HOW DO SOLAR PANELS WORK?

How is sunlight turned into electricity?

Solar or photovoltaic (photo = light, voltaic =
voltage or electricity) cells are created from
special materials such as Silicon (Si) mixed with
other elements, which when exposed to sunlight
will generate an electrical current. Basically
sunlight is absorbed into the photovoltaic
material, which in turn knocks electrons within
the material loose. This allows the electrons to
flow freely within the material structure,
creating an electrical current.

Why use Silicon?

Silicon is a common choice for solar cells because
of its inherent physical qualities. Silicon has 4
outer shell electrons from a possible 8 ‘holes’. It
will always try to fill the other 4 ‘holes’, and does
this by sharing electrons with neighbouring silicon
atoms. This creates a lattice type structure,
where every atom in the structure bonds with
four other atoms in the structure.
When energy is added to the silicon, in the form of
sunlight, it can knock electrons free of the lattice
structure, but this requires a lot of energy and
generates very few free electrons. With few free
electrons, there is very little current flow, so
impurities are added to the silicon to increase its
current carrying properties. This process is called
‘doping’.
The silicon is ‘doped’ with atoms which contain
more electrons to create negatively charged
silicon or with atoms which contain less electrons
to create positively charged silicon. These
compounds are referred to as n-type and p-type
respectively.
When energy is added to n-type silicon there are a
lot more free electrons present within the
structure. This n-type silicon is placed next to
the p-type silicon, causing the free electrons in
the n-type silicon to rush towards the holes in the
p-type silicon, which creates a current flow.

Physicists Find Way to Convert Light into Matter

In 1934, American theoretical physicists Dr Gregory
Breit and Dr John A. Wheeler suggested that it
should be possible to turn light into matter by
smashing together only two particles of light –
photons, to create an electron and a positron.
“Despite all physicists accepting the theory to be
true, when Dr Breit and Dr Wheeler first proposed
the theory, they said that they never expected it
be shown in the laboratory,” Prof Rose explained.
But a new experiment conducted by his team shows
for the first time how the Breit and Wheeler’s
theory could be proven in practice.
“Today, nearly 80 years later, we prove them
wrong. What was so surprising to us was the
discovery of how we can create matter directly
from light using the technology that we have today
in the UK. As we are theorists we are now talking
to others who can use our ideas to undertake this
landmark experiment,” said Prof Rose, the senior
author of a paper published in the journal Nature
Photonics.
The photon-photon collider experiment that the
physicists have proposed involves two steps.
First, they would use a powerful high-intensity
laser to speed up electrons to just below the speed
of light.
They would then fire these electrons into a slab of
gold to create a beam of photons a billion times
more energetic than visible light.
The next stage of the experiment involves a tiny
gold can called a hohlraum. The scientists would fire
a high-energy laser at the inner surface of this
gold can, to create a thermal radiation field,
generating light similar to the light emitted by
stars.
They would then direct the photon beam from the
first stage of the experiment through the center of
the can, causing the photons from the two sources
to collide and form electrons and positrons. It would
then be possible to detect the formation of the
electrons and positrons when they exited the can.
“Although the theory is conceptually simple, it has
been very difficult to verify experimentally,” said
Oliver Pike, a PhD student at Imperial College and
the first author on the study.
“We were able to develop the idea for the collider
very quickly, but the experimental design we
propose can be carried out with relative ease and
with existing technology.”
“Within a few hours of looking for applications of
hohlraums outside their traditional role in fusion
energy research, we were astonished to find they
provided the perfect conditions for creating a
photon collider. The race to carry out and complete
the experiment is on!”
Demonstrating the Breit-Wheeler theory would
provide the final jigsaw piece of a physics puzzle
which describes the simplest ways in which light and
matter interact.