Environmental Engineering Reference
In-Depth Information
CAUTION!
SOLAR PANELS: LIFT THEM SAFELY!
Never climb ladders while carrying solar panels.
Always use lifting equipment whenever possible, such as ladder
hoists, swing hoists, or truck-mounted cranes/conveyors.
If lifting equipment is not used, manually lift panels to the
roof using ropes, platforms, or other methods in accordance
with best materials handling practices.
P
hotovoltaics
Photovoltaic (
photo
, light;
volt
, from electricity pioneer Alessandro Volta) technol-
ogy makes use of the abundant energy in the sun by employing a semiconductor
material—traditionally silicon but, increasingly, other materials as well—to con-
vert sunlight directly into electricity. Photovoltaics is the direct conversion of light
into electricity at the atomic level. Some materials exhibit a property known as the
photoelectric effect
(discovered and described by Becquerel in 1839) that causes
them to absorb photons of light and release electrons. When these free electrons
are captured, an electric current results (i.e., electricity is the flow of free elec-
trons) that can be used as electricity. The first photovoltaic module (billed as a
solar battery) was built by Bell Laboratories in 1954. In the 1960s, the space pro-
gram began to make the first serious use of the technology to provide power aboard
spacecraft. Space program use helped this technology make giant advancements
in reliability and helped to lower costs associated with photovoltaics; however, it
was the oil embargo of the 1970s (the so-called energy crisis) that focused attention
on using photovoltaic technology for applications other than the space program.
Photovoltaics can be used in a wide range of products, from small consumer items
to large commercial solar electric systems.
Figure 3.1
i
illustrates the operation of a basic
photovoltaic cell
, also called a
solar
cell
. Solar cells are made of silicon and other semiconductor materials such as ger-
manium, gallium arsenide, and silicon carbide that are used in the microelectronics
industry. For solar cells, a thin semiconductor wafer is specially treated to form
an electric field, positive on one side and negative on the other. When light energy
strikes the solar cell, electrons are jarred loose from the atoms in the semiconduc-
tor material. If electrical conductors are attached to the positive and negative sides,
DID YOU KNOW?
Solar energy is a completely free source of energy, and it is found in abun-
dance. Although the sun is 90 million miles from the Earth, it takes less than
10 minutes for light to travel that far.
