How Solar Cell is made
برای مشاهده متن به فارسی از مترجم وبلاگ در سمت راست
استفاده کنید.
Background
Photovoltaic solar cells are thin silicon disks that convert sunlight into electricity. These disks act as energy sources for a wide variety of uses, including: calculators and other small devices; telecommunications; rooftop panels on individual houses; and for lighting, pumping, and medical refrigeration for villages in developing countries. Solar cells in the form of large arrays are used to power satellites and, in rare cases, to provide electricity for power plants. When research into electricity began and simple batteries were being made and studied, research into solar electricity followed amazingly quickly. As early as 1839, Antoine-Cesar Becquerel exposed a chemical battery to the sun to see it produce voltage. This first conversion of sunlight to electricity was one percent efficient. That is, one percent of the incoming sunlight was converted into electricity. Willoughby Smith in 1873 discovered that selenium was sensitive to light; in 1877 Adams and Day noted that selenium, when exposed to light, produced an electrical current. Charles Fritts, in the 1880s, also used gold-coated selenium to make the first solar cell, again only one percent efficient. Nevertheless, Fritts considered his cells to be revolutionary. He envisioned free solar energy to be a means of decentralization, predicting that solar cells would replace power plants with individually powered residences.
With Albert Einstein's explanation in 1905 of the photoelectric effect-metal absorbs energy from light and will retain that energy until too much light hits it-hope soared anew that solar electricity at higher efficiencies would become feasible. Little progress was made, however, until research into diodes and transistors yielded the knowledge necessary for Bell scientists Gordon Pearson, Darryl Chapin, and Cal Fuller to produce a silicon solar cell of four percent efficiency in 1954. Further work brought the cell's efficiency up to 15 percent. Solar cells were first used in the rural and isolated city of Americus, Georgia as a power source for a telephone relay system, where it was used successfully for many years. A type of solar cell to fully meet domestic energy needs has not as yet been developed, but solar cells have become successful in providing energy for artificial satellites. Fuel systems and regular batteries were too heavy in a program where every ounce mattered. Solar cells provide more energy per ounce of weight than all other conventional energy sources, and they are cost-effective.
Only few large scale photovoltaic power systems have been set up. Most efforts lean toward providing solar cell technology to remote places that have no other means of sophisticated power. About 50 megawatts are installed each year, yet solar cells provide only about .1 percent of all electricity now being produced. Supporters of solar energy claim that the amount of solar radiation reaching the Earth's surface each year could easily provide all our energy needs several times over, yet solar cells have a long way to go before they fulfill Charles Fritts's dream of free, fully accessible solar electricity.
Raw Materials
The basic component of a solar cell is pure silicon, which is not pure in its natural state.
Pure silicon is derived from such silicon dioxides as quartzite gravel (the purest silica) or crushed quartz. The resulting pure silicon is then doped (treated with) with phosphorous and boron to produce an excess of electrons and a deficiency of electrons respectively to make a semiconductor capable of conducting electricity. The silicon disks are shiny and require an anti-reflective coating, usually titanium dioxide. The solar module consists of the silicon semiconductor surrounded by protective material in a metal frame. The protective material consists of an encapsulant of transparent silicon rubber or butyryl plastic (commonly used in automobile windshields) bonded around the cells, which are then embedded in ethylene vinyl acetate. A polyester film (such as mylar or tedlar) makes up the backing. A glass cover is found on terrestrial arrays, a lightweight plastic cover on satellite arrays. The electronic parts are standard and consist mostly of copper. The frame is either steel or aluminum. Silicon is used as the cement to put it all together.
The Manufacturing Process
1. Purifying the silicon
2. Making single crystal silicon
3. Making silicon wafers
4. Doping
5. Placing electrical contacts
6. The anti-reflective coating
7. Encapsulating the cell
8. Quality Control
To Know About the Manufacturing Process Please Wait.
Coming Soon.
Energy savings in black and white
Anyone who has ever stepped barefoot onto blacktop pavement on a hot sunny day knows the phenomenon very well: Black surfaces absorb the sun's heat very efficiently, producing a toe-scorching surface. In the wintertime, that can be a good thing: A dark roof heats up in the sun and helps reduce your heating bill. But in summertime, it's definitely a bad thing: Your house gets even hotter, and your air conditioning has to work harder. In most places, the summertime penalty is greater than the wintertime gain, it turns out, so that's why many people, including U.S. Secretary of Energy Steven Chu, strongly advocate switching to white roofs.
It's no small matter. In fact, Chu says that turning all the world's roofs white would eliminate as much greenhouse gas emissions in 20 years as the whole world produces in a year. But some critics point out that in northern cities, the gain in summer could be outweighed by the loss in winter. The ideal situation, then, would be to get the advantage of white roofs when it's hot and black roofs when it's cold.
Now, there may be a way to have both. A team of recent MIT graduates has developed roof tiles that change color based on the temperature. The tiles become white when it's hot, allowing them to reflect away most of the sun's heat. When it's cold they turn black and absorb heat just when it's needed.
The team's lab measurements show that in their white state, the tiles reflect about 80 percent of the sunlight falling on them, while when black they reflect only about 30 percent. That means in their white state, they could save as much as 20 percent of present cooling costs, according to recent studies. Savings from the black state in winter have yet to be quantified.
The team, which the students call Thermeleon (rhymes with chameleon, because of its color-changing property), was one of the competitors in this year's Making and Designing Materials Engineering Contest (MADMEC), a competition for teams of MIT students (or 2009 graduates). Now in its third year, the contest this year was specifically devoted to projects aimed at improving energy efficiency through innovative uses of materials. The final showdown was held Wednesday night, and the Thermeleon team took first place, earning $5,000 in the process.
Nick Orf PhD ’09, a member of the Thermeleon team, explains that he and his teammates originally tried to develop a color-shifting roof tile using a system of mixed fluids, one dark and one light, whose density would change with temperature: the dark substance would float to the top when it was cold, and white would float when it was hot. But the system proved too complicated, and instead they hit on a simpler, less expensive method.
Now, they use a common commercial polymer (in one version, one that is commonly used in hair gels) in a water solution. That solution is encapsulated — between layers of glass and plastic in their original prototype, and between flexible plastic layers in their latest version — with a dark layer at the back.
When the temperature is below a certain level (which they can choose by varying the exact formulation), the polymer stays dissolved, and the black backing shows through, absorbing the sun's heat. But when the temperature climbs, the polymer condenses to form tiny droplets, whose small sizes scatter light and thus produce a white surface, reflecting the sun's heat.
They are now working on an even simpler version in which the polymer solution would be micro-encapsulated and the tiny capsules carried in a clear paint material that could be brushed or sprayed onto any existing surface. The tiny capsules would still have the color-changing property, but the surface could easily be applied over an existing black roof, much more inexpensively than installing new roofing material.
Although they have not yet made specific plans for forming a business to commercialize their concept, Orf says the team members are determined to pursue the project and develop it into a marketable product.
Because the materials are common and inexpensive, team members think the tiles could be manufactured at a price comparable to that of conventional roofing materials — although that won't be known for sure until they determine the exact materials and construction of their final version.
The biggest remaining question is over durability, and answering it will require spending some time to do accelerated testing by running the material through repeated hot-cold cycles.
Hashem Akbari, leader of the Heat Island Group at Lawrence Berkeley National Laboratory in California, is a long-time advocate of white roofs as an energy-saving measure. He says that some other groups, including a team at the University of Athens, have done research on the use of color-changing materials for roofs, but that in those tests, "the cost and durability has been a serious issue."
The Thermeleon team hopes to address those concerns. "It's got to stand up to very harsh conditions," Orf says. "Those sorts of tests would have to be done before we'll know if we have a viable product."
From:mit.edu
It's no small matter. In fact, Chu says that turning all the world's roofs white would eliminate as much greenhouse gas emissions in 20 years as the whole world produces in a year. But some critics point out that in northern cities, the gain in summer could be outweighed by the loss in winter. The ideal situation, then, would be to get the advantage of white roofs when it's hot and black roofs when it's cold.
Now, there may be a way to have both. A team of recent MIT graduates has developed roof tiles that change color based on the temperature. The tiles become white when it's hot, allowing them to reflect away most of the sun's heat. When it's cold they turn black and absorb heat just when it's needed.
The team's lab measurements show that in their white state, the tiles reflect about 80 percent of the sunlight falling on them, while when black they reflect only about 30 percent. That means in their white state, they could save as much as 20 percent of present cooling costs, according to recent studies. Savings from the black state in winter have yet to be quantified.
The team, which the students call Thermeleon (rhymes with chameleon, because of its color-changing property), was one of the competitors in this year's Making and Designing Materials Engineering Contest (MADMEC), a competition for teams of MIT students (or 2009 graduates). Now in its third year, the contest this year was specifically devoted to projects aimed at improving energy efficiency through innovative uses of materials. The final showdown was held Wednesday night, and the Thermeleon team took first place, earning $5,000 in the process.
Nick Orf PhD ’09, a member of the Thermeleon team, explains that he and his teammates originally tried to develop a color-shifting roof tile using a system of mixed fluids, one dark and one light, whose density would change with temperature: the dark substance would float to the top when it was cold, and white would float when it was hot. But the system proved too complicated, and instead they hit on a simpler, less expensive method.
Now, they use a common commercial polymer (in one version, one that is commonly used in hair gels) in a water solution. That solution is encapsulated — between layers of glass and plastic in their original prototype, and between flexible plastic layers in their latest version — with a dark layer at the back.
When the temperature is below a certain level (which they can choose by varying the exact formulation), the polymer stays dissolved, and the black backing shows through, absorbing the sun's heat. But when the temperature climbs, the polymer condenses to form tiny droplets, whose small sizes scatter light and thus produce a white surface, reflecting the sun's heat.
They are now working on an even simpler version in which the polymer solution would be micro-encapsulated and the tiny capsules carried in a clear paint material that could be brushed or sprayed onto any existing surface. The tiny capsules would still have the color-changing property, but the surface could easily be applied over an existing black roof, much more inexpensively than installing new roofing material.
Although they have not yet made specific plans for forming a business to commercialize their concept, Orf says the team members are determined to pursue the project and develop it into a marketable product.
Because the materials are common and inexpensive, team members think the tiles could be manufactured at a price comparable to that of conventional roofing materials — although that won't be known for sure until they determine the exact materials and construction of their final version.
The biggest remaining question is over durability, and answering it will require spending some time to do accelerated testing by running the material through repeated hot-cold cycles.
Hashem Akbari, leader of the Heat Island Group at Lawrence Berkeley National Laboratory in California, is a long-time advocate of white roofs as an energy-saving measure. He says that some other groups, including a team at the University of Athens, have done research on the use of color-changing materials for roofs, but that in those tests, "the cost and durability has been a serious issue."
The Thermeleon team hopes to address those concerns. "It's got to stand up to very harsh conditions," Orf says. "Those sorts of tests would have to be done before we'll know if we have a viable product."
From:mit.edu
برچسب انرژی
در انتخاب و تهيه كالا خصوصا وسايل برقي توجه به مواردي چون شكل ظاهري، مدل، كارخانه سازنده و تكنولوژي ساخت، شرطهاي لازم در انتخاب يك كالا محسوب ميشوند اما توجه به نشان استاندارد و برچسب انرژي از شرطهاي ضروري در انتخاب و تهيه وسايل برقي خانگي است. چون اين علائم اطلاعات بسيار مفيدي را در زمينه ايمني؛ بازدهي و ميزان مصرف انرژي وسايل برقي با توجه به خدماتي كه ارائه ميدهند در اختيار مصرفكنندگان قرار ميدهد.
معرفي برچسب 7رنگ
يكي از موارد مهمي كه در سالهاي اخير مورد تاكيد قرار گرفته، مشخص كردن ملاكهايي براي مصرف انرژي كليه وسايل انرژي بر خانگي است كه كارخانههاي سازنده وسايل خانگي ملزم به رعايت آن هستند. حاصل اين كار تهيه و تدوين برچسبي بود تحت عنوان برچسب انرژي يا برچسب كارآيي انرژي.
برچسب انرژي چيست؟
برچسب انرژي امروزه در اغلب كشورهاي جهان وجود دارد و برچسبي است كه روي وسايل مصرفكننده انرژي نصب ميشود و مصرفكننده را با ميزان كارآيي و مصرف انرژي آن وسيله آشنا ميكند. همچنين اطلاعات مشترك در همه وسايل و اطلاعات اختصاصي مربوط به هر وسيله انرژي بر را در اختيار مصرفكنندگان قرار ميدهد.
در حال حاضر وقتي براي خريد وسايل برقي و گازي به فروشگاهها مراجعه ميكنيد برچسب انرژي را روي وسايل مشاهده ميكنيد. برچسب انرژي داراي قسمتهاي مختلفي است و هر قسمت نشان دهنده اطلاعاتي در خصوص دستگاه مربوطه است.
بخشهاي اول تا سوم برچسب در تمامي وسايل انرژي بر خانگي (كه داراي برچسب انرژي باشند) مشترك و بهترتيب نشاندهنده علامت تجاري شركت سازنده، نام شركت سازنده و مدل دستگاه است.
بخش چهارم بر چسب انرژي كه از اهميت خاصي نيز برخوردار است از 7 فلش رنگي (از سبز پررنگ تا قرمز تيره) كه روي هر يك از آنها يك حرف لاتين از A تا G درج شده تشكيل شده است كه هر حرف و هر فلش رنگي نشانگر درجهاي از مصرف انرژي دستگاه است.
حرف A نشانگر كمترين مصرف انرژي و بيشترين كارآيي و حرف G نشانگر بيشترين مصرف انرژي و كمترين كارآيي دستگاه است. بنابراين هر چه رتبه دستگاه بيشتر باشد كارآيي آن نسبت به ميزان انرژي كه مصرف ميكند بيشتر است.
برچسب انرژي در واقع به خريدار كمك ميكند كه در هنگام خريد، وسيلهاي را انتخاب كند كه در مقايسه با ساير وسايل موجود، مصرف انرژي كمتر و كارآيي بيشتري داشته باشد.
به عنوان مثال وقتي خريداري براي خريد يك يخچال فريزر به فروشگاهي مراجعه ميكند و با دو مدل يخچال كه از هر جهت مشخصات يكساني دارند روبهرو ميشود، در اين شرايط اگر يكي از يخچالها رتبه B داشته باشد و ديگري رتبه C مسلما آن يخچالي كه رتبه B دارد انتخاب خوبي براي خريد است، چون مصرف برق كمتري دارد. توجه داشته باشيد كه در يخچال و فريزرها به ازاي افزايش يك رتبه در برچسب انرژي حدود 14درصد صرفهجويي در مصرف برق صورت ميگيرد.
مهم است كه بدانيد استاندارد برچسب انرژي براي يخچال، يخچال فريزرهاي خانگي، ماشين لباسشويي، كولر آبي، كولر گازي، اتوي برقي و ساير وسايل برقي كوچك آشپزخانه تدوين شده است.
فوايد استفاده از برچسب انرژي
استفاده از برچسب انرژي مزايا و فوايد گوناگوني براي مصرفكنندگان اين گونه وسايل دارد كه از آن جمله ميتوان به موارد زير اشاره كرد:
- انتخاب درست و آگاهانه مردم در هنگام خريد وسايل برقي خانگي
- آشنا ساختن مصرف كنندگان با ميزان كارايي و بازدهي وسايل برقي خانگي
- بهينهسازي و كاهش مصرف انرژي
-كاهش هزينه انرژي مصرفي در خانوادهها
- كاهش آلودگي محيطزيست
- ارائه اطلاعات اختصاصي ويژه هر وسيله برقي
- ارائه اطلاعات مشترك در مورد وسايل برقي شامل علامت تجاري، نام شركت سازنده، مدل دستگاه و نشان استاندارد.
در حال حاضر 100درصد از خانوادههاي شهري و 90درصد از خانوادههاي روستايي از خدمات شبكه برق در كشور استفاده ميكنند. با توجه به افزايش سطح رفاه عمومي، افزايش مشتركين برق و استفاده عموم مردم از وسايل انرژيبر خانگي تعداد اين وسايل روز به روز در خانوادهها در حال افزايش است؛ بنابراين توجه به مرغوبيت، بازدهي مفيد، ميزان مصرف انرژي در وسايل انرژيبر و همچنين توجه به طراحي، ساخت مناسب و منطبق بر استانداردهاي معتبر و بهينه جهاني بايد مورد توجه توليدكنندگان اين وسايل قرار گيرد. از طرف ديگر اطلاع از نحوه استفاده درست از وسايل انرژيبر و توجه به ميزان كارايي و مصرف انرژي آنها نيز از جمله مواردي است كه بايد مورد توجه مصرفكنندگان باشد.
از:www.donya-e-eqtesad.com
اشتراک در:
پستها (Atom)