing of system components has led to unfavorable experiences. However in recent years PV has proved to be reliable if sufficient attention is paid to the design. In this chapter a closer look will be taken at those situations in which PV comes into consideration.

Subsequently some characteristics of a PV-system are discussed and some attention is paid to those aspects which are important in designing a system. Finally some interesting applications will be examined.

Fig 2.1: Sun light convert into electricity 3.1 Word History 3.1.1Solar energy Solar energy is the light and radiant heat from the Sun that influences Earth's Climate and weather and sustains life. Solar power is sometimes used as a synonym for solar energy or more specifically to refer to electricity generated from solar radiation. Solar radiation is secondary resources like as wind and wave power, hydroelectricity and biomass account for most of the available flow of renewable energy on Earth.

Solar energy technologies can provide electrical generation by heat engine or photovoltaic means, space heating and cooling in active and passive solar buildings; potable water via distillation and disinfection, day lighting, hot water, thermal energy for cooking, and high temperature process heat for industrial purposes. Solar energy refers primarily to the use of solar radiation for practical ends. All other renewable energies other than geothermal derive their energy from energy received from the sun. Solar technologies are broadly characterized as either passive or active depending on the way they capture, convert and distribute sunlight. Active solar techniques use Photo voltaic panels, pumps, and fans to convert sunlight into useful outputs. Passive solar techniques include selecting materials with

favorable thermal properties, designing spaces that naturally circulate air, and referencing the position of a building to the Sun. Active solar technologies increase the supply of energy and are considered supply side technologies, while passive solar technologies reduce the need for alternate resources and are generally considered demand side technologies.

3.2 Street Lamp Before we have incandescent lamps, gas lighting was in use in cities. The earliest of such street lamps were built in the Arab Empire, especially in Cordoba, Spain. The first electric street lighting employed arc lamps, initially the 'Electric candle', 'Jablochoff candle' or ‘Yablochkov candle’ developed by the Russian Pavel Yablochkov in 1875. This was a carbon arc lamp employing alternating current, which ensured that the electrodes burnt down at the same rate. Yablochkov candles were first used to light the Grands Magasins du Louvre, Paris where 80 were deployed. Soon after, experimental arrays of arc lamps were used to light Holborn Viaduct and the Thames Embankment in London - the first electric street lighting in Britain. More than 4,000 were in use by 1881, though by then an improved differential arc lamp had been developed by Friederich von Hefner-Alteneck of Siemens & Halske.

Arc lights had two major disadvantages. First, they emit an intense and harsh light which, although useful at industrial sites like dockyards, was discomforting in ordinary city streets.

Second, they are maintenance-intensive, as carbon electrodes burn away swiftly. With the development of cheap, reliable and bright incandescent light bulbs at the end of the 19th century, they passed out of use for street lighting, but remained in industrial use longer.

Incandescent lamps used for street lighting until the advent of high-intensity discharge lamps, were often operated as high-voltage series circuits. Today, street lighting commonly uses high-intensity discharge lamps, often HPS high pressure sodium lamps. Such lamps provide the greatest amount of photo illumination for the least consumption of electricity. However when photo light calculations are used, it can be see how wrong HPS lamps are for night lighting. White light sources have been shown to double driver peripheral vision and increase driver brake reaction time at least 25%. When S/P light calculations are used, HPS lamp performance needs to be reduced by a minimum value of 75%. This is now a standard design criteria for the roads.

Figure 2.2: Old, new style and solar street lamp 3.3 SOLAR PV ENERGY Photovoltaic energy is the conversion of sunlight into electricity. A photovoltaic Cell, commonly called a solar cell or PV, is the technology used to convert solar energy directly into electrical power.

Figure 2.3 Photovoltaic Cell Sunlight is composed of photons, or particles of solar energy. These photons Contain various amounts of energy corresponding to the different wavelengths of the solar spectrum. When photons strike a photovoltaic cell, they may be reflected, pass right through, or be absorbed.

Only the absorbed photons provide energy to generate electricity.

When enough sunlight energy is absorbed by the material that is a semiconductor, electrons are come out from the material's atoms. Special treatment of the material surface during manufacturing makes the front surface of the cell more receptive to free electrons, so the electrons naturally migrate to the surface.

When the electrons leave their position, holes are formed. When many electrons, each carrying a negative charge, travel toward the front surface of the cell, the resulting imbalance of charge between the cell's front and back surfaces creates a voltage potential like the negative and positive terminals of a battery.

When the two surfaces are connected through an external load, electricity flows.Photovoltaic cells, like batteries, generate direct current (DC) which is generallyused for small loads like electronic equipment. When DC from photovoltaic cells is used for commercial applications or sold to electric utilities using the electric grid, it must be converted to alternating current (AC) using inverters.

Advantages of photovoltaic systems are:  Conversion from sunlight to electricity is direct, so that bulky mechanical generator systems are unnecessary.  PV arrays can be installed quickly and in any size required or allowed.  The environmental impact is minimal, requiring no water for system cooling and generating no by-products.

3.4 Solar cells Solar radiation can be converted directly into electricity using semiconductor devices, which are known as photovoltaic (PV) cells. The most commonly used material is silicon. By diffusing phosphorus or boron into the silicon it is possible to create p- and n-type silicon, each with its own electrical characteristics. A thin silicon wafer is divided into two layers.

Both layers are provided with metallic contacts. When sunlight falls upon the solar cell a part of the light is absorbed. The energy of the light releases electrons inside the silicon. When both sides of the cell are connected an electric current will start flowing. The size of the current depends upon the intensity of the incoming radiation. Not all the energy of the light is converted into electrical energy.

3.5 General There are a number of semiconductor materials from which solar cells can be made. Until recently the most commonly used was mono-crystalline silicon. At the moment poly-

crystalline and amorphous silicon are becoming more important. Table 2 gives the theoretical and achieved conversion efficiencies for a few types of solar cell materials.

Instead of falling directly onto the flat plate modules, the sunlight can be concentrated first by the use of lenses or mirrors. The concentrated sunlight can be focused on a solar cell, which increases the efficiency of the cell. In this way a record efficiency of3l% was recently achieved for a silicon-gallium arsenide tandem cell. This method enables a reduction of the costs of the array but on the other hand extra costs are incurred by the lenses; the system as a whole also becomes more complex. The technology for concentrating sunlight is still under research and is not commercially available.

3.5.1 Mono-crystalline Silicon Mono-crystalline silicon solar cell technology is based on the semiconductor technology used in the transistor and integrated circuit industry. Using mono-crystalline silicon wafers solar cells can be manufactured with a conversion efficiency of 13 - 15%. The conventional Processes employed to obtain single crystal wafers are slow and very energy and material Consuming.

3.5.2 Polycrystalline Silicon Mono-crystalline silicon is gradually being replaced by polycrystalline silicon (sometimes also called semi-crystalline silicon). Polycrystalline silicon can be produced at lower costs.

The efficiency of polycrystalline cells is I to 2% lower than the efficiency of monocrystalline. However combined with the use of cheaper silicon feedstock material, large cost reductions compared to conventional production methods are expected.

3.5.3 Amorphous Silicon Another option to reduce the costs of the cells is the use of amorphous silicon solar cells.

These cells are very thin, and thus use very little material. Amorphous silicon has made considerable progress. The first cells were produced in 1974. In 1985 the market share already had reached 30%. Commercial applications have been found in pocket calculators, watches and battery chargers. One of the problems of amorphous silicon at the moment is the degradation of the cells. The cell efficiency decreases when light is falling upon the cell, especially during the first months of operation.

3.5.4 Other Materials

Besides silicon other materials are under research for use as solar cells. CuInSe 2, CdTe and GaAs look very promising in the long term, but in the coming years large-scale application of these types of cells is not expected. The same applies to stacked solar cells. In these structures two or more cells with different characteristics are combined in order to utilize as much of the solar energy as possible.

3.6 Balance of System All components of the system together, besides the modules, are called the balance-of system (BOS). The composition of the balance-of-system depends on the kind of application and on the location of the PV-system.

The balance-of-system may comprise: •

Array support structure

•

Connections/wiring

•

Power conditioning

•

Energy storage.

We will have a closer look at several elements of the balance-of-system.

Fig: 2.3 Photovoltaic technology 3.6.1 Array Support Structure The solar-cell modules rest on a array support structure. The array support structure is generally made out of aluminum or steel struts, resting on a concrete foundation. Research is being done to develop low cost constructions of wood and bamboo.

Another way of reducing costs is to mount the modules on the roofs of buildings. At the moment only limited experience with this kind of construction has been gained.

At present most systems have fixed arrays. In case of a tracking system it must keep the modules in an optimal orientation towards the sun.

There are several options.

•

Seasonally-adjusted tilt A few times a year the arrays can be adjusted to the elevation of the sun.

•

Single-axis or two-axis tracking. A drive mechanism keeps the modules in the direction of the sun during the whole day. The array structure can rotate in one or two directions.

3.6.2 Power Conditioning The power conditioning can be composed of the following elements: •

Controllers

•

Maximum power point tracking

•

DC-AC converters

•

Interface between the PV-system and the grid

•

Electronic protection of the system.

The maximum power point tracking ensures that at any given moment, with any given amount of sunlight and any given cell temperature the maximum power is extracted from the modules. In general electricity is supplied as AC (alternating current). Therefore a lot of equipment has been developed for AC-application. The PV modules, however, supply DC (direct current)- power. The consequence is that a choice has to be made between the use of DC-apparatus, not available for all appliances, and the installation of an inverter to convert DC into AC. To connect a PV-system with the grid, a special interface is needed including a DC-AC inverter.

To obtain the highest possible system efficiency it is important to lose only small amounts of energy in the power conditioning. At the moment an efficiency of 95% is possible. When the system is not working on full power the efficiency of the power conditioning does fall sometimes only about 70% efficiency is left. The cost of the power conditioning depends on the need for AC or DC-voltages.

3.7 Energy Storage If electrical power is required when the sun is not shining or if there is a short peak demand,

for instance to start an electric motor, some form of energy storage is needed or a back-up supply from a diesel or gasoline generator must be provided. When a PV-system is used to pump up water, in many cases the choice will be to store water instead of electricity. Several types of storage batteries are available; the lead acid battery is the most common, but NickelCadmium (NiCd) batteries are also suitable. The operation of the batteries requires much attention during the design of a PV-system. In a battery a certain amount of energy can be stored: this is the capacity of the battery. Lead acid batteries can only be discharged to 30% of the total capacity. From a technical point of view deeper discharge is possible, but the lifetime of the batteries then decreases dramatically. Moreover the total capacity of the battery will decline. Batteries can also be overcharged. This also has a bad influence on the performance of the battery. To keep the state of charge of the battery within the allowed range a battery controller can be used. This controller is part of the power conditioning. A NiCd battery has a better performance. Its design makes it impossible to overcharge or discharge the NiCd-batteries to deeply. Also 100% of the capacity can be used. However NiCd batteries are at the moment (1989) two to three times as expensive as lead acid ones.

Many different batteries are available. A distinction can be made between open and closed batteries. The hermetically closed batteries need no refilling, because the water cannot evaporate. Therefore closed batteries in general require less maintenance than open ones. For uses in developing countries it is often better to transport the battery and the acid apart, so the battery will not age during the often lengthy transport time. When air mail is used, it is not even permitted to transport ready-to-use batteries. Because of safety precautions battery and acid have to be transported separately. The number of charge/discharge cycles specifies the lifetime of the battery.

Another factor of importance to the lifetime is the temperature in which the battery has to operate. The higher the temperature the shorter the lifetime. Here too NiCd has better characteristics than lead acid.

3.8 Lifetime Battery lifetime is dependent upon a number of design and operational factors, including the components and materials of battery construction, temperature, frequency and depth of discharges, average state of charge and charging methods. As long as a battery is not overcharged, over discharged or operated at excessive temperatures, the lifetime of a battery is proportionate to its average state of charge. A typical flooded lead-acid battery that is maintained above 90 percent state of charge will provide two to three times more full

charge/discharge cycles than a battery allowed to reach 50 percent state of charge before recharging. This suggests limiting the allowable and average daily DOD to prolong battery life. Lifetime can be expressed in terms of cycles or years, depending upon the particular type of battery and its intended application. Exact quantification of battery life is difficult due to the number of variables involved, and generally requires battery test results under similar operating conditions. Battery manufacturers often do not rate battery performance under the conditions of charge and discharge experienced in PV systems.

3.8.1 Modularity PV-systems can easily be scaled to the electricity demand. A single module provides enough energy to light one house, a number of modules can provide enough energy for an entire medical centre. A new system could begin with one or two modules for the most urgent purposes. The system can be expanded when more applications are envisaged, or demand grows, or when additional funds become available. The original system in the mean time does not need to be replaced. When the expansion does take place the composition of the whole system, modules, storage and power conditioning, must be taken into consideration, in order to maintain an optimal performance.

3.8.2 Maintenance and Reliability Because a PV-system does not have moving parts and therefore no mechanical wear, maintenance requirements are minimal. The necessary maintenance comprises: •

Cleaning the collector surface

•

Electrical check on the modules; the wiring/connections and the power conditioning

•

Visual inspection of the modules for broken cells or surface, humidity, electrical connections and so on

•

Visual inspection of the mechanical connections and the supporting structure, especially on corrosion

•

Repairing or changing broken parts,

•

Maintenance and repair of the batteries.

Apart from the battery maintenance and (possibly) the collector cleaning a yearly service should be sufficient.

3.9 Battery Chargers

A battery charger is a device used to put energy into a secondary cell or rechargeable battery by forcing an electric current through it.

The charge current depends upon the technology and capacity of the battery being charged.

For example, the current that should be applied to recharge a 12 V car battery will be very different from the current for a mobile phone battery. A simple charger works by connecting a constant DC power source to the battery being charged.

The simple charger does not modify its output based on time or the charge on the battery.

This simplicity means that a simple charger is inexpensive, but there is a tradeoff in quality.

Typically, a simple charger takes longer to charge a battery to prevent severe over-charging.

Even so, a battery left in a simple charger for too long will be weakened or destroyed due to over-charging. These chargers can supply either a constant voltage or a constant current to the battery.

Chapter 4 Solar cell to AC current 4.1

Solar Based Battery Charging Circuit

To make this project successful we’ve used the circuit which is cheap to implement and its working principle is much easier.

4.1.1 Apparatus we needed: 1. Resistances

120R, 100R, 1K, 50K

2. Variable Resistance

5K

3. Diodes

1N4007

4. Capacitors

0. 1uF (poly), 100uF

5. Zener diodes

6V-1W

6. Transistor

T1P122

7. Voltage Regulator

LM 317

6. LED

Red

4.1.2 Circuit Diagram of Battery Charge

Fig.7: Circuit diagram of battery charging circuit 4.1.3 Working Principle The circuit uses a variable voltage regulator IC LM 317 to set the output voltage steady around 16 volts. Variable resistor VR controls the output voltage. When the solar panel generates current, D1 forward biases and Regulator IC gets input current. Its output voltage depends on the setting of VR and the output current is controlled by R1.This current passes through D2 and R3. When the output voltage is above (as set by VR) 16volts, Zener diode ZD2 conducts and gives stable 15 volts for charging. Charging current depends on R1 and R3. Around 250 to 300 miliampere current will be available for charging. Green LED indicates charging status. When the battery attains full voltage around 13 volts, Zener diode ZD1 conducts and T1 forward biases. This drains the output current from the regulator IC through T1 and charging process stops. When the battery voltage reduces below 12 volts, ZD1 turns off and battery charging starts again.

4.2 Solar Power Residential One way to save wer bill is to save energy in our home. Another way is to find alternative energy sources. Solar power can be one of the choices which can be considered seriously.

There are many other ways that we can use to have home energy saving. This article will talk about if it is difficult to make solar power residential. There are many reasons that we should consider making wer own solar power residential including: It is less expensive than buying the whole solar power system which can possibly cost we many thousands dollars.

It can be made out of the simple materials that can be bought at the local hardware stores.

There are step-by-step guides to make solar power panels by our self. We can find out one easily on the net The method is not difficult. We can enjoy doing that and have fun with wer kids. The cost is approximately within a couple of hundred dollars. It is estimated that we will be able to cut wer energy bill by fifty per cent. We can use solar power for many purposes for example, making electricity, cooking and heating.

There are also other choices of making solar power residential. For example, we can do it by combining solar panel kits. They are the tool kits to make solar panel. We can use that but the effectiveness will depend on the brand used. In addition, the cost will be more expensive than doing the whole by wer self.

Solar power residential is not difficult to make and it is not expensive. If we know how to do it, we can enjoy the saving of wer electricity bill.

4.3 Charging Dependable performance and long service life depend upon correct charging. Faulty procedures or inadequate charging equipment result in decreased battery life and/or unsatisfactory performance. The selection of suitable charging circuits and methods is as important as choosing the right battery for the application.

4.4 General view of Battery To charge a Power-Sonic battery, a DC voltage higher than the open-circuit voltage of 2.15 is applied to the terminals of the battery. Depending on the state of charge, the cell may temporarily be lower (after discharge) or higher (right after charging) than 2.15 volts. After some time, however, it should level off at about 2.15 volts per cell. Power-Sonic batteries may be charged by using any of the conventional charging techniques. To obtain maximum service life and capacity, along with acceptable recharge time and economy, constant voltagecurrent limited charging is recommended. During charge, the lead sulfate of the positive plate becomes lead dioxide. As the battery reaches full charge, the positive plate begins generating dioxide causing a sudden rise in voltage. A constant voltage charge, therefore, allows detection of this voltage increase and thus control of the charge amount.

4.4.1 Battery Charge Controller in PV system

The primary function of a charge controller in a stand-alone PV system is to maintain the battery at highest possible state of charge while protecting it from overcharge by the array and from over discharge by the loads. Although some PV systems can be effectively designed without the use of charge control, any system that has unpredictable loads, user intervention, optimized or undersized battery storage (to minimize initial cost) typically requires a battery charge controller. The algorithm or control strategy of a battery charge controller determines the effectiveness of battery charging and PV array utilization, and ultimately the ability of the system to meet the load demands. Additional features such as temperature compensation, alarms, meters, remote voltage sense leads and special algorithms can enhance the ability of a charge controller to maintain the health and extend the lifetime of a battery, as well as providing an indication of operational status to the system caretaker.

Important functions of battery charge controllers and system controls are: Prevent Battery Overcharge: to limit the energy supplied to the battery by the PV array when the battery becomes fully charged.

Prevent Battery over discharge: to disconnect the battery from electrical loads when the battery reaches low state of charge.

Provide Load Control Functions: to automatically connect and disconnect an electrical load at a specified time, for example operating a lighting load from sunset to sunrise.

4.4.2 Overcharge Protection A remote stand-alone photovoltaic system with battery storage is designed so that it will meet the system electrical load requirements under reasonably determined worst-case conditions, usually for the month of the year with the lowest insolation to load ratio. When the array is operating under good-to-excellent weather conditions (typically during summer), energy generated by the array often exceeds the electrical load demand. To prevent battery damage resulting from overcharge, a charge controller is used to protect the battery. A charge controller should prevent overcharge of a battery regardless of the system sizing/design and seasonal changes in the load profile, operating temperatures and solar insolation.

Charge regulation is the primary function of a battery charge controller, and perhaps the single most important issue related to battery performance and life. The purpose of a charge controller is to supply power to the battery in a manner which fully recharges the battery

without overcharging. Without charge control, the current from the array will flow into a battery proportional to the irradiance, whether the battery needs charging or not. If the battery is fully charged, unregulated charging will cause the battery voltage to reach exceedingly high levels, causing severe gassing, electrolyte loss, internal heating and accelerated grid corrosion. In most cases if a battery is not protected from overcharge in PV system, premature failure of the battery and loss of load are likely to occur.

Charge controllers prevent excessive battery overcharge by interrupting or limiting the current flow from the array to the battery when the battery becomes fully charged. Charge regulation is most often accomplished by limiting the battery voltage to a maximum value, often referred to as the voltage regulation (VR) set point. Sometimes, other methods such as integrating the ampere-hours into and out of the battery are used. Depending on the regulation method, the current may be limited while maintaining the regulation voltage, or remain disconnected until the battery voltage drops to the array reconnect voltage (ARV) set point.

4.4.3 Over discharge Protection During periods of below average insolation and/or during periods of excessive electrical load usage, the energy produced by the PV array may not be sufficient enough to keep the battery fully recharged. When a battery is deeply discharged, the reaction in the battery occurs close to the grids, and weakens the bond between the active materials and the grids. When a battery is excessively discharged repeatedly, loss of capacity and life will eventually occur. To protect batteries from over discharge, most charge controllers include an optional feature to disconnect the system loads once the battery reaches a low voltage or low state of charge condition.

In some cases, the electrical loads in a PV system must have sufficiently high enough voltage to operate. If batteries are too deeply discharged, the voltage falls below the operating range of the loads, and the loads may operate improperly or not at all. This is another important reason to limit battery over discharge in PV systems.

Over discharge protection in charge controllers is usually accomplished by open-circuiting the connection between the battery and electrical load when the battery reaches a pre-set or adjustable low voltage load disconnect (LVD) set point. Most charge controllers also have an indicator light or audible alarm to alert the system user/operator to the load disconnects

condition. Once the battery is recharged to a certain level, the loads are again reconnected to a battery.

Non-critical system loads are generally always protected from over discharging the battery by connection to the low voltage load disconnect circuitry of the charge controller. If the battery voltage falls to a low but safe level, a relay can open and disconnect the load, preventing further battery discharge. Critical loads can be connected directly to the battery, so that they are not automatically disconnected by the charge controller. However, the danger exists that these critical loads might over discharge the battery. An alarm or other method of user feedback should be included to give information on the battery status if critical loads are connected directly to the battery.

4.4.4 Charge Controller Terminology and Definitions Charge regulation is the primary function of a battery charge controller, and perhaps the single most important issue related to battery performance and life. The purpose of a charge controller is to supply power to the battery in a manner to fully recharge the battery without overcharging. Regulation or limiting the PV array current to a battery in a PV system may be accomplished by several methods. The most popular method is battery voltage sensing, however other methods such as amp hour integration are also employed. Generally, voltage regulation is accomplished by limiting the PV array current at a predefined charge regulation voltage. Depending on the regulation algorithm, the current may be limited while maintaining the regulation voltage, or remain disconnected until the battery voltage drops to the array reconnect set point.

While the specific regulation method or algorithm vary among charge controllers, all have basic parameters and characteristics. Charge controller manufacturer's data generally provides the limits of controller application such as PV and load currents, operating temperatures, parasitic losses, set points, and set point hysteresis values. In some cases the set points may be dependent upon the temperature of the battery and/or controller, and the magnitude of the battery current. A discussion of basic charge controller terminology follows: 4.4.5 Charge Controller Set Points The battery voltage levels at which a charge controller performs control or switching functions are called the controller set points. Four basic control set points are defined for most charge controllers that have battery overcharge and over discharge protection features.

The voltage regulation (VR) and the array reconnect voltage (ARV) refer to the voltage set points at which the array is connected and disconnected from the battery. The low voltage load disconnect (LVD) and load reconnect voltage (LRV) refer to the voltage set points at which the load is disconnected from the battery to prevent over discharge. Figure 12-1 shows the basic controller set points on a simplified diagram plotting battery voltage versus time for a charge and discharge cycle. A detailed discussion of each charge controller set point follows.

Charge Controller Set Points

Time Figure 3. Controller set points 4.4.6 Voltage Regulation (VR) Set Point The voltage regulation (VR) set point is one of the key specifications for charge controllers.

The voltage regulation set point is defined as the maximum voltage that the charge controller allows the battery to reach, limiting the overcharge of the battery. Once the controller senses that the battery reaches the voltage regulation set point, the controller will either discontinue battery charging or begin to regulate (limit) the amount of current delivered to the battery. In some controller designs, dual regulation set points may be used. For example, a higher regulation voltage may be used for the first charge cycle of the day to provide a little battery overcharge, gassing and equalization, while a lower regulation voltage is used on subsequent cycles through the remainder of the day to effectively ‘float charge’ the battery.

The battery voltage levels at which a charge controller performs control or switching functions are called the controller set points. Four basic control set points are defined for

most charge controllers that have battery overcharge and over discharge protection features.

The voltage regulation (VR) and the array reconnect voltage (ARV) refer to the voltage set points at which the array is connected and disconnected from the battery. The low voltage load disconnect (LVD) and load reconnect voltage (LRV) refer to the voltage set points at which the load is disconnected from the battery to prevent over discharge.

4.4.7 Array Reconnect Voltage (ARV) Set Point In interrupting (on-off) type controllers, once the array current is disconnected at the voltage regulation set point, the battery voltage will begin to decrease. The rate at which the battery voltage decreases depends on many factors, including the charge rate prior to disconnect, and the discharge rate dictated by the electrical load. If the charge and discharge rates are high, the battery voltage will decrease at a greater rate than if these rates are lower. When the battery voltage decreases to a predefined voltage, the array is again reconnected to the battery to resume charging. This voltage at which the array is reconnected is defined as the array reconnect voltage (ARV) set point.

If the array were to remain disconnected for the rest of day after the regulation voltage was initially reached, the battery would not be fully recharged. By allowing the array to reconnect after the battery voltage reduces to a set value, the array current will ‘cycle’ into the battery in an on-off manner, disconnecting at the regulation voltage set point, and reconnecting at the array reconnect voltage set point. In this way, the battery will be brought up to a higher state of charge by ‘pulsing’ the array current into the battery.

It is important to note that for some controller designs, namely constant-voltage and pulsewidth-modulated (PWM) types, there is no clearly distinguishable difference between the VR and ARV set points. In these designs, the array current is not regulated in a simple on-off or interrupting fashion, but is only limited as the battery voltage is held at a relatively constant value through the remainder of the day.

4.5 INVERTER 4.5.1 INTRODUCTION An inverter is an electrical device that converts direct current (DC) to alternating current (AC); the converted AC can be at any required voltage and frequency with the use of appropriate transformers, switching, and control circuits. It is a high-power electronic oscillator. It is so named because early mechanical AC to DC converters were made to work

in reverse, and thus were “inverted, to convert DC to AC. batteries.

Inverter is suitable for: •

Electric drills, fret saws, circular saws, electric chain saws, grinders

•

Vacuum cleaners, coffee machines, irons, dryers, mixers, sewing machines, electric razors, etc.

•

Lamps, energy-savings lamps

•

Electronic devices, e.g. music amplifiers, battery chargers

•

Computers and accessories, UPS

•

Televisions and radios

•

Ham radio transmitters, high voltage generators, among other things

Commonly specified inverter characteristics •

Input voltage: Range and nominal

•

Output power

•

Output Voltage

•

Regulation of output voltage and frequency vs load and input voltage

•

Output frequency accuracy

•

Load power factor

•

Output waveform

•

Harmonic distortion of output

•

Overall efficiency vs loading

•

Operating environment

•

Size and weight

•

Protection required

Technological advances have led to very sophisticated, solid-state inverters. From 100 to over 5,000 watts, ultra-efficient, with all sorts of advantages. Some of these use less than 10% of the energy consumed when fully loaded and way less than 1% at lesser inputs to run their own components.

4.5.2 Output of Power Inverter Power inverters produce one of three different types of wave output: •

Square Wave

•

Modified Sine Wave

•

Pure Sine Wave

A type of electrical inverter that produces a square wave output that consists of a DC source, four switches, and the load. The switches are power semiconductors that can carry a large current and withstand a high voltage rating. The switches are turned on and off in correct sequence, at a certain frequency. The square wave inverter is the simplest and the least expensive type of inverter The second category consists of relatively inexpensive units, producing modified sine-wave outputs, which could logically be called “modified square waves” instead. They are basically square waves with some dead spots between positive and negative half-cycles. Switching techniques rather than linear circuits are used in the power stage, because switching techniques are more efficient and thus less expensive. These inverters require no highfrequency switching, as the switching takes place at line frequency.

The modified sine inverter is different from a pure sine power inverter because the wave is in more of a step wave and because appliances are not specifically designed to work with this type of inverter. Although many appliances will still work with a modified sine inverter, some may not work as efficiently. As such, it may take more power to run appliances with a modified sine inverter. The pure sine inverter, which is also referred to as a “true” sine wave, utilizes sine wave in order to provide wer appliances with power. A sine wave, which is produced by rotating AC machinery, is the type of wave that is generally provided by the utility company with the help of a generator.

4.6 MOSFET Based Single Phase Inverter 4.6.1 MOSFET as a Switch MOSFET is used as the electronic switches, because it makes the most efficient high-current switches. N-channel, Enhancement-mode MOSFET operates using a positive input voltage and has an extremely high input resistance (almost infinite) making it possible to interface with nearly any logic gate or driver capable of producing a positive output. When it off it is virtually an open circuit, yet when it is on it is very close to a short circuit (only a few milliohms). So, very little power is wasted as heat. Also, due to this very high input (Gate) resistance many different MOSFET’s can be paralleled together until required current handling .limit is achieved. In DC-AC inverters designed to deliver high. power, there are a no. of MOSFET connected to each side of the transformer primary, to share the heavy current. However because MOSFETS are essentially connected in parallel they behave like very high-power MOSFETs, able to switch many tens of amps. Connecting together various

MOSFET’s enables to switch high current or high voltage loads, but doing so becomes expensive and impractical in both components and circuit board space. To overcome this problem Power Field Effect Transistors or Power FET’s was developed.

By applying a suitable drive voltage to the Gate of an MOSFET, the resistance of the DrainSource channel can be varied from an “OFF-resistance” of many hundreds of kQ’s, effectively an open circuit, to an “ON-resistance” of less than 1 Q, effectively a short circuit.

MOSFET can be turned “ON” fast or slow, or to pass high currents or low currents. This ability to turn the MOSFET “ON” and “OFF” allows the device to be used as a. very efficient switch with switching speeds much faster than standard bipolar junction transistors.

But when using MOSFET’s to switch either inductive or capacitive loads some form of protection is required to prevent the MOSFET device from becoming damaged. If the resistive load was to be replaced by an inductive load such as a coil or solenoid, a “Flywheel” diode would be required in parallel with the load to protect the MOSFET from any back-emf.

Driving an inductive load has the opposite effect from driving a capacitive load. FOr example, a capacitor without an electrical charge is a short circuit, resulting in a high “inrush” of current and when voltage from an inductive load is removed a large reverse voltage build up as the magnetic field collapses, resulting in an induced back-emf in the windings of the inductor. For the power MOSFET to operate as an analogue switching device, it needs to be switched between its “Cut-off Region” where V(GS) = 0 and its “Saturation Region” where V(GS)(on) = +ve. The power dissipated in the MOSFET (PD) depends upon the current flowing through the channel at saturation and also the “ONresistance”.

4.7 Apparatus •

IC

TLC 494

•

Diode

1N4007.

•

MOSFET

IRE 540.

•

Resistor

10k, 22k, 100k, 470.

•

Potentiometer

I k.

•

Capacitor

0.luF, 0.22uF, 0.OluF.

•

Transformer

12-0-12:220V.

4.7.2 TLC 494 TLC 549 is a 16 pin IC that consists of a 555 timer. It could me made to operate in both mono-stable and astable mode.

4.7.3 555 Timer The 8-pin 555 timer must be one of the most useful ICs ever made. 555 timer is very reliable, low cost and easy to use in variety of application. It can operate from supply voltage of +5V to +18V, making it compatible with both TTL(Transistor- Transistor logic) circuits and opamp circuits. The 555

timer is considered as a functional block that contains two

comparators, two transistors, three equal resistor.

A popular version is the NE555 and this is suitable in most cases where a ‘555 time’ is specified. The 556 is a dual version of the 555 housed in a 14-pin package, the two timers (A and B) share the same power supply pins. The circuit diagrams on this page show a 555, but they could all be adapted to use one half of a 556.

Standard 555 and 556 ICs create a significant ‘glitch’ on the supply when their output changes state. This is rarely a problem in simple circuits with no other ICs, but in more complex circuits a smoothing capacitor should be connected across the +Vs and OV supply near the 555.

4.7.4 Inputs of 555 Trigger input When it is less then lower threshold this makes the output high. It monitors the discharging of the timing capacitor in an astable circuit It has a high input impedance above 2M. Threshold input When greater then upper threshold is this makes the output low. It monitors the charging of the timing capacitor in astable and monostable circuits. It has a high input impedance above 10M Reset input When it is less than about 0.7V this makes the output low, overriding other inputs. When not

required it should be connected to +Vs. It has an input impedance of about 10k.

Fiq.5:Astable operation of 555

Controlinput It can be used to adjust the threshold. Usually this function is not required and the control input is connected to OV with a 0.01 j.tF capacitor to eliminate electrical noise. It can be left unconnected if noise is not a problem.

4.7.5 Astable Operation An astable circuit produces a square wave, this is a digital waveform with sharp transitions between low (O.V) and high (+Vs). The circuit is called an astable because it is not stable in any state: the output is continually changing between ‘low’. and ‘high’.

The time period (T) of the square wave is the time for one complete cycle.

T=O.7x(Rl +2R2)xCl The time period can be split into two parts: T = Tm + Ts Mark time (output high): Tm = 0.7 x (Rl + R2) x Cl Space time (output low): Ts = 0.7 x R2 x CI With the output high (+Vs) the capacitor Cl is charged by current flowing through Ri and R2. The threshold and trigger inputs monitor the capacitor voltage and when it reaches 2/3Vs (threshold voltage) the output becomes low and the discharge pin is connected to OV. The capacitor now discharges with current flowing through R2 into the discharge pin. When the voltage falls to 1/3Vs (trigger voltage) the output becomes high again and the discharge pin is disconnected, allowing the capacitor to start charging again.

This cycle repeats continuously unless the reset input is connected to OV which forces the output low while reset is OV.

An astable can be used to provide the clock signal for circuits such as counters.

A low frequency astable (< 10Hz) can be used to flash an LED on and off, higher frequency flashes are too fast to be seen clearly. Driving a loudspeaker or piezoelectric transducer with a low frequency of less than 20Hz will produce a series of and this can be used to make a simple metronome.

An audio frequency astable (20Hz to 20kHz) can be used to produce a sound from a loudspeaker or piezoelectric transducer. The sound is suitable for buzzes and beeps. The natural (resonant) frequency of most piezoelectric transducers is about 3kHz and this will make them produce a particularly loud sound.

4.8 Circuit Diagram of Inverter

Fig: Inverter

Circuit

4.8.1 Working Principle TLC 494 produces periodic pulses using the 555 timer in astable operation. Pulse train Vi is shown in fig. Pulse train is rectified and only positive half cycle appears on TI. Output from Ti is again inverted. A logic is implemented so that pulses become slightly displaced in time.

These pulses are the applied to MOSFETs. It is necessary to allow a small interval between powering the transformer one way and powering it the other, the switches are pairs of MOSFETS and if they switch simultaneously there would be a risk of shorting out the power supply. Hence, a small wait is needed to avoid this problem. This wait time is called “Dead Time” and is necessary to avoid transistor shoot-through.

The above arrangement is push-pull scheme. The term push—pull is sometimes used to generally refer to any inverter with bidirectional excitation of the transformer. However, push —pull more commonly refers to a two-switch topology with a split primary winding.

The operation of the circuit means that both MOSFETs are actually pushing, and the pulling is done by a low pass filter (coil) in general, and by a center tap of the transformer in the converter application. But because the transistors push in an alternating fashion, the arrangement is called a push—pull scheme.

DC from the battery is converted into AC very simply, by using a pair of power MOSFETs (Q1 and Q2) acting as very efficient electronic switches. The positive 10V DC from the 37 battery is connected to the centre-tap of the transformer primary, while each MOSFET is connected between one end of the primary and earth (battery negative). So by switching on Q1, the battery current can be made to flow through the top half of the primary and to earth via Q1. Conversely by switching on Q2 instead, the current is made to flow the opposite way

through the lower half of the primary and to earth. Therefore by switching the two MOSFETs on alternately, the current is made to flow first in one half of the primary and then in the other, producing an alternating magnetic flux in the transformers core. As a result a corresponding AC voltage is induced in the transformers secondary winding, and as the secondary has more number of turns in the primary, the induced AC voltage is much higher.

Because the switching MOSFETs are simply being turned on and off, this inverter does not produce AC of the pure sine wave as the AC power mains. The output waveform is essentially alternating rectangular pulses as shown in the fig.

4.9 Improved Design An improved design is achieved by varying the width of the rectangular pulses, to control the form factor and hence the RMS value of the output voltage. This is called pulse width modulation (PWM), and is usually done by having a feedback system which senses the inverter output voltage (or load current). When this feedback senses that the load on the inverter output has increased, the inverter control circuitry acts to increase the width of the pulses which turn on the MOSFETs. So the MOSFETs turn on for longer each half-cycle, automatically correcting the RMS value of the output to compensate for any droop in peakto-peak output. The resulting regulation is usually capable of keeping the RMS value close to constant, for loads up to the inverter’s full rated output power. However this approach does have limitations, mainly because it can generally only increase the pulse width to a certain point. This may not be sufficient to allow the inverter to deliver enough RMS output voltage in short-term overload or surge conditions. When many types of appliance are first turned on, they draw a startup current which is many times greater than the current drawn when they are running. This type of surge can overload the inverter, and its protection circuitry may shut it down to prevent damage to the transformer and MOSFETs. Incorporating special feature like soft start circuitry allows the inverter to cope with this type of short load current surge. The output voltage and power may drop, but at least the inverter keeps operating and allows the appliance to start up.

4.9.1 Voltage Spikes Another complication is that due to fairly high harmonic content in the output of inverters high inductive load can develop fairly high voltage spikes due to inductive back EMF. These spikes can be transformed back into the primary of the inverter’s transformer, where they have the potential to damage the MOSFETs and theirdriving circuitry. The risk’of damage is fairly small during the actual power pulses of each cycle, because at these times one end of the primary is effectively earthed. Transformer action thus prevents the other end from rising

higher than about twice the battery voltage. However from Fig.2, it is seen that there are times during â&#x20AC;&#x2DC;every cycle of operation â&#x20AC;&#x2DC;when neither of the switching MOSFETs is conducting, the flats between the rectangular pulses. At these times that the spikes can produce excessive voltage across the MOSFETs, and potentially cause damage. For this reason that many inverters have a pair of high-power zener diodes connected across the MOSFETs. The zeners conduct heavily as soon as the voltage rises excessively, protecting the MOSFETs from damage. Another approach is to have high-power standard diodes connected from each end of the primary to a large electrolytic capacitor, which becomes charged up to twice the battery voltage. When the ends of the primary attempt to rise higher than this voltage, the diodes conduct and allow the capacitor to absorb the spike thergy.

These type of protection allows the inverter to be tolerant of moderately inductive loads.

However they may not be able to cope with heavy loads that are also strongly inductive.

Quite apart from the generation of voltage spikes, heavily inductive loads tend to demand current which is strongly shifted in phase relative to the inverters output voltage pulses. This makes it hard for the inverter to cope, because the only energy available to the load between the pulses is that stored in the transformer.

4.9.2 Frequency stability Although most appliances and tools designed for mains power can tolerate a small variation in supply frequency, they can malfunction, overheat or even be damaged if the frequency changes significantly. To avoid such problems, most DC-AC inverters include circuitry to ensure that the inverters output frequency stays very close to the nominal mains frequency 50Hz. In some inverters this is achieved by using a quartz crystal oscillator and divider system to generate the master timing for the MOSFET drive pulses. Others simply use a fairly stable oscillator with R-C timing, fed via a voltage regulator to ensure that the oscillator frequency does not change even if the battery voltage varies quite widely.

4.9.3 Inverters & safety Couple of important safety aspects should be maintained using a DC-AC inverter. A low power inverter rated at a mere 60 watts has an output which is potentially fatal. Such an inverter can typically deliver up to about 360mA at 230V, which is over ten times the current level needed to stop human heart and cause fatal fibrillation. There is also another kind of safety risk associated with inverters, which arises from the fact that in many inverters, there is a direct electrical path between the mains-voltage output circuit and the low voltage input circuitry (including the battery leads). This path is usually via the auto turn-on sensing, and possibly also the voltage or current sensing used for output regulation.

Chapter 5 Control Circuit operation and Economical & Environmental aspects 5.1 Control Circuit 5.1.1Microcontroller Microcontroller is a small computer on a single integrated circuit containing a processor core, memory, and programmable input/output peripherals. Microcontrollers are designed for embedded applications, in contrast to the microprocessors used in personal computers or other general purpose applications. Microcontrollers are used in automatically controlled products and devices, such as automobile engine control systems, implantable medical devices, remote controls, office machines, appliances, power tools, toys and other embedded systems. By reducing the size and cost compared to a design that uses a separate microprocessor, memory, and input/output devices, microcontrollers make it economical to digitally control even more devices and processes. Mixed signal microcontrollers are common, integrating analog components needed to control non-digital electronic systems 5.1.2 Relay A simple electromagnetic relay consists of a coil of wire surrounding a soft iron core, an iron yoke, which provides a low reluctance path for magnetic flux, a movable iron armature, and a set of contacts. The armature is hinged to the yoke and mechanically linked to a moving contact or contacts.

It is held in place by a spring so that when the relay is de-energized there is an air gap in the magnetic circuit. When an electric current is passed through the coil, the resulting magnetic field attracts the armature and the consequent movement of the movable contact or contacts either makes or breaks a connection with a fixed contact. if the set of contacts was closed when the relay was de-energized, then the movement opens the contacts and breaks the connection, and vice versa if the contacts were open. When the current to the coil is switched off, the armature is returned by a force, approximately half as strong as the magnetic force, to its relaxed position.

Since relays are switches, the terminology applied to switches is also applied to relays. A relay will switch one or more poles, each of whose contacts can be thrown by energizing the coil in one of three ways: â&#x20AC;˘

Normally-open (NO) contacts connect the circuit when the relay is activated and the circuit is disconnected when the relay is inactive. It is also called a Form A contact or

“make” contact.

•

Normally-closed (NC) contacts disconnect the circuit when the relay is activated and the circuit is connected when the relay is inactive. It is also called a Form B contact or “break” contact.

•

Change-over (CO), or double-throw, contacts control two circuits: one normally-open contact and one normally-closed contact with a common terminal. It is also called a Form C contact or “transfer” contact. If this type of contact utilizes“make before break” functionality, then it is called a Form D contact.

5.1.3 Light Dependent Resistor (LDR) A photoresistor or light dependent resistor or cadmium sulfide (CdS) cell is a resistor whose resistance decreases with increasing incident light intensity. It can also be referred to as a photoconductor.

A photoresistor is made of a high resistance semiconductor. if light falling on the device is of high enough frequency, photons absorbed by the semiconductor give bound electrons enough energy to jump into the conduction band. The resulting free electron conduct electricity, thereby lowering resistance.

A photoelectric device can be either intrinsic or extrinsic. An intrinsic semiconductor has its own charge carriers and is not an efficient semiconductor. In intrinsic devices the only 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 do pants, added whose ground state energy is closer to the conduction band, since the electrons do not have as far to jump, lower energy photons are sufficient to trigger the device.

If a sample of silicon has some of its atoms replaced by phosphorus atoms there will be~ extra electrons available for conduction.

5.1.4 Dual Mode Control Circuit Diagram

5.1.5 Working Principle First sensor is the photocell sensor that detects the concentration of the light. When sensor detect that have light, then will determine to switch RL1, for this region ADC go in to the Microcontroller ATMETG8 and the Microcontroller will energies to switch RL2 and RL3.The street lamp is connected to solar power and this turns on. When solar energy is not sufficient then it shifts into grid power. The control circuit will switch off the lamp when the photocell sensor detects the light from the sun in the early morning and the charging process of battery will continue until evening or no light (cloudy).In this way street lamp operates in dual mode at solar and grid power and also lamp will is on-off automatically.

5.2 Economical view 5.2.1 Advantages 1. No operating cost 2. Not paid bill used for electricity 3. Safe extra money 4. Continue renewable energy 5. No load shedding 5.2.3 Disadvantage 1. Initial cost is high 5.4 Environmental view Renewable energy is the cleanest power sources among others all power sources. Solar is one

of most useable renewable energy. Here not use fuel and others green effected raw materials so that it not affects green house. It also not pollutes environment. So solar is good option for balance environment.

Chapter 6 Conclusion We have faced some problem during working on dual mode control circuit and others parameter. Battery is charged with solar energy. We know that the output of solar energy is dependent on the intensity of the sunlight. So the charging time of the battery is dependent on specific solar panel. For funny day it will take less time a huge time is needed to charge up the battery in a dull day. If the battery is not fully charged due to the lack of sunlight, it cannot contribute to supply the output for a long time. By improving the dual mode operation of control circuit, we can recover the problem. If the solar energy is not available /insufficient then grid power works as supply power.

We have tried to make this project cost effective and to supply power continue without any disturbing. For this region here we use microcontroller and dual mode operation.

Constructed this project part physically we face more difficult situation. The some problems are given below and tried to give a solution to them.

To ensure output wave is properly and connection of circuit. Burning out are all resistors , mosfets , realy, microcontroller and others apparatus. It was really hard situation that construct solar system in appropriately, convert DC to AC and dual mode operation was in proper way.

Future Works In this project, having huge opportunity is to do work further in future. Normally many street lamps are available in street, so interconnection of all street lamps in one place for easy operation is also vital option .It is also need modified and reduced cost for effective and efficient output. Without this structure is also applicable by some modified in others useful area like household, Industry, Dairy farm etc. Itâ&#x20AC;&#x2122;s really huge opportunity to research about this related topic in future. Thus this project help them for buildup their thinking and an idea about this kinds of field.