radiation produced by nuclear fusion reactions deep in
the Sunís core. Solar energy travels to Earth through
space in discrete packets of energy called photons19. A Photon is defined as a packet or
quantum of a wave-like fluctuations in electric and
magnetic fields traveling through free space or a
The simplest example of solar energy use is your calculator. As
long as there is light in the room, the calculator will
always work by converting light into useful energy. The
solar cells on a calculator are called photovoltaic cells
and are made of semiconductors, like silicon19.
On the side of Earth facing the Sun, a square kilometer at the
outer edge of our atmosphere receives 1,400 megawatts of
solar power every minute. Only half of that amount
reaches Earthís surface. The amount of light that reaches
any point on the ground depends on the time of day. The
total radiation power varies only slightly, about 0.2
percent every 30 years. Any considerable change would
alter or end life on Earth19.
Greenhouses and solariums are common examples of the direct use of
solar energy, having glass surfaces that allow the
passage of visible light from the sun but slow down the
escape of heat and infrared energy3.