CHAPTER ONE
1.1 INTRODUCTION
Solar cells are raised light sources which are powered by photovoltaic panel generally mounted on the lighting poles; it is made automatic by the application of the circuit called the photocell switching circuit. Its operation is to switch the street lamp ON at night and switching it OFF in the day time.
It is crucial in everyday activity for the continuity of normal life. From plants to animals, from human beings to domestic insects, from technology to science, nothing seems to maximize its existence without the availability of sun light (Garg, and Prakash, 2000). Even the human eye requires some amount of light to function well (Perlin, 1999).
Light from the sun is natural and it is called sunlight. This sunlight can serve as a source of solar power which is converted to electric power for both household and industrial utilization. Solar power is the generation of electricity from sunlight.
This can be direct as with photovoltaic (PV) or indirect as with concentrating solar power (CSP) (Holladay, 2008) where the sun’s energy is focused to boil water which is then used to provide energy. Solar power is a predictably intermittent energy source, meaning that while solar power is not available at all times, we can predict with a very good degree of accuracy when it will not be available (Wikipedia, 2010).
One area of application of solar energy is found in the construction of solar-powered street lights. This is the equipment that is paramount to meeting the security needs of every community in the 21st century (Maloney,1996). Solar street lights are beneficial in that the day to day running and maintenance costs are reduced, it is safe energy, environment friendly and convenient to install.
It is powered by mono-crystalline and poly-crystalline solar panels which convert the solar energy into electricity saved in the storage batteries without maintenance (Callister, 1997). It can be controlled by a control system to prevent storage batteries from over-charging and over discharging.
Automatic streetlight needs no manual operation of switching ON and OFF. The system itself detects whether there is need for light or not. When darkness rises to a certain level then automatically streetlight is switched ON and when there is other source of light, the streetlight switches OFF. This is done by a sensor called light dependent resistor (LDR) which senses the light like our eyes. This vital use of light gives rise to the idea of using solar energy to power street lights as an alternative to electricity. These solar-powered street lights can then be used for the provision of illumination on streets at night to enhance security and prevent accidents that may otherwise occur due to poor visibility.
1.2 BACKGROUND
Solar radiator is a secondary resource like as wind and wave power, hydroelectricity and biomass that account for most of the available flow of renewable energy in the world.
It can be used so long as there is sunshine. It is especially suitable for high grade housing and outdoor lighting.Solar Street lights have been available for quite some time now, having originally been designed for use in less developed countries.
The technology guiding the use of solar energy has progressed significantly to enable projects to be feasible throughout the world. Electric street lighting is rightly regarded as an enormous consumer of electricity, at a vast financial environmental cost. However, because of the safety and security benefits which result from a good street lighting system, authorities everywhere are keen to implement cost-effective and environmentally friendly lights. Solar street lights can deliver that much-desired outcome and offer an exceptional lighting program while, at the same time, produce considerable economic and environment savings. The most recent development with regard to the technology behind solar street lighting have been in connection with LEDs.
1.3 AIM AND OBJECTIVE
The main objective of this project is to develop some portable solar street lamps with the DC voltage as the source generated from the solar energy. It involves building technology that will illuminate an area; whose lamp turns ON and OFF automatically with the help of a photocell switching circuit.
1.4 SIGNIFICANCE OF STUDY
Solar street light can be used not only on streets, and highways but can also provide cost-effective environmentally friendly lighting for both military and civilian security installations, parking areas, airports, and for whole communities.
The day to day running and maintenance cost are slashed and this brings about a positive environmental impact. They improve commercial prosperity, improve safety and reduce accidents, injuries, and death caused on the way.
Automatic solar powered street lighting system is a lighting system which has so many benefits that makes it to be the best option for the economy. Solar street lights are independent of the utility grid, hence the operation costs are minimized.
1.5 SCOPE OF STUDY
This study covers the area of design to be carried out, the design chosen for both the photocell switching circuit and lamp circuit along with the constructions and the theories behind the project
1.6 PRINCIPLE OF OPERATION
When light falls on a solar cell, electrons in the absorber layer are excited from a lower-energy “ground state”, in which they are bound to specific atoms in the solid to higher “excited state,” in which they can move through the solid. In the absence of the junction-forming layers, these “free” electrons are in random motion, and so there can be no oriented direct current. The addition of junction forming layers, however, induces a built-in electric field that produces the photovoltaic effect.
In effect; the electric field gives a collective motion to the electrons that flow past the electrical contact layers into an external circuit where they can do useful work The solar tracker in the solar panel tracks the sunlight and the light detected is converted to electric power using the photovoltaic effect.
The electric power is used to charge the battery and the charger controller embedded in the street light system is used to prevent the overcharging of the battery.
The photocells to detect light are needed. Photocells are light sensitive sensors that respond to the amount of light detected. When the light is too low, such as at dusk or under heavy overcast skies, the sensor tells the switching circuit within the street light system to activate the flow of electricity and the electricity is sent through high-intensity discharge lamps. When the sensor detects too much light, the sensor will deactivate the street light.
1.7 DEFINITION OF TERMS AND COMPONENTS
- Solar cells
Electric cells that convert solar radiation directly into electricity.
- Solar panel
This is a large panel containing solar cells or heat absorbing plates that convert the sum’s radiation into energy for use. Solar panel is one of the most important parts of solar street lights. There are 2 types of solar panel: mono-crystalline and poly-crystalline. Conversion rate of mono-crystalline solar panel is much higher than poly-crystalline.
This is a power source that produces a direct current through the conversion of chemical energy into electrical energy.
Battery will store the electricity from solar panel during the day and provide energy to the fixture during night. The life cycle of the battery is very important to the lifetime of the solar light and the capacity of the battery will affect the backup days of the lights. There are usually 2 types of batteries: Gel Cell Deep Cycle Battery and Lead Acid Battery
- LED fixture (Light Emitting Diode)
This is a semiconductor used for indicator lights. It emits light when current passes through it. LED is usually used as lighting source for modern solar street light, as the LED will provide much higher Lumens with lower energy consumption. The energy consumption of LED fixture is at least 50% lower than high speed fixture which is widely used as lighting source in Traditional street lights. LEDs’ lack of warm up time also allows for use of motion detectors for additional efficiency gains.
- Charge controller
This is also known as solar regulator. It is used to sense when the batteries are fully charged and to stop, or decrease the amount of current flowing into the battery. It also prevents the battery from back feeding into the solar panel at night and hence flattering the battery. Controller is also very important for solar street light. A controller will usually decide whether to switch on /off charging and lighting. Some modern controllers are programmable so that the user can decide the appropriate time of charging, lighting and dimming. The charge controller serves as an interface between the current generated by the module and the battery charging during the day. The battery is prevented from over-current or over- charging by the charge controller. The charge controller is an electronic circuit comprising an operational amplifier (connected in comparator mode), an electronic switch (transistor) and an electromechanical switch (relay). The circuit is switched ON or OFF by the transistor in saturation region or cut off region respectively, which is controlled by the signal from LDR. The collector current from the transistor toggles between ON or OFF modes.
Pole
Long straight strong pieces of wood, metal or other material with a round cross-section. It is along hollow shaped iron which helps in holding the solar panel on top, the head lamp is placed by the side and sometimes the battery cage is placed at the top of the ground. Strong Poles are necessary to all street lights, especially to solar street lights as there are components mounted on the top of the pole: Fixtures, Panels and sometime batteries. Wind resistance should also be taken into consideration when choosing the pole.
- Bases plate
It is a flat heavy iron which is used in holding the pole in an erect position. It protects it from the effect of the wind.
- Lamp arm
This holds the lamp in the required position on the pole. The lamp arm holds the lamp firm to the pole.
1.8 LIMITATIONS
There were lots of limitations encountered during the construction of this project causing delay in completing the project. The limitation includes;
- Cost of materials
- Insufficient fund
- Unavailability of materials
- Inaccurate results in the photocell switching circuit and lamp circuit
There is also limitation during the construction of the photocell switching circuit; several circuits were constructed before getting precise result.
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