A solar simulator is a device that provides illumination
approximating natural sunlight. The purpose of the solar simulator is to
provide a controllable indoor test facility under laboratory conditions, used
for the testing of solar cells, sun screen, plastics, and other materials and
devices. The basic idea of a solar cell is to convert light energy into
electrical energy. The energy of light is transmitted by photons, small packets
or quanta of light. Electrical energy is stored in electromagnetic fields,
which in turn can make a current of electrons flow. Thus a solar cell converts
light, a flow of photons, to electric current, a flow of electrons.
When photons are
absorbed by matter in the solar cell, their energy excites electrons higher
energy states where the electrons can move more freely. The perhaps most
well-known example of this is the photoelectric effect, where photons give
electrons in a metal enough energy to escape the surface. In an ordinary
material, if the electrons are not given enough energy to escape, they would
soon relax back to their ground states. In a solar cell however, the way it is
put together prevents this from happening. The electrons are instead forced to
one side of the solar cell, where the build-up of negative charge makes a
current flow through an external circuit. The current ends up at the other side
(or terminal) of the solar cell, where the electrons once again enter the
ground state, as they have lost energy in the external circuit
