Solar Photovoltaic Technology
Solar cells, also called photovoltaic (PV) cells by scientists,
convert sunlight directly into electricity. PV gets its name from
the process of converting light (photons) to electricity (voltage),
which is called the PV effect. The PV effect was discovered in 1954,
when scientists at Bell Telephone discovered that silicon (an
element found in sand) created an electric charge when exposed to
sunlight. Soon solar cells were being used to power space satellites
and smaller items like calculators and watches. Today, thousands of
people power their homes and businesses with individual solar PV
systems. Utility companies are also using PV technology for large
power stations.
Solar panels used to power homes and businesses are typically made
from solar cells combined into modules that hold about 40 cells. A
typical home will use about 10 to 20 solar panels to power the home.
The panels are mounted at a fixed angle facing south, or they can be
mounted on a tracking device that follows the sun, allowing them to
capture the most sunlight. Many solar panels combined together to
create one system is called a solar array. For large electric
utility or industrial applications, hundreds of solar arrays are
interconnected to form a large utility-scale PV system.
Traditional solar cells are made from silicon, are usually flat-plate,
and generally are the most efficient. Second-generation solar cells are
called thin-film solar cells because they are made from amorphous silicon or
nonsilicon materials such as cadmium telluride. Thin film solar cells use
layers of semiconductor materials only a few micrometers thick. Because of
their flexibility, thin film solar cells can double as rooftop shingles and
tiles, building facades, or the glazing for skylights.
Third-generation solar cells are being made from variety of new materials
besides silicon, including solar inks using conventional printing press
technologies, solar dyes, and conductive plastics. Some new solar cells use
plastic lenses or mirrors to concentrate sunlight onto a very small piece of
high efficiency PV material. The PV material is more expensive, but because
so little is needed, these systems are becoming cost effective for use by
utilities and industry. However, because the lenses must be pointed at the
sun, the use of concentrating collectors is limited to the sunniest parts of
the country.