Green IT Strategies and Applications Essay Example | Topics and Well Written Essays - 1000 words

All About the Economics of Interest

About the Economics of Interest What is Interest?: Enthusiasm, as characterized by financial specialists, is the pay earned by the loaning of a total of cash. Regularly the measure of cash earned is given as a level of the whole of cash loaned - this rate is known as the financing cost. All the more officially, the Glossary of Economics Terms characterizes the financing cost as the yearly cost charged by a bank to a borrower all together for the borrower to acquire a credit. This is normally communicated as a level of the aggregate sum advanced. Intrigue Types and Types of Interest Rates: Not a wide range of advances procure a similar pace of intrigue. Ceteris paribus (all else being equivalent), advances of longer length and credits with more hazard (that is, advances that are more averse to be paid off) are related with higher financing costs. The article Whats the Difference Between all the Interest Rates in the Newspaper? examines the distinctive assortment of loan costs. What Determines the Interest Rate?: We can think about the loan cost similar to a cost - the cost to get an aggregate of cash for a year. Like practically all different costs in our economy, it is controlled by the twin powers of gracefully and request. Here flexibly alludes to the gracefully of loanable assets in an economy, and request is the interest for advances. National banks, for example, the Federal Reserve and the Bank of Canada can impact the flexibly of loanable assets in a nation by expanding or diminishing the gracefully of cash. To become familiar with the cash flexibly observe: Why does cash have esteem? furthermore, Why Dont Prices Decline During A Recession? Loan costs That Are Adjusted for Inflation: While deciding if to credit cash, one needs to consider the way that costs go up after some time - what costs $10 today may cost $11 tomorrow. On the off chance that you advance at a 5% financing cost, yet costs rise 10% you will have less buying power by making the credit. This wonder is talked about in Calculating and Understanding Real Interest Rates. Loan costs - How Low Can They Go?: More then likely we will never observe a negative ostensible (non-swelling balanced) pace of intrigue, however in 2009 negative financing costs got famous as a potential method to animate the economy - see Why Not Negative Interest Rates?. These future hard to execute by and by. Indeed, even a loan fee of precisely zero would cause issues, as examined in the article What Happens if Interest Rates Go To Zero?

The Best Ways To Offer Effective Feedback - Focus

The Best Ways To Offer Effective Feedback - Focus As a freelancer, I get lots of benefits that dont come with most full-time jobs. I get to choose the work I do and the clients I take on, I make my own hours, and I work from homeâ€"in my pajamas, if I want to. But there are upsides and downsides to everything. Freelancing means youre your own boss, and its up to you to keep yourself on task. You also have to think about saving for retirement and paying for insurance, which might be covered if you were an employee. It might sound strange, but not getting feedback is one of the downsides of freelancing, if you ask me. I thrive on feedback. I love hearing about what I did well (who doesnt) and I like knowing what to work on (note my change of language thereâ€"I dont actually like to hear  about what I can improve on, but I do like to know what needs work; if only I could have one without the other). Anyone whos had to manage people knows how uncomfortable it can be to give feedback to your team members. Even providing positive feedback can be awkward if youre not sure how to do it well. So we end up with a mumbled good job now and then, and managers frustrated over criticisms they can’t share, because giving feedback well is rarely taught to managers. Ive been in this situation before, and I know Ive done a horrible job. I can remember uncomfortable conversations where I had to criticise someones performance, and I only wish Id known how to handle it well. But better late than never, right? Lets look at what the experts say about handling a feedback conversation effectively. (Spoiler: we’re about to learn that the “shit sandwich” is a terrible approach, among other practical advice.) Be Prepared For managers, offering feedback is part of the job. You do your star a disservice if you fail to help her figure out how she can continue to grow,” says  Jean-François Manzoni, author and Professor of Leadership and Organizational Development at IMD International. Though top performers tend to be overlooked when it comes to feedback, its something you should be providing for everyone on your team. Kim Castelda, senior vice president at software company Bullhorn, says  shes rarely met someone who didnt want to be successful, and giving feedback is an essential part of that. To start your feedback session on the right foot, Castelda suggests taking your role seriously and being prepared before your meeting starts. Leaders should walk in centered, prepared, and organized, she says. You should also prepare examples and data in advance, she says, to back up the points you want to make. Be Specific with Correctional Feedback, General with Directional Feedback When you actually deliver feedback, conflicting advice abounds on how to go about it. In particular, how specific you should be. But there does seem to be a general consensus depending on the situation. When youre providing feedback for creative work, to help an employee understand the direction you want them to take their project in, take a tip from the experts. Pixar director Pete Docter says  the best way to provide feedback in this case is to keep it general. Dont tell them exactly what to do, when, and how, he says, but take advantage of your employees creative skills and let them do what they were hired for. If you can use a language that allows them to put in their own specifics, then it becomes much more truthful. â€" Pete Docter Docter provides an example from working with animators. Rather than telling them how to animate a particular scene, and at what point the character should do something, he says, it makes more sense to use imagination and memory to evoke the feeling  he wants to come across in this part of the film. Reminding the animator of how it felt to squabble with siblings when they were young is enough to get them thinking about how to make that mischievous feeling come through in the film, without telling them exactly what to do. But you may be in an entirely other situation. One where you need to offer corrective feedback to help someone adjust their behavior or the way they approach their work. In this case, most experts agree specificity is important, but with a caveat:  feedback should be squarely aimed at the work or behavior itself, not the person. Always describe behaviors, not traits, says Amy Gallo, author of the HBR Guide to Managing Conflict at Work. The more general the coaching advice, say authors Roger Fisher and Alan Sharp  in their book Getting It Done: How to Lead When Youre Not in Charge, the more it is taken as a personal indictment. Again, Pixar has this process down pat. When criticising early versions of a film, the Pixar team knows theyre dealing with work that reflects strongly on the artists behind it. To avoid egos and hurt feelings getting in the way of improving the movie, criticism is always clearly aimed at the film itself, rather than its makers. Team management made simple. Get started with MeisterTask Its free! Get started with MeisterTask Start with the Negatives When youre delivering negative news, theres one more thing to remember: if youve ever heard of the shit sandwich approach, nows the time to discard it. The idea of sandwiching bad news between two bits of positive news sounds great in theory, but doesnt work in practice. Evolution has primed us to respond to and remember negative events more strongly, since theyre more often related to life-or-death danger than positive events. A close run-in with a tiger, for instance, would have stuck in our ancestors minds more strongly than a nice meal. They needed to learn from the encounter with the tiger and avoid it happening again, so their brains remembered it vividly. Fortunately, we rarely face life-or-death dangers these days. Unfortunately, we still react more strongly to negative events. Which is why criticism stings so harshly, and we have a hard time letting go of negative experiences. This is why the shit sandwich doesnt work: sandwiching the bad news isnt enough to overcome our natural tendencies to focus on it. The good news is, theres another approach that might work. According to Roy F. Baumeister, professor of social psychology at Florida State University, many  good events can overcome the psychological effects of one bad event in our mind. Because it takes many positives to outweigh negatives, Clifford Nass, professor of communication at Stanford University, and author of The Man Who Lied to His Laptop  suggests  starting with the bad news first, then following it up with lots of positives. This helps to overwhelm the employees brain with good vibes, so they cant dwell on the bad feedback. Be Empathetic Speaking of egos, we all know how much it hurts to get bad feedback on something youve done. Whether its your work, a suggestion you offered in a meeting, or a joke that doesnt land, no one likes the feeling that we could have done better. When youre offering feedback to an employee, remember this. Marcia Reynolds, author of The Discomfort Zone: How Leaders Turn Difficult Conversations into Breakthroughs  says  we need to be empathetic when discussing feedback. Even if you disagree with their perspective, she says, honor the human in front of you. To ensure the process is respectful and useful to everyone involved, feedback discussions need to be a two-way conversation, not a lecture. Liane Davey, author of You First: Inspire Your Team to Grow Up, Get Along, and Get Stuff Done, says  to avoid making the mistake of attributing intent, and instead to just focus on the impact of the behavior. Its all too easy to assume we know why  someone made a particular decision, but without asking and truly listening, we cant know for sure. Rather than making harmful assumptions, be open to hearing your employees point of view. Davey suggests asking open-ended questions to learn how your employee took the feedback, whether theyve understood you clearly, and what they plan to do differently next time. Amy Gallo agrees that checking for understanding should be part of your process. She also suggests you and your team member agree on clear next steps and a fair way to measure progress. One final thought: Castelda, who leads a training program on delivering difficult messages, suggests managers keep in mind the positive reasons for providing feedback. If youre finding a conversation difficult or nerve-wracking, remember that your aim in providing feedback is to help your team members succeed and grow. Research shows  53% of managers avoid difficult conversations due to lack of training in how to handle those moments effectively. A 2014 study  also found 43% of managers felt that offering corrective feedback was a stressful and difficult experience. If you fit into either of those groups, I hope this research will prove helpful in approaching future feedback sessions. And if nothing else, remember that youre dealing with another human being, and do your best to be empathetic to their point of view. Communicate. Collaborate. Create. Try MeisterTask Its free! Try MeisterTask The Best Ways To Offer Effective Feedback - Focus As a freelancer, I get lots of benefits that dont come with most full-time jobs. I get to choose the work I do and the clients I take on, I make my own hours, and I work from homeâ€"in my pajamas, if I want to. But there are upsides and downsides to everything. Freelancing means youre your own boss, and its up to you to keep yourself on task. You also have to think about saving for retirement and paying for insurance, which might be covered if you were an employee. It might sound strange, but not getting feedback is one of the downsides of freelancing, if you ask me. I thrive on feedback. I love hearing about what I did well (who doesnt) and I like knowing what to work on (note my change of language thereâ€"I dont actually like to hear  about what I can improve on, but I do like to know what needs work; if only I could have one without the other). Anyone whos had to manage people knows how uncomfortable it can be to give feedback to your team members. Even providing positive feedback can be awkward if youre not sure how to do it well. So we end up with a mumbled good job now and then, and managers frustrated over criticisms they can’t share, because giving feedback well is rarely taught to managers. Ive been in this situation before, and I know Ive done a horrible job. I can remember uncomfortable conversations where I had to criticise someones performance, and I only wish Id known how to handle it well. But better late than never, right? Lets look at what the experts say about handling a feedback conversation effectively. (Spoiler: we’re about to learn that the “shit sandwich” is a terrible approach, among other practical advice.) Be Prepared For managers, offering feedback is part of the job. You do your star a disservice if you fail to help her figure out how she can continue to grow,” says  Jean-François Manzoni, author and Professor of Leadership and Organizational Development at IMD International. Though top performers tend to be overlooked when it comes to feedback, its something you should be providing for everyone on your team. Kim Castelda, senior vice president at software company Bullhorn, says  shes rarely met someone who didnt want to be successful, and giving feedback is an essential part of that. To start your feedback session on the right foot, Castelda suggests taking your role seriously and being prepared before your meeting starts. Leaders should walk in centered, prepared, and organized, she says. You should also prepare examples and data in advance, she says, to back up the points you want to make. Be Specific with Correctional Feedback, General with Directional Feedback When you actually deliver feedback, conflicting advice abounds on how to go about it. In particular, how specific you should be. But there does seem to be a general consensus depending on the situation. When youre providing feedback for creative work, to help an employee understand the direction you want them to take their project in, take a tip from the experts. Pixar director Pete Docter says  the best way to provide feedback in this case is to keep it general. Dont tell them exactly what to do, when, and how, he says, but take advantage of your employees creative skills and let them do what they were hired for. If you can use a language that allows them to put in their own specifics, then it becomes much more truthful. â€" Pete Docter Docter provides an example from working with animators. Rather than telling them how to animate a particular scene, and at what point the character should do something, he says, it makes more sense to use imagination and memory to evoke the feeling  he wants to come across in this part of the film. Reminding the animator of how it felt to squabble with siblings when they were young is enough to get them thinking about how to make that mischievous feeling come through in the film, without telling them exactly what to do. But you may be in an entirely other situation. One where you need to offer corrective feedback to help someone adjust their behavior or the way they approach their work. In this case, most experts agree specificity is important, but with a caveat:  feedback should be squarely aimed at the work or behavior itself, not the person. Always describe behaviors, not traits, says Amy Gallo, author of the HBR Guide to Managing Conflict at Work. The more general the coaching advice, say authors Roger Fisher and Alan Sharp  in their book Getting It Done: How to Lead When Youre Not in Charge, the more it is taken as a personal indictment. Again, Pixar has this process down pat. When criticising early versions of a film, the Pixar team knows theyre dealing with work that reflects strongly on the artists behind it. To avoid egos and hurt feelings getting in the way of improving the movie, criticism is always clearly aimed at the film itself, rather than its makers. Team management made simple. Get started with MeisterTask Its free! Get started with MeisterTask Start with the Negatives When youre delivering negative news, theres one more thing to remember: if youve ever heard of the shit sandwich approach, nows the time to discard it. The idea of sandwiching bad news between two bits of positive news sounds great in theory, but doesnt work in practice. Evolution has primed us to respond to and remember negative events more strongly, since theyre more often related to life-or-death danger than positive events. A close run-in with a tiger, for instance, would have stuck in our ancestors minds more strongly than a nice meal. They needed to learn from the encounter with the tiger and avoid it happening again, so their brains remembered it vividly. Fortunately, we rarely face life-or-death dangers these days. Unfortunately, we still react more strongly to negative events. Which is why criticism stings so harshly, and we have a hard time letting go of negative experiences. This is why the shit sandwich doesnt work: sandwiching the bad news isnt enough to overcome our natural tendencies to focus on it. The good news is, theres another approach that might work. According to Roy F. Baumeister, professor of social psychology at Florida State University, many  good events can overcome the psychological effects of one bad event in our mind. Because it takes many positives to outweigh negatives, Clifford Nass, professor of communication at Stanford University, and author of The Man Who Lied to His Laptop  suggests  starting with the bad news first, then following it up with lots of positives. This helps to overwhelm the employees brain with good vibes, so they cant dwell on the bad feedback. Be Empathetic Speaking of egos, we all know how much it hurts to get bad feedback on something youve done. Whether its your work, a suggestion you offered in a meeting, or a joke that doesnt land, no one likes the feeling that we could have done better. When youre offering feedback to an employee, remember this. Marcia Reynolds, author of The Discomfort Zone: How Leaders Turn Difficult Conversations into Breakthroughs  says  we need to be empathetic when discussing feedback. Even if you disagree with their perspective, she says, honor the human in front of you. To ensure the process is respectful and useful to everyone involved, feedback discussions need to be a two-way conversation, not a lecture. Liane Davey, author of You First: Inspire Your Team to Grow Up, Get Along, and Get Stuff Done, says  to avoid making the mistake of attributing intent, and instead to just focus on the impact of the behavior. Its all too easy to assume we know why  someone made a particular decision, but without asking and truly listening, we cant know for sure. Rather than making harmful assumptions, be open to hearing your employees point of view. Davey suggests asking open-ended questions to learn how your employee took the feedback, whether theyve understood you clearly, and what they plan to do differently next time. Amy Gallo agrees that checking for understanding should be part of your process. She also suggests you and your team member agree on clear next steps and a fair way to measure progress. One final thought: Castelda, who leads a training program on delivering difficult messages, suggests managers keep in mind the positive reasons for providing feedback. If youre finding a conversation difficult or nerve-wracking, remember that your aim in providing feedback is to help your team members succeed and grow. Research shows  53% of managers avoid difficult conversations due to lack of training in how to handle those moments effectively. A 2014 study  also found 43% of managers felt that offering corrective feedback was a stressful and difficult experience. If you fit into either of those groups, I hope this research will prove helpful in approaching future feedback sessions. And if nothing else, remember that youre dealing with another human being, and do your best to be empathetic to their point of view. Communicate. Collaborate. Create. Try MeisterTask Its free! Try MeisterTask

The Federalists And Democratic Republicans - 1434 Words

From 1789 to 1816, the Federalists and Democratic-Republicans approached many problems differently, sometimes however, they had the same solutions to problems which were posed by England and the Native Americans. The Federalists and Democratic-Republicans both had different and sometimes similar viewpoints on how to solve the problems they faced during this particular time period. Federalists supported a strong, huge government that had a loose constriction of the constitution. They also supported the National Bank, exercise tax. Also, they thought tariffs should be high, and they believed in an industrial world filled with huge businesses and mass production of goods. However, the Democratic- Republicans wanted a more agrarian culture. They did not want a huge government, National bank, excise taxes, and they wanted the tariffs to be low. Some difficulties that the two parties faced were that the British created were impressments of sailors, assisting the Native Americans in war aga inst the United States, and the Orders in Council of 1805. The Native Americans also generated problems for America because they resisted land expansion. Because of their standards and beliefs, this shows how the two parties faced these particular problems that were caused by Britain and the Native Americans. Therefore, the Federalists and Democratic-Republicans solved problems differently, but sometimes they had the same idea to work together in order to effectively fix both of the parties’Show MoreRelatedFederalists vs. Democratic Republicans922 Words   |  4 Pagesthat was supposed to preserve our freedoms and certain liberties. All Americans at that time wanted to keep America a free an independent nation with rights for its people. However there was two different groups, the Federalists lead by Alexander Hamilton and the Democratic-Republicans led by Thomas Jefferson, which thought this could be achieved in very different ways. Thomas Jefferson and Alexander Hamilton were very different in their methods to try and develop America as a nation. The twoRead MoreFederalists vs. Democratic-Republicans Essay743 Words   |  3 Pagesgovernment grew and the nation prospered, the rise of leaders and political figures came about and with this, conflicting principles and ideology spawned, thus creating the first of the political parties; the Federalists and the Democratic-Republicans. Although the Federalists and the Democratic-Republicans ideology and stances on the power of the federal government, domestic economic policies and the group of constituents they represented differed vastly, members of both parties often compromised theirRead MoreFederalists vs. Democratic Republicans Essay484 Words   |  2 PagesFederalists vs. Democratic Republicans George Washington himself wanted to avoid a party system in America. Unfortunately, even when saying this he was part of the beginning of one of the first parties in United States politics. There have been many different parties surface since the beginning of the American political system. They all have different thoughts, policies, and motivations. Each party has come and gone, some have made significant contributions and others have not. The first splitRead MoreReform Of Action : Federalists Vs Democratic Republican1440 Words   |  6 PagesPlan of Action: Federalists vs Democratic-Republican From 1789 to 1816, the Federalists and Democratic-Republicans approached many problems differently, sometimes however, they had the same solutions to problems which were posed by England and the Native Americans. The Federalists and Democratic-Republicans both had different and sometimes similar viewpoints on how to solve the problems they faced during this particular time period. Federalists supported a strong, huge government that had a looseRead More1998 Dbq1014 Words   |  5 Pageson government and the Constitution. The Democratic Republicans, led by Thomas Jefferson and James Madison, were always characterized by following the strict construction of the constitution. The Federalists, led by Alexander Hamilton, were characterized by following the broad construction of the constitution. The presidencies of Jefferson and Madison proved this characterization to be somewhat accurate. Although the Democratic Republicans and the Federalists did support their own ideas and views,Read MoreThe First American Party System Essay1646 Words   |  7 PagesIn 1794, the major political parties were the Federalists and the Democratic-Republicans. The major difference between these two was that the Federalists favored a strong central government, while the Democratic-Republicans preferred a central government with limited power and more state control. At the time of the election, it seemed that the prominent, distinguished Federalist Party clearly had the upper hand, but in the end the Democratic-Republican candidate ended up winning. Despite the factRead MoreThe Federalist And The Anti Federalist864 Words   |  4 PagesIn America today there are many political parties which include the Democrats and the Republicans. The beginning of political parties started in 1787 with the federalist, then later on the anti-federalist in 1796. Alexander Hamilton was the leader of the federalist party. Thomas Jefferson was the leader of the anti-federalist; who called themselves the Democratic-Republicans. Our first president, George Washington warned us about having parties and the danger of them. However, not until CongressRead MoreEssay on American Political Parties1589 Words   |  7 Pagespossible. During the time when the Constitution was being debated over the first two political parties surfaced in the United States, the Federalists, and the Anti-Federalists. After the Constitution was ratified the Anti-Federalists, led by Thomas Jefferson, became the Democratic Republicans. The war of 1812 ended the Federalist Party. The Democratic Republicans began to split over issues and some supported Andrew Jacksons policies and became known as Democrats. Those who opposed Andrew JacksonsRead MoreBeliefs and Ideals of Democrats and Republicans954 Words   |  4 Pagesï » ¿Decisions and Actions Democratic-Republican Partys Beliefs and Ideals Federalist Partys Beliefs and Ideals Initiated the first Barbary War Aligned most with the Federalists party because it was a display of national power. They were terrified of a strong national government. They were strong believers of a central government Bought the Louisiana Purchase Aligned most with the Federalist party because they believed in expanding national power by expanding their territory and property. TheyRead MoreMadison And Jeffersons Federalist Ideas Essay968 Words   |  4 PagesStates. The Federalist and Democratic-Republican parties were in strong opposition of one another. Though the Republicans were usually characterized as strict constructionists, who were opposed to the broad constructionism of the Federalists, both Jefferson and Madisons presidencies highlighted Federalist ideals in many of their decisions. This included Jeffersons unconstitutional decision in purchasing the vast Louisiana territory and MadisonsÂ… The standard Democratic-Republican had many beliefs

Essay on Saint Augustine of Hippo - 810 Words

As one of the most prominent figures of the early church, Saint Augustine is not only recognized for his leadership but also for his knowledge and influence on the thinking and doctrine of the Christian Church. As a priest, he was an important leader of the early African Church; as a philosopher, he brought a new approach to Church Doctrine through the ideas of pagan philosophy (TeSelle 892). These accomplishments put him among the ranks of Thomas Aquinas and other great Church philosophers whose ideas revolutionized the Church. Because of his accomplishments and influence, Augustine was named a Doctor of the Church. Aurilius Augustine was born in Tagaste in 354 A.D. to a pagan father and a saintly mother. His father, although poor and†¦show more content†¦This duelist sect believed in the Devine God who was the embodiment of everything good and an equal evil power. They also believed that the flesh was inherently evil. In the next few years after settling his beliefs with M anechaeism and realizing its faults, Augustine would fall into believing in several other non-Christian movements (Brown 31). After being encouraged to do so by many of his friends, he read many of the writings of the Greek philosophers known as neoplatonists. Along with the sermons of Saint Ambrose, the bishop of Milan, these writings convinced Augustine to contemplate his return to the Christian faith. Eventually he overcame his numerous encounters with heresy, and was baptized into the Catholic Church in the year 387 (Brown 43). From this point on, Augustine became a great leader in the Church, eventually becoming bishop o Hippo. After the death of his mother, Monica, Augustine moved back to his Africa where he entered the monastic life and started a monastery (TeSelle 892). He soon joined the priesthood, and after only four years the people of Hippo elected him to be their bishop (Brown 78). At this point in his life, Augustine is recognized for doing many things for the Chur ch as a priest, author, and defender of faith. As an author he wrote Confessions, his spiritual autobiography, and City of God, his great work describing the Christian philosophy throughout history. In this magnificent work,Show MoreRelatedSaint Augustine Of Hippo And Saint Thomas Aquinas1590 Words   |  7 Pageshave transformed, faded, and attempted to bring concrete answers to questions regarding human life. Saint Augustine of Hippo and Saint Thomas Aquinas are considered to be the greatest of their times, and are influential in understanding current Christian Church teachings along with philosophical teachings in general. The keystone work of Saint Augustine must be his very personal Confessions while Saint Thomas Aquinas’s keystone work must be his renowned Summa Theologiae. These two works are regardedRead MoreBiography Of Saint Augustine Of Hippo1163 Words   |  5 PagesSaint Augustine of Hippo lived his life always striving to excel in whatever he did. His accompli shments are woven into today’s society as his influence was one of the most powerful. A man of such importance that his thoughts influenced the way people of his time and people today think and perceive the world. He is known as being one of the most important people involved in the development of Western Christianity. Born as Aurelius Augustinus on November 13th, 354 in what is present day Tagaste, heRead MoreSaint Augustine Of Hippo Once Stated1247 Words   |  5 PagesSaint Augustine of Hippo once stated, â€Å"The world is a book and those who do not travel read only one page.† It was after stumbling across this statement that I was influenced to call up my friend and suggest a road trip. When we started off, it was a beautiful day. The bright morning sun peeked over the Appalachian mountains to bid us farewell as we packed our belongings into the 2011 Chevy Cruze. Dew still perched on the delicate leaves of various summer flowers while we rode down the road towardsRead MoreThe Hero and the Saint: Paul and Augustine656 Words   |  3 PagesThe Hero and the Saint: Paul and Augustine The idea of the hero in Greco-Roman culture was integrated into the idea of the saint (in the process of conversion and totalization) by way of Christianitys adoption of and ancestry in the Greco-Roman culture. As Professor Ambrosio indicates, The need and the search for meaning is shared by all human beings (Hero or Saint Saul of Tarsus). Thus, it is no surprise to find that a pagan Greco-Roman title is applicable to a Christian whose virtue is viewedRead MoreSt. Augustine s Life1283 Words   |  6 PagesMany saints were first some of the most frequent sinners. How could a leopard rub off all of his spots? Can people truly change their ways? Stories of conversion may seem unlikely, but for some they are pure fact. One of the most renowned stories of conversion is the one of Saint Augustine. Saint Augustine of Hippo by his own omission started his life in a circle of lust, pride, and vanity. He says in his book Confessions, â€Å"here proud, there superstitious, everywhere va in.† Saint Augustine’sRead MoreAnalysis Of Aurelius Augustine : A Treatise On The Gift Of Perseverance786 Words   |  4 PagesIn an attempt to refute the views of a theologian named Pelagius, Aurelius Augustine published a work entitled â€Å"A Treatise on the Gift of Perseverance†, and in this work he explains a view on the gift of perseverance that is not fully in line with what scripture teaches. First I will describe Augustines ideals and stance on Perseverance of the Saints. I will continue by describing that his stance on this topic matter is not entirely coherent with scripture, and then show the overall result his doctrineRead MoreEssay on Saint Augustine970 Words   |  4 Pages Saint Augustine was born on 354 CE in Tagaste, Africa. His given name was Aurelius Augustinus. His father was Patricius, a pagan who was baptized Christian before he died, and his mother was Monica, a baptized Christian with an influential role in the life of her son. Augustine is regarded as one of the most intelligent Christian theologians and bishops of all time. His works and actions have left a major imprint on the Church and its doctrine. As a boy, Augustine was not baptized andRead MoreSt. Augustine of Hippo, Bishop and Theologian Essay1693 Words   |  7 Pages St. Augustine, Bishop of Hippo, was one of the greatest theologians of his time. He is still regarded in the highest manner. He was raised in a divided home, but through time he found the truth. He was always a superb student. He fully mastered Latin; however, he never grasped Greek. He was also very crafty in speech - a black-belt of rhetoric if you will. After his teenage flings and rebellions, he found a heretical sect in which he became involved for a while. He traveled and landedRead MoreSaint Augustine Essays719 Words   |  3 PagesSaint Augustine Saint Augustine, b. Nov. 13, 354, d. Aug. 28, 430, was one of the foremost philosopher-theologians of early Christianity and, while serving (396-430) as bishop of Hippo Regius, the leading figure in the church of North Africa. He had a profound influence on the subsequent development of Western thought and culture and, more than any other person, shaped the themes and defined the problems that have characterized the Western tradition of Christian Theology. Among his many writingsRead MoreEssay about St. Augustine916 Words   |  4 Pages Saint Augustine of Hippo Theologians, Biblical scholars and Christians all over the world often wrestle with two extremely important questions about their faith. These questions are, quot;What is God like?quot; and quot;How should we live in response to God?quot; Some feel that we need others to direct us, some feel we need them to challenge us, but everyone agrees that we need others. That is exactly how Saint Augustine struggles to find his faith and beliefs. He found it extremely difficult

Street Light Free Essays

string(56) " and referencing the position of a building to the Sun\." INDEX |S. NO |TITLE |PAGE NO | |1 |Introduction |1 | |2 |Solar Energy |4 | |3 |Photovoltaics |24 | |4 |Solar Cell |28 | |5 |Solar Roadway |51 | |6 |Component description |55 | |7 |Working of Project |82 | |8 |Conclusion |86 | |9 |Images |91 | |10 |Bibliography |93 | INTRODUCTION INTRODUCTION: Solar energy, radiant light and heat from the sun, has been harnessed by humans since ancient times using a range of ever-evolving technologies. Solar energy technologies include solar heating, solar photovoltaics, solar thermal electricity and solar architecture, which can make considerable contributions to solving some of the most urgent energy problems the world now faces. We will write a custom essay sample on Street Light or any similar topic only for you Order Now Solar power is the conversion of sunlight into electricity, either directly using photovoltaic (PV), or indirectly using concentrated solar power (CSP). Concentrated solar power systems use lenses or mirrors and tracking systems to focus a large area of sunlight into a small beam. Photovoltaics convert light into electric current using the photoelectric effect. A Street light, lamppost, street lamp, light standard, or lamp standard is a raised source of light on the edge of a road or walkway, which is turned on or lit at a certain time every night. Modern lamps may also have light-sensitive photocells to turn them on at dusk, off at dawn, or activate automatically in dark weather. In older lighting this function would have been performed with the aid of a solar dial. It is not uncommon for street lights to be on posts which have wires strung between them; such as on telephone poles or utility poles. New street lighting technologies, such as LED or induction lights, emit a white light that provides high levels of scotopic lumens allowing street lights with lower wattages and lower photopic lumens to replace existing street lights. Photovoltaic-powered LED luminaires are gaining wider acceptance. Preliminary field tests show that some LED luminaires are energy-efficient and perform well in testing environments. This project is a LED based Solar Lights is an automatic street lightening system using a LDR and 6V/5W solar panel. During day time, the internal rechargeable battery receives charging current from the connected solar panel. Here IC 555 is wired as a medium current inverting line driver, switched by an encapsulated light detector (LDR). When ambient light dims, the circuits drive the white LEDs. When the ambient light level restores, circuit returns to its idle state and light(s) switched off by the circuit. Block Diagram: SOLAR ENERGY SOLAR ENERGY Solar energy, radiant light and heat from the sun, has been harnessed by humans since ancient times using a range of ever-evolving technologies. Solar energy technologies include solar heating, solar photovoltaics, solar thermal electricity, solar architecture and artificial photosynthesis, which can make considerable contributions to solving some of the most urgent energy problems the world now faces. Solar technologies are broadly characterized as either passive solar or active solar depending on the way they capture, convert and distribute solar energy. Active solar techniques include the use of photovoltaic panels and solar thermal collectors to harness the energy. Passive solar techniques include orienting a building to the Sun, selecting materials with favorable thermal mass or light dispersing properties, and designing spaces that naturally circulate air. In 2011, the International Energy Agency said that â€Å"the development of affordable, inexhaustible and clean solar energy technologies will have huge longer-term benefits. It will increase countries’ energy security through reliance on an indigenous, inexhaustible and mostly import-independent resource, enhance sustainability, reduce pollution, lower the costs of mitigating climate change, and keep fossil fuel prices lower than otherwise. These advantages are global. Hence the additional costs of the incentives for early deployment should be considered learning investments; they must be wisely spent and need to be widely shared†. The Earth receives 174 petawatts (PW) of incoming solar radiation (insolation) at the upper atmosphere. Approximately 30% is reflected back to space while the rest is absorbed by clouds, oceans and land masses. The spectrum of solar light at the Earth’s surface is mostly spread across the visible and near-infrared ranges with a small part in the near-ultraviolet. Earth’s land surface, oceans and atmosphere absorb solar radiation, and this raises their temperature. Warm air containing evaporated water from the oceans rises, causing atmospheric circulation or convection. When the air reaches a high altitude, where the temperature is low, water vapor condenses into clouds, which rain onto the Earth’s surface, completing the water cycle. The latent heat of water condensation amplifies convection, producing atmospheric phenomena such as wind, cyclones and anti-cyclones. Sunlight absorbed by the oceans and land masses keeps the surface at an average temperature of 14  °C. By photosynthesis green plants convert solar energy into chemical energy, which produces food, wood and the biomass from which fossil fuels are derived. The total solar energy absorbed by Earth’s atmosphere, oceans and land masses is approximately 3,850,000 exajoules (EJ) per year. In 2002, this was more energy in one hour than the world used in one year. Photosynthesis captures approximately 3,000 EJ per year in biomass. The technical potential available from biomass is from 100–300 EJ/year. The amount of solar energy reaching the surface of the planet is so vast that in one year it is about twice as much as will ever be obtained from all of the Earth’s non-renewable resources of coal, oil, natural gas, and mined uranium combined. Solar energy can be harnessed at different levels around the world, mostly depending on distance from the equator. [pic] Average insolation showing land area (small black dots) required to replace the world primary energy supply with solar electricity. 18 TW is 568 Exajoule (EJ) per year. Insolation for most people is from 150 to 300 W/m2 or 3. 5 to 7. 0 kWh/m2/day. Solar energy refers primarily to the use of solar radiation for practical ends. However, all renewable energies, other than geothermal and tidal, derive their energy from the sun. Solar technologies are broadly characterized as either passive or active depending on the way they capture, convert and distribute sunlight. Active solar techniques use photovoltaic panels, pumps, and fans to convert sunlight into useful outputs. Passive solar techniques include selecting materials with favorable thermal properties, designing spaces that naturally circulate air, and referencing the position of a building to the Sun. You read "Street Light" in category "Essay examples" Active solar technologies increase the supply of energy and are considered supply side technologies, while passive solar technologies reduce the need for alternate resources and are generally considered demand side technologies. APPLICATIONS OF SOLAR TECHNOLOGY Average  insolation  showing land area (small black dots) required to replace the world primary energy supply with solar electricity. 18 TW is 568 Exajoule (EJ) per year. Insolation for most people is from 150 to 300 W/m2  or 3. 5 to 7. 0 kWh/m2/day. Solar energy refers primarily to the use of  solar radiation  for practical ends. However, all renewable energies, other than  geothermal  and  tidal, derive their energy from the sun. Solar technologies are broadly characterized as either passive or active depending on the way they capture, convert and distribute sunlight. Active solar techniques use photovoltaic panels, pumps, and fans to convert sunlight into useful outputs. Passive solar techniques include selecting materials with favorable thermal properties, designing spaces that naturally circulate air, and referencing the position of a building to the Sun. Active solar technologies increase the supply of energy and are considered  supply side technologies, while passive solar technologies reduce the need for alternate resources and are generally considered demand side technologies ARCHITECTURE AND URBAN PLANNING [pic] Darmstadt University of Technology  in Germany  won the 2007  Solar Decathlon  in Washington, D. C. with this  passive house designed specifically for the humid and hot subtropical climate. Sunlight has influenced building design since the beginning of architectural history. Advanced solar architecture and urban planning methods were first employed by the  Greeks  and  Chinese, who oriented their buildings toward the south to provide light and warmth. The common features of  passive solar  architecture are orientation relative to the Sun, compact proportion (a low surface area to volume ratio), selective shading (overhangs) and  thermal mass. When these features are tailored to the local climate and environment they can produce well-lit spaces that stay in a comfortable temperature range. Socrates’  Megaron House is a classic example of passive solar design. The most recent approaches to solar design use computer modeling tying together  solar lighting,  heating  and  ventilation  systems in an integrated  solar design  package. Active solar equipment such as pumps, fans and switchable windows can complement passive design and improve system performance. Urban heat islands (UHI) are metropolitan areas with higher temperatures than that of the surrounding environment. The higher temperatures are a result of increased absorption of the Solar light by urban materials such as asphalt and concrete, which have lower  albedos  and higher  heat capacities  than those in the natural environment. A straightforward method of counteracting the UHI effect is to paint buildings and roads white and plant trees. Using these methods, a hypothetical â€Å"cool communities† program in  Los Angeles  has projected that urban temperatures could be reduced by approximately 3  Ã‚ °C at an estimated cost of US$1  billion, giving estimated total annual benefits of US$530  million from reduced air-conditioning costs and healthcare savings. [23] AGRICULTURE AND HORTICULTURE [pic] Greenhouses  like these in the Westland municipality of the  Netherlands  grow vegetables, fruits and flowers. Agriculture  and  horticulture  seek to optimize the capture of solar energy in order to optimize the productivity of plants. Techniques such as timed planting cycles, tailored row orientation, staggered heights between rows and the mixing of plant varieties can improve crop yields. [24][25]  While sunlight is generally considered a plentiful resource, the exceptions highlight the importance of solar energy to agriculture. During the short growing seasons of the  Little Ice Age, French and  English  farmers employed fruit walls to maximize the collection of solar energy. These walls acted as thermal masses and accelerated ripening by keeping plants warm. Early fruit walls were built perpendicular to the ground and facing south, but over time, sloping walls were developed to make better use of sunlight. In 1699,  Nicolas Fatio de Duillier  even suggested using a  tracking mechanism  which could pivot to follow the Sun. [26]  Applications of solar energy in agriculture aside from growing crops include pumping water, drying crops, brooding chicks and drying chicken manure. [27][28]  More recently the technology has been embraced by vinters, who use the energy generated by solar panels to power grape presses. [29] Greenhouses  convert solar light to heat, enabling year-round production and the growth (in enclosed environments) of specialty crops and other plants not naturally suited to the local climate. Primitive greenhouses were first used during Roman times to produce  cucumbers  year-round for the Roman emperor  Tiberius. [30]  The first modern greenhouses were built in Europe in the 16th century to keep exotic plants brought back from explorations abroad. [31]  Greenhouses remain an important part of horticulture today, and plastic transparent materials have also been used to similar effect in  polytunnels  and  row covers. TRANSPORT AND RECONNAISSANCE [pic] Australia hosts the  World Solar Challengewhere solar cars like the Nuna3 race through a 3,021  km (1,877  mi) course from Darwin to Adelaide. Development of a solar powered car has been an engineering goal since the 1980s. The  World Solar Challenge  is a biannual solar-powered car race, where teams from universities and enterprises compete over 3,021 kilometres (1,877  mi) across central Australia from  Darwin  to  Adelaide. In 1987, when it was founded, the winner’s average speed was 67 kilometres per hour (42  mph) and by 2007 the winner’s average speed had improved to 90. 87 kilometres per hour (56. 46  mph). [32]  The  North American Solar Challenge  and the planned  South African Solar Challenge  are comparable competitions that reflect an international interest in the engineering and development of solar powered vehicles. [33][34] Some vehicles use solar panels for auxiliary power, such as for air conditioning, to keep the interior cool, thus reducing fuel consumption. [35][36] In 1975, the first practical solar boat was constructed in England. [37]  By 1995, passenger boats incorporating PV panels began appearing and are now used extensively. [38]  In 1996,  Kenichi Horie  made the first solar powered crossing of the Pacific Ocean, and the  sun21  catamaran made the first solar powered crossing of the Atlantic Ocean in the winter of 2006–2007. [39]  There are plans to circumnavigate the globe in 2010. [40] [pic] Helios UAV  in solar powered flight. In 1974, the unmanned  AstroFlight Sunrise  plane made the first solar flight. On 29 April 1979, the  Solar Riser  made the first flight in a solar powered, fully controlled, man carrying flying machine, reaching an altitude of 40 feet (12  m). In 1980, the  Gossamer Penguin  made the first piloted flights powered solely by photovoltaics. This was quickly followed by the  Solar Challenger  which crossed the English Channel in July 1981. In 1990  Eric Scott Raymond  in 21 hops flew from California to North Carolina using solar power. [41]  Developments then turned back to unmanned aerial vehicles (UAV) with the  Pathfinder  (1997) and subsequent designs, culminating in the  Helios  which set the altitude record for a non-rocket-propelled aircraft at 29,524 metres (96,864  ft) in 2001. 42]  The  Zephyr, developed by  BAE Systems, is the latest in a line of record-breaking solar aircraft, making a 54-hour flight in 2007, and month-long flights are envisioned by 2010. [43] A  solar balloon  is a black balloon that is filled w ith ordinary air. As sunlight shines on the balloon, the air inside is heated and expands causing an upward  buoyancy  force, much like an artificially heated  hot air balloon. Some solar balloons are large enough for human flight, but usage is generally limited to the toy market as the surface-area to payload-weight ratio is relatively high. [44] DAYLIGHTING [pic] Daylighting features such as this  oculusat the top of the  Pantheon, in  Rome, Italy have been in use since antiquity. The history of lighting is dominated by the use of natural light. The Romans recognized a  right to light  as early as the  6th century  and English law echoed these judgments with the Prescription Act of 1832. [45][46]  In the 20th century artificial  lighting  became the main source of interior illumination but daylighting techniques and hybrid solar lighting solutions are ways to reduce energy consumption. Daylighting  systems collect and distribute sunlight to provide interior illumination. This passive technology directly offsets energy use by replacing artificial lighting, and indirectly offsets non-solar energy use by reducing the need for  air-conditioning. 47]  Although difficult to quantify, the use of  natural lighting  also offers physiological and psychological benefits compared to  artificial lighting. [47]  Daylighting design implies careful selection of window types, sizes and orientation; exterior shading devices may be considered as well. Deciduous trees at the east and west ends of buildings offer shade in the summer and do not block the sun in the winter. [48]  Individual features include sawtooth roofs,  clerestory windows, light shelves,  skylights  and  light tubes. They may be incorporated into existing structures, but are most effective when integrated into a  solar design  package that accounts for factors such as  glare, heat flux and  time-of-use. When daylighting features are properly implemented they can reduce lighting-related energy requirements by 25%. [49] Hybrid solar lighting  (HSL) is an  active solar  method of providing interior illumination. HSL systems collect sunlight using focusing mirrors that  track the Sun  and use  optical fibers  to transmit it inside the building to supplement conventional lighting. In single-story applications these systems are able to transmit 50% of the direct sunlight received. [50] Solar lights that charge during the day and light up at dusk are a common sight along walkways. [51]  Solar-charged lanterns have become popular in developing countries where they provide a safer and cheaper alternative to kerosene lamps. [52] Although  daylight saving time  is promoted as a way to use sunlight to save energy, recent research reports contradictory results: several studies report savings, but just as many suggest no effect or even a net loss, particularly when  gasoline  consumption is taken into account. Electricity use is greatly affected by geography, climate and economics, making it hard to generalize from single studies. [53] SOLAR THERMAL Solar thermal technologies can be used for water heating, space heating, space cooling and process heat generation. [54] WATER HEATING [pic] Solar water heaters facing the  Sun  to maximize gain. Solar hot water systems use sunlight to heat water. In low geographical latitudes (below 40  degrees) from 60 to 70% of the domestic hot water use with temperatures up to 60  Ã‚ °C can be provided by solar heating systems. [55]  The most common types of solar water heaters are evacuated tube collectors (44%) and glazed flat plate collectors (34%) generally used for domestic hot water; and unglazed plastic collectors (21%) used mainly to heat swimming pools. [56] As of 2007, the total installed capacity of solar hot water systems is approximately 154  GW. [57]  China is the world leader in their deployment with 70  GW installed as of 2006 and a long term goal of 210  GW by 2020. [58]  Israel  and  Cyprus  are the per capita leaders in the use of solar hot water systems with over 90% of homes using them. 59]  In the United States, Canada and Australia heating swimming pools is the dominant application of solar hot water with an installed capacity of 18  GW as of 2005. [18] HEATING, COOLING AND VENTILATION [pic] Solar House #1 of  Massachusetts Institute of Technology  in the United States, built in 1939, used  Seasonal thermal energy storage (STES)  for year-round heating. In the United States,  heating, ventilation and air conditioning  (HVAC) systems account for 30% (4. 65  EJ) of the energy used in commercial buildings and nearly 50% (10. 1  EJ) of the energy used in residential buildings. [49][60]  Solar heating, cooling and ventilation technologies can be used to offset a portion of this energy. Thermal mass is any material that can be used to store heat—heat from the Sun in the case of solar energy. Common thermal mass materials include stone, cement and water. Historically they have been used in arid climates or warm temperate regions to keep buildings cool by absorbing solar energy during the day and radiating stored heat to the cooler atmosphere at night. However they can be used in cold temperate areas to maintain warmth as well. The size and placement of thermal mass depend on several factors such as climate, daylighting and shading conditions. When properly incorporated, thermal mass maintains space temperatures in a comfortable range and reduces the need for auxiliary heating and cooling equipment. [61] A solar chimney (or thermal chimney, in this context) is a passive solar ventilation system composed of a vertical shaft connecting the interior and exterior of a building. As the chimney warms, the air inside is heated causing an  updraft  that pulls air through the building. Performance can be improved by using glazing and thermal mass materials[62]  in a way that mimics greenhouses. Deciduous  trees and plants have been promoted as a means of controlling solar heating and cooling. When planted on the southern side of a building, their leaves provide shade during the summer, while the bare limbs allow light to pass during the winter. [63]  Since bare, leafless trees shade 1/3 to 1/2 of incident solar radiation, there is a balance between the benefits of summer shading and the corresponding loss of winter heating. 64]  In climates with significant heating loads, deciduous trees should not be planted on the southern side of a building because they will interfere with wint er solar availability. They can, however, be used on the east and west sides to provide a degree of summer shading without appreciably affecting winter solar gain. [65] WATER TREATMENT [pic] Solar water disinfection  in  Indonesia [pic] Small scale solar powered sewerage treatment plant. Solar distillation can be used to make  saline  or  brackish water  potable. The first recorded instance of this was by 16th century Arab alchemists. [66]  A large-scale solar distillation project was first constructed in 1872 in the  Chilean  mining town of Las Salinas. 67]  The plant, which had solar collection area of 4,700  m2, could produce up to 22,700  L  per day and operated for 40  years. [67]  Individual  still  designs include single-slope, double-slope (or greenhouse type), vertical, conical, inverted absorber, multi-wick, and multiple effect. [66]  These stills can operate in passive, active, or hybrid modes. Double-slope stills are the most economica l for decentralized domestic purposes, while active multiple effect units are more suitable for large-scale applications. [66] Solar water  disinfection  (SODIS) involves exposing water-filled plastic  polyethylene terephthalate  (PET) bottles to sunlight for several hours. 68]  Exposure times vary depending on weather and climate from a minimum of six hours to two days during fully overcast conditions. [69]  It is recommended by theWorld Health Organization  as a viable method for household water treatment and safe storage. [70]  Over two million people in developing countries use this method for their daily drinking water. [69] Solar energy may be used in a water stabilisation pond to treat  waste water  without chemicals or electricity. A further environmental advantage is thatalgae  grow in such ponds and consume  carbon dioxide  in photosynthesis, although algae may produce toxic chemicals that make the water unusable. [71][72] COOKING [pic] The Solar Bowl in  Auroville,  India, concentrates sunlight on a movable receiver to produce  steam  for  cooking. Solar cookers use sunlight for cooking, drying and  pasteurization. They can be grouped into three broad categories: box cookers, panel cookers and reflector cookers. [73]  The simplest solar cooker is the box cooker first built by  Horace de Saussure  in 1767. [74]  A basic box cooker consists of an insulated container with a transparent lid. It can be used effectively with partially overcast skies and will typically reach temperatures of 90–150  Ã‚ °C. [75]Panel cookers use a reflective panel to direct sunlight onto an insulated container and reach temperatures comparable to box cookers. Reflector cookers use various concentrating geometries (dish, trough, Fresnel mirrors) to focus light on a cooking container. These cookers reach temperatures of 315  Ã‚ °C and above but require direct light to function properly and must be repositioned to track the Sun. [76] The  solar bowl  is a concentrating technology employed by the Solar Kitchen at  Auroville, in  Tamil Nadu,  India, where a stationary spherical reflector focuses light along a line perpendicular to the sphere’s interior surface, and a computer control system moves the receiver to intersect this line. Steam is produced in the receiver at temperatures reaching 150  Ã‚ °C and then used for process heat in the kitchen. [77] A reflector developed by  Wolfgang Scheffler  in 1986 is used in many solar kitchens. Scheffler reflectors are flexible parabolic dishes that combine aspects of trough and power tower concentrators. Polar tracking  is used to follow the Sun’s daily course and the curvature of the reflector is adjusted for seasonal variations in the incident angle of sunlight. These reflectors can reach temperatures of 450–650  Ã‚ °C and have a fixed focal point, which simplifies cooking. [78]  The world’s largest Scheffler reflector system in Abu Road,  Rajasthan, India is capable of cooking up to 35,000 meals a day. [79]As of 2008, over 2,000 large Scheffler cookers had been built worldwide. [80] PROCESS HEAT Solar concentrating technologies such as parabolic dish, trough and Scheffler reflectors can provide process heat for commercial and industrial applications. The first commercial system was the  Solar Total Energy Project  (STEP) in Shenandoah, Georgia, USA where a field of 114 parabolic dishes provided 50% of the process heating, air conditioning and electrical requirements for a clothing factory. This grid-connected cogeneration system provided 400  kW of electricity plus thermal energy in the form of 401  kW steam and 468  kW chilled water, and had a one hour peak load thermal storage. [81] Evaporation ponds are shallow pools that concentrate dissolved solids through  evaporation. The use of evaporation ponds to obtain salt from sea water is one of the oldest applications of solar energy. Modern uses include concentrating brine solutions used in leach mining and removing dissolved solids from waste streams. [82] Clothes lines,  clotheshorses, and clothes racks dry clothes through evaporation by wind and sunlight without consuming electricity or gas. In some states of the United States legislation protects the â€Å"right to dry† clothes. [83] Unglazed transpired collectors (UTC) are perforated sun-facing walls used for preheating ventilation air. UTCs can raise the incoming air temperature up to 22  Ã‚ °C and deliver outlet temperatures of 45–60  Ã‚ °C. [84]  The short payback period of transpired collectors (3 to 12  years) makes them a more cost-effective alternative than glazed collection systems. 84]  As of 2003, over 80 systems with a combined collector area of 35,000  m2  had been installed worldwide, including an 860  m2  collector in  Costa Rica  used for drying coffee beans and a 1,300  m2  collector in  Coimbatore, India used for drying marigolds. [28] ELECTRICITY PRODUCTION [pic] The  PS10  concentrates sunlight from a field of heliostats on a central tower. Solar power is the conversion of sunlight into  electricity, either directly using  photovoltaics  (PV), or indirectly using  concentrated solar power  (CSP). CSP systems use lenses or mirrors and tracking systems to focus a large area of sunlight into a small beam. PV converts light into electric current using the  photoelectric effect. Commercial CSP plants were first developed in the 1980s. Since 1985 the eventually 354 MW  SEGS  CSP installation, in the Mojave Desert of California, is the largest solar power plant in the world. Other large CSP plants include the 150 MW  Solnova Solar Power Station  and the 100 MWAndasol solar power station, both in Spain. The 250 MW  Agua Caliente Solar Project, in the United States, and the 214 MW  Charanka Solar Park  inIndia, are the  world’s largest  photovoltaic plants. Solar projects exceeding 1 GW are being developed, but most of the deployed photovoltaics are in small rooftop arrays of less than 5 kW, which are grid connected using net metering and/or a feed-in tariff. [85] Concentrated solar power Concentrating Solar Power (CSP) systems use lenses or mirrors and tracking systems to focus a large area of sunlight into a small beam. The concentrated heat is then used as a heat source for a conventional power plant. A wide range of concentrating technologies exists; the most developed are the parabolic trough, the concentrating linear fresnel reflector, the Stirling dish and the solar power tower. Various techniques are used to track the Sun and focus light. In all of these systems a  working fluid  is heated by the concentrated sunlight, and is then used for power generation or energy storage. [86] PHOTOVOLTAICS PHOTOVOLTAICS A solar cell, or photovoltaic cell (PV), is a device that converts light into electric current using the photoelectric effect. The first solar cell was constructed by Charles Fritts in the 1880s. In 1931 a German engineer, Dr Bruno Lange, developed a photo cell using silver selenite in place of copper oxide. Although the prototype selenium cells converted less than 1% of incident light into electricity, both Ernst Werner von Siemens and James Clerk Maxwell recognized the importance of this discovery. Following the work of Russell Ohl in the 1940s, researchers Gerald Pearson, Calvin Fuller and Daryl Chapin created the silicon solar cell in 1954. These early solar cells cost 286 USD/watt and reached efficiencies of 4. 5–6%. By 2012 available efficiencies exceed 20% and the maximum efficiency of research photovoltaics is over 40%. OTHERS Besides concentrated solar power and photovoltaics, there are some other techniques used to generated electricity using solar power. These include: †¢Dye-sensitized_solar_cells, Luminescent solar concentrators (a type of concentrated photovoltaics or CPV technology), †¢Biohybrid solar cells, †¢Photon Enhanced Thermionic Emission systems. Development, deployment and economics Beginning with the surge in coal use which accompanied the In dustrial Revolution, energy consumption has steadily transitioned from wood and biomass to fossil fuels. The early development of solar technologies starting in the 1860s was driven by an expectation that coal would soon become scarce. However development of solar technologies stagnated in the early 20th century in the face of the increasing availability, economy, and utility of coal and petroleum. [109] The 1973 oil embargo and 1979 energy crisis caused a reorganization of energy policies around the world and brought renewed attention to developing solar technologies. Deployment strategies focused on incentive programs such as the Federal Photovoltaic Utilization Program in the US and the Sunshine Program in Japan. Other efforts included the formation of research facilities in the US (SERI, now NREL), Japan (NEDO), and Germany (Fraunhofer Institute for Solar Energy Systems ISE). Commercial solar water heaters began appearing in the United States in the 1890s. These systems saw increasing use until the 1920s but were gradually replaced by cheaper and more reliable heating fuels. As with photovoltaics, solar water heating attracted renewed attention as a result of the oil crises in the 1970s but interest subsided in the 1980s due to falling petroleum prices. Development in the solar water heating sector progressed steadily throughout the 1990s and growth rates have averaged 20% per year since 1999. [57] Although generally underestimated, solar water heating and cooling is by far the most widely deployed solar technology with an estimated capacity of 154 GW as of 2007. The International Energy Agency has said that solar energy can make considerable contributions to solving some of the most urgent problems the world now faces: The development of affordable, inexhaustible and clean solar energy technologies will have huge longer-term benefits. It will increase countries’ energy security through reliance on an indigenous, inexhaustible and mostly import-independent resource, enhance sustainability, reduce pollution, lower the costs of mitigating climate change, and keep fossil fuel prices lower than otherwise. These advantages are global. Hence the additional costs of the incentives for early deployment should be considered learning investments; they must be wisely spent and need to be widely shared. In 2011, the International Energy Agency said that solar energy technologies such as photovoltaic panels, solar water heaters and power stations built with mirrors could provide a third of the world’s energy by 2060 if politicians commit to limiting climate change. The energy from the sun could play a key role in de-carbonizing the global economy alongside improvements in energy efficiency and imposing costs on greenhouse gas emitters. The strength of solar is the incredible variety and flexibility of applications , from small scale to big scale†. We have proved †¦ that after our stores of oil and coal are exhausted the human race can receive unlimited power from the rays of the sun. —Frank Shuman, New York Times, July 2, 1916 SOLAR CELL SOLAR CELL A solar cell made from amonocrystalline silicon wafer Solar cells can be used devices such as this portable monocrystalline solar charger. A solar cell (also called a photovoltaic cell) is an electrical device that converts the energy of light directly into electricity by the photovoltaic effect. It is a form of photoelectric cell (in that its electrical characteristics—e. g. urrent, voltage, or resistance—vary when light is incident upon it) which, when exposed to light, can generate and support an electric current without being attached to any external voltage source. The term â€Å"photovoltaic† comes from the Greek (phos) meaning â€Å"light†, and from â€Å"Volt†, the unit of electro-motive force, the volt, which in turn comes from the last name of the Italian physicist Alessandro Volta, inventor of the battery (electrochemical cell). The term â€Å"photo-voltaic† has been in use in English since 1849. Photovoltaics is the field of technology and research related to the practical application of photovoltaic cells in producing electricity from light, though it is often used specifically to refer to the generation of electricity from sunlight. Cells can be described as photovoltaic even when the light source is not necessarily sunlight (lamplight, artificial light, etc. ). In such cases the cell is sometimes used as a photodetector (for example infrared detectors), detecting light or other electromagnetic radiationnear the visible range, or measuring light intensity. The operation of a photovoltaic (PV) cell requires 3 basic attributes: 1. The absorption of light, generating either electron-hole pairs or excitons. 2. The separation of charge carriers of opposite types. 3. The separate extraction of those carriers to an external circuit. In contrast, a solar thermal collector collects heat by absorbing sunlight, for the purpose of either direct heating or indirect electrical power generation. Photoelectrolytic cell† (photoelectrochemical cell), on the other hand, refers either a type of photovoltaic cell (like that developed by A. E. Becquerel and modern dye-sensitized solar cells) or a device that splits water direct ly into hydrogen and oxygen using only solar illumination. FURTHER IMPROVEMENTS In the time since Berman’s work, improvements have brought production costs down under $1 a watt, with wholesale costs well under $2. â€Å"Balance of system† costs are now more than the panels themselves. Large commercial arrays can be built at below $3. 40 a watt,[12][13]  fully commissioned. As the semiconductor industry moved to ever-larger boules, older equipment became available at fire-sale prices. Cells have grown in size as older equipment became available on the surplus market; ARCO Solar’s original panels used cells with 2 to 4  inch (51 to 100  mm) diameter. Panels in the 1990s and early 2000s generally used 5  inch (125  mm) wafers, and since 2008 almost all new panels use 6  inch (150  mm) cells. This material has less efficiency, but is less expensive to produce in bulk. The widespread introduction of  flat screen televisions  in the late 1990s and early 2000s led to the wide availability of large sheets of high-quality glass, used on the front of the panels. In terms of the cells themselves, there has been only one major change. During the 1990s, polysilicon cells became increasingly popular. These cells offer less efficiency than their monosilicon counterparts, but they are grown in large vats that greatly reduce the cost of production. By the mid-2000s, poly was dominant in the low-cost panel market, but more recently a variety of factors has pushed the higher performance mono back into widespread use. CURRENT EVENTS Other technologies have tried to enter the market. First Solar  was briefly the largest panel manufacturer in 2009, in terms of yearly power produced, using a thin-film cell sandwiched between two layers of glass. Since then silicon panels reasserted their dominant position both in terms of lower prices and the rapid rise of Chinese manufacturing, resulting in the top producers being Chinese. By late 2011, efficient production in China, coupled with a drop in European demand due to budgetary turmoil had dropped prices for crystalline solar-based modules further, to about $1. 09[13]  per watt in October 2011, down sharply from the price per watt in 2010. A more modern process, mono-like-multi, aims to offer the performance of mono at the cost of poly, and is in the process of being introduced in 2012[citation needed]. APPLICATIONS [pic] Polycrystalline  photovoltaic cells laminated to backing material in a module [pic] [pic] Polycrystalline photovoltaic cells Solar cells are often electrically connected and encapsulated as a  module. Photovoltaic modules often have a sheet of glass on the front (sun up) side, allowing light to pass while protecting the emiconductor  wafers  from abrasion and impact due to wind-driven debris,  rain,  hail, etc. Solar cells are also usually connected in  series  in modules, creating an additive  voltage. Connecting cells in parallel will yield a higher current; however, very significant problems exist with parallel connections. For example, shadow effects can shut down the weaker (less illuminated) parallel string (a number of series connected cells) causing substantial power loss and even damaging the weaker string because of the excessive  reverse bias  applied to the shadowed cells by their illuminated partners. Strings of series cells are usually handled independently and not connected in parallel, special paralleling circuits are the exceptions. Although modules can be interconnected to create an  array  with the desired peak DC voltage and loading current capacity, using independent MPPTs (maximum power point trackers) provides a better solution. In the absence of paralleling circuits, shunt diodes can be used to reduce the power loss due to shadowing in arrays with series/parallel connected cells. To make practical use of the solar-generated energy, the electricity is most often fed into the electricity grid using inverters (grid-connected  photovoltaic systems); in stand-alone systems, batteries are used to store the energy that is not needed immediately. Solar panels can be used to power or recharge portable devices. THEORY The solar cell works in three steps: 1. Photons  in  sunlight  hit the solar panel and are absorbed by semiconducting materials, such as silicon. 2. Electrons  (negatively charged) are knocked loose from their atoms, causing an electric potential difference. Current starts flowing through the material to cancel the potential and this electricity is captured. Due to the special composition of solar cells, the electrons are only allowed to move in a single direction. 3. An array of solar cells converts solar energy into a usable amount of  direct current  (DC) electricity. EFFICIENCY Solar panels on the International Space Station absorb light from both sides. These Bifacial cells are more efficient and operate at lower temperature than single sided equivalents. The efficiency of a solar cell may be broken down into reflectance efficiency, thermodynamic efficiency, charge carrier separation efficiency and conductive efficiency. The overall efficiency is the product of each of these individual efficiencies. A solar cell usually has a voltage dependent efficiency curve, temperature coefficients, and shadow angles. Due to the difficulty in measuring these parameters directly, other parameters are measured instead: thermodynamic efficiency, quantum efficiency,integrated quantum efficiency, VOC ratio, and fill factor. Reflectance losses are a portion of the quantum efficiency under â€Å"external quantum efficiency†. Recombination losses make up a portion of the quantum efficiency, VOC ratio, and fill factor. Resistive losses are predominantly categorized under fill factor, but also make up minor portions of the quantum efficiency, VOC ratio. The fill factor is defined as the ratio of the actual maximum obtainable power to the product of the open circuit voltage and short circuit current. This is a key parameter in evaluating the performance of solar cells. Typical commercial solar cells have a fill factor ; 0. 70. Grade B cells have a fill factor usually between 0. 4 to 0. 7. 14] Cells with a high fill factor have a low equivalent series resistance and a high equivalent shunt resistance, so less of the current produced by the cell is dissipated in internal losses. Single p–n junction crystalline silicon devices are now approaching the theoretical limiting power efficiency of 33. 7%, noted as the Shockley–Queisser limit in 1961. In the extreme, with an infinite number of layers, the corresponding limit is 86% using concentrated sunlight. [pic] Reported timeline of solar cell energy conversion efficiencies (from National Renewable Energy Laboratory (USA)) MATERIALS [pic] [pic] The  Shockley-Queisser limit  for the theoretical maximum efficiency of a solar cell. Semiconductors with  band gapbetween 1 and 1. eV, or near-infrared light, have the greatest potential to form an efficient cell. (The efficiency â€Å"limit† shown here can be exceeded by  multijunction solar cells. ) Various materials display varying efficiencies and have varying costs. Materials for efficient solar cells must have characteristics matched to the spectrum of available light. Some cells are designed to efficiently convert wavelengths of solar light that reach the Earth surface. However, some solar cells are optimized for light absorption beyond Earth’s atmosphe re as well. Light absorbing materials can often be used in  multiple physical configurations  to take advantage of different light absorption and charge separation mechanisms. Materials presently used for photovoltaic solar cells include  monocrystalline silicon,  polycrystalline silicon,  amorphous silicon,  cadmium telluride, andcopper indium selenide/sulfide. [25][26] Many currently available solar cells are made from bulk materials that are cut into  wafers  between 180 to 240  micrometers thick that are then processed like other semiconductors. Other materials are made as  thin-films  layers, organic  dyes, and organic  polymers  that are deposited on  supporting substrates. A third group are made from  nanocrystals  and used as  quantum dots  (electron-confined  nanoparticles). Silicon remains the only material that is well-researched in both  bulkand  thin-film  forms. CRYSTALLINE SILICON [pic] Basic structure of a silicon based solar cell and its working mechanism. By far, the most prevalent bulk material for solar cells is crystalline silicon (abbreviated as a group as c-Si), also known as â€Å"solar grade silicon†. Bulk silicon is separated into multiple categories according to crystallinity and crystal size in the resulting ingot, ribbon, orwafer. 1. monocrystalline silicon (c-Si): often made using the Czochralski process. Single-crystal wafer cells tend to be expensive, and because they are cut from cylindrical ingots, do not completely cover a square solar cell module without a substantial waste of refined silicon. Hence most c-Si panels have uncovered gaps at the four corners of the cells. 2. olycrystalline silicon, or multicrystalline silicon, (poly-Si or mc-Si): made from cast square ingots — large blocks of molten silicon carefully cooled and solidified. Poly-Si cells are less expensive to produce than single crystal silicon cells, but are less effi cient. United States Department of Energy data show that there were a higher number of polycrystalline sales than monocrystalline silicon sales. 3. ribbon silicon is a type of polycrystalline silicon: it is formed by drawing flat thin films from molten silicon and results in a polycrystalline structure. These cells have lower efficiencies than poly-Si, but save on production costs due to a great reduction in silicon waste, as this approach does not require sawing from ingots. 4. ono-like-multi silicon: Developed in the 2000s and introduced commercially around 2009, mono-like-multi, or cast-mono, uses existing polycrystalline casting chambers with small â€Å"seeds† of mono material. The result is a bulk mono-like material with poly around the outsides. When sawn apart for processing, the inner sections are high-efficiency mono-like cells (but square instead of â€Å"clipped†), while the outer edges are sold off as conventional poly. The result is line that produces mon o-like cells at poly-like prices. Analysts have predicted that prices of polycrystalline silicon will drop as companies build additional polysilicon capacity quicker than the industry’s projected demand. On the other hand, the cost of producing upgraded metallurgical-grade silicon, also known as UMG Si, can potentially be one-sixth that of makingpolysilicon. Manufacturers of wafer-based cells have responded to high silicon prices in 2004–2008 prices with rapid reductions in silicon consumption. According to Jef Poortmans, director of IMEC’s organic and solar department, current cells use between eight and nine grams of silicon per watt of power generation, with wafer thicknesses in the neighborhood of 0. 200 mm. At 2008 spring’s IEEEPhotovoltaic Specialists’ Conference (PVS’08), John Wohlgemuth, staff scientist at BP Solar, reported that his company has qualified modules based on 0. 180 mm thick wafers and is testing processes for 0. 16 mm wafers cut with 0. 1 mm wire. IMEC’s road map, presented at the organization’s recent annual research review meeting, envisions use of 0. 08 mm wafers by 2015. Gallium arsenide multijunction: High-efficiency multijunction cells were originally developed for special applications such as satellites and space exploration, but at present, their use in terrestrial concentrators might be the lowest cost alternative in terms of $/kWh and $/W. [35] These multijunction cells consist of multiple thin films produced using metalorganic vapour phase epitaxy. A triple-junction cell, for example, may consist of the semiconductors: GaAs, Ge, and GaInP2. [36] Each type of semiconductor will have a characteristic band gap energy which, loosely speaking, causes it to absorb light most efficiently at a certain color, or more precisely, to absorb electromagnetic radiation over a portion of the spectrum. Combinations of semiconductors are carefully chosen to absorb nearly the entire solar spectrum, thus generating electricity from as much of the solar energy as possible. GaAs based multijunction devices are the most efficient solar cells to date. In October 15, 2012, triple junction metamorphic cell reached a record high of 44%. [37] Tandem solar cells based on monolithic, series connected, gallium indium phosphide (GaInP), gallium arsenide GaAs, and germanium Ge p–n junctions, are seeing demand rapidly rise. Between December 2006 and December 2007, the cost of 4N gallium metal rose from about $350 per kg to $680 per kg. Additionally, germanium metal prices have risen substantially to $1000–1200 per kg this year. Those materials include gallium (4N, 6N and 7N Ga), arsenic (4N, 6N and 7N) and germanium, pyrolitic boron nitride (pBN) crucibles for growing crystals, and boron oxide, these products are critical to the entire substrate manufacturing industry. Triple-junction GaAs solar cells were also being used as the power source of the Dutch four-time World Solar Challenge winners Nuna in 2003, 2005 and 2007, and also by the Dutch solar carsSolutra (2005), Twente One (2007) and 21Revolution (2009). The Dutch Radboud University Nijmegen set the record for thin film solar cell efficiency using a single junction GaAs to 25. 8% in August 2008 using only 4  µm thick GaAs layer which can be transferred from a wafer base to glass or plastic film. THIN FILMS [pic] Market share of the different PV technologies  In 2010 the market share of thin film declined by 30% as thin film technology was displaced by more efficient crystalline silicon solar panels (the light and dark blue bars). Thin-film technologies reduce the amount of material required in creating the active material of solar cell. Most thin film solar cells are sandwiched between two panes of glass to make a module. Since silicon solar panels only use one pane of glass, thin film panels are approximately twice as heavy as crystalline silicon panels. The majority of film panels have significantly lower conversion efficiencies, lagging silicon by two to three percentage points. 31]  Thin-film solar technologies have enjoyed large investment due to the success of First Solar and the largely unfulfilled promise of lower cost and flexibility compared to wafer silicon cells, but they have not become mainstream solar products due to their lower efficiency and corresponding larger area con sumption per watt production. Cadmium telluride  (CdTe),  copper indium gallium selenide  (CIGS) and  amorphous silicon  (A-Si) are three thin-film technologies often used as outdoor photovoltaic solar power production. CdTe technology is most cost competitive among them. [32]  CdTe technology costs about 30% less than CIGS technology and 40% less than A-Si technology in 2011. CADMIUM TELLURIDE SOLAR CELL A cadmium telluride solar cell uses a cadmium telluride (CdTe) thin film, a  semiconductor  layer to absorb and convert sunlight into electricity. Solarbuzzhas reported that the lowest quoted thin-film module price stands at US$0. 84 per  watt-peak, with the lowest crystalline silicon (c-Si) module at $1. 06 per watt-peak. [33] The  cadmium  present in the cells would be toxic if released. However, release is impossible during normal operation of the cells and is unlikely during ? res in residential roofs. [34]  A square meter of CdTe contains approximately the same amount of Cd as a single C cell  Nickel-cadmium battery, in a more stable and less soluble form. [34] COPPER INDIUM GALLIUM SELENIDE Copper indium gallium selenide (CIGS) is a  direct band gap  material. It has the highest efficiency (~20%) among thin film materials (see  CIGS solar cell). Traditional methods of fabrication involve vacuum processes including co-evaporation and sputtering. Recent developments at  IBM  and  Nanosolar  attempt to lower the cost by using non-vacuum solution processes. GALLIUM ARSENIDE MULTIJUNCTION High-efficiency multijunction cells were originally developed for special applications such as  satellites  and  space exploration, but at present, their use in terrestrial concentrators might be the lowest cost alternative in terms of $/kWh and $/W. 35]  These multijunction cells consist of multiple thin films produced using  metalorganic vapour phase epitaxy. A triple-junction cell, for example, may consist of the semiconductors:  GaAs,  Ge, and  GaInP2. [36]  Each type of semiconductor will have a characteristic  band gap  energy which, loosely speaking, causes it to absorb light most efficiently at a certain color, or more precisely, to absorb  electromagnetic radiation  over a portion of the spectrum. Combinations of semiconductors are carefully chosen to absorb nearly all of the solar spectrum, thus generating electricity from as much of the solar energy as possible. GaAs based multijunction devices are the most efficient solar cells to date. In October 15, 2012, triple junction metamorphic cell reached a record high of 44%. [37] Tandem solar cells based on monolithic, series connected, gallium indium phosphide (GaInP), gallium arsenide GaAs, and germanium Ge p–n junctions, are seeing demand rapidly rise. Between December 2006 and December 2007, the cost of 4N gallium metal rose from about $350 per kg to $680 per kg. Additionally, germanium metal prices have risen substantially to $1000–1200 per kg this year. Those materials include gallium (4N, 6N and 7N Ga), arsenic (4N, 6N and 7N) and germanium, pyrolitic boron nitride (pBN) crucibles for growing crystals, and boron oxide, these products are critical to the entire substrate manufacturing industry. Triple-junction GaAs solar cells were also being used as the power source of the Dutch four-time  World Solar Challenge  winners  Nuna  in 2003, 2005 and 2007, and also by the Dutch solar carsSolutra (2005),  Twente One (2007)  and 21Revolution (2009). The Dutch  Radboud University Nijmegen  set the record for thin film solar cell efficiency using a single junction GaAs to 25. 8% in August 2008 using only 4  Ã‚ µm thick GaAs layer which can be transferred from a wafer base to glass or plastic film. Light-absorbing dyes (DSSC) Dye-sensitized solar cells  (DSSCs) are made of low-cost materials and do not need elaborate equipment to manufacture, so they can be made in a  DIY  fashion, possibly allowing players to produce more of this type of solar cell than others. In bulk it should be significantly less expensive than older  solid-state  cell designs. DSSC’s can be engineered into flexible sheets, and although its  conversion efficiency  is less than the best  thin film cells, its  price/performance ratio  should be high enough to allow them to compete with  fossil fuel electrical generation. Typically a  ruthenium  metalorganic  dye  (Ru-centered) is used as a  monolayer  of light-absorbing material. The dye-sensitized solar cell depends on a  mesoporous  layer of  nanoparticulate  titanium dioxide  to greatly amplify the surface area (200–300 m2/g TiO2, as compared to approximately 10 m2/g of flat single crystal). The photogenerated electrons from the  light absorbing dye  are passed on to the  n-type  TiO2, and the holes are absorbed by an  electrolyte  on the other side of the dye. The circuit is completed by a redox couple in the electrolyte, which can be liquid or solid. This type of cell allows a more flexible use of materials, and is typically manufactured by  screen printing  or use of  Ultrasonic Nozzles, with the potential for lower processing costs than those used for  bulk  solar cells. However, the dyes in these cells also suffer from  degradation  under heat and  UV  light, and the cell casing is difficult to  seal  due to the solvents used in assembly. In spite of the above, this is a popular emerging technology with some commercial impact forecast within this decade. The first commercial shipment of DSSC solar modules occurred in July 2009 from G24i Innovations. [38] Quantum Dot Solar Cells (QDSCs) Quantum dot solar cells  (QDSCs) are based on the Gratzel cell, or  dye-sensitized solar cell, architecture but employ low  band gap  semiconductor  nanoparticles, fabricated with such small crystallite sizes that they form  quantum dots  (such as  CdS,  CdSe,  Sb2S3,  PbS, etc. ), instead of organic or organometallic dyes as light absorbers. Quantum dots (QDs) have attracted much interest because of their unique properties. Their size quantization allows for the  band gap  to be tuned by simply changing particle size. They also have high  extinction coefficients, and have shown the possibility of  multiple exciton generation. [39] In a QDSC, a  mesoporous  layer of  titanium dioxide  nanoparticles forms the backbone of the cell, much like in a DSSC. This TiO2  layer can then be made photoactive by coating with semiconductor quantum dots using  chemical bath deposition,  electrophoretic deposition, or successive ionic layer adsorption and reaction. The electrical circuit is then completed through the use of a liquid or solid  redox couple. During the last 3–4 years, the efficiency of QDSCs has increased rapidly[40]  with efficiencies over 5% shown for both liquid-junction[41]  and solid state cells. [42]  In an effort to decrease production costs of these devices, the  Prashant Kamat  research group[43]  recently demonstrated a solar paint made with TiO2  and CdSe that can be applied using a one-step method to any conductive surface and have shown efficiencies over 1%. [44] Organic/polymer solar cells Organic solar cells  are a relatively novel technology, yet hold the promise of a substantial price reduction (over thin-film silicon) and a faster return on investment. These cells can be processed from solution, hence the possibility of a simple roll-to-roll printing process, leading to inexpensive, large scale production. Organic solar cells and  polymer solar cells  are built from thin films (typically 100  nm) of  organic semiconductors  including polymers, such as  polyphenylene vinylene  and small-molecule compounds like copper phthalocyanine (a blue or green organic pigment) and  carbon fullerenes  and fullerene derivatives such as  PCBM. Energy conversion efficiencies achieved to date using conductive polymers are low compared to inorganic materials. However, it has improved quickly in the last few years and the highest  NREL  (National Renewable Energy Laboratory) certified efficiency has reached 8. 3% for the  Konarka  Power Plastic. [45]  In addition, these cells could be beneficial for some applications where mechanical flexibility and disposability are important. These devices differ from inorganic semiconductor solar cells in that they do not rely on the large built-in electric field of a PN junction to separate the electrons and holes created when photons are absorbed. The active region of an organic device consists of two materials, one which acts as an electron donor and the other as an acceptor. When a photon is converted into an electron hole pair, typically in the donor material, the charges tend to remain bound in the form of an  exciton, and are separated when the exciton diffuses to the donor-acceptor interface. The short exciton diffusion lengths of most polymer systems tend to limit the efficiency of such devices. Nanostructured interfaces, sometimes in the form of bulk heterojunctions, can improve performance. [46] In 2011, researchers at the Massachusetts Institute of Technology and Michigan State University developed the first highly efficient transparent solar cells that had a power efficiency close to 2% with a transparency to the human eye greater than 65%, achieved by selectively absorbing the ultraviolet and near-infrared parts of the spectrum with small-molecule compounds. 47]  [48]Researchers at UCLA more recently developed an analogous polymer solar cell, following the same approach, that is 70% transparent and has a 4% power conversion efficiency. [49]   The efficiency limits of both opaque and transparent organic solar cells were recently outlined. [50]  [51]  These lightweight, flexible cells can be produced in bulk at a low cost, and could be used to create power generating windows. Silicon thin films Silicon thin-film cells  are mainly deposited by  chemical vapor deposition  (typically plasma-enhanced, PE-CVD) from  silane  gas and  hydrogen  gas. Depending on the deposition parameters, this can yield:[52] 1. Amorphous silicon  (a-Si or a-Si:H) 2. Protocrystalline  silicon or 3. Nanocrystalline silicon  (nc-Si or nc-Si:H), also called microcrystalline silicon. It has been found that protocrystalline silicon with a low volume fraction of nanocrystalline silicon is optimal for high open circuit voltage. [53]  These types of silicon present dangling and twisted bonds, which results in deep defects (energy levels in the bandgap) as well as deformation of the valence and conduction bands (band tails). The solar cells made from these materials tend to have lower  energy conversion efficiency  than  bulk  silicon, but are also less expensive to produce. The  quantum efficiency  of thin film solar cells is also lower due to reduced number of collected charge carriers per incident photon. An amorphous silicon (a-Si) solar cell is made of amorphous or microcrystalline silicon and its basic electronic structure is the  p-i-n  junction. -Si is attractive as a solar cell material because it is abundant and non-toxic (unlike its CdTe counterpart) and requires a low processing temperature, enabling production of devices to occur on flex ible and low-cost substrates. As the amorphous structure has a higher absorption rate of light than crystalline cells, the complete light spectrum can be absorbed with a very thin layer of photo-electrically active material. A film only 1 micron thick can absorb 90% of the usable solar energy. [54]  This reduced material requirement along with current technologies being capable of large-area deposition of a-Si, the scalability of this type of cell is high. However, because it is amorphous, it has high inherent disorder and dangling bonds, making it a bad conductor for charge carriers. These dangling bonds act as recombination centers that severely reduce the carrier lifetime and pin the Fermi energy level so that doping the material to n- or p- type is not possible. Amorphous Silicon also suffers from the Staebler-Wronski effect, which results in the efficiency of devices utilizing amorphous silicon dropping as the cell is exposed to light. The production of a-Si thin film solar cells uses glass as a substrate and deposits a very thin layer of silicon by  plasma-enhanced chemical vapor deposition  (PECVD). A-Si manufacturers are working towards lower costs per watt and higher conversion efficiency with continuous research and development on  Multijunction solar cells  for solar panels. Anwell Technologies Limited  recently announced its target for mul How to cite Street Light, Essay examples