1. Thermodynamics Laws.
The first law of thermodynamics (the conservation energy law for heat processes) has several mutually equivalent formulations. For example, the amount of heat conducted in a system is spent to change its internal energy and to the work of the system over external bodies. In particular, if the process is isothermal, then all the heat obtained from the gas from the heater is spent for the work. From the practical point of view, the first law states: no first-kind eternal engine (i.e., an engine producing energy from nothing) is possible.
The second law of thermodynamics (the entropy increase law) states: if a system is closed (i.e., isolated in the sense of heat transfer and in the sense of mechanics), then its energy is either constant (if invertible equilibrium processes take place in the system) or increases (in the case of non-equilibrium processes) and achieves its maximum once the system gets an equilibrium state. From the practical point of view, the second law states: no second-kind eternal engine (i.e., an engine producing energy by means of the entropy decrease) is possible. For example, no machine producing energy by means of the heat conduction from a colder body to a warmer one is possible.
The third law of thermodynamics (the Nernst theorem) states: for any physical system, its entropy is left unchanged as the temperature tends to the absolute zero. This law has only a theoretical relation to our topic, so we do not provide details.
The main practical conclusion deduced from law of thermodynamics in the framework of our topic is as follows: renewable energy sources should be sought in order to avoid the heat death ( Kaganovich et al. 143-152; Kaganovich and Filippov 326-339).
2. Power Industry Perspectives: a Review
Below, several main renewable energy sources are reviewed ( Belyaev et al. 311-326).
Sun radiation. During 48 hours, the Sun sends to the Earth the energy equivalent to the energy provided by all planet reserves of coal, oil, and blacks. The point is just to invent a sufficiently efficient tool to transform the sun energy to the electric one. Several implementations able to be used in practice already exist. They are, for example, sun batteries feeding space objects by the energy. They work according to the photoelectric transformation scheme, their efficiency already exceeds 20%, and it demonstrated a substantial potential to grow. The said growth is to be achieved if chemically clean and expensive semiconductors are replaced by cheaper, but more efficient materials (for example, silicon and arsenide of gallium are to be changed for alloys of stibium with aluminum and indium). Sun energy devices of this type are called photoelectric ones: they directly (without any engine) transform the sun energy to the electric one. Another type is thermodynamic ones, where the sun energy is transformed into the heat, which is used by traditional heat machines then. Thermodynamic devices have an advantage if the power does not exceed dozens of kilowatts; for higher powers, photoelectric devices get the advantage due to the simplicity of their construction.
Wind energy is classified as Sun energy too, because it appears as a result of the heating of the atmosphere by the Sun rays. Wind energy devices are not efficient from the commercial viewpoint yet: they are complicated and cumbersome, they catch no more than half of the wind energy, and they act only in a very narrow diapason of the wind velocity. However, they can be improved to be used at convection power stations and on systems accumulating the energy.
Biomass energy. Biohumus consisting of guano, animal dung, human biowaste, and biodegraded plants is a very valuable renewable energy source. Their waste recycling yields ecologically cleaned biogas (70% СН4 and 30% СО2) with the combustion heat between 5500 and 6000 kilocalorie/m3. Additionally, this yields the disinfection of harmful germs and the production of high-quality manurial and various modifications of group B vitamins. The above manufacturing clearly improves the ecology situation.
Water energy. This kind of power industry is based on the transformation of potential energy of the falling water into electric energy. Everything depends on the potential energy of the falling water and the efficiency of the turbine transforming that potential energy into an electric one. The power of the hydroelectric station is determined both by the water amount and the location level of the device. To obtain a same power, a high-head power plant requires less amount of water. Moreover, the size of the turbine depends on the water head so this affects the cost of the device as well.
However, building huge hydroelectric power stations, we negatively affect the environment: unique flora and fauna is destroyed, comprehensive agriculture areas are flooded, river sinks are reduced, etc. Moreover, if the station is huge, then a high pressure to a small Earth area appears: this increases the seismic danger. Thus, small hydroelectric power stations (and even micro ones) are preferable.
Hydrogen energy. Hydrogen is a very efficient energy source. For example, consider the water electrolysis. The process itself is very simple. While a direct current is going through an element consisting of the cathode and anode immersed in an aqueous electrolyte, the hydrogen is extracted at the cathode and the oxygen is extracted at the anode. Recently, other ways to decompose water into hydrogen and oxygen are developed, including biological, biochemical, and synthetic ones. The first one uses microorganisms, the second one uses ferments, and the third one uses photolysis without any bio-components.
Comparing with any other kind of fuel, hydrogen is the most cheap and clear from the ecological viewpoint. The transition of cars to the hydrogen fuel would require only slight changes of the carburetor and ignition. For such car engines, the exhaust gas is just the vapor and a slight amount of the nitrogen: no unburnt hydrocarbons, no lead compounds, and no carbonic oxide.
Geothermal energy. The volume of our planet is approximately equal to 1085 billion of km3. Apart from a very thin layer of Earth's crust, that volume has a very high temperature. Besides, taking into account the heat capacity of the Earth formations, we can conclude that the geothermal is the largest energy source available to the humankind nowadays. Moreover, this is already a heat so it doesn't need to burn a fuel or create reactors to obtain it. The first geothermal power station in the world was built in Italy in 1904. In California, about 30 stations of the total power of 2400 megawatt worked in the beginning of 1990s. There are regions, where the geothermal energy reaches the surface as a steam or overheated water becoming a steam once it gets outside. The natural steam can be directly used to produce the power energy. Also, there are regions, where the geothermal water is used to heat houses and greenhouses (such as the whole Iceland country or the Russian region Kamchatka).
Works Cited
Kaganovich B. M., Filippov S. P., Keiko A. V., and Shamanskii V. A. "Thermodynamic Models of Extreme Intermediate States and Their Applications in Power Engineering." Thermal Engineering 58.2 (2011): 143-152.
Kaganovich B. M. and Filippov S. P. "Development of Equilibrium Thermodynamic Models for Studying Technical and Environment Problems in Energy." Int. J. Global Energy Issues 20.4 (2003): 326-339.
Belyaev L.S., Filippov S. P., Marchenko O. V., and Tyrtyshnyi V. N. "Studies on the Potential Role of Different Energy Sources in the 21st Century." Int. J. Global Energy Issues 17.4 (2002): 311-326.
