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Why Use Solar Cells?

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Why Use Solar Cells? Low maintenance, long lasting sources of energy Provides cost-effective power supplies for people remote from the main electricity grid – PowerPoint PPT presentation

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Title: Why Use Solar Cells?


1
Why Use Solar Cells?
  • Low maintenance, long lasting sources of energy
  • Provides cost-effective power supplies for people
    remote from the main electricity grid
  • Non-polluting and silent sources of electricity
  • Convenient and flexible source of small amounts
    of power
  • Renewable and sustainable power, as a means to
    reduce global warming
  • In 2002, the global market for photovoltaic
    panels and equipment was valued at 3.5 billion
    dollars

2
The Solar Cell
  • The most common type of solar cells are
    Photovoltaic Cells (PV cells)
  • Converts sunlight directly into electricity
  • Cells are made of a semiconductor material (eg.
    silicon)
  • Light strikes the PV cell, and a certain portion
    is absorbed
  • The light energy (in the form of photons) knocks
    electrons loose, allowing them to flow freely,
    forming a current
  • Metal contacts on the top and bottom of PV cell
    draws off the current to use externally as power

3
The Single Crystalline Silicon Solar Cell
  • Pure silicon is a poor conductor of electricity
  • Doping of silicon with phosphorus and boron is
    necessary to create n-type and p-type regions
  • This allows presence of free electrons and
    electron-free holes
  • The p-n junction generates an electric field that
    acts as a diode, pushing electrons to flow from
    the P side to the N side

4
The Solar Cell
5
When Light Hits the Cell
  • Light energy (photons) ionizes the atoms in the
    silicon and the internal field produced by the
    junction separates some of the positive charges
    (holes) from the negative charges (electrons)
  • The holes are swept into the p-layer and the
    electrons are swept into the n-layer
  • The charges can only recombine by passing through
    an external circuit outside the material
  • Power is produced since the free electrons have
    to pass through the load to recombine with the
    positive holes

6
Efficiency of Solar Cells
  • The amount of power available from a PV device is
    determined by
  • Type and area of the material
  • The intensity of the sunlight
  • The wavelength of the sunlight
  • Single crystalline solar cells ? 25 efficency
  • Polycrystalline silicon solar cells ? less than
    20
  • Amorphous silicon solar cells ? less than 10
  • Cells are connected in series to form a panel to
    provide larger voltages and an increased current

7
Arrays and Systems
  • Panels of solar cells can be linked together to
    form a larger system an array

(a) a PV panel array, ranging from two to many
hundreds of panels(b) a control panel, to
regulate the power from the panels(c) a power
storage system, generally comprising of a number
of specially designed batteries(d) an inverter,
for converting the DC to AC power (eg 240 V
AC)(e) backup power supplies such as diesel
startup generators (optional)(f) framework and
housing for the system(g) trackers and sensors
(optional)
8
Solar Cells are used in a wide variety of
applications
  • Toys, watches, calculators
  • Electric fences
  • Remote lighting systems
  • Water pumping
  • Water treatment
  • Emergency power
  • Portable power supplies
  • Satellites

9
Future Applications
The Flexible Solar Cell
  • Looks like denim
  • Can be draped over any shape
  • No rigid, silicon base
  • Made of thousands of flexible, inexpensive solar
    beads between two layers of aluminum foil
  • Each bead functions as a tiny solar cell

10
Future Applications
Organic Solar Cells
  • Based on photosynthesis in plants
  • Use of light-sensitive dyes
  • Cost of manufacture is decreased by 60

New Alloys
  • Indium, gallium, and Nitrogen
  • Converts full spectrum of sunlight from
    near-infrared to far-ultraviolet

11
Future Applications
Nano Solar Cells
  • Tiny rods are embedded in a semi-conducting
    plastic layer sandwiched between two electrodes
  • Rods act like wires, absorbing light to create an
    electric current

Tetrapod Nanocrystals
  • May double the efficiency of plastic solar
    cells
  • Made of cadmium, tellurium
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