Surse de Energie Regenerabila
UNIVERSITY OF BUCHAREST
Faculty of Physics
MASTER
SURSE DE ENERGII REGENERABIlE
ȘI ALTERNATIVE (RENEWABLE AND ALTERNATIVE ENERGY SOURCES)
Mustafa Khalil Alhussainy
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Solar Panels, the Bright Future
A study on a Solar Panel with Different Configuration of the Cells
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Dissertation Thesis
BUCHAREST, 2016
Contents
List of Figures………………………………………………………………………………………………………4
List of Tables ………………………………………………………………………………………………….6
List of Symbols ………………………………………………………………………………………………7
Introduction…………………………………………………………………………………………………..12
Chapter I. ………………………………………………………………………………………………..14
1.1 Overview on Solar energy ………………………………………………………………………….16
1.2: How to store the energy ……………………………………………………….……….20
1.3: Other Renewable Energy Resources ………………………………………….…….. 22
1.3.1: Hydroelectric Power
1.3.2 The Wind Power
1.3.3: Biomass and Bioenergy
Chapter II. …………………………………………………..………………………..… 32
2.1: Solar Thermal Energy ……………………………………..……………………..… 32
2.2: Birth of Current Sun Cells ……………………………….….…………………..…. 32
2.3: Some Concepts on Solar Cells …………………………………..……………….… 34
2.3.1: Criterion Illumination Conditions
2.3.2: Fill Factor
2.3.3: Efficiency
2.3.4: Peak Watt
2.4: Types of Solar Cells …………………………………………………………………. 36
2.5: Energy Balance ……………………………………………..………..……………… 36
2.6: Economics of Solar Energy ………………………………………..……..………… 37
2.7: Moral Equivalence of War …………………………………….……………………. 41
2.8: Solar Water Heaters around the world ………….……………….…..……….….. 43
2.9: Earth Rotation and Revolution ……………………………..……..………………. 43
2.10: Angle of Declination ……………………………………………….……………… 45
2.11: Altitude and Azimuth Angles of Sun …………………………….………………. 46
2.12: Hour angle ……………………………………………………….…………………… 47
2.13: Latitude Angle …………………………………………………………..……….…. 48
Capitolul III. ……………………………………………………………………………………………. 49
3.1: Analyzing and calculating the electrical performance of photovoltaic modules …. 49
3.2: Semiconductors Conductor, Semiconductor, and Insulator ……………….……… 52
3.3: Electrons and Holes ………………………………………………….…………….… 54
3.4: p-Type and n-Type Semiconductors …………………………….………………..… 56
3.5: Formation of a pn-Junction …………………………………….……………………. 57
3.6: Analysis of pn-Junctions …………………………………….…………………….… 62
3.7: Semiconductor Solar Cells ………………………………….……………………….. 63
3.8: Basic Concepts …………………………………………….…………………………. 63
Chapter IV. …………………………………………………….………………………… 66
4.1: The Effect of Tilt Angle on Solar Panels ……………………….…………………… 66
4.2: The Effect of Tilt Angle on Dust Accumulation ………………….………………… 67
4.3: The Effect of Tilt Angle on the Performance of Solar Module …………….…..…. 68
4.3.1: The Optical Losses
4.3.2: The Geometrical Losses
Conclusion ………………………………………………………………….…………….. 74
Future Work ……………………………………………………………….……….……. 75
References ………………………………………………………………….…………….. 76
List of Figures
Figure 1 …………………………………………………………………………………………………..…pag. 15
Figure 2 …………………………………………………………………………………………………..…pag. 16
Figure 3 …………………………………………………………………………………………………..…pag. 19
Figure 4 …………………………………………………………………………………………………..…pag. 19
Figure 5 …………………………………………………………………………………………………..…pag. 20
Figure 6 …………………………………………………………………………………………………..…pag. 24
Figure 7 …………………………………………………………………………………………………..…pag. 25
Figure 8 …………………………………………………………………………………………………..…pag. 26
Figure 9 …………………………………………………………………………………………………..…pag. 27
Figure 10 …………………………………………………………………………………………………..…pag. 30
Figure 11 …………………………………………………………………………………………………..…pag. 32
Figure 12 …………………………………………………………………………………………………..…pag. 35
Figure 13 …………………………………………………………………………………………………..…pag. 37
Figure 14 …………………………………………………………………………………………………..…pag. 38
Figure 15 …………………………………………………………………………………………………..…pag. 39
Figure 16 …………………………………………………………………………………………………..…pag. 40
Figure 17 …………………………………………………………………………………………………..…pag. 41
Figure 18 …………………………………………………………………………………………………..…pag. 43
Figure 19 …………………………………………………………………………………………………..…pag. 44
Figure 20 …………………………………………………………………………………………………..…pag. 46
Figure 21 …………………………………………………………………………………………………..…pag. 48
Figure 22 …………………………………………………………………………………………………..…pag. 52
Figure 23 …………………………………………………………………………………………………..…pag. 53
Figure 24 …………………………………………………………………………………………………..…pag. 54
Figure 25 …………………………………………………………………………………………………..…pag. 57
Figure 26 …………………………………………………………………………………………………..…pag. 59
Figure 27 …………………………………………………………………………………………………..…pag. 60
Figure 28 …………………………………………………………………………………………………..…pag. 64
Figure 29 …………………………………………………………………………………………………..…pag. 64
Figure 30 …………………………………………………………………………………………………..…pag. 65
Figure 31 …………………………………………………………………………………………………..…pag. 67
Figure 32 …………………………………………………………………………………………………..…pag. 68
Figure 33 …………………………………………………………………………………………………..…pag. 71
Figure 34 …………………………………………………………………………………………………..…pag. 71
Figure 35 …………………………………………………………………………………………………..…pag. 72
Figure 36 …………………………………………………………………………………………………..…pag. 73
Figure 37 …………………………………………………………………………………………………..…pag. 73
Figure 38 …………………………………………………………………………………………………..…pag. 75
Figure 39 …………………………………………………………………………………………………..…pag. 75
List of Tables
Table 1 …………………………………………………………………………………………………..…pag. 17
Table 2 …………………………………………………………………………………………………..…pag. 18
Table 3 …………………………………………………………………………………………………..…pag. 23
Table 4 …………………………………………………………………………………………………..…pag. 28
Table 5 …………………………………………………………………………………………………..…pag. 29
Table 6 …………………………………………………………………………………………………..…pag. 45
Table 7 …………………………………………………………………………………………………..…pag. 51
Table 8 …………………………………………………………………………………………………..…pag. 52
Table 9 …………………………………………………………………………………………………..…pag. 65
Table 10 …………………………………………………………………………………………………..…pag. 70
Introduction:
Some countries are blessed with an abundance of natural resources such as oil, metals, gold or diamonds. Add to all this Iraq has the sun.Lots of it.
The sun is the most important alternative energy resource, clean and available for humans without any costs of search or extraction and it is renewable. This means that there is no shortage of solar energy. Harnessing this important amount of power it is possible now with the help of the solar cells since the calculated energy of the falling beam from the sun per square meter equal to 1000 watts, which makes this kind of energy an important resource for every country or community looking for possibilities to improve the living conditions.
There are few kinds of solar radiation fallen on the earth's surface which is the direct solar radiation, scatter solar radiation and also reflected solar radiation, furthermore solar energy is also clean energy does not cause harmful emissions to the environment as it is the case in the fossil energy resources (coal, oil, natural gas and nuclear fuel), so that’s why we can call it clean energy, over and above the sun renewed not expected to die on for at least four billion years as we found in the latest researches. We can take advantage of solar energy in several areas, including the production of electricity through the work of solar cells and also help to produce electricity in large power plants through heated water in power plants using the steam produced with the help of the sunlight. The cost of raw materials for devices that use solar energy is considered the most important obstacle which prevents them from being used at a bigger scale, in addition to the large areas that you need to put the bundled devices to sunlight and despite of all these factors, there are some uses of solar energy are considered economic at the present time, including water heating, uses in wireless transmission, cathodes protection systems and light signals.
The research and perseverance in finding alternatives to fossil energy is nothing but for the purpose of providing useful alternatives and vitality energy sources, because conventional energy resources has become in some countries a execration with reason it became areas of conflict in order to gain influence and power of the great countries in the world, in light of the fact that owning energy sources means owning sources of funding and through owning the economy and control the world as a whole.
The Electro Solar cells converters take energy from the sun and convert it into another type of energy where the solar cells convert sunlight into electricity and expel a large amount of heat without any of effective measures (noise or pollution or radiation or maintenance etc.).
There are kinds of solar cells that can provide electrical energy converted from the sun, which use different technologies and we will mention these types briefly according to their importance and efficiency of converting solar energy into electrical energy.
Monocrystalline Silicon Cells, The innovation that began it all, mono crystalline boards, started in the 1950s. The cells are cut from silicon in a cylindrical shaped design, and every cell resembles a wafer. Joined, several wafers make up a mono crystalline panel. This kind has some advantages like Monocrystalline panels are mostly built from high-quality silicon, giving them the most noteworthy execution rates in solar panels industry, more often than not up to 21 percent. By comparing, mono crystalline panels with the Thin film by four to one. They rationalization in the exploitation of the place, so they offer a powerful yield for every square meter. Guarantees regularly keep going for a long time more than 25 years, and these panels perform preferable in low-light conditions over their poly-counterparts. On the other hand, it has disadvantages like
Polycrystalline Silicon Cells, also called polysilicon or poly-Si, and it is a very pure silicon Christalat formula, used as a raw material in the electronics industry and the industry producing solar cells.And the polysilicon production of mineral formula for silicon by Purification process involved chemicals in the chemical composition of the material, or the so-called Siemens process. This process involves a summary of volatile silicon compounds, and analyzes to the silicon at high temperatures. An emerging, alternative process of refinement uses a fluidized bed reactor. Polysilicon consists of small crystals, also known as crystallites; it gives the effect of metallic materials status flake form. While polysilicon and multisilicon often used as substitutes, usually multicrystalline the term refers to greater than 1 mm crystals.
Multicrystalline solar cells are the most common type of solar cells in the photovoltaic market that is experiencing rapid growth and consume more of the polysilicon produced in the world. Amorphous Silicon Cells, (A-Si) it is a non-crystalline form of silicon. It is considered the most sophisticated technology and well growth industry in the present day, where he is in the market for more than 15 years. It is used widely in calculators and electronic watches, but it also provides some of the houses and buildings of small facilities by the electrical energy converted from solar energy. While crystalline silicon achieves productivity of approximately 18% amorphous solar cells remained at the same level of production which is 7%. The lack of efficiency resulting from the impact and who revealed himself in the early hours of solar cells exposed to the light of the sun and begins decreasing efficiency of 10 percent to 7 percent. The main advantage that which distinguishes silicon amorphous solar cells is low cost of their manufacturing, which makes there is high competition between the manufacturers of these cells. One of the main drawbacks of this type of cells is that the life expectancy of the cells amorphous is shorter than the age of crystalline cells, even though we are so difficult to determine, especially as the technology is still developing. By reading the reports, it seems that life expectancy is still in the range of approximately 25 years or so.
In this project, we are working together to build a simple solar cells in different formats including flat and curved shape, then face them in different angles to the sun, to find out what is the most appropriate angle position to receive sunlight and produce electricity from solar energy.
Chapter One
This project would like to be an apposition and a experiment between the practical and the theoretical part of one and the same project. We will write on the renweble energy and especially we will talk about the solar energy provided by the sun. The devices that convert the solar energy to electric energy they are called solar cells. A solar cell or photovoltaic cell is a device which generates electricity directly from visible light by means of the photovoltaic effect. In order to generate useful power, it is necessary to connect a number of cells together to form a solar panel, also known as a photovoltaic module. There is more about the the different types of solar cell here. The nominal output voltage of a solar panel is usually 12 Volts, and they may be used singly or wired together into an array. The number and size required is determined by the available light and the amount of energy required Solar cells are usually made from silicon, the same material used for transistors and integrated circuits. The silicon is treated or "doped" so that when light strikes it electrons are released, so generating an electric current. There are three basic types of solar cell.
Monocrystalline cells are cut from a silicon ingot grown from a single large crystal of silicon whilst polycrystalline cells are cut from an ingot made up of many smaller crystals. The third type is the amorphous or thin-film solar cell. There are three kinds of solar cells that can provide electrical energy converted from the sun, which use different technologies and we will mention these types briefly according to their importance and efficiency of converting solar energy into electrical energy.
Multicrystalline solar cells are the most common type of solar cells in the photovoltaic market that is experiencing rapid growth and consume more of the polysilicon produced in the world. Amorphous Silicon Cells, (A-Si) it is a non-crystalline form of silicon. It is considered the most sophisticated technology and well growth industry in the present day, where he is in the market for more than 15 years. It is used widely in calculators and electronic watches, but it also provides some of the houses and buildings of small facilities by the electrical energy converted from solar energy. While crystalline silicon achieves productivity of approximately 18% amorphous solar cells remained at the same level of production which is 7%. The lack of efficiency resulting from the impact and who revealed himself in the early hours of solar cells exposed to the light of the sun and begins decreasing efficiency of 10 percent to 7 percent. The main advantage that which distinguishes silicon amorphous solar cells is low cost of their manufacturing, which makes there is high competition between the manufacturers of these cells. One of the main drawbacks of this type of cells is that the life expectancy of the cells amorphous is shorter than the age of crystalline cells, even though we are so difficult to determine, especially as the technology is still developing. By reading the reports, it seems that life expectancy is still in the range of approximately 25 years or so.
1.1: Overview on Solar energy
Depending on reliable estimations, the average power density of solar radiation simply outside the atmosphere of the Earth is 1366 W/m2, generally known as the solar constant. The simplification of the meter is one over 10,000,000 of Earth's meridian, from the North Pole to the equator as you can see in figure(1); this definition is still entirely precise as indicated by modern measurements. In this manner, the radius of Earth is: (2/π) × 107 m. The total power of solar radiation reaching Earth is then:
Solar power = 1366W/m2 (1-1)
Every day has 86,400 s, and on average, every year has 365.2422 days. The total energy of solar radiation reaching Earth per year is:
Solar energy ratio during the year =
1.73× J (1-2)
On the other hand 5,460,000 EJ/year. To have a thought of the amount of energy that is, let us look at it with yearly worldwide energy utilization; as shown in figure (2). In the years 2005–2010, the yearly vitality utilization of the whole world was around 500 EJ. A simple 0.01% of the yearly solar energy achieving Earth can fulfill the energy need of the whole world.
Not all solar radiation falls on Earth’s atmosphere achieves the ground. Around 30% of solar radiation is reflected into space. Around 20% of solar radiation is absorbed by clouds and molecules in the air. Around seventy five percent of the Earth surfaces are water. In any case, regardless of the possibility that even if only 10% of total solar radiation is utilizable, 0.1% of it can power the whole world.
It is fascinating to analyze the yearly solar energy that achieves Earth with the demonstrated aggregate store of various fossil fuels as we can see in table (1). The numbers demonstrate that the all-out demonstrated stores of fossil fuel are around 1.4% of the solar energy that reaches the surface of Earth every year. Fossil fuels are solar energy put away as concentrated biomass over many millions of years. Really, just a little rate of solar energy could be saved for humankind to investigate. The present yearly consumption of fossil fuel energy is roughly 300 EJ. If the current level of consumption of fossil fuel continues, the entire fossil energy reserve will be depleted in about 100 years.
At present, the use of renewable energy is still a small percentage of total energy consumption; see the next table, demonstrates the rate of various sorts of energy in the United States in 2006. The usage of solar energy through photovoltaic (PV) innovation represents 0.07% of the total energy consumption. However, all around, solar photovoltaic energy is the quickest developing energy resource. Depending on plenty of facts, we think solar photovoltaic will someday become the dominant source of energy.
In definitely that fossil fuel will eventually be replaced by solar energy is simply a geological fact: The total recoverable reserve of crude oil is finite. For example, the United States used to be the largest oil producer in the world. By 1971, about one-half of the recoverable crude oil reserve in the continental United States (the lower 48 states) was depleted. Since then, crude oil production in this area started to decline.
In this manner, crude oil production from more difficult geological and environmental conditions must be explored. Not just has the expense of oil penetrating expanded, additionally the energy devoured to produce the raw petroleum has likewise expanded. But also the energy consumed to generate the crude oil has also increased. To evaluate the merit of an energy production process, the energy return on energy invested (EROI), additionally called energy balance, is regularly utilized: The definition is:
EROI =
In the 1930’s, the EROI value to produce crude oil was around 100. In 1970, it was 25. For deep-sea oil drilling, typical value is around 10. Shale oil, shale gas, and tar sands also have low EROI values. If the EROI of an energy production process is decreased to nearly 1, there is no value in pursuing in the process.
On the other hand, although currently the cost of solar electricity is higher than that from fossil fuels, its technology is constantly being improved and the cost is constantly being reduced.around 2015, the cost of solar electricity will be lower than conventional electricity, to reach grid parity. After that, a rapid growth of solar electricity will take place, as we can see in figure (3).
Energy industry trend in the twenty-first century. Source of information: German Solar Industry Association, 2007; see www.solarwirtschaft.de. The driving force of twenty-first century energy revolution is economy. Because natural resources of fossil fuels and nuclear materials are finite, the cost of production will increase with time. Solar radiation energy and the raw material to make solar cells, silicon, are inexhaustible. Mass production of solar cells will bring the cost down. At some time, the cost of solar electricity will be lower than that of conventional electricity, to reach grid parity. In 2007, it was estimated that grid parity would be reached between 2020 and 2030. After that, an explosive expansion of solar electricity would take place. Recent development indicates that grid parity will be reached around 2015. The rapid implementation of solar electricity will take place sooner than that 2007 prediction.
1.2: How to store the energy
The amount of power generated by solar cells is determined by the amount of light falling on them, which is in turn determined by the weather and time of day. In the majority of cases some form of energy storage will be necessary.
In a Grid-connected system, the solar array is connected to the mains. Any surplus power is sold to the electricity company, and power is bought back from them when it is needed.
In a Stand-alone system, however, this is not possible. In this type of system the usual choice for energy storage is the lead-acid battery. The number and type of batteries is dependent on the amount of energy storage needed. The power generated by the solar panels is usually used to charge a lead-acid battery. Other types of battery such as nickel-cadmium batteries may be used, but the advantages of the lead-acid battery ensure that it is still the most popular choice. A battery is composed of individual cells; each cell in a lead-acid battery produces a voltage of about 2 Volts DC, so a 12 Volt battery needs 6 cells. The capacity of a battery is measured in Ampere-hours or Amp-hours (Ah). The number of times a battery can be discharged is known as its cycle life, and this is what determines its suitability for use with solar cells.
Car batteries are the most common type of lead-acid battery, but will survive only 5 or 10 cycles so are unsuitable for our purposes. For solar applications a battery needs to be capable of being discharged hundreds or even thousands of times. This type of battery is known as a deep-cycle battery, and some of the many different types are explained here like Leisure Batteries or caravan batteries whice are usually the cheapest type of deep-cycle battery. They look similar to a car battery but have a different plate construction. Their capacity is normally in the range of 60 to 120 Ah at 12 Volts, making them most suitable for smaller systems. The cycle life of leisure batteries is limited to a few hundred cycles, meaning that they are most suitable for systems which will not be used every day, such as those in caravans or holiday homes.and we have Traction Batteries, The term traction battery relates to all batteries used to power electric vehicles. This can mean anything from a mobility scooter to a fork-lift truck, so encompasses capacities from 30 or 40 Ah to many hundreds. The smaller traction batteries are usually 6 or 12 Volt units; where the largest are single 2 Volt cells. Traction batteries are ideal for solar power applications, as they are intended to be fully discharged and recharged daily. The larger traction batteries can withstand thousands of discharge cycles. There are also batteries known as semi-traction batteries, which can be thought of as higher quality leisure batteries, exhibiting a greater cycle life. Marine batteries also fall into this category.and also we have Sealed Batteries, There are many types of sealed lead-acid batteries, ranging from those of 1 or 2 Ah to single cell traction batteries of hundreds of Amp-hours. The advantages of sealed batteries are obvious; they need no maintenance and are spill-proof. They do have disadvantages however; they are more expensive than other battery types, they require more accurate charging control and can have a shorter life, especially at high temperatures. Sealed batteries are most appropriate where the solar power system will need to operate for long periods without maintenance.
1.3: Other Renewable Energy Resources
Because of the limited reserve of fossil fuel and the expense, from the earliest starting point of the manufacture age, renewable energy resources have been investigated. Although solar energy is by a wide margin the biggest asset of renewable energy, other renewable energy assets, counting hydropower, wind power, and shallow and deep geothermal energy, has been widely used. Except for deep geothermal energy, every one of them is gotten from sunlight based energy.
1.3.1: Hydroelectric Power
Hydroelectric Power is an entrenched innovation. Since the late nineteenth century, it has been delivering significant measures of energy at competitive prices. Presently, it produces around one 6th of the world's electric yield, which is more than 90% of all renewable energy. As appeared in the next figure (5), for some nations as an example, Norway generates more than 98% of all its electricity from hydropower; in Brazil, Iceland, and Colombia, more than 80% of electricity is generated by hydropower.
And also we can see in table (3) a list of the utilization of hydropower in different regions on the world.
The physics of hydropower is unpretentious. A hydropower system is recognize by the effective head, the height H of the water fall, in meters; and the flow rate, the rate of water flowing through the turbine, Q, in cubic meters per second. The power carried by the water mass is given as:
P (kW) = g × Q × H (1-4)
Where, g = 9.81m/s2, is the gravitational acceleration. Because a 2% error is insignificant, in the engineering field, it always takes g ≈ 10m/s2. Therefore, in terms of kilowatts,
P (kW) = 10 × Q × H (1-5)
The standard hardware is the Francis turbine, invented by American engineer James B. Francis in 1848. With this machine, the proficiency η of changing over water power to mechanical power is extremely high. Under ideal conditions, the general efficiency of changing over water power into electric power is much bigger than 90%, which makes it one of the most effective machines. The electric power created by the hydroelectric system is:
P (kW) = 10 η QH (1-6)
An important advantage over other renewable energy resources is that hydropower gives an energy storage mechanism of very high round-trip efficiency. The energy losses in the storage process are negligible. Subsequently, the hydropower station together with the reservoir makes a highly efficient and economic energy storage system. Figure (6) is a photograph of one of the world's biggest hydropower station, the Itaipu hydropower station, which supplies around 20% of Brazil's power.
1.3.2 The Wind Power
The kinetic energy in a volume of air with mass m and velocity v is:
(1-7)
If the density of air is ρ, the mass of air passing through a surface of area A perpendicular to the velocity of wind per unit time is:
m = ρvA (1-8)
The wind power P0, or the kinetic energy of air moving through an area A per unit time, then:
(1-9)
Under standard conditions (1 atm pressure and 18◦C), the density of air is 1.225 kg/m3.
If the wind speed is 10 m/s, the wind power density is:
P0 ≈ 610 W/m2 (1-10)
It is of the same order of magnitude as the solar power density. However, the efficiency of a wind turbine is not as high as that of hydropower. Because the air velocity before the rotor, v1, and the air velocity after the rotor, v2, are different, see the next Figure (7), the air mass flowing through area A per unit time is determined by the average wind speed at the rotor,
(1-11)
So, the kinetic energy picked up by the rotor is:
(1-12)
Combining the previous two equations, we obtain an expression of the wind power P picked up by the rotor:
(1-13)
Rearranging to the consequent equation, we can define the fraction C of wind power picked up by the rotor, or the rotor efficiency, as:
(1-14)
Wherefore,
(1-15)
The dependence of rotor efficiency C with speed ratio x is shown in the next figure (8). It is straightforward to show that the maximum occurs at x = 1/3 where c = 16/27 = 59.3%.This result was first derived by Albert Betz in 1919 and is widely known as Betz’s theorem or the Betz limit.
The estimate of worldwide available wind power varies. A conservative estimate shows that the total available wind power, 75 TW, is more than five times the world’s total energy consumption. In contrast to hydropower, currently, only a small fraction of wind power has been utilized. However, it is growing very fast from 2000 to 2009.
Total capacity grew nine fold to 158.5 GW. The Global Wind Energy Council expects that by 2014, total wind power capacity will reach 409 GW. Because of a shortage of conventional energy resources, in the late nineteenth century, Denmark began to developed wind power and accelerated production after the 1970 energy crisis. Denmark is still the largest manufacturer of wind turbines, led by Vestas Cooperation, and it has about 20% of wind power in its electricity blend.
However, Denmark’s success in wind energy could not be achieved without its neighbors: Norway, Sweden, and Germany. Because wind power is intermittent and irregular, a stable supply of electricity must be accomplished with a fast-responding power generation system with energy storage. Fortunately, almost 100% of the electricity in Norway is generated by hydropower, and the grids of the two countries share a 1000-MW interconnection. In periods of heavy wind, the excess power generated in Denmark is fed into the grid in Norway. By using the reversible turbine, the surplus electrical energy is stored as potential energy of water in the reservoirs. In 2005, the author visited the Tonstad Hydropower Station in Norway on a Sunday afternoon. I asked a Norwegian engineer why the largest turbine was sitting idle. He explained that one of the missions of that power station is to supply power to Denmark. On Monday morning, when the Danes brew their coffee and start to work, that turbine would run full speed.
1.3.3: Biomass and Bioenergy
Over the many thousands of years of human history, until the industrial revolution when fossil fuels began to be used, the direct use of biomass was the main source of energy. Wood, straw, and animal waste was used for space heating and cooking. Candle (made of whale fat) and vegetable oil were used for light. The mechanical power of the horse was energized by feeding biomass. In less developed countries of the world, this situation remains the norm. Even in well-developed countries, direct use of biomass is still very common: for example, firewood for fireplaces and wood-burning stoves.
Biomass is created by photosynthesis from sunlight. Although the efficiency of photosynthesis is only about 5% and land coverage by leaves is only a few percent, the total energy currently stored in terrestrial biomass is estimated to be 25,000 EJ, roughly equal to the energy content of the known fossil fuel reserve of the world, as we can see in the next Table(4). The energy content of the annual production of land biomass is about six times the total energy consumption of the world; see Table (4). Currently there is a well-established industry to generate liquid fuel using biomass for transportation. Two approaches are widely used: produce ethanol from sugar and produce biodiesel from vegetable oil or animal oil.
In the following table (5) we will see the efficiency of solar cells types and how they differ
Scientists have achieved in 2014 to a new world record for the direct conversion of sunlight into electricity has been established. The multi-junction solar cell converts 46% of the solar light into electrical energy and was developed by Soitec and CEA-Leti, France, together with the Fraunhofer Institute for Solar Energy Systems ISE, Germany. Multi-junction cells are used in concentrator photovoltaic (CPV) systems to produce low-cost electricity in photovoltaic power plants, in regions with a large amount of direct solar radiation. It is the cooperation’s second world record within one year, after the one previously announced in September 2013, and clearly demonstrates the strong competitiveness of the European photovoltaic research and industry.
Multi-junction solar cells are based on a selection of III-V compound semiconductor materials. The world record cell is a four-junction cell, and each of its sub-cells converts precisely one quarter of the incoming photons in the wavelength range between 300 and 1750 nm into electricity. When applied in concentrator PV, a very small cell is used with a Fresnel lens, which concentrates the sunlight onto the cell. The new record efficiency was measured at a concentration of 508 suns and has been confirmed by the Japanese AIST (National Institute of Advanced Industrial Science and Technology), one of the leading centers for independent verification of solar cell performance results under standard testing conditions.
A special challenge that had to be met by this cell is the exact distribution of the photons among the four sub-cells. It has been achieved by precise tuning of the composition and thicknesses of each layer inside the cell structure. ”This is a major milestone for our French-German collaboration. We are extremely pleased to hear that our result of 46% efficiency has now been independently confirmed by AIST in Japan”, explains Dr. Frank Dimroth, project manager for the cell development at the German Fraunhofer Institute for Solar Energy Systems ISE. “CPV is the most efficient solar technology today and suitable for all countries with high direct normal irradiance.”
Jocelyne Wasselin, Vice President Solar Cell Product Development for Soitec, a company headquartered in France and a world leader in high performance semiconductor materials, says: “We are very proud of this new world record. It confirms we made the right technology choice when we decided to develop this four-junction solar cell and clearly indicates that we can demonstrate 50% efficiency in the near future.” She adds: “To produce this new generation of solar cells, we have already installed a line in France. It uses our bonding and layer-transfer technologies and already employs more than 25 engineers and technicians. I have no doubt that this successful cooperation with our French and German partners will drive further increase of CPV technology efficiency and competitiveness.”
Chapter Two
2.1: Solar Thermal Energy
Obviously in the first half of the twenty-first century, fossil fuel will be drained to a degree that it does not meet the needs of human community. There are several sorts of renewable energy assets. A large portion of them have confinements, including hydropower, wind energy, and geothermal energy. Sunlight based warm applications such as solar water heaters can fill just a little part of the aggregate energy request. Solar photovoltaic is the absolute most encouraging substitute for fossil energy.
2.2: Birth of Current Sun Cells
In 1953, Chime Labs set up an examination for devices to give energy source to remote parts of the world where no network force was accessible. The main researcher, Darryl Chapin, recommended utilizing sun based cells, and his proposition was endorsed by his chiefs. Around then, the photovoltaic impact in selenium, found in the 1870s, was at that point marketed as a gadget for the estimation of light force in photography. A layer of Se is connected on a copper substrate, and then wrapped by a semitransparent film of gold. At the point when the gadget is enlightened by obvious light, a voltage is produced, which thusly creates a current. The force of electric current relies on upon the force of light. It has been a standard instrument in the to start with half of the twentieth century for picture takers to gauge light conditions. This gadget is a great deal more tough and advantageous than photoresistors in light of the fact that there are no moving parts and no battery is required.
Chapin began his test with selenium photocells. He found that the efficiency, 0.5%, is too low to produce adequate power for telephony applications. At that point, a stroke of fantastic luck, two Bell Lab researchers required in the spearheading push to create silicon transistors, Calvin Fuller and Gerald Pearson, joined Chapin in utilizing the beginning silicon innovation for solar cells.
The silicon solar cell was produced using a solo crystal of silicon. By judicially controlling the doping profile, a p–n intersection is framed. The n-side of the intersection is thin and profoundly doped to permit light to go to the p–n intersection with practically nothing constriction; however the horizontal electric conduction is sufficiently high to gather the current to the front contact through a configuration of silver fingers.
The rear side of the silicon is wrapped with metal film, commonly used aluminum. The essential structure of the silicon solar cell has remained verging on unaltered up to this time.
The first exposition the solar cell to the general population in New York City was an exhibition. What's more, the expense of building such sun powered cells was high. From the mid-1950s to the mid-1970s, photovoltaic innovative work was coordinated essentially toward space applications and satellite power. In 1976, the U.S. Department of Energy (DOE) was set up. A Photovoltaics Project was made. The DOE, and also numerous other global associations, started financing research in photovoltaics at obvious levels. A terrestrial solar cell industry was quickly established. Economies of scale also, advance in innovation diminished the cost of solar cells significantly.
2.3: Some Concepts on Solar Cells
In the following I present you a list of key terms and concepts regarding solar cells
2.3.1: Criterion Illumination Conditions
The effectiveness and force yield of a solar module (or a solar cell) are tried under the taking after standard conditions: 1000 W/m2 intensity, 25◦C encompassing temperature, and a range that identifies with daylight that has gone through the atmosphere when the sun is at 42◦ rise from the skyline.
2.3.2: Fill Factor
The open-circuit voltage Vop is the voltage between the terminals of a solar cell under Criterion illumination conditions when the load has infinite resistance that is open. In this case, the current is zero.The short-circuit current Isc is the current of a solar cell under Criterion illumination conditions when the load has zero resistance. In this case, the voltage is zero. By using a resistive load R, the voltage V will be smaller than Vop, and the current I is smaller than Isc. The power P = IV. The maximum power output is determined by the following equation
dP = d (IV ) = IdV + V dI = 0 (2-1)
Denoting the point of maximum power by Imp and Vmp, we have Pmax = ImpVmp.
The fill factor of a solar cell FF is defined as
(2-2)
The typical value of the fill factor is between 0.8 and 0.9.
2.3.3: Efficiency
The efficiency of a solar cell is defined as the proportion of the produced electric power over the info sun oriented radiation power under Criterion Illumination Conditions at the ultimate power point.
Maximum power and fill factor. By connecting a load resistor to the two terminals of a solar cell, the solar cell provides power to the load. The ultimate power point occurs when P = IV reaches maximum.
At that point, Pmax = ImpVmp. Obviously, there is always Imp < Isc and Vmp < Voc. The fill factor of a solar cell is defined as FF = Pmax/IscVoc = ImpVmp/IscVoc.
2.3.4: Peak Watt
The “peak watt” (WP) rating of a solar module is the power (in watts) produced by the solar module under Criterion illumination conditions at the ultimate power point. The real Produced power of a solar cell clearly depends on the actual illumination conditions.
2.4: Types of Solar Cells
The crystalline silicon solar cell was the first functional solar cell invented in 1954. The efficiency of such solar cells as mass delivered is 14–20%, which is still the most elevated in single-intersection solar cells. It additionally has a long life and a status for large scale manufacturing. To date, regardless it represents more than 80% of the solar cells market. There are two forms of the crystalline silicon solar cells: monocrystalline and polycrystalline. Amorphous silicon thin-film silicon solar cells are significantly less costly than the crystalline ones. Be that as it may the efficiency is just 6–10%. In the middle of are CIGS (copper indium gallium selenide) and CdTe–CdS thin film solar cells, with typical efficiency of around 10% and record for around 15% of the business field. With reason of the high retention coefficient, the quantity of materials required is little, and the generation procedure is less complex; consequently the unit cost per watt is lower than crystalline silicon sun based cells. To date, organic solar cells still have low efficiency and a short lifetime, and the market share is insignificant.
2.5: Energy Balance
In general we need power to make solar cells. In this manner, the researches of the (EROI) are Important. Here we examine the energy equalization for the most costly case, crystalline silicon solar cells. The energy investment includes that for delivering silicon feedstock, ingot and wafers, cell creation, module get together, and establishment. A standard benchmark number to assess the energy balance of photovoltaic is payback time. By setting the solar cells in a given illumination condition, the solar cells will create energy in the form of electricity.
Payback time is the number of years it takes for the power created by the solar cell to adjust for the energy resources which we put into the generation and establishment process.
In the previous figure (13) represents a conservative estimate of payback time for crystalline silicon solar cells based on European insolation conditions. For Central Europe, with annual insolation of 1000 W/m2, the payback time is 3.6 years. Its lifetime is typically 25 years, which results in an EROI of 7. In Southern Europe and most places in the United States, the EROI is above 10. The EROI for thin-film solar cells is even better. However, because of lower efficiency, these require more space to generate the same power.
2.6: Economics of Solar Energy
The early history of solar water heaters in the United States strikingly represents the exchange of material science, building and financial aspects. In the nineteenth century, prior the development of advanced heated water frameworks, making boiling water for a shower as costly also, troublesome.
Water must be warmed in a huge pot over flame, and then scooped into the bathtub. It was particularly costly in California, where fuel, for example, coal must be imported and wood was valuable. Artificial gas and electricity were exceptionally costly. Be that as it may, daylight is bounty there, and the weather is temperate.
In 1891, Clarence Kemp protected compelling and usable solar water heater, named Climax (U.S. Patent 451,384). Initially advertised in Maryland, Kemp's business was definitely not very successful. At that point he sold the exclusive right to two Pasadena businessmen and made an incredible business achievement in California. By 1900, 600 units were sold in southern California alone. Be that as it may, the Climax water heater had a disadvantage in that it took a couple of hours of daylight to warm up the water and after sunset the water temperature would drop rapidly. In this way, it could only be used in the afternoon of a sunny day.
In 1910 William J. Bailey created and invented the Day-and-Night solar water heater (U.S. Patent 966,070), which determined the real issues and turned into the model of prototype of later solar water heaters.as you can see in the next figure (15), In the first place, the heat collector A is made of a parallel network of copper channels welded on a level bit of copper plate. Second, it uses a water tank C placed above the heat collector, intensely protected by cork, D. Such an arrangement enables water circulation by natural convection and effective energy storage. At the point when water is warmed by daylight, the particular gravity diminishes. It streams naturally upward through channel B into water tank C. The colder water then streams consequently downwards through pipe E once more into the heat collector A. If the insulation is sufficient, the water can stay hot overnight. In this way, it works in the day and also in the night. In spite of the fact that the Day-and-Night framework cost about $180 at that time, much higher than a Climax system, it immediately vanquished the customers. Climax was constrained bankrupt. By the end of World War I, more than 4000 Day-and-Night solar water heaters were sold.
In the mid-1920s, a numerous natural gas was found in the Los Angeles Basin. The cost of natural gas in 1927 was just a quarter of that in 1900 for town gas. The gas-worked water heater, much cheaper in initial investment than the solar heater furthermore, more suitable to use, step by step supplanted the once popular solar water heaters. Bailey’s company, being quite experienced in water heater systems, immediately adjusted into a gas heater business. As yet keeping Day-and-Night as the company name, it soon got to be one of the biggest makers of gas water heaters in the country.
The downfall of the solar water heater business in California was not the end of it. Florida, with a real estate boom in the 1920s through the 1940s and no natural gas available, turned into the sweet spot of solar water heaters; as you can see in the next Figure. It is assessed that from 25,000 to 60,000 solar water heaters were installed in Miami during 1920– 1941. Amid World War II, cost of copper skyrocketed. After the war, the cost of electricity collapse. The outcome was the continuous substitution of solar water heaters by electric water heaters. In the United States, the solar water heaters had lost its glory.
A Day-and-Night solar water heater in Florida. From 1920 to 1941, more than 25,000 solar water heaters were manufactured and installed in Florida. After 80 years, thousands of them are still working. The photo, taken in Miami in August 2010, is a solar water heater installed in 1937. The insulated water tank is disguised as a chimney. Even with a broken pane, it is still working properly.
2.7: Moral Equivalence of War
Government policies on energy have a major effect on renewable energy development. In the United States, the new energy policies during the Carter administration in the 1970s created a golden period for renewable energy research and development. After World War II, the United States enjoyed cheap crude oil, staying below $20 per barrel (inflation adjusted in January 2008 dollars) for three decades. In 1973, an oil embargo triggered the first energy crisis. The price of crude oil jumped dramatically; see the next figure (17).
Coincidentally, the timing of the energy crisis matched the prediction of M. King Hubbert in 1956 that shortly after 1970 the production of crude oil in the United States would peak and start to decline. The coincidence is not accidental. As crude oil production in the United States started to decline, consumption was still growing. In 1971, the United States paid $3.7 billion for importing crude oil; in 1977, it increased 10-fold to $37 billion (in 1977 dollars). Obviously, excessive dependence on foreign oil poses severe economic and security threats. On April 18, 1977, then President Jimmy Carter delivered a televised speech about his new energy policy. He called the struggle for greater energy independence the moral equivalence of war — one that “will test the character of the American people.” He said:
Tonight I want to have an unpleasant talk with you about a problem unprecedented in our history. With the exception of preventing war, this is the greatest challenge our country will face during our lifetimes. The energy crisis has not yet overwhelmed us, but it will if we do not act quickly. It is a problem we will not solve in the next few years, and it is likely to get progressively worse through the rest of this century. We must not be selfish or timid if we hope to have a decent world for our children and grandchildren. We simply must balance our demand for energy with our rapidly shrinking resources. By acting now, we can control our future instead of letting the future control us.
The major points of Carter’s energy policy included energy conservation, increasing domestic traditional energy exploration, and developing renewable energy resources. In his words, “we must start now to develop the new, unconventional sources of energy we will rely on in the next century.” A few days later President Carter signed the Department of Energy Organization Act and on August 4, 1997, formed the U.S. Department of Energy. Then, the National Energy Act (NEA) was established in 1978 with tax incentives for renewable energy projects, especially solar energy. This legislation initiated a significant boost to the research, development, and installation of solar water heaters, solar cells, and solar-operated buildings.
In 1978, the Carter administration enacted the first National Energy Act (NEA) to promote fuel efficiency and renewable energy. The research and development funding for renewable energy is greatly increased. Part of the 1978 NEA is an Energy Tax Act that gave an income tax credit to private residents who use solar, wind, or geothermal sources of energy. The 1978 Energy Tax Act was expired in 1986. However, many other countries followed the example of the United States and provided government financial support for renewable energy utilization. As anticipated by Jimmy Carter, during the rest of the twentieth century, several factors made the energy problem “progressively worse”: Due to a steady decline and an increasing consumption, crude oil import into the United States increased from 1.8 billion barrels in 1980 to 5.0 billion barrels in 2000s. The price of crude oil (in 2008 dollars) increased from about $20 to more than $100 a barrel in late 2000s; see Fig. 1.29. The petroleum crisis in the 1970s reappeared, but with an even more gruesome context: According to Hubbert, in the early 2000s, the world’s crude oil production peaked and started to decline; The world’s two most populous countries, India and China, are experiencing rapid economic development, which consume a growing proportion of the dwindling production of the world’s crude oil. Both India and China have very limited crude oil resource and therefore have an even more severe energy problem.
2.8: Solar Water Heaters around the world
As we have previously showed, the Solar Water Heaters was designed in the United States and it was entirely well known in the first half of the twentieth century. However, in spite of the energy crisis and strong government motivation in the 1970s, the establishment volume in the United States is still low. In any case, in late decades, the solar water heater has delighted in an unstable development globally, particularly in China. As appeared in the next figure (18). In 2007, China introduced 80% of the new solar water heaters with 16 GW limit; the aggregate establishment limit of solar water heaters is 84 GW, representing 66% of the world's aggregate.
2.9: Earth Rotation and Revolution
The term Earth rotation refers to the spinning of our planet on its axis. Because of rotation, the Earth's surface moves at the equator at a velocity of about 467 m per second or slightly over 1675 km per hour. If you could look down at the Earth's North Pole from space you would notice that the direction of rotation is counter-clockwise as you can see in the next figure (19). And it’s the opposite when you viewed from the South Pole. One rotation requires exactly twenty-four hours and is called a mean solar day. The Earth’s rotation is responsible for the daily cycles of day and night. Every single moment, one half of the Earth is in sunlight, while the other half is in darkness. The edge dividing the daylight from night is known the circle of illumination. The Earth’s rotation also creates the apparent movement of the Sun across the horizon.
The orbit of the Earth around the Sun is called an Earth revolution. This empyreal motion takes 365.26 days to complete one cycle. Further, the Earth's orbit around the Sun is not circular, but oval or elliptical . An elliptical orbit causes the Earth's distance from the Sun yearly. Till now, this phenomenon is not responsible for the Earth’s seasons! This difference in the distance from the Sun causes the amount of solar radiation received by the Earth per year by about 6 %.
2.10: Angle of Declination
The earthۥs equator is considered to be in the equatorial plane.By drawing a line between the center of the earth and the sun. The angle of declination is derived. The declination angle varies between -23.45° on December 21 to +23.45° on June 21. Stated simply, the declination angle has the same numerical value as the latitude at which the sun is directly on top of the sky at solar noon on a given day, where the extremes are the tropics of cancer (23.45°N) and Capricorn (23.45°S). The angle of declination, δS, is estimated by use of the following equation:
(2-1)
where dn is the day number during the year with the first of January set as dn =1, and dn can be conveniently obtained with the help of table 2-1. From NASA Research Center, the monthly averaged declination angle can be listed in the next table (6). The angle of declination is drawn as a function of days from year in figure (20).
2.11: Altitude and Azimuth Angles of Sun
In order to simplify calculations, it will be assumed that the earth is fixed and the sun’s apparent motion is described in a coordinate system fixed to the earth with the origin being at the site of interest, it allows for the position of the sun to be described at any time by the altitude and azimuth angles. The altitude angle, A, is the angle between a line collinear with the sun’s rays and the horizontal, and can be calculated by use of the following equation:
sin (A) = sin (L) sin () + cos (L) cos () cos (hs) (2-2)
Where L is the latitude of site, δS is the declination angle of sun and hs is the hour angle. The angle between the site to the sun line and the vertical at site is the zenith angle, Zs, which is found by subtracting the altitude angle from ninety degrees as in the following equation:
Zs = 90 – A (2-3)
The azimuth angle, AZs, is the angle between a south line and the projection of the site to the sun line on the horizontal plane. For the azimuth angle, the sign convention used is positive if west of south and negative if east of south. The azimuth angle is found by using the following equation:
(2-4)
2.12: Hour angle
The altitude and azimuth angles are not fundamental angles and must be related to the fundamental angular quantities of hour angle (hs), latitude (L), and declination (δS). The hour angle is the angular distance between the meridian of the observer and the meridian whose plane contains the sun. It becomes zero at solar and increases 15° every hour. An expression to calculate the hour angle from solar time is:
hs = 15 (Tsol. – 12) (2-5)
Where Tsol. Is the solar time in hours. The conversion between solar time and clock time requires knowledge of the location (longitude), the day of the year, and local standard meridian as in the following equation:
Tsol. = ST + 4 (Lst – Lloc) + ET (2-6)
Where ST is the local standard time, Lst is the standard meridian for local time zone, Lloc is the longitude of location, and ET is the equation of time in minutes and equal to:
ET = 9.87sin (2B) – 7.53cos (B) – 1.5sin (B) (2-7)
B = 360 (dn-81)/364 (2-8)
Where dn is the day number of the year (1≤ dn ≤ 365). the values of the hour angle east due south (morning) are negative; and the values west of due south (afternoon) are positive.
2.13: Latitude Angle
The latitude angle, L, is defined as the angle between the line from the center of the earth to the site of interest and the equatorial plane; and can be found on an atlas or by use of Global positioning system.
Chapter Three
3.1: Analyzing and calculating the electrical performance of photovoltaic modules
The following equations define the model used for analyzing the electrical performance of photovoltaic modules. The same equations apply equally well for individual cells and for large arrays of modules. The form of the model given by equations 2-54 to 2-62 are used to calculate the expected Isc, Voc and Pm produced by a module. The solar resource and weather data required by the model can be obtained from NASA Langley Research Center or from direct measurements.
(3-1) (3-2)
Pm = Im Vm = FF Isc Voc (3-3)
(3-4)
Where:
I SC, Im: are the short circuit and maximum current respectively, Ampere.
I SCO: is the short circuit current under standard test conditions {Ht = 1000
W/m2, TC = To °C, AM = 1.5, AIO = 0°}, Ampere.
AM: is the air mass.
AIO: is the solar angle of incidence.
Voc, Vm: are the open circuit and maximum voltage, respectively, volt.
Voco: is the open circuit voltage under standard test conditions, volt.
Pm: is the maximum output power, Watt.
FF: is the fill factor of the solar cell module.
Hb: is the beam solar irradiance, W/m2.
Hr: is the reference solar irradiance, typically, 1000 W/m2.
Hd: is the diffuse solar irradiance, W/m2.
He: is the effective irradiance.
Ht: is the total solar irradiance (beam + diffuse), W/m2.
Ns: is the number of cells connected in series in a module.
TC: is the cell temperature inside module (°C).
To: is the reference temperature for cells in module, typically, 25°C.
fd: is the fraction of diffuse irradiance used by module, typically assumed to be one for flat plate modules and zero for concentrating systems.
βvoc: is the temperature coefficient (V/°C).
: is the temperature coefficient (A/°C).
: is the empirically determined "AM function" for solar spectral influence.
: is the empirically determined "AOI function" for angle of incidence affects.
δ(Tc) : is the thermal voltage per cell at temperature Tc.
The equations used to calculate,, δ(Tc), Hb, and TC can be written as follows:
(3-5)
…. (3-6)
(3-7)
(3-8)
δ (TC) = mK (TC + 273.15)/q (3-9)
Where to and to are the air mass and angle of incidence coefficients respectively, Hb,N is the beam normal irradiance (W/m2), Ta is the ambient temperature (°C), and are the temperature coefficient specified for used solar cell module, ws is the wind speed in (m/s), m is the diode factor, typically near unity, K is the Boltzman constant and q is the elementary charge.
The electrical characteristics of solar module under standard test conditions and the coefficients required in the mathematical model for the used solar cell module are listed in the two next tables (7) and (8).
A fundamental parameters Imp, Vmp, and VOC of a module are behaved and predictable when described as a function of ISC and cell temperature only, in other words, for a given ISC and cell temperature the shape of the current-voltage curve will be the same for any solar spectrum and angle of incidence.
In this chapter, we try to explain the working principle of solar cells, which rely on the work of the Semiconductor and in The following an explanation about the semiconductors and how they works.
3.2: Semiconductors
Conductor, Semiconductor, and Insulator
At the point when a huge number of atoms come together to form a solid, the wavefunctions of atoms intract to frame stretched out holes which are loke like in the one-dimensional crystal. A number of energy bands are formative. As a rule, the quantity of holes is interminable. As indicated by the Pauli exclusion principle,
every hole must be taken by one electron. presume electrons queue added to a system one by one, starting from the lowest energy. At a certain point, the number of electrons equivalent to the number of protons in the system and the system becomes neutral. As per the relative position of the energy bands and the highest occupied energy level, there are three different cases, as shown in the next figure (23) .
In the figure (23), the highest occupied energy level is in the middle of an energy band.
The electrons can move to the unoccupied parts of the energy band. This type of material is called a conductor or a metal.If the highest occupied energy level matches the top of an energy band, which is called the valence band, marked as Ev, and the distance to the next energy band is large, the electrons are not easily excited to the higher band. This type of materials is called an insulator. An important case between those two is the semiconductor, where the gap between the top of the valance band EV and the bottom of the next energy band Ec is small such that when the temperature is not too low electrons can be transmitted to the next energy band, the conduction band. Typically the energy gap is less than a few electron volts. Once the electrons are excited to the conduction band, some conduction can take place.
3.3: Electrons and Holes
At low temperature, pure semiconductors have almost no mobile electrons, and the conductivity is very low. If we put the temperature a littile bit higher, electrons in the valance band can be excited to the conduction band; see the next figure (24). Therefore, a semiconductor has an important property: Conductivity depends critically on temperaturewhich means: higher the temperature, higher the conductivity.
According to Fermi–Dirac statistics, at temperature T, the concentration of electrons n0 at the bottom of the conduction band is:
n0 = Nc f (Ec) (3-10)
where Nc is the effective density of states of the conduction band, a quantity determined by the property of the semiconductor, and f(Ec) is the Fermi function, the distribution function of electrons at absolute temperature T. At room temperature, kBT ≈ 0.026 eV, the value of Ec−EF is about 1 eV, and the factor 1 in the Fermi function can be neglected. To high accuracy, we have:
(3-11)
Therefore, the concentration of electrons in the conduction band is:
n0 = Nc e− (Ec−EF)/kBT (3-12)
In the valance band, there is a deficiency of electrons from the saturated situation.The deficiency of electrons in the valence band forms the mobile carriers, the holes. Similarly, the concentration of holes, p0, is given as:
p0 = Nv[1 − f(Ev)] ≈ Nv e− (EF−Ev)/kBT (3-13)
where Nv is the effective density of states in the valence band and Ev is the energy level of the top of the valence band.
It is an interesting and important fact that the product n0 p0 is independent of the Fermi level.Actually, by combining the two previous equations(3-12) and (3-13).
(3-14)
(3-15)
For intrinsic semiconductors, or semiconductors without impurities, charge neutrality requires that n0 = p0. Therefore, an intrinsic carrier concentration ni can be defined:
(3-16)
with the general property
(3-17)
which is valid even for semiconductors with impurities.
3.4: p-Type and n-Type Semiconductors
Semiconductors have an even more important property: their conductivity critically depends on the type and concentration of impurities. According to the position of the energy level of the atoms in the band gap of a semiconductor, there are two major types of impurities.
The energy level of donor atoms is just below the bottom of the conduction band.The impurity atom can easily be ionized to contribute an electron to the conduction band. For silicon and germanium, atoms from group V of the periodic table (N, P, As and Sb) are effective donors. The Fermi distribution is still valid, but the Fermi level has shifted toward the conduction band, as shown in the next figure. Assume the concentration of donor atoms is ND. If the temperature is moderately high, all donor atoms could be ionized. The concentration of free electrons in an n-type semiconductor, nn, approximately equals the concentration of donor atoms,
nn = ND. (3-18)
On the other hand, the energy level of acceptor atoms is just above the top of the valence band. An electron in the valence band can easily be trapped by the acceptor atoms and leave a hole in the valence band. For silicon and germanium, atoms from Group IIIA (B, Al, Ga, and In) are effective acceptors. The Fermi distribution is still valid, but the Fermi level has shifted toward the valence band, as shown in the next figure(25). Assuming the concentration of acceptor atoms is NA. If the temperature is moderately high, all acceptor atoms become negative ions. The concentration of holes in a p-type semiconductor, pp, approximately equals the acceptor concentration,
pp = NA. (3-19)
In both cases, the product of the concentrations of free electrons and holes equals the square of the intrinsic carrier concentration,
(3-20)
Where pn is the hole concentration in an n-type semiconductor and np is the free-electron concentration in a p-type semiconductor. Each is a minority-carrier concentration.
3.5: Formation of a pn-Junction
When a p-type semiconductor and an n-type semiconductor are brought together, a built-in potential is established. Because the Fermi level of a p-type semiconductor is close to the top of the valence band and the Fermi-level of an n-type semiconductor is close to the bottom of the conduction band, there is a difference between the Fermi levels of the two sides. When the two pieces are combined to form a single system, the Fermi levels must be aligned. As a result, the energy levels of the two sides must undergo a shift with a potential V0. Letting Ecp be the energy level of the bottom of the conduction band for the p-type semiconductor versus the Fermi level and Ecn that for the n-type semiconductor, the built-in potential is:
qV0 = Ecp − Ecn (3-21)
The establishment of a built-in potential near the boundary of a pnjunction can be understood from another point of view, the flow of carriers. Because in the n-region the hole concentration is very low, the holes diffuse from the p-region to the n-region. After a number of holes move to the n-region, an electrical field is formed to drive the holes back to the p-region. At equilibrium, the net current Jp(x) must be zero,
(3-22)
where μp is the mobility of the holes, p(x) is the concentration of holes as a function of x, Ex(x) is the x-component of electric field intensity as a function of x, and Dp is the diffusion coefficient of the holes. Using Einstein’s relation,
(3-23)
And the relation between the potential V (x) and electric field intensity, Ex(x) = −dV (x)/dx, and the equation becomes:
(3-24)
By Integrating the last equation (3-24) over the entire transition region produce:
(3-25)
Because Vn − Vp = V0, the previos equation (3-25) can be rewritten as:
(3-26)
Similarly, because in the p-region the free-electron concentration is very low, the free electrons diffuse from the n-region to the p-region. After a number of free electrons move to the p-region, an electrical field is formed to drive the free electrons back to the n-region. At equilibrium, the net current of free electrons must be zero. A similar equation is found,
(3-27)
The meaning of the previos two equations is as follows: pn is the concentration of holes in the n-region of the pn-junction and pp is the concentration of holes in the p-region of the pn-junction. Because of the potential established by the space charge, V0, the former is reduced by a factor of exp(−qV0/kBT) from the latter. The situation for the concentration of free electrons is similar.
To make a mental picture, we will make an order-of-magnitude estimate of the two equations. A typical value of the built-in potential is V0 ≈ 0.75 eV. At room temperature, kBT ≈ 0.026 eV. The factor exp(−0.75/0.026) ≈ 10−12.5. Therefore, the absolute values are very small. For obvious reasons, both pn and np are called minority carriers.
The previos two equations (3-26) and (3-27) are substantial in being able to understand the current-voltage behavior of the pn-junction and the derivation of the diode equation.
To better understand the pn-junction, we need to establish a mathematical model for the space charge and the potential curve. A very effective and fairly accurate model is based on the depletion approximation; as in the next figure. Under such an approximation, in the p-region near the junction boundary there is a layer of thickness xp where all the holes are removed and the charge density ρp is determined by the density of the acceptors NA, which are negatively charged,
ρp = −qNA. (3-28)
The electrostatic potential φ in this region is given by Poisson’s equation,
(3-29)
Where is the dielectric constant or permittivity of the semiconductor and is the product of the permittivity of a vacuum, 0, and the relative dielectric constant r of the semiconductor.The permittivity of a vacuum is given as 0 = 8.85 × 10−14 F/cm. For example, for silicon, r = 11.8, ≈ 1.04 × 10−12 F/cm.
As another option or possibility we can write the last equation expressed in terms of electric field intensity,
(3-30)
Similarly, there is a slab of thickness xn where all the free electrons are removed, and the charge density ρn is determined by the density of the donors, ND, which are positively charged,
ρn = qND (3-31)
Poisson’s equation gives
(3-32)
And the corresponding equation for electric field intensity is:
(3-33)
The boundary conditions for equation. (3-29), (3-30), and (3-32) are as follows. First, the charge neutrality of the entire transition region requires that
NAxp = NDxn (3-34)
Second, outside the transition region, the electric field should be zero:
Ex = 0 for x ≤ -xp and x ≥ xn (3-35)
Third, the electrostatic potential should match the values at the boundaries of the transition region:
φ = 0, at x = −xp, φ = V0, at x = xn (3-36)
The solutions of Eqs 8.20 and 8.23 with boundary condition Eq. 8.25 are
(3-37)
(3-38)
Using boundary conditions in equation (3.26) and the definition of the width of the transition region W,
W = xp + xn (3-39)
The following relation is obtained:
(3-40)
The width of the transition region as a function of V0 is
(3-41)
Most solar cells are manufactured from a lightly doped p-type silicon wafer as the base, typically 100 – 300 μm thick, doped with boron of density NA ≈ 1 × 1016 cm−3 having resistivity ρ ≈ 1Ω · cm. The n-type emitter is created by doping heavily on one side with phosphorus, with density ND ≈ 1 × 1019 cm−3, having resistivity ρ ≈ 10−3 Ω · cm. For the case of ND NA, equation (3-40) and (3-41) are simplified to
(3-42)
(3-43)
From equation (3-43), we obtain the capacitance of the pn-junction
(3-44)
3.6: Analysis of pn-Junctions
As we found in Formation of a pn-Junction section, particularly in Figure (3-5), without outer connected voltage, there is no present going through a pn-intersection, on the grounds that the dispersion current and the float current wipe out each other for both gaps and free electrons. By applying an outside voltage on a pn-intersection, the balance is broken and a net current is produced. Subjectively, the system can be clarified as takes after; see Figure (27). At balance, as appeared in Figure (27) (a), for both electrons and openings, there is a focus slope which offers ascend to dissemination and an electrical field indicating −x-direction which drives the transporters in an inverse course. The net current is zero. By applying a positive inclination voltage, to be specific, associating the positive terminal of a battery to the p-side and the negative terminal to the n-side, as appeared in Figure (26) (b), the outer potential pushes the openings to the n-side and the free electrons to the p-side. The potential boundary is decreased. Dispersion streams of both openings and free electrons are expanded. The float current, contingent upon the accessible transporters, are unaltered. The net current is nonzero. Then again, by applying a switched predisposition, as appeared in Figure (27), the gaps are pushed further over into the p-area and the free electrons are pushed further once again into the n-district. The dissemination current is further diminished. The float streams are unaltered and turn into the overwhelming variable. In the long run the current scopes an immersed esteem controlled by the float streams.
3.7: Semiconductor Solar Cells
The photovoltaic impact, the immediate era of electric influence by light in a strong material, was found by English researchers William Grylls Adams and his understudy Richard Levels Day in the 1870s utilizing selenium. A couple of years after the fact, Charles Fritt of New York developed the main photovoltaic module for producing power from daylight. In any case, the effectiveness of the selenium solar cells was under 0.5%, which implied it would not produce adequate energy economically.
A vital leap forward was made in the 1950s by Gerald Pearson, Darryl Chapin, and Calvin Fuller at Chime Labs. Utilizing silicon, they exhibited a solar cell of productivity 5.7%, ten times more prominent than that of the selenium solar cell.
Solar cells first discovered applications in space. The proficiency of silicon cells has been enhanced to around 24% in the mid 2000s, near the hypothetical furthest reaches of 28%. To date, semiconductor soalr cells represent approximately 90% of the business sector share.Especially; silicon solar cells represent more than 80% of the sun powered cell market. Thinfilm solar cells, particularly those in view of CIGS (copper–indium–gallium–selenide) and CdTe-Compact discs are second to silicon solar cells in piece of the overall industry. Organic solar cells, is a promising developing innovation.
3.8: Basic Concepts
The solar cell is a strong state gadget which changes over daylight, as a flood of photons, into electrical force. Figure (28) demonstrates the structure of a regular silicon solar cell.The base is a bit of p–type silicon, delicately doped with boron, a small amount of a millimeter thick. Exceptionally doped n–type silicon, with a thickness of a small amount of one micrometer was created by doping with phosphorus of much higher focus. On account of the implicit capability of the pn-intersection, electrons move to the n–type locale, and create electric force like an electrochemical battery. Radiation, as a surge of photons, collaborates with a semiconductor in two ways.A photon with energy more noteworthy than the crevice energy of the semiconductor material can be retained and make an electron–hole pair. An electron–hole pair can recombine what's more; emanate a photon of energy generally equivalent to the energy hole of the semiconductor.As per the standard of itemized parity the two procedures ought to break even with. This has a noteworthy result to the proficiency of solar cells.
Since the potential energy of the electron–hole pair breaks even with the estimation of the energy band, the best material ought to have a band hole near the focal point of the solar range. Another variable that influences the productivity of solar cells is the kind of the energy crevice. Contingent upon the relative positions of the highest point of the valence band and the base of the conduction band in the wavevector space, the energy hole of a semiconductor can be immediate or circuitous; see Figure (29).
For semiconductors with a direct hole, for example, GaAs, CuInSe2, and CdTe, a photon can straightforwardly energize an electron from the valence band to the conduction band; the assimilation coefficient is high, regularly more noteworthy than 1×104 cm−1. For semiconductors with a backhanded crevice, for example, Ge and Si, the highest point of valence band and the base of the conduction band are not adjusted in the wavevector space, and the excitation must be intervened by a phonon, as it were, by grid vibration. In this manner, the ingestion coefficient is low, normally littler than 1 × 103cm−1. A thicker substrate is required.
Chapter Four
4.1: The Effect of Tilt Angle on Solar Panels
In this chapter we will work togather to demonstrate how solar panels react to the direct and indirect rays from the sun or an artificial light source in order to produce electricity.The suitable value of tilt angle of the fixed solar cell systems varies according to places of these systems on the earth and it varies along the year seasons for the same place. It is known that the perfect tilt angle is that make the solar module in face with the sun at solar noon to utilize from the most amount of incident solar radiation. The deviation from this value may be useful in dusty countries because that the amount of accumulation dust is decreased by increasing in the module tilt angle. On the other hand, this procedure leads to increase in the amount of reflecting radiation. Thus, in the present work it will be determined which is the best by carrying out an experiment in which the output power of solar module (see figure 30) recorded as a function of tilt angle at different times along the day. Then calculating associated losses and comparing them with the losses that are due to the dust.and we will adjust the angle of the solar panelrelative to the sun or artificial light source and measure voltage, current and power flowing into a resistor load. They correlate the tilt angle to the electrical measurements to determine the differences in electrical generation caused by the angle of tilt. They then determine the best tilt angle for a commercial solar panel at their geographical location and time of year. They analyze and explain the results. They are also introduced to a Sun Tracker.we can A device called a Sun Tracker can keep solar panels correctly oriented at the sun all day long in order to generate the maximum power from the solar panel.
4.2: The Effect of Tilt Angle on Dust Accumulation
In some countries they installed the solar cell modules for street lighting systems at tilt angle of about (50°-60°). It is thought that the increasing in the tilt angle of the solar cell module will be decreasing the amount of accumulated dust and then reducing the losses. The true solution, in this case, is related to the outdoor practical experiment.
Figure (31 a,b,c,d)
This experiment is done for slides are set up at height of 6m and subjected to dust for about one month. The optical transmittance is measured as a function of tilt angle. The results indicate that the optical transmittance increased with increasing the tilt angle as demonstrated in figure (31).
4.3: The Effect of Tilt Angle on the Performance of Solar Module
The angle defined by the sunۥs rays and normal to the solar cell moduleۥs surface is the angle of incidence (AOI). The angle of incidence is computed by using sunۥs and moduleۥs angles. When the beam solar radiation makes angle of incidence with the normal to the surface of solar module except zero degree, in other words, oblique incidence there are two effects which can be illustrate in the following two sections:
4.3.1: The Optical Losses
Optical misfortunes primarily impact the influence from a solar cell by bringing down the short out current. Optical misfortunes comprise of light which could have produced an electron-opening pair, however does not, on account of the light is reflected from the front surface, or on the grounds that it is not caught up in the solar cell. For the most well-known semiconductor solar cells, the whole obvious range (350 – 780 nm) has enough energy to make electron-opening sets and along these lines all noticeable light would preferably be retained wellsprings of optical misfortune in a solar cell.
There are a number of ways to reduce the optical losses:
Top contact coverage of the cell surface can be minimised (although this may result in increased series resistance). This is discussed in more detail in Series Resistance;
Anti-reflection coatings can be used on the top surface of the cell.
Reflection can be reduced by surface texturing.
The solar cell can be made thicker to increase absorption (although light that is absorbed more than a diffusion length from the junction has a low collection probability and will not contribute to the short circuit current).
The optical path length in the solar cell may be increased by a combination of surface texturing and light trapping.
4.3.2: The Geometrical Losses
Open cavity recipients can be utilized to proficiently retain concentrated solar radiation at high temperatures. Utilizing beam following and a stochastic streamlining technique, the geometry of such beneficiaries is enhanced taking a gander at transmit misfortunes as it were. Results affirm the real part of the opening in cavity misfortunes moderation and highlight the flux dissemination minor departure from geometries with practically identical transmit exhibitions.
In Concentrated Solar Power (CSP) systems, the receiver, placed at the focus of the light-concentrator, absorbs concentrated solar radiation and transfers this heat to a Heat Carrier (HC). Recent advances in CSP applications target higher temperatures of operation for receivers in order to increase the thermodynamic efficiency of the overall CSP system. In the present study, the geometry of cavity receivers is analysed using a stochastic brute force optimisation technique.
To do the Experiment we need to bring some materials like Solar panel, Goose neck table lamp, 100 ohm potentiometer, Protractor (for measuring tilt angle) and some Wires. And we will start the experiment by adjust the angle of the solar panel relative to the sun or artificial light source and measure voltage, current and power flowing into a resistor load. And we will correlate the tilt angle to the electrical measurements to determine the differences in electrical generation caused by the angle of tilt.then determine the best tilt angle for a commercial solar panel at their geographical location and time of year. After that analyze and explain the results. Use the protractor to set the solar panel at a 90 degree angle (vertical to the table) and record the voltage. Change the angle of the solar panel to each of the next settings of 75, 60, 45, 30, 15 and 0 degrees and record the voltage at each setting. During this time Use the protractor to set the solar panel at a 90 degree angle (vertical to the table) and then Record the voltage, current and power at 90 degree. And we start to take the readings and put in a table (4-2) as it is shown,
In the previouse Table (10), we have some of the results that we've made in the earlier application as an example
Using the data in the table we can make a graph that plots the voltage, current and power (vertical axis) against the tilt angle (horizontal axis).
First your geographical location – or more specifically, its latitude – needs to be determined. Your location’s latitude is the angular distance from the Equator to either the North or South Pole depending on what part of the world your location is. We will assume that our location is in the Northern Hemisphere for this example. If your location is in the
Southern Hemisphere then simply reverses some of the references. Latitude is the measure of distance from the equator to either the North or South Pole expressed in degrees from 00 at the equator to 900 at either pole. Latitude in the northern hemisphere is expressed as a positive number while latitude in the southern hemisphere is expressed as a negative number. Lines of latitude circle the Earth as concentric circles that are parallel to the equator and to one another. Each degree of latitude is subdivided into 60 minutes and each minute is sub-divided into 60 seconds.Now that you have your location’s latitude you need to consider the time of year for best results from the solar panel. We know that the sun is higher in the sky in summer and lower in winter as shown in Figure (34).
.
So it seems like the best angle to position the solar panel would be between the highest and lowest points of the sun’s apparent angle in the sky. You can use Figure (35) as a way to determine the best latitude for the season of the year. Just add or subtract about 15 degrees to to adjust for the season.
Now, what if you could have the solar panel move with the sun as it appears to travel across the sky during the day? You could certainly capture more of the sun’s energy and produce more power. There are devices that allow you to do this – they are called Sun Trackers. A Sun Tracker is really a mechanical device that keeps the solar panel pointed directly at the sun during the day and, with some models, during the seasons. The basic type is called a single-axis Sun Tracker because it only moves the solar panel back and forth as the sun moves across the sky during the day. A more powerful model called a dual-axis sun tracker moves the solar panel up and down depending on the elevation of the sun during the year. Figure (36, 37) shows the advantage of using the Sun Tracker.
Conclusion
This dissertation is intended to provide a brief summary for those who are interested in solar energy technologies and as a reference for those who want to invest or work in this field.
Tilt angle plays a key role in solar output fluctuation, since the amount of solar radiation received by solar panels varies by tilt angle and time of year we can conclude that more solar radiation in the summer will give more electricity energy production by solar panel and vice in the winter.
Big particles like dirt and dust travel short distances and adversely impact the output of solar panels closest to these particle sources and small particles settle on solar panels surfaces over time, and have higher concentrations in the summer than winter.
The suitable value of tilt angle of the fixed solar cell systems varies according to places of these systems on the earth and it varies along the year seasons for the same place. It is known that the perfect tilt angle is that make the solar module in face with the sun at solar noon to utilize from the most amount of incident solar radiation. The deviation from this value may be useful in dusty countries because that the amount of accumulation dust is decreased by increasing in the module tilt angle.
Visible light (insolation) is the main energy source collected by systems that provide space heat, water heat, and electricity for homes. Because of the Earth’s axial tilt, the amount of solar insolation incident at any one spot on the Earth’s surface varies throughout the year. On a daily and a seasonal basis, the amount of light energy incident on a surface varies from sunrise to sunset. The atmospheric conditions and elevation at the site are also factors that influence the amount of light reaching the Earth’s surface.
Future Work
By Taking advantage of this research, we will manufacture a Solar Thermal system by placing water pipes to be heated under the solar cells So that you can take advantage of this to provide hot water and heating during the winter.
Before installing a solar water-heating system, you must first consider the site's solar resource, since the efficiency and design of a solar water-heating system depend on how much of the sun's energy reaches the solar Panel. And also we will calculate howmuch we need to site and size a solar water-heating system.
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