Transcript Solar Energy - Photovoltaics

Solar Energy - Photovoltaics
UTI-111
Prof. Park
Essex County College
Energy from the Sun
• The sun’s outer surface, called the photosphere, radiates
energy in the form of light and heat.
• The sun’s inner core is composed of primarily of dense
Hydrogen and Helium at a temperature of approximately
27 million F. The light and heat from the sun is produced
when these gases undergo fusion.
• Of the total energy from the sun that reaches the earth,
about 30% is reflected back to space, 47% is absorbed
and converted to heat and 23% drive the water cycle.
• The solar energy that the earth received is called
insolation.
Conversion of Solar Energy
• Conversion of solar energy into electrical energy
involves the use of solar cells.
• Solar cells, also called photovoltaics (PV), convert
sunlight directly into electricity.
• For example, a calculator can be powered by solar cells.
History of PV
• In 1839, French physicist Edmond Becquerel (3/24/1820
– 5/11/1891) discovered the process of using sunlight to
produce an electric current in a solid material.
• In 1883, New York electrician Charles Edgar Fritts,
constructed a selenium solar cell and filed a patent.
• In 1953, Bell Lab researchers Chaplin-Fuller-Pearson
team produced doped silicon solar cells with an
efficiency of 6%.
Photoelectric Effect
• The Photoelectric Effect is the physical process by which
a PV cell converts sunlight into electricity.
• When light strikes a PV cell, it may be reflected,
absorbed, or pass through.
• The light that is absorbed produces electricity.
• The light energy absorbed by the PV excites the
electrons in the atoms of the PV cell. The electrons
escapes from their original positions in the atoms of the
semiconductor material and becomes part of the
electrical flow, or current, in an electrical circuit.
PV Cells Construction
• To induce the built-in electric field within a PV cell, two
layers of different semiconductor materials are placed in
contact with one another.
• The conductivity of semiconductor increases with
temperature and in the presence of impurities.
• The addition of these impurities is called doping.
• In a PV cell, photons are absorbed in the p-layer. It is
important to optimize this layer to the properties of
incoming photons to absorb as many as possible, and
thus, to free up as many electrons as possible while
keeping the electrons from meeting up with holes and
recombining with them before they can escape from the
PV cell.
PV Cells Construction
• Electrical contacts are essential to a PV cell because
they bridge the connection between semiconductor
material and the external electrical connection.
• The back contact of a cell consists of a layer of
aluminum or molybdenum.
• The front contact is complicated by the need to design a
low resistance point that will collect the maximum
current.
• To do this, contacts must be placed across the entire
surface of a PV cell.
• This is normally done with a gird of metal strips or
fingers. Since this grid will absorb light, the design must
balance shading and electrical losses.
Solar Cells, Modules, and Arrays
• Solar cells are typically combined into modules that hold
about 40 cells; About 10 of these modules are mounted
in a PV arrays that can measure up to several meters on
a side.
• These PV arrays can be 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 over the course of a day.
• About 10 to 20 PV arrays can provide enough power for
a household; for a large utility or industrial applications,
hundreds of arrays can be interconnected to form a
single large system.
Regional Ranking of Global PV Cell Production in 2008
(Crystalline and Thin Film, Percentage Ranking by Production in Watts)