Solar power

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Solar power

• The sun is the basic source of energy of our
  planet. The sun is a star of medium size that
  because of the big temperatures of its elements
  which compose it, the hydrogen, the molecules
  but also their particles are in a stage of
  plasma.
• In these temperatures, certain millions of oC,
  the very rapidly moved cores of hydrogen (H) are
  join together , and create cores of element of
  helium (He). This nuclear reaction - fusion of
  cores is exothermic and is going with enormous
  quantities of energy or heat or as is used to be
  said solar energy, that radiated to all
  directions in space.
• This happens continuously for 5 billions years
  roughly, the sun contains enormous quantities of
  hydrogen and it is not expected to be a reduction
  of energy which is radiated by the sun.
• In our country the sunlight lasts more than 2700
  hours per year. In Western Macedonia and the
  Ipirus it presents smaller prices from 2200
  until 2300 hours, while in Rhodes and southern
  Crete it exceeds the 3100 hours annually.

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Solar power
The Earth receives only the one billion of
energy the Sun radiates ( huge quantity )
The solar power that earth takes from the sun in
one week is equal in the energy of all fuels in
the planet
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Solar Energy
Solar hot water systems use sunlight to heat
water. Commercial solar water heaters began
appearing in the United States in the 1890s.
These systems saw increasing use until the 1920s
but were gradually replaced by relatively cheap
and more reliable conventional heating fuels. The
economic advantage of conventional heating fuels
has varied over time resulting in periodic
interest in solar hot water however, solar hot
water technologies have yet to show the sustained
momentum they had until the 1920s. Solar water
heating technologies have high efficiencies
relative to other solar technologies. Performance
will depend upon the site of deployment, but
flat-plate and evacuated-tube collectors can be
expected to have efficiencies above 60 percent
during normal operating conditions In addition,
solar water heating is particularly appropriate
for low-temperature (25-70 C) applications such
as swimming pools, domestic hot water, and space
heating. The most common types of solar water
heaters are batch systems, flat plate collectors
and evacuated tube collectors.
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Heating, ventilation, and air conditioning (HVAC)
systems of buildings are closely interrelated.
All seek to provide thermal comfort, acceptable
indoor air quality, and reasonable installation,
operation, and maintenance costs. Conventional
HVAC systems account for roughly 28 percent of
the energy used in the United States and European
Union.Many solar heating, cooling, and
ventilation technologies can be used to offset a
portion of this energy. Thermal mass materials
store solar energy during the day and release
this energy during cooler periods. Common thermal
mass materials include stone, cement, and water.
The proportion and placement of thermal mass
should consider several factors such as climate,
daylighting, and shading conditions. When
properly incorporated, thermal mass can passively
maintain comfortable temperatures while reducing
energy consumption. More advanced thermal mass
systems can be also be used for ventilation.
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Electricity can be generated from the sun in
several ways. Photovoltaics (PV) has been mainly
developed for small and medium-sized
applications, from the calculator powered by a
single solar cell to the PV power plant. For
large-scale generation, concentrating solar
thermal power plants have been more common but
new multi-megawatt PV plants have been built
recently. Other solar electrical generation
technologies are still at the experimental stage.
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Active Solar Domestic Water Heating
The active water systems that can be used to heat
domestic hot water are the same as the ones that
provide space heat. A space heat application will
require a larger system and additional connecting
hardware to a space heat distribution system.
There are five major components in active solar
water heating systems Collector(s) to capture
solar energy. Circulation system to move a fluid
between the collectors to a storage tank Storage
tank Backup heating system Control system to
regulate the overall system operation
There are two basic categories of active solar
water heating systems - direct or open loop
systems and indirect or closed loop systems.
Direct Systems The water that will be used as
domestic hot water is circulated directly into
the collectors from the storage tank (typically a
hot water heater which will back up the solar
heating). Indirect Systems that use antifreeze
fluids need regular inspection (at least every 2
years) of the antifreeze solution to verify its
viability. Oil or refrigerant circulating fluids
are sealed into the system and will not require
maintenance. A refrigerant system is generally
more costly and must be handled with care to
prevent leaking any refrigerant.
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Passive Solar Energy
Passive solar energy systems require no energy to
operate and are an intrinsic part of the home
design. Passive systems add little additional
cost, operate with almost no supervision and
require little or no maintenance. The basic
elements of all passive systems are south-facing
windows and internal thermal mass. Solar heating
is simply sunlight entering the house that is
absorbed and converted into heat energy which is
later released inside the house as it cools. A
passive solar home is one where the design and
construction of the home itself is made to keep
the house naturally warm in the winter using the
sun's energy. The design should also keep the
house naturally cool during the summer .The sun
is a very intense source of energy.  When
designed properly, a passive solar home can
experience heating costs that are 80 to 95
lower than for the average home. Air conditioning
costs can also be reduced to a minimal level.
The basic idea of passive solar home design is
to invite sunlight into the house during the
winter, and once it is inside the home, to hold
it in and store it until nighttime. Conversely,
the sun needs to be kept out during the summer.
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Electricity from the Sun
Electricity can be generated from solar energy in
two ways. The first is to capture heat from the
sun and use this to power a conventional turbine
or generator. The other is to use the
photovoltaic effect, which converts light
directly into electricity using materials called
semiconductors.
Solar Thermal Electric Power PlantsThe two main
types of solar thermal power plants are Solar
Chimneys (where heated air in a tower rises to
drive turbines) and Concentrating Solar Power
(CSP) plants (which use various types of
reflectors to concentrate sunlight into a heat
absorber). These are both industrial scale
applications which are not suitable for the urban
environment.
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Photovoltaic CellsThe word photovoltaic is a
marriage of the words photo, which means light,
and voltaic, which refers to the production of
electricity. Photovoltaic technology generates
electricity from light. Electricity is the
existence (either static or flowing) of
negatively charged particles called electrons.
Certain materials, called semiconductors, can be
adapted to release electrons when they are
exposed to light. One of the most common of these
materials is silicon (an element found in,
amongst other things, sand), which is the main
material in 98 of solar PV cells made today.
All PV cells have at least two layers of such
semiconductors one that is positively charged
and one that is negatively charged. When light
shines on the semiconductor, the electric field
across the junction between these two layers
causes electricity to flow - the greater the
intensity of the light, the greater the flow of
electricity. Although the photovoltaic effect was
known to the Victorians, it was not until
humanity launched into the space race that the
unique qualities of solar PV as a power source
began to be fully explored. Following this
kick-start the technology has raced along a path
to commercialization and the cost of PV generated
electricity has plummeted as manufacturing costs
have decreased and cell efficiencies have
improved.
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Anatomy of a Solar Cell Before now, our silicon
was all electrically neutral. Our extra electrons
were balanced out by the extra protons in the
phosphorous. Our missing electrons (holes) were
balanced out by the missing protons in the boron.
When the holes and electrons mix at the junction
between N-type and P-type silicon, however, that
neutrality is disrupted. Do all the free
electrons fill all the free holes? No. If they
did, then the whole arrangement wouldn't be very
useful. Right at the junction, however, they do
mix and form a barrier, making it harder and
harder for electrons on the N side to cross to
the P side. Eventually, equilibrium is reached,
and we have an electric field separating the two
sides. This electric field acts as a diode,
allowing (and even pushing) electrons to flow
from the P side to the N side, but not the other
way around. It's like a hill -- electrons can
easily go down the hill (to the N side), but
can't climb it (to the P side). So we've got an
electric field acting as a diode in which
electrons can only move in one direction. When
light, in the form of photons, hits our solar
cell, its energy frees electron-hole pairs. Each
photon with enough energy will normally free
exactly one electron, and result in a free hole
as well. If this happens close enough to the
electric field, or if free electron and free hole
happen to wander into its range of influence, the
field will send the electron to the N side and
the hole to the P side. This causes further
disruption of electrical neutrality, and if we
provide an external current path, electrons will
flow through the path to their original side (the
P side) to unite with holes that the electric
field sent there, doing work for us along the
way. The electron flow provides the current, and
the cell's electric field causes a voltage. With
both current and voltage, we have power, which is
the product of the two. There are a few more
steps left before we can really use our cell.
Silicon happens to be a very shiny material,
which means that it is very reflective. Photons
that are reflected can't be used by the cell. For
that reason, an antireflective coating is applied
to the top of the cell to reduce reflection
losses to less than 5 percent. The final step is
the glass cover plate that protects the cell from
the elements. PV modules are made by connecting
several cells (usually 36) in series and parallel
to achieve useful levels of voltage and current,
and putting them in a sturdy frame complete with
a glass cover and positive and negative terminals
on the back.                                
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Photovoltaic Cells (Solar Cells), How They Work
d N-type silicon is created by doping
(contaminating) the Si with compounds that
contain one more valance electrons than Si does,
such as with either Phosphorus or Arsenic. Since
only four electrons are required to bond with the
four adjacent silicon atoms, the fifth valance
electron is available for conduction.
e P-type silicon is created by doping with
compounds containing one less valance electrons
than Si does, such as with Boron. When silicon
(four valance electrons) is doped with atoms that
have one less valance electrons (three valance
electrons), only three electrons are available
for bonding with four adjacent silicon atoms,
therefore an incomplete bond (hole) exists which
can attract an electron from a nearby atom.
Filling one hole creates another hole in a
different Si atom. This movement of holes is
available for conduction.
a The encapsulate, made of glass or other clear
material such clear plastic, seals the cell from
the external environment.
b The contact grid is made of a good conductor,
such as a metal, and it serves as a collector of
electrons.
c Through a combination of a favorable
refractive index, and thickness, this layer
serves to guide light into the PV Cell. Without
this layer, much of the light would bounce off
the surface of the cell. The RTWCG method of
depositing this AR Coating is by far the most
desirable technique known to us.
The back contact, made out of a metal, covers the
entire back surface and acts as a conductor.
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The path of the photon. After a photon makes it's
way through the encapsulate it encounters the
antireflective layer. The antireflective layer
channels the photon into the lower layers of the
solar cell. Click on the following link if you
would like to learn about our novel room
temperature wet chemical growth antireflective
layer (RTWCG - AR).   Once the photon passes the
AR coating, it will either hit the silicon
surface or the contact grid metallization. The
metallization, being opaque, lowers the number of
photons reaching the Si surface. The contact grid
must be large enough to collect electrons yet
cover as little of the solar cell's surface,
allowing more photons to penetrate.   A photon
causes the photoelectric effect. The photon's
energy transfers to the valance electron of an
atom in the n-type Si layer. That energy allows
the valance electron to escape its orbit leaving
behind a hole. In the n-type silicon layer, the
free electrons are called majority carriers
whereas the holes are called minority carriers.
As the term "carrier" implies, both are able to
move throughout the silicon layer, and so are
said to be mobile. Inversely, in the p-type Si
layer, electrons are termed  minority carriers
and holes are termed majority carriers, and of
course are also mobile.   The pn-junction. The
region in the solar cell where the n-type and
p-type Si layers meet is called the
pn-junction.   As you may have already guessed,
the p-type Si layer contains more positive
charges, called holes, and the n-type Si layer
contains more negative charges, or electrons.
When p-type and n-type materials are placed in
contact with each other, current will flow
readily in one direction (forward biased) but not
in the other (reverse biased).   An interesting
interaction occurs at the pn-junction of a
darkened photovoltaic cell. Extra valance
electrons in the n-type layer move into the
p-type layer filling the holes in the p-type
layer forming what is called a depletion zone.
The depletion zone does not contain any mobile
positive or negative charges. Moreover, this zone
keeps other charges from the p and n-type layers
from moving across it.   So, to recap, a region
depleted of carriers is left around the junction,
and a small electrical imbalance exists inside
the solar cell. This electrical imbalance amounts
to about 0.6 to 0.7 volts. So due to the
pn-junction, a built in electric field is always
present across the solar cell.
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