Another good report from a student about Energy and sustainability
Figures and references have been omitted. For a full copy of the report, just contact me.
Tallinn University of
Technology
Thomas Johann Seebeck
Department of Electronics
Energy
and sustainability
Student: R. K.
Professor: Valerio Alessandroni
Tallinn 2014
Contents
Introduction
Biomass and bioenergy
Wind energy
Tidal energy
Wave power
Solar energy
Hydroelectric power
Geothermal Energy
DESERTEC - Super GRID
Conclusion
References
Throughout history, the use of energy has been vital for the
functioning and development of human societies. But during the last couple of
centuries, humanity learned how to harness the highly concentrated forms of
energy contained within fossil fuels. However during this century it has become
obvious that this way of living might not be the wisest, since they will not last
forever and we are too dependable on them. History has shown that because of
the fossil fuels many wars have taken place.
One
of the world’s most driving forces is the rapid growth in the world’s
population, which in turn results in the increase of energy consumption. Most
of the advanced industrialized nations are at zero population growth (or
negative), but most of the less developed countries are growing at a rapid
rate.
Another aspect to consider is
the release of carbon dioxide and other greenhouse gases released by fossil
fuel burning. This again has an effect on the human health and the natural
environment, leading to disruption of agriculture and ecosystems, to sea level
rises that could overwhelm some low-lying countries and to accelerated melting
of glaciers and polar ice. Lets also not forget the oil spillages from tankers
that pollute beaches and kill wildlife.
Luckily not all energy sources
are of fossil origin. The renewable energy sources are increasingly considered
likely to play an important part in the sustainable energy systems in the
future. The main renewable energy sources are solar and its derivatives in the
form of bioenergy, hydroelectricity, wind and wave power. These sources are
replenished by natural processes and so do not become depleted. Although they
are quite pricey to use and their usage has not yet overcome the fossil fuels,
they are still the future energy resources. The following describes what they
are and where and how we could use them.
Plants in the process of photosynthesis can combine
atmospheric carbon dioxide and water, which are converted into carbohydrates.
These, in the form of wood or other biomass, can be used as fuels –called biofuels,
which are sources of bioenergy. Biomass
feedstocks for alternative energy production include trees, forestry products,
agricultural crops, animal wastes, municipal solid waste and many others. These
biomass feedstocks can be converted to biofuels and bioenergy through a variety
of chemical, biological and thermal conversion processes. Heat, power,
bioethanol, biodiesel and fuel-cell hydrogen can be produced from these
processes.
As shown in Figure
1 (omitted), bioenergy is considered to be renewable when the biomass resource consumed
in the energy conversion process is replenished by the growth of an equivalent
amount of biomass [2]. When forests are managed sustainably in this way, the
CO2 absorbed in growing replacement trees should equal the CO2 given off when
the original trees are burned. Some other downsides to consider are: increased
demand for fertilizers, herbicides and pesticides leading to increased
pollution and greenhouse gas emissions and also use of genetically engineered
crops and microorganisms to produce bioproducts and bioenergy possibly
affecting ecosystems.
One of the main biomass based electricity generators are USA, Japan and Germany.
Since the sun is
heating the atmosphere unevenly the warmer air starts to move towards the
colder and this causes wind, as we know it.
Wind energy is the way of using the wind and converting it into electricity
with the means of turbines. Usually several turbines are located together and
they form a wind park. They can be located in the mainland, on the shore or
even in the sea. Where ever the winds efficiency is the highest. In fact in the
windiest countries owing to the increasing cost of fossil fuels, value being
given for greenhouse gas emission reductions and the reducing cost of wind
turbine technology, wind projects are beginning to compete directly with
fossil-fuel plant as a source of electricity generation.
Offshore wind
installations are presently only a small part of the total wind energy
installed worldwide. However, as land-based sites are used up, it is natural to
consider offshore sites. They have the advantages of good wind resource and
lack of neighbors, making very large projects possible. They are expensive to
construct and maintain, but as the fossil-fuel prices rise, it will become more
viable. When comparing them to onshore windfarms, they are 150%-200% more
costly.
In order to get
more power from the turbine, the trend is to increase the blade diameter and
the height of the turbine. Installed wind generating capacity has doubled every
two and a half years since 1991, and at the end of 2001 the world total was
over 23 000MW. As figure 2 shows (omitted) in 2012 the total capacity was
282,482MW.
The slow but
regular rise and fall of the tides around our coastlines is principally caused
by the gravitational pull of the moon on the world’s oceans. Also the sun with
its gravitational pull plays a very small role in the tidal movement. Solar
gravitational influence is greatest at perihelion (when the earth is closest to
the sun), in January and least at aphelion, in July.
The Rance Tidal Power Station in France is a good example of the principal
technology for harnessing tidal energy. It consists of a low dam, across the
estuary of a suitable river. The dam has inlets that allow the rising sea
levels to build up behind it. Once the sea level is the highest, the inlets are
closed and the water that is behind the dam is then released in a controller
manner through a turbine-generator like the ones used in a dam of a hydroelectric
plant. This specific dam has a capacity of 240MW. Figure 3 (omitted) illustrates the
idea of how a barrage works.
Researches show that UK has the biggest resource in
this field.
Another way of
harvesting tidal energy involves the use of underwater turbines. One of these
turbines was used at LochLinne, in Scotland.
When being on the
beach, we can see the great power of waves when they hit the shore. The waves
are built up from the winds that are blowing on the ocean. There are various
techniques on how to harness the wave power, of which the ‘oscillating water
column (OWC)’ is perhaps the most widely used. The idea is to use the air
movement in an enclosed chamber, where the waves do the job. The air is then used
to rotate a special turbine and generate electricity. The second is the
oscillating body, either submerged or on the surface, is moved up and down or
back and forth by waves. Its motion is used to drive an electric generator.
Then there is also
the ‘’over topping device’’, which is a large structure shore based or in the
ocean, that channels waves into a basin. Once the water level is high enough,
it is drained and run through a hydro generator.
As to wave power
harvesting there are several challenges to overcome also, of which one is the
ability to withstand the larger waves during a storm. In some cases they can
even be 100 times the rating. So it is important that the structure can
withstand these forces.
Sun has been used by plants for a very long time in
the process of photosynthesis. In time the humanity has started to use its
power also. The sun emits visible light of its surface temperature of 6000deg
Celsius. The earth reflects away 30%. The amount of power that still comes to
the earth is still 10 000 times our current rate of consumption of
conventional fuels that is available in principle to human civilization. The
process of converting solar radiation to electricity is called photovoltaic. Photovoltaic
modules are made of specially-prepared layers of semiconducting materials that
generate electricity when photons of sunlight fall upon them. Figure 4 (omitted) illustrates
the use of solar energy.
Photovoltaics may well make a significant contribution to world needs in coming
decades, but at present its contribution is very small. This is mainly due to
the high cost of the photovoltaic modules.
When talking about renewable energy and photovoltaics the question of how
renewable the solar energy harvesting technology really is arises- since the
production of photovoltaic cells itself is quite energy consuming. Studies show
that it all depends of the cell type and the region in which it is used. Nijs
and Morten [9] estimated that the energy payback for 1996 silicon wafer PV was
in the range of 2.5 -5 years.
Power of flowing
water has been one of the energy sources that humanity has been harnessing for
many centuries. They used it for milling corn, pumping and driving machinery.
Nowadays we use it to produce electricity. We can say that hydroenergy‘s original
source is also the sun, which causes water to evaporate and creating rivers and
streams when falling down again. Hydroenergy is said to account for 16 percent
of global electricity generation.
Hydroenergy is
mainly used in two forms: run-of-river and storage, differ in the ability to
store a substantial part of the annually available water in a reservoir. In
times of low electricity consumption the excess is used to pump water to a
higher ground and then used to reproduce the energy.
When building large
dams the two main impacts are the loss of land and the ecological impact.
There are about
45 000 large dams (>15m) worldwide for power generation, irrigation,
domestic water use and flood control. Today one of the leading hydropower
producers are China (196 GW), Canada (88GW), Brazil (69GW) , US(79GW) and
Russia(45GW). The main construction took place in the 1950s-to 1970s. After
that the global dam construction rate fell sharply, because most of the
potential had been used. Now there are still new projects going on and also the
old dams are been renovated for higher efficiency. Another thing to note is
that this type of energy production is currently the most effective technology
for electricity production, with the efficiency of 75% to 90%.
The Source for the geothermal energy is the earth’s
internal heat, which originates mainly from the decay of long-lived radioactive
elements. The most useful geothermal resources occur where underground bodies
of water called aquifers can collect this heat, especially in those areas where
volcanic or tectonic activity brings the heat close to the surface. Hot water
and steam from that is used to generate electricity. One of the biggest advantages of geothermal
energy is that it’s constantly
available. As shown in figure 5 (omitted) cold
water is injected to the ground. The heated water and steam in the ground is
then used to move the turbines and generate electricity.
As of May 2012 the biggest countries generating geothermal power are:
·
United states 3,187MW
·
Philippines 1,904MW
·
Indonesia 1,222MW
·
Mexico 958MW
·
Italy 883MW
·
New Zealand 768MW
The total usage of
geothermal energy is 11,224MW.
The DESERTEC
vision is to supply as many people and businesses as possible with renewable,
clean energy from the deserts and arid regions of the earth. This should
provide opportunities for prosperity for lots of people and protect the climate.
Since deserts all
around the world offer and almost inexhaustible source of energy in the form of
wind and sun, it is very efficient to use that resource. With the right
technology we can convert these forms of energy into electricity and transport
it over long distances. It is said that only 1% of the desert surface would be
enough to provide all human kind with energy. The deserts are also suitable for
these large energy harvesting, since the population density in most desert
areas is quite low and flora and fauna are very sparse. For illustration figure
6 shows the potential from using solar energy since nearly 90% of the world
population nears within a 3000km radius of a desert.
Since solar energy
can be used during the daytime, it is also needed to storage and buffer the
energy in some form that it is possible to produce electricity during night
also. This component is called Concentrating Solar Thermal Power (CSP). In this
method, heat is stored and then used at night to produce steam for the turbine
to thus generate electricity. In this way the fluctuating electricity supply
from photovoltaic and wind power can be balanced out.
Figure 7 (omitted) shows the
concept of producing electricity from the solar and wind energy in the northern
Africa and then connecting it with the European power grid.
There have been
several studies for the DESERTEC project. One of them showed that the high
solar radiation in the deserts off the Middle East and North Africa outweighs
the 10-15% transmission losses between the desert regions and Europe. This
means that solar thermal power plants in the desert regions are more economical
than the same kinds of plants in southern Europe.
With the growing
population and energy demand, the need for water also increases. So a portion
of the electricity is used for desalination of salt or sea water.
With the
increasing population we will face big problems concerning energy and sustainability,
if other alternatives for conventional power plants will not be implemented in
a large scale. We also need to consider the environmental impact for burning
fossil fuels. At one point they will run out and other ways for energy
production will be needed. Also the CO2 emissions need to be lowered.
There are several
possible technologies for using renewable energy. Harvesting energy from
flowing water, tides, waves, sun and from geothermal activity are only some of
them. Since fossil fuels will eventually run out, it is also very important to
note that the cost for renewable technology devices will also increase, when
using the energy from burning fossil fuels.
Around the world
there are many projects going on, how to implement renewable energy production
in a large scale and how to connect them. One of which is the DESERTEC project,
which aims for using the wind and solar energy in the deserts and then distributing
the electricity in up to a 3000 km radius.
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