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

Introduction

 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.

Biomass and bioenergy

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.

Wind energy

 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.

Tidal energy 

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.

Wave power

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.

Solar energy

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.

Hydroelectric power

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%.

Geothermal Energy

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.

DESERTEC - Super GRID

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.

Conclusion

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.