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TRAMS AND ALTERNATE POWER

INTRODUCTION: We were given an assignment on power. We had to select a power source and something that uses power. For our case we chose solar power and trams. Our goal was to see if trams could run off solar power and what would have to be done to do this.

SOLAR POWER: There are three main ways to use the sun's energy and convert it in to solar energy.

1) Solar Cells (really called "photovoltaic" or "photoelectric" cells) that convert light directly into electricity. In a sunny climate, you can get enough power to run a 100W light bulb from just one square meter of solar panel. This was originally developed in order to provide electricity for satellites, but these days many of us own calculators powered by solar cells.

2) Solar water heating, where heat from the Sun is used to heat water in glass panels on your roof. This means you don't need to use so much gas or electricity to heat your water at home. Water is pumped through pipes in panel. The pipes are painted black, so they get hot when the Sun shines on them. This helps out your central heating system, And cuts your fuel bills. However, in the UK you must remember to drain the water out to stop the panels freezing in the winter. Solar heating is worthwhile in places like California and Australia, where you get lots of sunshine.

3) Solar Furnaces use a huge array of mirrors to concentrate the Sun's energy into a small space and produce very high temperatures. It can achieve temperatures up to 33'000 degree Celsius.

Silicon makes a good base for the solar panels because a silicon atom only contains 14 electrons, which are arranged in 3 shells. The first two shells are completely full of electrons, so they are not looking for any more. The outer shell however, only has4 electrons, so will try and get 4 more electrons. To try and get the 4 more electrons the atom wants, it will join with four other silicon atom to form what we call a crystalline structure. This is a pure silicon cell, which is a bad conductor.

A solar cell has silicon with impurities -- other atoms mixed in with the silicon atoms, changing the way things work a bit. We usually think of impurities as something undesirable, but in our case, our cell wouldn't work without them. These impurities are actually put there on purpose. Consider silicon with an atom of phosphorous here and there, maybe one for every million silicon atoms. Phosphorous has five electrons in its outer shell, not four. It still bonds with its silicon neighbour atoms, but in a sense, the phosphorous has one electron that doesn't have anyone to hold hands with. It doesn't form part of a bond, but there is a positive proton in the phosphorous nucleus holding it in place.

When energy is added to pure silicon, for example in the form of heat, it can cause a few electrons to break free of their bonds and leave their atoms. A hole is left behind in each case. These electrons then wander randomly around the crystalline lattice looking for another hole to fall into. These electrons are called free carriers, and can carry electrical current. There are so few of them in pure silicon, however, that they aren't very useful. Our impure silicon with phosphorous atoms mixed in is a different story. It turns out that it takes a lot less energy to knock loose one of our "extra" phosphorous electrons because they aren't tied up in a bond -- their neighbours aren't holding them back. As a result, most of these electrons do break free, and we have a lot more free carriers than we would have in pure silicon. The process of adding impurities on purpose is called doping, and when doped with phosphorous, the resulting silicon is called N-type ("n" for negative) because of the prevalence of free electrons. N-type doped silicon is a much better conductor than pure silicon is.

 Conventional Power Generation – Coal power stations

1.Coal is delivered to the power station from the coal storage area on a conveyer. Coal contains chemical energy stored, which is potential energy.

2.  From the conveyers, the coal is delivered to the boilers and is burnt. This creates heat, which is an energy transformation.

3.  The heat from burning coal boils water circulating at high pressure in the boiler tubes. The water circulating is movement and therefore kinetic energy.

4.  The steam created by the water vapor travels through the pipes at high pressure, which is also kinetic energy.

5.  1. The steam is taken by pipes to the steam turbine.

6.  Here the steam is used to turn the turbines at high speed, creating kinetic energy.

7.  From the turbine, the steam enters the condenser and passes over tubes containing cooling water. It is the transformed back into water and creates a vacuum which helps advance the flow of steam through the turbine. The water is returned to the boiler under pressure by a series of pumps.

8.  The generator consists of a rotor…

9.     … and a stator. The rotor, which is an electro-magnet* made of a number of windings mounted on a shaft, is joined to the turbine shaft so that it is turned at high speed with the turbine and generates electricity in more windings that make up the stator.

10.  A small generator driven from the end of the rotor shaft produces the current required to energize the rotor.

11.  In the largest modern generators electricity may be generated at about 25,000 volts but for efficient transmission over long distances the voltage is increased by transformers to275,000 or 400,000 volts.

12.  The voltage is reduced by other transformers to 132,000 volts for local transmission and reduced still further for distribution to consumers at suitable voltages 33,000 volts for heavy industries, 11,000 volts for light industries and 240 volts for homes and farms.http://www.transport.alstom.com.au/

REFERENCES:

http://www.transport.alstom.com.au/photo_citadis_diagram_lge.jpg

Comments:

From Siebert - 6/8/05 1:25 PM