How Solar Cells Work

1
How Solar Cells Work
2
Free Green Electricity

• A solar cell can convert light into electricity.
  This is particularly beneficial if the light is
  free as in daylight? Given the costs and
  environmental consequences of fuels such as oil,
  gas and coal used in generating electricity,
  isnt it nice that solar cells can give us energy
  for free without releasing greenhouse gases?

3
Electrical energy and electric circuits

• Electrical energy from a mains socket
• this comes from power stations over a grid of
  wires that spans the country
• some wires are underground, but some you can see
  on pylons

• Electrical energy from a battery
• this comes from a chemical reaction in the
  battery
• when the chemicals are all used up the battery
  dies

4
Electrical energy and solar cells

• Electrical energy from a solar cell
• in a solar cell light energy from the Sun is
  converted into electrical energy
• the more light energy striking the solar cell the
  more electrical energy will be generated

5
Electric currents

• An electric current is due to the flow of
  billions upon billions upon billions of tiny
  particles called electrons.
• Electrons flow from a region of low (or negative)
  voltage to one with a higher (or positive)
  voltage (this can be created by a battery).

6
Electrons
Meet an electron. It is part of a vast family
where everyone looks identical. Each electron is
a tiny particle that causes electricity. Electron
s are found in every material.
Like most family members electrons need their own
space and repel other family members if they get
too close.
7
Electrons and conductors and insulators

• In an electrical conductor electrons are free to
  move about easily. Metals are electrical
  conductors.
• In an electrical insulator electrons are not able
  to move about easily. Materials such as
  plastics, rubber and glass are common electrical
  insulators.

8
Electrons and semiconductors

• Some electrons live in materials called
  semiconductors.
• A semiconductor is a funny material where some
  electrons may have enough energy to travel about
  freely, but only if they are warm enough, or in a
  bright light.
• As its name suggests, a semiconductor has
  properties in between those of an electrical
  conductor and an electrical insulator.

9
Electrons and semiconductors

• When two semiconductors are joined together, they
  can form a step.
• For the electrons to flow around the circuit they
  must gain energy to jump from the lower level up
  on to the step.
• A solar cell can be made from two semiconductors
  joined in this way.

10
Solar cells

• In a bright enough light, the electrons are
  lifted by the light energy and given enough
  energy to jump up the step.
• When they jump up the step, they generate a
  voltage difference that allows them to then
  travel back though an external circuit.
• This forms an electric current which supplies
  energy to a load such as a lamp or motor just
  like a battery.
• With no light, the electrons cannot jump up the
  step, there is then no current and no energy is
  transferred around the circuit.

11
Using solar cells

• Solar cells can be of various sizes and used to
  provide energy that can be stored in rechargeable
  batteries, or used directly, to power lights,
  fans, road signs, calculators, homes and even
  whole towns.
• They are, however, rather costly and inefficient
  further research and development should solve
  these problems.

12
Summary

• A solar cell converts light energy to electrical
  energy.
• A solar cell is like a battery but powered by
  light instead of a chemical reaction.
• A solar cell is made from semiconductor
  materials.
• Shining light on to the solar cell causes
  electrons in the solar cell to gain electrical
  energy.
• When there is a complete conducting circuit the
  electrons which have gained electrical energy can
  flow around the circuit transferring their energy
  to some form of load such as a lamp or a motor.