Transcript Solar Cells are used in a wide variety of applications

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
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
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
The Solar Cell
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
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
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);
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
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
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
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