Solar Cell



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 a 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.

To make solar cells, the raw materials—silicon dioxide of either quartzite gravel or crushed quartz—are first placed into an electric arc furnace, where a carbon arc is applied to release the oxygen. The products are carbon dioxide and molten silicon. At this point, the silicon is still not pure enough to be used for solor cells and requires further purification.
To make solar cells, the raw materials—silicon dioxide of either quartzite gravel or crushed quartz—are first placed into an electric arc furnace, where a carbon arc is applied to release the oxygen. The products are carbon dioxide and molten silicon. At this point, the silicon is still not pure enough to be used for solor cells and requires further purification.
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

Purifying the silicon

Making single crystal silicon

Making silicon wafers

Doping

Placing electrical contacts

The anti-reflective coating

Encapsulating the cell

Quality Control

Quality control is important in solar cell manufacture because discrepancy in the many processes and factors can adversely affect the overall efficiency of the cells. The primary research goal is to find ways to improve the efficiency of each solar cell over a longer lifetime. The Low Cost Solar Array Project (initiated by the United States Department of Energy in the late 1970s) sponsored private research that aimed to lower the cost of solar cells. The silicon itself is tested for purity, crystal orientation, and resistivity. Manufacturers also test for the presence of oxygen (which affects its strength and resistance to warp) and carbon (which causes defects). Finished silicon disks are inspected for any damage, flaking, or bending that might have occurred during sawing, polishing, and etching.

During the entire silicon disk manufacturing process, the temperature, pressure, speed, and quantities of dopants are continuously monitored. Steps are also taken to ensure that impurities in the air and on working surfaces are kept to a minimum.

The completed semiconductors must then undergo electrical tests to see that the current, voltage, and resistance for each meet appropriate standards. An earlier problem with solar cells was a tendency to stop working when partially shaded. This problem has been alleviated by providing shunt diodes that reduce dangerously high voltages to the cell. Shunt resistance must then be tested using partially shaded junctions.

An important test of solar modules involves providing test cells with conditions and intensity of light that they will encounter under normal conditions and then checking to see that they perform well. The cells are also exposed to heat and cold and tested against vibration, twisting, and hail.

The final test for solar modules is field site testing, in which finished modules are placed where they will actually be used. This provides the researcher with the best data for determining the efficiency of a solar cell under ambient conditions and the solar cell's effective lifetime, the most important factors of all.

The Future

Considering the present state of relatively expensive, inefficient solar cells, the future can only improve. Some experts predict it will be a billion-dollar industry by the year 2000. This prediction is supported by evidence of more rooftop photovoltaic systems being developed in such countries as Japan, Germany, and Italy. Plans to begin the manufacture of solar cells have been established in Mexico and China. Likewise, Egypt, Botswana, and the Philippines (all three assisted by American companies) are building plants that will manufacture solar cells.

Most current research aims for reducing solar cell cost or increasing efficiency. Innovations in solar cell technology include developing and manufacturing cheaper alternatives to the expensive crystalline silicon cells. These alternatives include solar windows that mimic photosynthesis, and smaller cells made from tiny, amorphous silicon balls. Already, amorphous silicon and polycrystalline silicon are gaining popularity at the expense of single crystal silicon. Additional innovations including minimizing shade and focusing sunlight through prismatic lenses. This involves layers of different materials (notably, gallium arsenide and silicon) that absorb light at different frequencies, thereby increasing the amount of sunlight effectively used for electricity production.

A few experts foresee the adaptation of hybrid houses; that is, houses that utilize solar water heaters, passive solar heating, and solar cells for reduced energy needs. Another view concerns the space shuttle placing more and more solar arrays into orbit, a solar power satellite that beams power to Earth solar array farms, and even a space colony that will manufacture solar arrays to be used on Earth.

Where To Learn More

Books

Bullock, Charles E. and Peter H. Grambs. Solar Electricity: Making the Sun Work for You. Monegon, Ltd., 1981.

Komp, Richard J. Practical Photovoltaics. Aatec Publications, 1984.

Making and Using Electricity from the Sun. Tab Books, 1979.

Periodicals

Crawford, Mark. "DOE's Born-Again Solar Energy Plan," Science. March 23, 1990, pp. 1403-1404.

"Waiting for the Sunrise," Economist. May 19, 1990, pp. 95+.

Edelson, Edward. "Solar Cell Update," Popular Science. June, 1992, p. 95.

Murray, Charles J. "Solar Power's Bright Hope," Design News. March 11, 1991, p. 30.

Rose Secrest



Also read article about Solar Cell from Wikipedia

User Contributions:

1
alvin
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Mar 2, 2006 @ 6:18 pm
i think it was alexander edmund becquerel who discovered pv effect....
2
Thiagarajan
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Aug 30, 2006 @ 11:11 am
1) Useful to teach for my students
2) Clear Pictures
3) External web links are needed
4) Real Photo images will add importance to article
3
Tuan Nguyen
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May 31, 2008 @ 1:13 pm
very useful article for me, as I want to learn more about the manufacturing process.
Would be good if there are some more figures / pictures of the solar modules production line, and not only about the solar cell production process.
4
Donny M W
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Jun 22, 2008 @ 7:07 am
It's very useful and a lot of benefit that I get, and hopefully solar cells system could be utilize immediately in my country in this near time so we can solve electricity outage matters.
5
Ashish
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Sep 12, 2008 @ 6:06 am
A very useful artical but it is very old can you suggest some new artical on the same topic.
6
N.K. Maker
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Aug 9, 2009 @ 11:23 pm
Excellent easy to understand information for begginers. I am going to share information with my son who is going to High School this year. Thank you for making it available for public at no cost.
7
Shahid Mahmood
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Dec 27, 2009 @ 4:04 am
Very easy to understand. It would be good if there are some more figures. I would like to have some information on AR coating of SiN
8
VINEET SHARMA
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Jan 30, 2010 @ 4:04 am
excillent work to provide the basics of solar cell manufacturing process
9
kavita
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Sep 5, 2010 @ 10:22 pm
How solar cell can be used at domestic level? is it possible to make it cheaper to use at domestic level?
10
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Sep 5, 2011 @ 3:03 am
Nice information about solar cell. Solar power can be very useful and demanding in pakistan in case provided in low cost.
11
Monocrystalline Solar Cell
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Dec 18, 2011 @ 11:23 pm
This monocrystalline solar cell is a kind of photovoltaic solar panel made from high-purity single crystal silicon rod.
And the present photoelectric conversion efficiency of it can be as much as 18.1%.

As a professional manufacturer of monocrystalline solar cell in China, Eoplly can also provide many other solar products for you, such as and polycrystalline and monocrystalline solar panel, polycrystalline and monocrystalline solar modules, solar lighting projects, building integrated photovoltaic systems, on grid and off grid solar power systems, portable solar chargers, and solar tracking systems. So far our products have received many certificates like IEC, TUV, CE, UL, MCS of the United Kingdom, ISO9001:2000, KSC of South Korea, and many other relevant authoritative certificates of Europe, America, and Asia. With high performance and competitive price, our products have been exported to North America, Europe, Oceania, Eastern Europe, East Asia, etc. If you need monocrystalline solar cell (monocrystalline solar panel), please contact us freely.
12
ramir
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Aug 15, 2012 @ 12:00 am
good information... thanks for the information. please send me how to build my own monocrystalline solar panel.
13
san
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Aug 17, 2012 @ 4:04 am
it may be helpfull those who like to manufacturing and trading.
14
Kamal
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Jul 30, 2013 @ 9:21 pm
Very good information. Appreciate the work done to spread the knowledge leading to Eco-friendly way of life. God or Nature whatever we call, has purposefully placed the Sun 150 million KM's away from Earth for our safety. I wish one day we could replace the nuclear power option with such a safe technology.
15
irfanali
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Oct 16, 2013 @ 10:22 pm
very good attempt to know the basic things about manufacturing of solar cells but it would be more effective if the of assembly line of manufacturing process is shown as pictures.
16
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Sep 1, 2014 @ 12:00 am
I am very interested in solar power, I someday wanting to install panels on my rooftop.
I was Wondering if anybody has bought them $100 off $250 kits to put together solar panels from Harbor Freight Tool's and if they work right and do save you Money.

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