Green Energy and Technology 1st Edition

Description

Energy is indispensable in present society. All depend on a constant and reliable source of energy, whether it be for transport, industrial or home applications. The use of such energy sources can present some inconveniences, such as source depletion, pollution or health problems. The different kinds of energy use one may think of are electricity, mechanical conversion or heating. Fossil fuels are the main energy sources that are used for these kinds of energies. However, the transport sector and the industry, one of the primary energy consumers, contribute a lot to the pollution of the atmosphere. Many ways can be opted in order to reduce the impact of pollution on the environment. One may think of renewable energy sources or new, alternative energy conversion processes that pollute less or a combination of these two. These three ways of rational energy use, reducing altogether its impact on the environment, are the main thought of this book.

Even if there is a range of energy use, renewable energy sources are generally to be used for three purposes: power generation, energy conversion for transport and the generation of heat and electricity (keeping in mind, the production of cold as well). The sources, in this case, are meant to be inexhaustible, such as the sun, the wind, the geothermic heat, the flowing of water, or also replaceable such as fuels extracted from plants. The combustion of fossil fuels generates greenhouse gases as well as other harmful pollutants. Renewable energy, however, has the great potential to produce less greenhouse gases and other pollutants. Caution needs also to be made when considering renewable energy sources from biological origin, especially if it is alimentary. The competition with the food industry needs to be avoided. Some renewable energy sources do not reduce the carbondioxide level, but are said to be carbon neutral, as for instance biomass. The carbondioxide production when using biomass is balanced by its absorption when producing the organic material. Such an energy source needs to be studied thoroughly in order to avoid a higher carbondioxide production than its absorption by carefully examining the whole life-cycle (or well-to-wheel process in case of transport applications) of such an energy source.

As said before, different renewable energy sources can be thought of, principally of solar (photovoltaic cells for electricity production or solar thermal systems for heating), wind (wind turbines for electricity generation or conventional windmill for water pumping), water (hydro electric, wave and tidal systems for electricity generation), biomass (combustion applications of the produced gas, electricity generation or heat production), biofuel (mainly for combustion for transport purposes) and geothermal (using the temperature of the earth for heat and/or electricity generation) nature. Some major energy uses are depicted in Fig. 1.

Figure 1: The energy sources in the world: renewable versus total.

The aforementioned six renewable energies have the main characteristic that they are natural phenomena. However, their use does not depend only on the natural resources, but also on the technologies that are needed to make these energies usable. Using solar energy has great potential. Solar radiation, which provides the energy, can be converted by photovoltaics or heat engines in order to generate electricity, heating or cooling. Besides the technologies that can convert solar radiation into useful energy, one may also think of using the warmth of solar radiation in an intelligent way by arranging building spaces or choosing building material in such a way that the sunlight is well captured and evenly distributed. Wind energy needs wind turbines in order to be useful as a renewable energy. Since the power output from a wind turbine depends strongly on the wind speed, wind energy will gain much success in areas where there are strong winds at an average constant rate. One may think of high altitudes such as plateaus, the situation of hills or offshore facilities. Another renewable energy source, water, has an interesting capacity of storing energy and using it when needed. The much greater density of water (with respect of air) permits producing a considerable amount of energy with even a small flow. Plants and the biological domain can offer great advantages if properly used in order not to affect the nature. On one side, there is biomass, relying on the capturing of energy of the sun by plants by means of photosynthesis. When these plants are used for combustion purposes, the stored energy is then released. Biomass can thus be considered as the natural storage of solar energy. On the other side, there is biofuel from different kind of natural sources such as trees, grass, sugar, starch crops or vegetable oils, to mention a few. In most cases, the biofuel is used as an additive to either gasoline or diesel, attaining in some cases reduced levels of particulates, CO and hydrocarbons from internal combustion engines. The last example of renewable energy, mentioned before, is geothermal energy. This type of energy is obtained by the heat of the earth itself. This heat can be used for making steam out of water, which can be used directly in a steam turbine, creating electricity. Another form of geothermal energy is hot water coming from within the earth that can be used through heat exchangers alimenting another turbine circuit. Of course, this depends largely on the closeness of hot water and regions where the heat is closer to the earth’s surface.

These are some important examples of the various green energies that are used and/or are in development. Another side is the existing technology for the green energies and the (economic/commercial) feasibility of the processes. Many renewable energy technologies show an increasing growth in the past few years. These forms of energy can be expensive. However, as time passes, renewable energy can become cheaper. This can be understood by the fact that once the facilities for using renewable energy are built, the renewable energy source is free (i.e. sun, wind). Furthermore, the improvement of the existing technologies renders such processes more efficient and less costly. The latter is also achieved if these technologies will be used at a larger scale (the material costs decrease if the production is increased). This has the consequence that many other new renewable energy technologies are being developed and others still under research.

As can be seen, renewable energies and the corresponding needed technologies, in other words, green energy and technology, are of great interest. Already some developments are performed and others need yet to be made. This book aims at discussing and presenting some important results in this field concerning recent developments and an up-to-date synthesis of parts of the studied green energy technologies. This book is divided in three parts. The first part treats how green energy can reduce the impact on the environment. The second part deals with renewable energy sources. The third part shows various applications of green energy on the transport sector. The chapters in these three parts discuss a wide variety of green energy technologies, their applications as well as feasibility studies. As such, it presents an overall look of the present state-of-the-art in this field and of new results, both of which present a critical and promising look on the present and future use of green energy and technology.