SOLAR CELL

Presenter: Damion Lawrence, M.Sc., B.Ed.

1

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

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 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

• 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

The Flexible Solar Cell

Future Applications

• Based on photosynthesis in plants

• Use of light-sensitive dyes

• Cost of manufacture is decreased by 60%

Organic Solar Cells

New Alloys

• Indium, gallium, and Nitrogen

• Converts full spectrum of sunlight from

near-infrared to far-ultraviolet

Future Applications

• 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

Nano Solar Cells

Tetrapod Nanocrystals

• May double the efficiency of plastic solar cells

• Made of cadmium, tellurium