<?xml-model href="../schema_3302.rng" type="application/xml" schematypens="http://relaxng.org/ns/structure/1.0"?><!--the second line in the document associates the schema, so be sure not to change it-->
<DOC>
<docHead>
<!--required header includes metadata about the assignment (title, author, version)-->
<title>Writing Project 3</title>
<version n="4" date="2016-08-22"/>
</docHead>
<blog_post>
<title>How does solar energy work?</title>
<background>
<section_header>How does solar energy work?</section_header>
<question>How does sunlight shining on a solar panel generate electricity?</question>
<misconception>You may have seen solar panels along the highway and thought you
understood how they work. Simply, you may state that when the shun shines on the
panel, electricity is generated. <visual type="photo" url="javascript:void(img9.show());"/>You would be correct, but this answer
is much more complicated than it first appears, as the act of sunlight shining on a
panel does not create electricity out of nothing. To understand how a solar panel
works, there are certain laws of nature that must be made clear.</misconception>
<technical_principle>One of the fundamental theories of the universe is the
<important_idea>Conservation of Energy.</important_idea></technical_principle>
</background>
<answer>
<section_header>The Conservation of Energy</section_header>
<technical_principle>The theory of the Conservation of Mass states that
<important_idea>energy cannot be created or destroyed, only
transformed.</important_idea> Therefore, in the case of solar panels, the
electricity (energy) generated by the panels is not magically created from nothing
when the sun shines. The electricity generated is thus a transformation of the only
other energy source available, light. An easier way to think of this concept is to
imagine baking a cake. <visual type="photo" url="http://www.how-to-draw-funny-cartoons.com/images/cartoon-cake-7.gif"/><analogy>All of the ingredients required to make a cake; the eggs, flour, milk etc.
can be thought of as a type of energy source. <visual type="photo" url="http://www.exclusivelyfood.com.au/uploaded_images/crepe1-792519.JPG"/>They all exist initially and once they are mixed together to form the batter,
none of the initial ingredients have been created or destroyed. The eggs, milk
and flour are all still in the bowl, just mixed together. Nothing has been lost.
The oven facilitates the transformation of the batter into the final product of
a cake, or the second form of energy.</analogy>The solar panels are simply a
method of facilitating this transformation of energy, from light to electricity,
much like the oven transforms the mixture of ingredients into the final form of a
cake.</technical_principle>
<section_header>So how do solar panels facilitate this energy
transformation?</section_header>
<technical_principle>A solar panel is made up of many individual
<important_idea>photovoltaic cells.</important_idea><visual type="photo" url="http://science.nasa.gov/media/medialibrary/2002/01/01/solarcells_resources/cell.gif"/>A photovoltaic cell has a design similar to a common battery, containing both
positive and negative charges, that when aligned properly can release electricity.
However, a photovoltaic cell relies on the use of a thin wafer made of a
semiconductor, usually silicon. The semiconductor wafer is specially treated to form
an electric field, with a positive charge on one side, and a negative charge on the
other. These individual cells are grouped together in groups of 12 to form a module,
similar to a 12 V battery. These modules are then combined to form a single solar
panel commonly seen on rooftops.</technical_principle>
<technical_principle>A semiconductor is a material that has the conductivity, or the
ability to carry an electrical current, between that of a good conductor, such as
metal, and that of an insulator, such as rubber. Semiconductors are used as they can
be altered and controlled quite easily to obtain the necessary level of electrical
resistance required to perform electrical operations. Common metals heat up too
quickly and conduct electricity too well, making it hard to use them in modern
electronics. <analogy>Just as we were told as children not to stand near metal
during a lightning storm, utilizing a metal conductor in a solar panel is just
as dangerous. The solar panels would overheat as there would be no resistance to
the electrical current, and the panels would likely catch fire.</analogy></technical_principle>
<section_header>So how do photovoltaic cells work?</section_header>
<technical_principle>Sunlight is made up of photons, atomic sized particles that radiate
from the sun.</technical_principle>
<explanation>When sunlight shines on the solar panels, the individual photons strike the
silicon and transfer their energy to the electrons of the silicon, knocking them
loose from the silicon atoms. <analogy>A photon can be thought of as the white (cue)
ball in the game of pool, and the electrons as the remaining stripes and solids.
Just after racking the balls (electrons), they are "stuck" in that position and
will not move unless a force acts upon them. <visual type="photo" url="http://img.aws.livestrongcdn.com/ls-article-image-640/cme/cme_public_images/www_livestrong_com/photos.demandstudios.com/getty/article/64/37/466394942_XS.jpg"/> When the cue ball (photon) smacks into the other balls during the break, the
energy is transferred to the other balls and they are knocked free of their
initial position.</analogy> These loose electrons are now free of the silicon,
but need to be directed to form an electrical current. This is achieved by the
photovoltaic cell by the use of an <important_idea>electric
field.</important_idea></explanation>
<section_header>What is an electric field?</section_header>
<technical_principle> An electric field is achieved by creating an imbalance within the
photovoltaic cell. This is done by taking two slightly different types of silicon
and placing them near each other. The electrons on the two types of silicon are
arranged differently, giving one side a slightly positive charge, and the other a
slightly negative charge. The two work together to create a path for the loose
electrons to move along, forming an orderly electric current. As electrons are
negatively charged, they will be pushed away from the negative side and towards the
positive side.<analogy> Just as water will always flow downhill due to the effects
of gravity, an electron will always move away from negatively charged objects
and towards a positive charge. This scientific principle will always hold true,
unlike the laws of nature when depicted in cartoons. <visual type="comic" url="http://itsfunny.org/wp-content/uploads/2013/05/Gravity-in-cartoons.jpg"/></analogy>The electric field directs this current to a node, which transfers
it out of the individual photovoltaic cells and converts it to an alternating
current (AC) form of electricity, which is able to be used on the
grid.</technical_principle>
<section_header>How much energy can be generated by solar panels?</section_header>
<technical_principle>Solar panels have a notoriously low <important_idea>energy
efficiency.</important_idea> Solar panels have an average efficiency of about
22%, meaning that only 22% of the electrons knocked loosed by the photons are
captured in the form of an electrical current. The remaining energy is usually lost
in the form of heat. The effectiveness of a solar panel is thus determined by how
well the electric field created by the semiconductor can direct the electrical
current to the node which transfers the electricity out of the photovoltaic
cells.<analogy> Going back to our pool example: A good pool player may hit a few
of the balls from the break into the pockets, but most will remain on the table.
The balls (electrons) that fall into the pockets represent the 22% efficiency of
the panels, as a majority of the balls still remain on the table.</analogy> New
technology is attempting to improve the efficiency of solar panels by changing the
surface of the silicon semiconductor. Thus more of the electrons would be captured
by the electric field and transferred out of the cell as electricity. The improved
technology would be in effect, <analogy>cutting channels in the pool table that
guide the balls to the pockets, increasing the likelihood they would go
in.</analogy></technical_principle>
<section_header>What have we learned?</section_header>
<conclusion>Solar energy is quite easy to understand once these basic concepts have been
explained. Sunlight, which is made up of photons, strike the photovoltaic cells
contained within the solar panels and knock electrons loose from the silicon
semiconductor. These electrons are then directed by the electric field created by
the PV cell into an electric current that can be transferred out of the cell and
onto the power grid. The efficiency of the panels at directing these loose electrons
into a current have a direct impact at the cost of energy generation and improving
the efficiency of the panels remains the most important research in the solar
technology field.</conclusion>
</answer>
<sources>
<citation style="APA" n="1"><title level="w">Florida Solar Energy Center</title><title level="a">Solar Energy Basics</title><ref>http://www.fsec.ucf.edu/en/consumer/solar_electricity/basics/index.htm</ref>
Web. 20 August 2016 </citation>
<citation style="APA" n="2"><title level="w">National Aeronautics and Space Administration</title><ref>http://science.nasa.gov/science-news/science-at-nasa/2002/solarcells/</ref>
Web. 18 August 2016 </citation>
<citation style="APA" n="3"><title level="w">The Physics Classroom</title><title level="a">Electric Field and the Movement of Charge</title><ref>http://www.physicsclassroom.com/class/circuits/Lesson-1/Electric-Field-and-the-Movement-of-Charge</ref>
Web. 21 August 2016 </citation>
<citation style="APA" n="4">
<title level="w">NW Wind and Solar</title>
<title level="a">How do solar systems generate electricity?</title>
<ref>http://www.nwwindandsolar.com/solar-power-in-seattle-and-the-northwest/how-do-solar-systems-produce-energy/</ref>
</citation>
</sources>
</blog_post>
</DOC>