Seminar
Paper Photovoltaic 25.02.2014
Abstract
In this seminar paper with the
topic photovoltaic systems I will write about the photovoltaic
effect, different types of Pv panels and some other interesting facts
about the history of photovoltaic and applications where it is used
in nowadays life. Furthermore I will explain how a Pv system can be
installed at home and give a short overview of the so called power
stations.
Table of contents
Inhalt
Table of figures
Figure 1: Structure of a photovoltaic cell
Figure 2: Current-voltage characteristics of a
photovoltaic cell
Figure
3: Monocrystalline module
Figure 4: Polycrystalline module
Figure 5: Thin film module
Figure 6: power station
Figure 7: spacecraft application
General aspects
The word “photovoltaic” is a
combination of the two words “photo” which means light and the
word “voltaic” which stands for electricity. Therefore
photovoltaic technology means the conversion form light into
electrical energy.
The secret to this process is
the use of a semi-conductor material which can be adapted to release
electrons. The most commonly used semi-conductor material used in
photovoltaic cells is silicon, an element most commonly found in
sand.
All Pv cells have at least two
layers of such semi-conductors, one positively charged and one
negatively charged. When light shines on the semi-conductor, the
electric field across the junction between these two layers causes
electricity. It generates DC current, the greater the intensity of
the light, the greater the flow of electricity.
Figure 1: Structure of a photovoltaic cell
The History
In
1839 the French man Alexandre Edmond Becqurel spots the photoelectric
effect. He scaled a higher current flowing throw a platinum electrode
when light was shining at the electrode.
Some
years later in 1905 Albert Einstein was able to explain the
photovoltaic effect in the right way. 16 years later he won the
Nobel Prize for this explanation.
In
1954 a laboratory accomplished it to produce a silicon solar cell.
This invention was very important for the whole mankind because
nowadays every satellite runs with photovoltaic panels based on this
technology. The first silicon solar cell had an efficiency of about
5%. Since then this technology had a continuous grow and nowadays
modern silicon cells can have an efficiency of up to 15%.
Characteristics
The out coming voltage from a
single cell is between 0,5 and 0,7V whereas it depends on the used
semi-conductor. The named values are typical for silicon. Furthermore
the voltage depends on the radiation of light and the current changes
with the luminosity.
Figure 2: Current-voltage characteristics of a
photovoltaic cell
The usable power of a Pv panel
is next to the material and the luminosity
dependent on the ambient
temperature. Here we can say, when the temperature of a panel rises
the efficiency decreases.
Different cell types
Monocrystalline modules
Single crystal modules are
composed of cells which are cut from a piece of continuous crystal.
The material forms a cylinder which is sliced into thin circular
wafers. To minimize the waste, the cells are fully round or trimmed
into other shapes. Because each cell is cut from a single crystal, it
has a uniform colour which is dark blue.
Figure
3: Monocrystalline module
Polycrystalline modules
Polycrystalline cells are made
from similar silicon material except that instead of being grown into
a single crystal, they are melted and poured into a mold. This forms
a square block that can be cut into square wafers with less waste of
space or material than round single-crystal wafers. When the material
cools, it crystallizes in an imperfect manner that forms random
crystal boundaries. The efficiency of energy conversion is slightly
lower.
Figure
4: Polycrystalline module
Thin film modules
For thin film modules, a thin
layer is deposited on a support material. The thin film is made out
of amorphous or crystalline silicon, but also sometimes
cadmium-telluride, gallium arsenide, or copper indium selenide. The
market for thin film modules growing despite this modules have an
efficiency of only about 6 to 10 percent
Figure
5: Thin film module
Efficiency
Researchers
are continually striving to improve the efficiency of Pv panels. The
record at the moment stands at an efficiency of around 40%, using
special multi junction cells, each layer is tuned to trap different
frequencies of the light. This type of cell is very expensive to
produce and has been used in the past mainly in the space where
efficiency may be more important.
Researchers
also strive to increase the amount of light entering the cell.
Cells
used in photovoltaic panels for electricity production are usually
single junction type with an efficiency of somewhere around 15%.
Economy
A
big disadvantage of PV panels is their high price because of the
costly production. Next to this another big point in Austria is that
you get not very well paid when you send current to the national
grid. Without a claim a PV system wouldn´t be rental in Austria.
With the support the system is normally paid off after about 13
years. The issue in Austria is that only a few get such a claim,
whereas in Germany everybody gets a support who asks for it
Applications
Installing a solar electric
system in your home
Photovoltaic panels produce DC
so you need a DC-AC converter. This converter converts, as the name
already says, DC into AC. When you install an Pv system at your home
you can choose between two different systems
Grid
connected System
One solution is the grid
connected system. This system provides your household with electrical
energy. If the Pv system produces more energy then you need, the
needless energy flows into over an electric meter into the national
grid. You get paid from your Technical Unit Electricity Supplier for
every kWh current which flows into the national grid.
Standalone
System
The
second system is based on the idea of storing energy. As in the other
system the photovoltaic panel’s provides your household with
electrical energy. The big difference is that the unneeded energy is
stored in batteries. The disadvantage of this system is that the
batteries are expensive and they have a limited lifespan. It is
mostly used in remote areas which are not connected to the national
power grid, or for mobile applications like caravans and boats.
Power stations
Power stations are giant areas
with Pv panels. They have been built many power stations
all over the world and much more will come in the future.
Many solar photovoltaic power
stations have been built, mainly in Europe.
Here I have listed some power
stations:
the
Agua Caliente Solar Project (USA, 247 MW)
Charanka
Solar Park (India, 214 MW)
Golmud
Solar Park (China, 200 MW)
Figure 6: power station
Spacecraft applications
As I already mentioned in the
history Photovoltaic solar cells are used in spacecraft applications.
In the space they are the perfect generators for any satellites,
because out there they have sunshine all the time.
Figure 7: spacecraft application
Conclusion
Nowadays photovoltaic systems
are shown in the public as very environmental friendly electricity
producers. What most people do not see are the high production costs
and the enormous expenditure of energy behind pv systems. That is
also the main reason why such a system is so expensive.
When you
want to buy a photovoltaic system here in Austria such a system would
not be rental, because you get not very well paid for the current
which flows into the national grid. In Austria you can request for a
support when you are going to buy a pv system, with this support you
get more cent per kWh which flows from your panels into the national
grid. With this support a photovoltaic system is normally paid off
after about 10 to 13 years. So you have approximately 10 years where
you really earn money with your system. The problem in Austria is
that it is very hard and complicated to get this support.
In some
years scientists will probably find a way to produce pv panels in an
economical friendlier way and with a higher efficiency. What we
certainly can say is that photovoltaic systems accompany us in the
next decades and that they are presumable a good way in an atomic
free future.
Bibliography
EA
Skriptum 5
science.howstuffworks.com