Solar cells convert sunlight into electricity by using semiconductor materials, most commonly silicon, where photons knock electrons loose allowing them to flow as an electric current; different types of solar cells have varying efficiencies with single crystalline silicon cells being the most efficient at 25%; solar cells can be connected together in panels and arrays to provide power for various applications from small electronics to entire homes.
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. 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
4. The Single Crystalline Silicon
Solar Cell
⢠Pure silicon is a poor
conductor of electricity
⢠âDopingâ 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 âholesâ
⢠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
6. 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
7. Efficiency of Solar Cells
⢠The amount of power available from a PV device
is determined by
â Type and area of the material
â The intensity of the sunlight
â The wavelength of the sunlight
⢠Single crystalline solar cells ď 25% efficency
⢠Polycrystalline silicon solar cells ď less than
20%
⢠Amorphous silicon solar cells ď less than 10%
⢠Cells are connected in series to form a panel to
provide larger voltages and an increased current
8. Arrays and Systems
⢠Panels of solar cells can be linked together
to form a larger system â 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);
9. 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
10. 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
11. 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
12. 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