Modern society depends on electricity, which is the main type of available energy. Most of the electricity is generated using nonrenewable resources. Accessible oil and gas reserves are slightly higher than their current annual extraction. However, when comparing the figures related to the assessment of known reserves of most available fuels with the numbers of their current consumption, humanity can estimate the maximum time, for which these reserves may be sufficient. For oil, time is 65 years; for gas, it is 44 years; for coal, it is 320 years. In order to solve the energy problems by technical means, specialists offer two contrasting scenarios: the development of new techniques of energy production and the development of technology for energy efficiency. Thus, the development of new techniques of energy production using alternative sources of energy and the ability to replace oil and gas by them should be considered.
Today, for the conversion of solar radiation into electrical energy, people have two possibilities: to use solar energy as a heat source to generate electricity by conventional means (for instance, using turbo) or directly convert solar energy into electricity in solar cells. The implementation of both options is still undeveloped. Solar energy is used for melting substances, heating, distillation of water, as well as heating after concentration by mirrors. As solar energy is distributed over a large area (in other words, has a low density), any system for the direct use of solar energy should have a collecting device (collector) with a sufficient surface. The simplest device of this kind is the flat-plate collector, a black stove, well insulated from the bottom. It is covered with glass or plastic that transmits light, but does not allow the infrared heat radiation. In the space, between the plate and black glass tube, through which water, oil, mercury, air, sulfur dioxide flow, are placed. Solar radiation penetrating through glass or plastic in the collector pipe is absorbed by the black stove and heat the working medium in the tubes. Thermal radiation cannot escape from the reservoir; therefore, the temperature in it is much higher (200-500 ° C pa) than the ambient air temperature. This reflects the so-called greenhouse effect. Ordinary garden greenhouses, in fact, are simple solar collectors. However, the farther away the equipment is from the tropics, the less effective the horizontal collector is, since turning it after the sun is too difficult and expensive. Therefore, these collectors are usually set at a certain optimum angle to the south.
More difficult and expensive collector is a concave mirror, which focuses the incident radiation in a small volume around a certain geometric point - focus. The reflective surface of the mirror is made of metallized plastic or made up of many small plane mirrors attached to a large parabolic base. Due to the special mechanisms, this type of collector is constantly turned to the sun; thus, it can collect the largest possible amount of solar radiation. The temperature in the working space of mirror reaches 3000 ° C (Orloff, 2008).
Arguments against the Use of Solar Energy
Solar energy refers to the type of energy, which consumes a lot of material resources for production. Large-scale use of solar energy results in a substantial increase of demand of materials and, consequently, the labor force for the production of raw materials, enrichment, obtaining materials, manufacturing heliostats, collectors, other equipment, transportation. Calculations show that the production of 1 MWh of electricity per year would cost between 10 000 and 40 000 hours of human labor, comparing with the figure 200-500 000 hours in traditional energy sphere. Electricity produced by of the solar rays is much more expensive than the energy obtained by conventional methods.
Bioethanol is, in fact, a normal ethanol, which is produced by hydrolysi or fermentation of sugar-containing plants or straw and husks with subsequent distillation or purification. Biodiesel is a type of biofuel on the basis of vegetable or animal fats (oils), as well as the products of esterification, which are used in pure form or as various blends with diesel fuel. Any type of vegetable oil can be used for the production of biodiesel, but, as a rule, for these purposes specific oils are used such as canola (84%), sunflower (13%) and soybean (2%) oils.
The main advantages of biodiesel are:
- Renewable energy sources;
- Preservation of natural resources;
- Can be used in conventional, unmodified diesel engines;
- Storage conditions are similar to conventional diesel fuel;
- The possibility of extending the life of diesel engines is higher than of fuel oil;
- The production and use of biodiesel have about 80% less carbon dioxide emissions, and almost 100% - sulfur dioxide (reducing pollution) (Brown, 2007).
Moreover, the use of 5% bioethanol results in reduced carbon emissions by 3.5% and E85 (85% alcohol fuel) by 50%. In the biofuels, the presence of 15% ethanol reduces CO2 in the exhaust gas by 25%, hydrocarbons and nitrogen oxides - by 5-15%.
In addition to the environmental benefits, the use of biofuels makes a considerable commercial value; General Motors, Ford and Daimler-Chrysler created hundreds of thousands vehicles, operating on a conventional gasoline, as well as on a gasoline mixed with ethanol. Oil companies are also looking for an alternative and increasingly conceive projects for the production of biofuels. Thus, this year known oil company Shell will produce ethanol with Brazil's Cosan, the largest exporter of sugar cane, and will invest in the project hundreds of millions of dollars (Brown, 2007).
Resources of wind energy are more than a hundred times higher than the water energy of all the rivers of the world. Total wind energy potential of the Earth is 1200 TW. The average wind speed at a height of 20-30 m above the surface of the Earth should be large enough that the power of the air flow, passing through the properly oriented vertical section, reaches a value that is acceptable for conversion. Wind power stations are built mostly DC. Fantail drives the dynamo-electric generator, which also charges the parallel connected batteries. The battery pack is automatically connected to the generator at a time, when the voltage at its output terminals is greater than on the battery terminals and is also automatically turned off.
Theoretically, coefficient of the efficiency of energy use of the air flow can be equal to 59.3%. In practice, the maximum coefficient of beneficial use of wind energy in the real wind turbine is about 50%. In addition, some of the energy of the air flow is lost in the conversion of mechanical energy into electrical energy, which is carried out with an efficiency of typically 75-95%. Taking into account all these factors, the specific electric power supplied by real wind power units, apparently, is 30-40% of the capacity of the air flow (Melis, 2001).
The most crucial argument against this type of alternative energy is the high cost of a wind machine.
Energy land or geothermal energy is based on the use of the natural heat of the earth. The upper part of the earth's crust is the thermal gradient, equal to 20-30 ° C per 1 km depth, and, according to White (1965), the amount of heat contained in the earth's crust to a depth of 10 km (excluding the surface temperature), is about 12,6*10 26 J. These resources are equivalent to the heat content of 4,6 • 1016 tons of coal, which is more than 70 thousand times greater than the heat content of technically and economicallly recoverable coal resources of the world.
For electricity production in the fields of hot water, a method based on the use of the vapor formed by evaporation of hot liquid on the surface is used. This method uses the phenomenon that when the hot water under high pressure in wells goes from the pool to the surface, its pressure falls, and about 20% of the liquid boils and turns to steam. This vapor is separated from the water and sent to the turbine. Water coming out of the separator can be subjected to further processing, depending on its mineral composition. This water can be pumped back into the rocks at once, or if it is economically justified, with a preliminary extraction of its minerals (Orloff, 2008).
Arguments against the Use of Geothermal Energy
High prime cost, high cost of facilities for producing energy from geysers are the principal arguments against this type of alternative energy. Furthermore, obtaining geothermal energy directly from magma is not technically feasible. However, geothermal heat in the upper part of the crust (to a depth of 10 km) is too scattered to solve world's energy problems. Resources suitable for industrial use are separate fields of geothermal energy, focusing on accessible depth. They have a certain amount of heat, sufficient for their use for the production of electricity or heat. Technologies, needed to use energy of the hot dry rock, just begin to develop.
Ocean Thermal Energy
Last decade is characterized by certain success in the use of ocean thermal energy. Thus, stations for mini-OTEC (Ocean Thermal Energy Conversion) are created. For the first time in the history of technology, mini-OTEC system could give the external load utility power, at the same time covering its own needs. Experience gained in the operation of mini-OTEC, will faster enable to build a more powerful OTEC-1 and begin to design more powerful systems of this type.
Arguments against are the technological complexity of implementing and high cost of the construction of such a facility (Horton, 2008).
The Energy of the Tides
For centuries, people have speculated on the cause of tides. Today, it is reliably known that this powerful natural phenomenon, a rhythmic movement of sea water, is caused by gravity of the Moon and the Sun. The maximum possible power from one tide to another can be expressed by the equation W=p*g*S*R2,where p is the density of water, g is the acceleration due to gravity, S is the area of the Tidal Basin, R is the difference in level at high tide. As it can be seen from the formula for tidal energy, some places are the most suitable on the coast, where the tides have large amplitude, while contour and coastal features can make a big closed "basins".
Capacity of plants in some areas can reach 2-20 MW. First maritime tidal power station with capacity of 635 kW was built in 1913 in the Bay of Dee near Liverpool. In 1935, the building of a tidal power plant in the U.S. was begun. Americans dammed part of Passamakvodi Bay on the East Coast, spent $ 7 million, but the work was stopped. Argentine experts offered to use substantially high tidal waves in the Strait of Magellan, but the government did not approve the expensive project. Since 1967, at the mouth of the Rance River in France, at high tide of 13 meters, a tidal power station with the capacity of 240 thousand kW with an annual return 540 thousand kW has been working. Soviet engineer Bernstein developed a convenient way of blocks building on TPS, hauled afloat to the right places, and calculated the cost-effective procedure for the inclusion of TPS in the grid in the hours of their peak load by consumers (Horton, 2008).
Arguments against this kind of alternative energy are inconvenience for the construction due to the lack of conditions (mismatch in seabed, etc.) and high cost of installation.