from the Sun
The Sun is our
greatest energy source: powerful, lasting, reliable, and available
all over the world. Every hour the sunlight that reaches the earth
is greater than the amount of energy used by every person on the
planet in an entire year.
a versatile and flexible technology, can be designed to meet almost
any need in practically any location. In space and in air, on land
and at sea, photovoltaics produce energy when and where it is needed.
The term photovoltaic
is derived by combining the Greek word for light, photos,
with voltaic, named for Alessandro
Volta, a pioneer in the study of electricity. Thus, a solar photovoltaic
(PV) cell is one that converts sunlight
- as opposed to sun heat - to electricity.
cells perform this conversion without any moving parts, noise, pollution,
radiation, or maintenance. PV cells are made of a semiconducter
material, typically silicon (from beach sand, an abundant resource),
which is treated chemically to create a positive charge layer and
a negative charge layer. When sunlight strikes a PV cell,
an electron is dislodged. These loose electrons are gathered by
wires attached to the cell, forming an electrical current. The more
cells, the greater the current and voltage. A number of PV cells
laid side-by-side form a rectangular module;
several modules together form an array.
PV modules sold commercially range in power output from about 5
watts to 300 watts, and produce a direct current (DC) like the current
from a car's battery.
PV systems are
already part of our lives. The smallest systems power calculators
and wrist watches. Larger systems provide electricity for water
pumps, highway signs, communications equipment, satellites, mobile
homes, medical purposes (to power medical equipment, water purifiers,
and refrigerators holding vaccines), navigation buoys, streetlights,
and even for lighting homes and running appliances.
Oceanic and Atmospheric Administration (NOAA) uses this solar-powered
buoy to collect weather data off the coast of the United States.
Stand-alone photovoltaic applications, whether for remote buildings,
service applications or island power supplies, represent about 90%
of installed PV power today. Stand Alone PV systems provide power
when and where it is needed, without the need for a utility grid.
Batteries are included to provide energy storage to operate loads
during the night and during cloudy or stormy weather. The solar
module(s) recharge the batteries when average or good weather returns.
PV modules and batteries are sized to meet the power requirements
of the particular load. If Alternating Current (AC) power is desired,
as in an off-grid remote home, a DC-AC inverter
is required. For most Stand Alone applications, a PV system is the
most cost-effective alternative to providing power. There are over
25,000 homes in California today that are off-grid and powered primarily
Systems get the job done without the need for batteries. Solar module(s)
produces DC current that is immediately used by a DC motor load.
As sunlight rises and falls, current and voltage rise and fall,
and the motor speeds up and slows down proportionately. There is
no storage, the motor does not operate at night, and operates slowly
during cloudy or stormy weather. Solar water pumps used in the Sahara
are an example of this type of application.
Grid-tied photovoltaics are the new frontier. Buildings consume
vast amounts of energy: more than two-thirds of the energy used
in the United States goes to heating, cooling, and lighting buildings.
Photovoltaic materials can be integrated into every building, new
or old, to harness the Sun's energy to generate electricity. Grid
tied PV systems are wired into buildings that are connected to the
Utility Grid, hence the term grid tied. Energy produced by your
PV system can be used directly in your home or business, or if there
is an excess, flow out through your meter, providing power to your
neighbors. In many States, you receive a credit for this excess
power, to be used later, at night for example, when you need power
from the grid. This is an arrangement called Net
Metering and helps to improve the economics of a grid-tied
PV system. Batteries are generally not required since the utility
grid acts as a huge 'battery' in this application. An exception
would be to provide power for critical loads, during utility outages,
which would require a small onsite battery bank.
Photo Gallery to see
more Photovoltaic applications.