CHAPTER ONE

INTRODUCTION

1.1       Background to the Study

Over the years the use of fossil fuels to generate electricity has not produced enviable results. Besides, fossil fuels have caused a lot of havoc to the ecosystem with Africa not being able to tap into the advantages of using fossil fuels to generate electricity. Therefore, the need for an alternative source of generating electricity arises. The alternative source must be cheap, reliable and efficient. An alternative energy source is solar energy. This is a preferable choice as Africa is in the tropics with considerable amount of sunlight in a day that can be converted into electricity.

Solar energy utilization is on the rise in our modern world as the fossil fuels have great adverse effect on our environment. Solar energy as a form of renewable energy has been in use since the times of Archimedes in 212 BC. At the time solar energy was being converted to heat energy for defense purposes. Other notable scientists have made countless improvements in the utilization of solar energy since then. In 1839, Edmond Becquerel a French scientist discovered the photovoltaic effect. In 1966 the first orbiting astronomical observatory was launched by National Aeronautics and Space Administration (N.A.S.A) which was powered by 1 kW photovoltaic array. As at 1999 the cumulative installed photovoltaic capacity in the world had skyrocketed to 1000MW. Today, solar energy is being used to generate electricity worldwide.

Light 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 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.

          The AC / Solar rechargeable lantern is a valuable device that can be used in homes and offices. It has been observed over the years in Nigeria that power failure and fuel scarcity has been a serious problem over the decade. Due to this fact we have designed a portable handy dual rechargeable lantern, while many have designed an A.C lantern and a solar lantern.

The aim of this project was to achieve a simple reliable lighting system, by converting alternating current (AC) voltage from mains supply together with direct current (DC) voltage from a solar panel to a constant charging voltage for feeding a lead-acid battery, to provide voltage and current for LED lightning.

  Literature review

Solar energy is one of the most available forms of energy on the Earth’s surface, besides; it is very promising and generous. The earth’s surface receives a daily solar dose of 10E+8 KW-hr, which is equivalent to five billion oil barrels that is one thousand times any oil reserve known to man. The solar energy is collector area dependent, and is a diluted form of energy and is available for only a fraction of the day. Also, its availability depends on several factors such as latitude and sky clearness (Duffie& Beckman, 2000; Mittal, Kasana and Thakur, 2005).

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, 2015a). 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).

At the same time, its system requires high initial cost. But on the other hand, it has some attractive features such as its system requiring minimum maintenance and operation cost, and it does not have negative effects on the environment. Another important feature of solar energy is its ability to satisfy rural areas where conventional energy systems might be not suitable or uneconomical. Solar energy is being invested in many forms. The first form is the most familiar and that is using it for supplying domestic hot water for residences which is the most worldwide spread form of solar energy use. Another form is the photovoltaic, and these are special cells that transfer solar energy to electric ones (Friefeld& Coleman, 2006).

Electric lamps or lanterns provide superior lighting for almost any application and are preferred over lighting from any other fuel source for general, localized and orientation lighting. Candles and kerosene-type lanterns are a common source of lighting in remote areas where electric power is not routinely available. Additionally, few non-western countries have a reliable supply of electric power, even in the more developed parts of those countries.

So many times even those who are connected to the electric grid find that they have a need for supplemental lighting during times when electricity is not available. The goal of this project was to develop lighting potential to meet these needs. Portable solar rechargeable LED lamps are widely used; we therefore need to design a portable AC/solar rechargeable LED lamp to give suitable luminosity for reading that consumes minimum power.

1.3     Solar lamp

A solar lamp is a portable light fixture composed of an LED lamp, a photovoltaic solar panel, and a rechargeable battery. Solar panel on top of the lamp recharges the battery. Outdoor lamps are used for lawn and garden decorations. Indoor solar lamps are also used for general illumination (i.e. for garages and the solar panel is detached of the LED lamp).

A solar lamp is a light fixture composed of an LED lamp, a photovoltaic solar panel, and a rechargeable battery. Outdoor lamps may have a lamp, solar panel and battery integrated in one unit. Indoor solar lamps, also referred to as shaftless skylights or tubeless skylights, have separately-mounted solar panels and are used for general illumination where centrally generated power is not conveniently or economically available. Solar-powered household lighting may displace light sources such as kerosene lamps, saving money for the user, and reducing fire and pollution hazards. Solar lamps recharge during the day. Automatic outdoor lamps turn on at dusk and remain illuminated overnight, depending on how much sunlight they receive during the day. Indoor solar lamps may or may not store power.

Solar garden lights are used for decoration, and come in a wide variety of designs. They are sometimes holiday-themed and may come in animal shapes. They are frequently used to mark footpaths or the areas around swimming pools. Solar lamps recharge during the day. At dusk, they turn on (usually automatically, although some of them include a switch for on, off and automatic) and remain illuminated overnight, depending on how much sunlight they receive during the day. Discharging time is generally 8 to 10 hours.

Some solar lights do not provide as much light as a line-powered lighting system, but they are easily installed and maintained, and provide a cheaper alternative to wired lamps. In India, solar lamps, commonly called solar lanterns, using either LEDs or CFLs, are being used to replace kerosene lamps.

1.4     Solar Cell

A solar cell, or photovoltaic cell, is an electrical device that converts the energy of light directly into electricity by the photovoltaic effect, which is a physical and chemical phenomenon. It is a form of photoelectric cell, defined as a device whose electrical characteristics, such as current, voltage, or resistance, vary when exposed to light. Solar cells are the building blocks of photovoltaic modules, otherwise known as solar panels (Pearce and Lau, 2002). Solar cells are described as being photovoltaic irrespective of whether the source is sunlight or an artificial light. They are used as a photo detector (for example infrared detectors), detecting light or other electromagnetic radiation near the visible range, or measuring light intensity.

The operation of a photovoltaic (PV) or solar cell requires 3 basic attributes:

• The absorption of light, generating either electron-hole pairs or excitons.
• The separation of charge carriers of opposite types.
• The separate extraction of those carriers to an external circuit.

In contrast, a solar thermal collector supplies heat by absorbing sunlight, for the purpose of either direct heating or indirect electrical power generation from heat. A "photo electrolytic cell" (photo electrochemical cell), on the other hand, refers either to a type of photovoltaic cell (like that developed by Edmond Becquerel and modern dye-sensitized solar cells), or to a device that splits water directly into hydrogen and oxygen using only solar illumination.

The basic idea of a solar cell (photovoltaic cell) is to convert light energy in to electrical energy. Light energy is transmitted by photons. Solar panel comprises of several solar cell to achieve a specific voltage. The solar cell contains a PN-junction, and may be treated as a diode; the equivalent circuit of a solar cell is shown in Figure 1.1 It consists of a current source and a diode which represents the photo current IPhoto and the dark current ID.

Fig 1.1: Equivalent circuit for a solar cell    (source:http://www.en.wikipedia.org)

1.5     How solar Panel Works

Solar power is arguably the cleanest, most reliable form of renewableenergy available, and it can be used in several forms to help power your home or business. Solar-powered photovoltaic (PV) panels convert the sun's rays into electricity by exciting electrons in silicon cells using the photons of light from the sun. This electricity can then be used to supply renewable energy to your home or business as shown in Figure.1.2.

Solar panels, also known as modules, contain photovoltaic cells made from silicon that transform incoming sunlight into electricity rather than heat. (”Photovoltaic” means electricity from light — photo = light, voltaic = electricity.) Solar panels turn energy from the sun’s rays directly into useful energy that can be used in homes and businesses. There are two main types: solar thermal and photovoltaic, or PV. Solar thermal panels use the sun’s energy to heat water that can be used in washing and heating. PV panels use the photovoltaic effect to turn the sun’s energy directly into electricity, which can supplement or replace a building’s usual supply.

Solar photovoltaic cells consist of a positive and a negative film of silicon placed under a thin slice of glass. As the photons of the sunlight beat down upon these cells, they knock the electrons off the silicon. The negatively-charged free electrons are preferentially attracted to one side of the silicon cell, which creates an electric voltage that can be collected and channeled. This current is gathered by wiring the individual solar panels together in series to form a solar photovoltaic array. Depending on the size of the installation, multiple strings of solar photovoltaic array cables terminate in one electrical box, called a fused array combiner. Contained within the combiner box are fuses designed to protect the individual module cables, as well as the connections that deliver power to the inverter. The electricity produced at this stage is DC (direct current) and must be converted to AC (alternating current) suitable for use 

Fig. 1.2: A Photovoltaic (PV) Panel(Source: https://www.edfenergy.com)

A PV panel is made up of a semiconducting material, usually silicon-based, sandwiched between two electrical contacts. To generate as much electricity as possible, PV panels need to spend as much time as possible in direct sunlight (1a). A sloping, south-facing roof is the ideal place to mount a solar panel. A sheet of glass (1b) protects the semiconductor sandwich from hail, grit blown by the wind, and wildlife. The semiconductor is also coated in an antireflective substance (1c), which makes sure that it absorbs the sunlight it needs instead of scattering it uselessly away.

When sunlight strikes the panel and is absorbed, it knocks loose electrons from some of the atoms that make up the semiconductor (1d). The semiconductor is positively charged on one side and negatively charged on the other side, which encourages all these loose electrons to travel in the same direction, creating an electric current. The contacts (1e and 1f) capture this current (1g) in an electrical circuit.

The electricity PV panels as shown in Figure 1.3 generate direct current (DC). Before it can be used in homes and businesses, it has to be changed into alternating current (AC) electricity using an inverter. The inverted current then travels from the inverter to a fuse box and from there to the appliance that needs it. PV systems installed in homes and businesses can include a dedicated metering box that measures how much electricity the panels are generating. 

Fig. 1.3: How a solar panel generates electricity

(Source: https://www.edfenergy.com)

1.6.2 Photovoltaic Systems

A photovoltaic system, also known as solar PV is a power system designed to supply usable solar power by means of photovoltaic. It consists of an arrangement of several components, including solar panel to absorb and convert sunlight into electricity, a solar inverter to change the electrical current from DC to AC, as well as mounting, cabling and other electrical accessories to set up a working system. It may also use a solar tracking system to improve the system's overall performance and include an integrated battery solution, as prices for storage devices are expected to decline. Strictly speaking, a solar array only encompasses the ensemble of solar panels, the visible part of the PV system, and does not include all the other hardware, often summarized as balance of system (BOS). Moreover, PV systems convert light directly into electricity and shouldn't be confused with other technologies, such as concentrated solar power or solar thermal, used for heating and cooling (Messenger and Ventre, 2004).

A typical PV panel generally consists of a number of small PV cells. A number of PV panels, when wired together in series and parallel connections for a certain voltage and/or current requirement, form an array. The most common material used for a PV panel is crystalline silicon (Messenger and Ventre, 2004).

There are two main types of Photovoltaic systems – systems that would be connected to the grid, which is the most common type; and stand-alone systems which are generally small scale (not connected to utility grid). Most residences, or buildings, that have PV panels integrated as part of the façade of a building are usually grid-tied so that during the night –time or during winter months, the electricity is generally taken from the utility grid. During summer months, or during day-time, when excess electricity is generated within the house than required, this power is sent back to the utility company.

1.7     LED Lighting

Solid state lighting technology has been one of the fastest emerging illumination sources in the current lighting market. The prediction is that as building owners, operators and occupants are increasingly aware of this new technology, within the next ten years LED’s will gain popularity within the lighting industry for general lighting application (Craig, 2002). And truly for the past five years, it has become the choice of manufacturers in the production of rechargeable lanterns across the globe. With green buildings and the LED rating system for buildings getting popular, the demand for better energy efficient lighting, which is cost-effective and that which adds to the aesthetics of the space, is increasing. One of the major challenges with light emitting diodes (LED’s), however, has been to keep up with the pace of this ever evolving technology. Anything related to this technology that was prevalent a few years ago, has now become outdated. With researchers and scientists working toward in better improving this technology, it is not long until we see a bigger and a more economic market utilizing LED’s for commercial applications.

LED’s are compound semiconductor devices that convert electricity to light. Some of the main advantages of LEDs are that they last a very long time when compared to their commonly used counterparts, the incandescent lamp, HID light sources or even the fluorescent lamp. The light output of LEDs however, degrades over time and hence reduces the useful lifetime of LEDs (Philips 2006). It is also said that although the lumens per watt of an LED might be higher for the chip itself, but when it is all packaged together as a luminaire, lumens per watt can decrease due to heat buildup.

In any case, the long lifetime of an LED luminare, contributes to very little maintenance over a long period of time. Hence, summarizing some of the key features in utilizing LED’s are; a long life-time, very little maintenance, low energy consumption (a few watts when compared to incandescent or even fluorescent sources these days), and that they work well in an exterior environment since LED’s can work well in colder temperatures (Alliance for Solid state illuminations and Technologies, 2007).

Summarizing some of the most common disadvantages of using LED’s in most common applications are; high initial costs (current market), poor color rendering (not an adequate measure for CRI- color rendering index) low lumens/watts (efficacy) for white LED’s and that they get very hot. Hence a good heat sink is an essential component of an LED luminaire. LED’s are usually known to operate well in colder temperatures. The primary cause of LED lumen depreciation is the heat generated at the LED junction.

Without adequate heat sinking or ventilation, the device temperature will rise resulting in lower light output and degradation of its performance over its lifetime. Hence, a heat sink that helps dissipate heat off the LED is an important feature of an LED luminaire (Hong and Narendran, 2004).

1.8     Photovoltaic LED lighting systems

Solar houses are an important feature of green building design. The LED rating system has a certain number of points for the use of building integrated photovoltaic panels (BIPV). Solar energy is not only a renewable source of energy, but can also reduce the typical energy consumption within a building. According to preliminary data published within the Earth policy institute in 2007, global PV production in the year 2007 was nearly 12,400 megawatts, while on an average the production has doubled every two years since 2002 (Dorn, Earth Policy Institute, 2007).

This impressive increase in PV production illustrates the need for more research and application of these systems worldwide. Of the possible research prospects, one aspect on which to focus is to make the ‘overall system’ more efficient. This means, every system component needs to be chosen to be highly efficient to reduce the overall losses in the creation of light. Considering that the research and manufacturing developments in LED’s is at a sky-rocketing pace; they present a huge potential for use with PV lighting systems.

Energy consumption of LEDs is typically very low, and hence if LED’s are used, the overall load demand could be reduced heavily, however if the lighting levels are also reduced proportionally. Some likely applications of such a system would be; landscape lighting, exterior façade lighting and street lighting. Colored LED lights combined with photovoltaic panels could also be used to create a glow or set a mood within any given architectural space without consuming a lot of energy.

Photovoltaic cells and LED’s – Two potentially ener