Light energy power generating component of the sun - -Solar cell

Author: Yang SuHua Use the University of Science and Technology in Kaohsjung
Cai TaiCheng Use the University of Science and Technology in Kaohsjung

People had already as early as period in the Spring and Autumn and the Warring states ago found how to utilize solar energy. Once recorded too in the history records ' department Yuan palm water flint, it fetch by fire at day ' and ' flint not positive meet on the day, fire being fire '. According to criticizing of a text, in ' the flint 's and ' the positive flint 's among them, collect the hot device in spotlight which is similar to the concave mirror.
As to history of solar energy development, is it get material cause behavior to shine only, early to find already in the 19th century. Having reached 1930 times, the exposure of the camera counts and widely uses this principle. Then, have reached 1950 times, with the thing gradual understanding of the semiconductor, and the progress of the process technology, the first solar cell emerged in Bell laboratory of U.S.A. in 1954. Because the sun is only abundant, with its natural energy not exhausted, besides there is no doubt that energy exhaustsing, can avoid the question that the energy is monopolized too, so various countries develop application science and technology of the sun energy actively, the ones that expected to be increased the sun energy are by lowering the dependence on fossil energy.

Abundant solar energy

Very huge from the energy coming out in solar radiation, it is the main energy that the mankind depended on supporting the family. After the solar energy is conveyed to the earth atmosphere, a part is absorbed by the atmosphere, a part is is it answer to reflect in the spaced, other one part will be received by the earth's surface, can be up to average each sq.m. ground to shine in the energy of the earth nearly there is watt 180. Recently, because a new line and other energy of environmental consciousness gradual and exhausted, the sun energy begins to be paid attention to by the everybody also. In addition, because Taiwan lacks energy resources, more than 90% of the energy must be imported from foreign countries, so, the research and development which strengthens the new energy has its essential ones.
Taiwan is located in the subtropical zone, it is sunny, the sunshine amount is great, very suitable for utilizing solar energy to be made for the new energy. Except solar energy can utilize directly with the method of tanning by the sun, collecting and only lighting etc., Dr.eye: can change it into heat energy and electric energy to use further too. For example, the commonly used solar water heater, but change the solar energy into a application instance of heat energy in daily life.
Change into the electric energy respect in the solar energy, the majority is to utilize solar energy to change the light energy into the electric energy stiffly, for example solar energy panels on the electronic calculator,etc. Dr.eye: are all concrete application examples. From the sun energy development trend is it watch to come during these years recently, make use of solar cell to realize development, the sun of energy, because technology is it fast, become 21st century most potential one of of photoelectric technology most probably very to develop.

Material of the solar cell

The power generating energy of the solar cell comes from the sunlight, and the spectrum of solar radiation mainly regards visible light as the centre, the wavelength is from 0.3 microns of ultraviolet ray to several microns of infrared and only main distribution ranges. If convert into the energy of the photon, probably between 0.3 to 4 electron-volts, so material on can crack within this range in size, as silicon material, will have kind photoelectric conversion efficiency.

The material of the solar cell of the silicon department, can be divided into 3 big classes of monocrystalline silicon, polycrystalline silicon and non-crystalline silicon mainly. In the material of the monocrystalline silicon, the periodic permutation with height of silicon atom. At present, the most important technology of monocrystalline silicon is to utilize the long brilliant law of firewood that grow up, in Gan pan, insert brilliant kind in silicon melting liquid high polycrystalline silicon melting of purity, rotated and draws and guides and makes into a brilliant post of silicon up slowly with the proper speed, then cut the brilliant post, can get the monocrystalline silicon brilliant and round.

Mean material by a different one light to commit while being single crystal as for polycrystalline silicon, its manufacture method is to cast solidification of the silicon of melting and transform into. The non-crystalline silicon refers to in the whole material, only in the ranges of several atoms or molecules, the permutation of the atom has periodicity, even in some materials, there is not periodic atom that arrange the structure at all. Manufacture method of it power consuming thick liquid type chemical gaseous phase Shen accumulate law is long to succeed membrane of non-crystalline silicon at base plate usually. Because the crystal structure of the material is different, so, while designing the solar cell with different materials, their photoelectric characteristics will be different to some extent too.

Generally speaking, it is the most effective that the photoelectricity of the solar cell of monocrystalline silicon is changed, it is longer too, relatively suitable for the use of such places as the power plant or the will of lighting number of the traffic,etc.. In the world, produce the big factory mainly of the solar cell, such as Siemens of Germany and Sharp Company of Japan, mainly product monocrystalline silicon solar cell of this type.

As for the solar cell of polycrystalline silicon, because brilliant characteristic much of it, at the formality that is cut and reprocessing, it is more difficult than the single crystal and non-crystalline silicon, efficiency is lower than that of solar cell of monocrystalline silicon too.: But a simple one make Cheng and cheap cost important characteristic most of it. So, in the electric application system of some low power, adopt the solar cell of this type. To solar cell of the non-crystalline silicon, because the price is the cheapest, the speed of production is the quickest too, so the solar cell of non-crystalline silicon is more often applied to on the consuming electronic product, and new application is in researching and developing constantly.

The solar cell can also adopt other materials to be made besides can select the silicon material for use ing, the materials of cadmium, GaAs indium, GaAs,etc. Dr.eye: chemical compound semiconductor such as Te, can make high-efficiency solar cell too. But, it is higher because of the cost of these materials, the component made is only suitable in some more special application.

The photoelectricity changes the principle
Let us is it construct most simple monocrystalline silicon solar cell to spend, is it prove light of solar cell blow electric principle to come. Spoken of by the material respect at first, the silicon is the most important in various kinds of semiconductor industries now, and most popular electronic material. Its source is the silicon sand ( Oxidize silicons two times) ,It is very easy for raw materials to obtain, the cost is lower too.

In the periodic table of elements, atom of silicon preface 14, crystal diamond structure, IV clan element. What is called IV clan element, is it at outer electronic rail land of it, have 4 electron run around the atomic nucleus to mean, and these 4 electrons are also called the valence electron. 4 outer electrons of each silicon, differentiate and 4 near silicon atom one of outer two two electron in pairs, form the covalent bond.

N Type semiconductor: If mix the atom with 5 valence electrons in the pure silicon, such as the phosphorus atom, this impurity and atom will replace the position of the silicon atom. However, when phosphorus atom and neighbouring silicon atom with 5 valence electrons form the covalent bond, will be 1 more more free electron, this free electron is a piece of something small and hard of year which brings negative electricity We call and construct the body this impurity and atom that offer the free electron, and mix the semiconductor which construct the body and is called the Model N semiconductor.

P Type semiconductor: Similarly, if mix the atoms of three prices in the pure silicon, such as the boron and atom, this impurity and atom of three prices will replace the position of the silicon atom. But because the boron and atom can only offer 3 valence electrons and neighbouring silicon atoms to form the covalent bond, so will produce a vacancy abound boron and atom, this vacancy is called the electric hole, this electric hole can be regarded as a piece of something small and hard of year taking positive electricity. Usually, we call the receptor this impurity and atom that offer the electric hole, call the semiconductor which mixes the receptor Model P semiconductor at the same time.

When P type and Model N semiconductor keep in touch each other, N the electron in the type semiconductor will pour into the Model P semiconductor, in order to fill in its electric hole inside. Connect surface nearby in P-N, because electron - electric combination of hole form one year son's empty exhausted district, and P type and Model N semiconductor have shoulder, positive charge separately too, form one build electric field. When the sunlight shines to this P-N structure, P type and Model N semiconductor produce electrons because of absorbing the sunlight - the electric hole is right. Because what the empty exhausted district offered builds electric field inside, can let the electron emerging in the semiconductor flow in the battery, so if draw the electric current via the electrode, can form an intact solar cell.

: Development of the solar cell

Begin since 1960 times, the satellite which U.S.A. launched has already utilized the solar cell to do for the source of energy. At the time of the energy crisis, people began to transfer the application of the solar cell to general people's livelihood use by the seventies.

At present, in such countries as U.S.A., Japan and Israel,etc., Dr.eye: have already used the solar energy to fit in a large amount, advance towards the commercialized goal. In these countries, U.S.A. set up the largest solar energy power plant in the world in California in 1983, its generation can be up to watt 16 million. South Africa, Botswana, Namibian and other countries in the south of Africa set up special project too, encourage the remote rural area to install the solar cell electricity generation system of the low cost.
And pursue the solar energy and generate electricity the most positive country firsts elect Japan. Japan implement incentive method of subsidizing, popularize each household 3,000 watt ' city electricity the sun of connecting in parallel etc. Dr.eye: photoelectricity can be systematic ' city electricity connecting in parallel type sun photoelectricity can be systematic ' is when the sunshine is sufficient, offered the electric energy by solar cell and used for own load, it is stored separately if there is surplus electricity. When generation or not generate electricity insufficiently, the electricity needed is and then offered by Utilities Electric Co..

By 1996, there is solar energy electricity generation system of 2,600 devices in Japan, the total capacity of the installation has watt 8 million. One year later, has had 9,400 devices already, the total capacity installed is up to watt 32 million too. The upsurge in environmental consciousness of cause and system of government subsidiaries in recent years, estimate Japan live in home demand of solar cell, can increase rapidly too in advance.

In industry, Japanese solar cell total output was watt 86 million in 1999, has already risen to watt 120 million by 2000, the output has occupied the first in the world for two years in succession. Recently, a lot of solar cell manufacturers in Japan, such as Sharp Company, Mitsubishi Heavy Industries Ltd, extend the production factory one after more another even more.

From U.S.A., ' Million Roofs Solar Power ' scheme which former president Mr. Dr.eye: Clinton puts forward, plan before 2010, finish constructing the electricity generation system of 100 ten thousand households of solar energy.

Besides Japan and U.S.A., Germany is from 1990 too, begin to implement a thousand rooms of plans, the capacity of the device that each solar energy generates electricity is while beginning 5 kilowtts in 1, the government subsidizes 70% of the funds. By 1995, 2,250 have installed solar energy systematically already, the capacity of the total device is up to watt 5.6 million too. In addition, the Dutch government estimated in 2020 too, the systematic capacity of total device of solar energy can be up to watt 1,450 million. As for other various countries, the countries, such as Switzerland, Norway and Australia,etc., both pursue the solar cell erection schedules of thousands of of every year.

: From Taiwan, the leading firm producing the solar cell at present has such companies as brilliance, luxuriant guiding and intellectual circles electrical machinery,etc.. Developed the scientific & technical corporation since 1988, mainlied product solar cell of non-crystalline silicon in brilliance, apply it to on the consuming electronic product mainly, like wrist-watch, calculator,etc.. In 1999, guiding the company luxuriantly begins to set up the factory in the scientific industrial area of Tainan, mainly product solar cell of monocrystalline silicon and polycrystalline silicon. Intellectual circles electrical machinery is it research and develop group get U.S.A. accept training, study solar energy manufacture and encapsulation technology of panel satellite use to send once too, at the same time after succeeding in launching the Chinese satellite for the first 1999, the solar cell gone still one step further to put into the people's livelihood use was researched and developed.
In addition, the material of research institute of the industrial technology develops the manufacture of the solar cell and encapsulation technology successfully, and is it give technology luxuriant to guide company and intellectual circles electrical machinery Company to shift, in order to popularize domestic solar energy generate electricity cause. In recent years, the investment in the undertaking of the solar cell of domestic manufacturer gets to feel the interest too, main reason except high demand of the international market, another factor from 1999 government, promote the solar cell to generate electricity in a more cost-effective manner at the beginning, and set about promoting every reward measure, so the person who invests family property of this undertaking obviously increases.
At present, the ones that are pursuing the solar energy and generating electricity are including some difficult problems at work at home, application formality that it is that more general market electricity and solar energy generate electricity that the main reason is, apply for city electricity obviously convenient a lot of, and establishment that solar energy generate electricity must invest a sum of fund first.: Because of the doing in the test amount of economy, it is really more difficult to accept for general people.

Even so, change one angle is it watch to come, Taiwan person who has sunshine abundance, semiconductor and electric and electronic industry development sound and government do one's utmost munificent terms of popularizing etc., combine with the possible energy crisis, and environmental consciousness is popularized etc., the solar energy generates electricity the undertaking really has very large development space in Taiwan. Believe that can only reduce the manufacturing cost by a wide margin, can try hard to catch up other countries, occupy a tiny space.

Prospect

Can't it generates electricity to be one great shortcoming of solar cell night, have two ways may be overcome to the shortcoming. The first way is to change the sun and light energy in daytime into other energy forms to store, for example battery, flywheel device, is it hold power plant,etc. to release, is it release to release energy that store and then in to night.

Another way is plans of ' the solar energy power plant of the satellite ' afoot of U.S.A. and two Japanese countries ( Satellite Solar Power Station, SPSS) ,The working project of this plan is to find a place that can accept the sunlight constantly in the space, for example the sky, launch the satellite with solar cell or heat energy electricity generation system near the equator, utilize satellites to absorb the solar energy to generate electricity in the space. Avoid day and night, difference in temperature and climate,etc. factor influenced, the satellite can not park and receive the solar energy steadily in succession, change it into the electric energy again, then pass the earth back by way of microwave, after the microwave acception station of the earth is received, and then change back and become electric energy, send to each place.

At present, because of the constant research of the scientists, combining with the progress of industry's technology of the semiconductor, the efficiency of the solar cell increases gradually too, and the unit cost of the electricity generation system is dropping year by year. So, with the increase, reducing of the cost and upsurge of environmental consciousness of the efficiency of the solar cell, the use of the solar cell will be more and more general too. Now, the solar cell has already been used in daily life extensively, such as wrist-watch, calculator, automobile, plane,etc., Dr.eye: it is obvious it has very great development potentiality, it is believed that the solar cell can play an important role in the application of the energy in the future.
: Source of the materials: >June of 2005, 390 issues, 50- 5 page (pdf shelf)