Construction

How A Photovoltic Cell Works ----

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The "photovoltaic effect" is the basic physical process through which a PV cell converts sunlight into electricity. Sunlight is composed of photons, or particles of solar energy. These photons contain various amounts of energy corresponding to the different wavelengths of the solar spectrum. When photons strike a PV cell, they may be reflected or absorbed, or they may pass right through. Only the absorbed photons generate electricity. When this happens, the energy of the photon is transferred to an electron in an atom of the cell (which is actually a semiconductor). With its newfound energy, the electron is able to escape from its normal position associated with that atom to become part of the current in an electrical circuit. By leaving this position, the electron causes a "hole" to form. Special electrical properties of the PV cell-a built-in electric field-provide the voltage needed to drive the current through an external load (such as a light bulb).

p-Types, n-Types, and the Electric Field

To induce the electric field within a PV cell, two separate semiconductors are sandwiched together. The "p" and "n" types of semiconductors correspond to "positive" and "negative" because of their abundance of holes or electrons (the extra electrons make an "n" type because an electron actually has a negative charge). Although both materials are electrically neutral, n-type silicon has excess electrons and p-type silicon has excess holes. Sandwiching these together creates a p/n junction at their interface, thereby creating an electric field. When the p-type and n-type semiconductors are sandwiched together, the excess electrons in the n-type material flow to the p-type, and the holes thereby vacated during this process flow to the n-type. (The concept of a hole moving is somewhat like looking at a bubble in a liquid. Although it's the liquid that is actually moving, it's easier to describe the motion of the bubble as it moves in the opposite direction.) Through this electron and hole flow, the two semiconductors act as a battery, creating an electric field at the surface where they meet (known as the "junction"). It's this field that causes the electrons to jump from the semiconductor out toward the surface and make them available for the electrical circuit. At this same time, the holes move in the opposite direction, toward the positive surface, where they await incoming electrons. Making n and p Material The most common way of making p-type or n-type silicon material is to add an element that has an extra electron or is lacking an electron. In silicon, we use a process called "doping." We'll use silicon as an example because crystalline silicon was the semiconductor material used in the earliest successful PV devices, it's still the most widely used PV material, and, although other PV materials and designs exploit the PV effect in slightly different ways, knowing how the effect works in crystalline silicon gives us a basic understanding of how it works in all devices. Absorption and Conduction In a PV cell, photons are absorbed in the p layer. It's very important to "tune" this layer to the properties of the incoming photons to absorb as many as possible and thereby free as many electrons as possible. Another challenge is to keep the electrons from meeting up with holes and "recombining" with them before they can escape the cell. To do this, we design the material so that the electrons are freed as close to the junction as possible, so that the electric field can help send them through the "conduction" layer (the n layer) and out into the electric circuit. By maximizing all these characteristics, we improve the conversion efficiency* of the PV cell.

To make an efficient solar cell, we try to maximize absorption, minimize reflection and recombination, and thereby maximize conduction. *The conversion efficiency of a PV cell is the proportion of sunlight energy that the cell converts to electrical energy. This is very important when discussing PV devices, because improving this efficiency is vital to making PV energy competitive with more traditional sources of energy (e.g., fossil fuels). Naturally, if one efficient solar panel can provide as much energy as two less-efficient panels, then the cost of that energy (not to mention the space required) will be reduced. For comparison, the earliest PV devices converted about 1%-2% of sunlight energy into electric energy. Today's PV devices convert 7%-17% of light energy into electric energy. Of course, the other side of the equation is the money it costs to manufacture the PV devices. This has been improved over the years as well. In fact, today's PV systems produce electricity at a fraction of the cost of early PV systems.

Every fact of life on earth uses Mathematics in one manner or another. For instance, when you drive a car, you are computing your speed and how many miles you have gone. Balancing your checkbook also uses math. Yes, even musicians use math when playing their instruments.

Besides just that, math is needed in nearly every job from a high school summer job such as a cashier to an architect, math skills are always needed. Any job or employer prefers an employee who knows math well and is skilled at most aspects of math. Math is prominent in all aspects of life. Math is the most common subject in life besides English . Math is an everyday tool . It is helped for life because if not the "Real World" would be a big confusion . example ~ when you go to the store and the cashier gives you the wrong amount of change AND if you don't know math you would be stupid enough to go out of the store with the amount the cashier gave you . You wouldn't want to be this person and not have a correct amount of money to spend on your bills or something Math is very important in life because it is very helpful and when you are cooking you have to know how much ingredients your have to put in your food. Also when you are in any other subject like math it is very helpful too because without math you really wouldn't be anywhere right now. Math you use at Jobs, English, Science,Social Studies and more subject and things like that and when your anywhere else you also use math to count how many hings you need. Like when you are at the store and you only have $85.00 and you have to see the total amount for the things that you get/if you don't you would have to put some things back and come back and that is kind of why you need to know Math and this is why it is important in life. Math is a big help no matter what you do.
its important because sometimes some peoples dont know how to add or subtract we need math because we are going to need it in or during college

Scottish engineer John Loudon McAdam devised a type of road construction around 1820. It used small rocks, layered, on the road.

However, he just expanded upon on this idea. People in the early US threw on rutty roads old food scraps (example: potato peels), dry grasses, corn husks, other ruined crops, and hay, plus rocks.