Hydroelectric Energy The hydroelectric energy, is the most important and widely used renewable source of energy. It represents the 19% of the total production of electricity.Today all over the world exist roughly big hydroelectric dams in operation. The country with the bigger production of hydroelectricity is Canada and follows the U.S.A and Brazil. It emanates from the exploitation of waters of rivers. The hydroelectric energy does not produce damaging gases and as a result has perceptibly smaller effect in atmosphere.

Up to today the unexploited hydroelectric potential of continental mainly Greece, it could cover important percentage of total energy consumption. In many regions of Greece small hydroelectric power stations could be manufactured from private individuals for the production of electric energy as the Community of Agistro – Serres made. It has to be mentioned here that while the electric energy is produced the moment it is required by the consumers the water which is saved up in tanks for future use for the production of electric energy can be used for irrigation at dry spells, as water reserve, the enrichment of lakes, athletic events, tourism etc At the same time,the main criterion for the manufacture or no of a hydroelectric factory is not only the possibility of production, cheap and clean for the environment, energy but also the ecological intervention in the nature for the maintenance of nature of the region and the right Regional growth of the country. The recent legislation that concerns the possibility of private sector of producing electric energy, is expected to strengthen considerably the interest of investors in the sector of A.P.E. A lot of Communities as well as private individuals have expressed their interest for the manufacture and exploitation of small hydroelectric factories. In addition, usually such investments are subsidized and part-financed by the Greek State and the European Union. The new developmental law subsidizes 40% to 50% of the total cost of the project

The water ‘s "circle" in the nature has dynamic energy, when it is found in regions with high altitude, which is changed in kinetics, when the water flows to lower regions. With the hydroelectric work (water tank, dam, closed driver of fall, water turbine, electric generator, tailrace) we exploited the energy of water for the production of electric current which is channeled in the consumption with the aim of the electric network. The transformation of energy of waterfalls with the use of hydraulic turbines produces the hydroelectric energy. The hydroelectric energy is categorized in big and small scale. S The mall scale hydroelectric energy differs considerably from big scale regarding the repercussions in the environment. Big scale hydroelectric units require the creation of dams and enormous reservoirs with important repercussions in the direct environment. The manufacture of dams for the stocking of water limits the locomotion of fish, wild life and influences the entire ecosystem. The small scale systems are placed next to rivers and channels and hasless repercussions in the environment ecosystem.

Hydroelectric units of less 30 Mw in size are characterized small scale and are considered as renewable sources. Fast moved water which is led through tunnel to turn turbines, creates thus mechanic energy. A generator changes this energy in electric. By contrast with what happens with mining fuels, the water is not made useless at the production of electric energy and it can be also used for other aims. Naturally, only in regions with important waterfalls, rich sources and suitable geological configuration it is possible to manufacture water tank. Usually the energy that is finally produced, is used only additionally with other conventional sources of energy, in hours of peak. In our country the hydroelectric energy satisfies the 10% of our energy needs.

The advantages from the use of hydroelectric energy are: The hydroelectric power stations are possible to be placed in operation as soon as it is asked more electric energy, contrary to the thermo stations of (coals, oil), that requires time of preparation Also through the water tanks is given the possibility to be satisfied other needs, as water supply, irrigation, interception of torrents, creation of wetlands, recreation, sports. In 140 countries, the dams provide cheap hydroelectric energy. In world scale, provide the 19% of produced energy and through the irrigation, the 16% of world feeding. Certain dams continue their function after years, providing current and water. The hydroelectric energy plays a serious role in the reduction of the emission of gases that they create the" greenhouse effect" at 13%,as it produces the equivalent of energy which in a different case would be produced in another way that would create greenhouse gases The advantages from the use of hydroelectric energy are: The hydroelectric power stations are possible to be placed in operation as soon as it is asked more electric energy, contrary to the thermo stations of (coals, oil), that requires time of preparation Also through the water tanks is given the possibility to be satisfied other needs, as water supply, irrigation, interception of torrents, creation of wetlands, recreation, sports. In 140 countries, the dams provide cheap hydroelectric energy. In world scale, provide the 19% of produced energy and through the irrigation, the 16% of world feeding. Certain dams continue their function after years, providing current and water. The hydroelectric energy plays a serious role in the reduction of the emission of gases that they create the" greenhouse effect" at 13%,as it produces the equivalent of energy which in a different case would be produced in another way that would create greenhouse gases

The disadvantages that usually are presented are: The big cost of the manufacture of dams and the equipment of the stations of generation of electricity, as well as, the time that is required up to the completion of work The intense environmental alteration in the region of tank (potential locomotion of populations, areas revalorization, change in the use of the ground, in the flora and fauna of the regions but also local climate, fulfillment of tanks with brought matters, increase of seismic danger, etc). The international practice today is directed in the manufacture of small dams. The hydroelectric dams built in order to provide electricity -water for irrigation but also in order to check the flow of rivers, they limit the floods and the droughts- have disproportionately acquired a big effect in the environment. Globally they have submerged more than square kilometers of ground, mainly fertile. Globally the one fifth of fish of sweet water either have been disappeared or are threatened seriously. Nearly 40 to 80 million persons have abandoned their houses because of dams, forced to settle in other, less fertile regions. On the other hand: the big dams have led to the loss of forests and biotopes but also to the biodiversity of the waters of the rivers. The big dams, in the majority of cases, failed systematically to contribute to the re-establishment of the negative consequences for the populations that were moved because of them. With roughly 80 millions persons to have been moved from their houses and many more who live in the lower parts of the flow of the river to suffer from the indirect repercussions (eg loss of fish catches), the efforts of mitigation of repercussions were ineffective. The disadvantages that usually are presented are: The big cost of the manufacture of dams and the equipment of the stations of generation of electricity, as well as, the time that is required up to the completion of work The intense environmental alteration in the region of tank (potential locomotion of populations, areas revalorization, change in the use of the ground, in the flora and fauna of the regions but also local climate, fulfillment of tanks with brought matters, increase of seismic danger, etc). The international practice today is directed in the manufacture of small dams. The hydroelectric dams built in order to provide electricity -water for irrigation but also in order to check the flow of rivers, they limit the floods and the droughts- have disproportionately acquired a big effect in the environment. Globally they have submerged more than square kilometers of ground, mainly fertile. Globally the one fifth of fish of sweet water either have been disappeared or are threatened seriously. Nearly 40 to 80 million persons have abandoned their houses because of dams, forced to settle in other, less fertile regions. On the other hand: the big dams have led to the loss of forests and biotopes but also to the biodiversity of the waters of the rivers. The big dams, in the majority of cases, failed systematically to contribute to the re-establishment of the negative consequences for the populations that were moved because of them. With roughly 80 millions persons to have been moved from their houses and many more who live in the lower parts of the flow of the river to suffer from the indirect repercussions (eg loss of fish catches), the efforts of mitigation of repercussions were ineffective.

Small Hydroelectric power station The hydraulic energy, the energy of water, is a renewable, and decentralised source of energy that served and serves man loyally in his course of progress. Many hydraulic wheels, watermills, sawmills, klwstoy!fantoyrgej'a and other mechanisms of hydro movement continue even today to use the force of water, contributing considerably in the progress of the local economy of many regions, in an absolutely friendly to the environment way. In many parts the of Greek country certain traditional, but also modern installations of Small Hydroelectric Work continue developing the energy of water for the production of mechanic work but mainly for the production of electric current nowadays. The exploitation of small hydrodynamic sources of mountainous Greece passes from the concretisation decentralised, developed small hydroelectric power stations of multiple expediency, that can function and for the simultaneous cover watering irrigatory and other local needs. In the wider region of Sjdirokastro 4 small hydroelectric works function that use a) the water from the lake Kerkini and b) the water of the tributaries water of Strimonas river in the region of Angistro.

Operation of Hydroelectric units The hydroelectric units use the energy of water and by using a simple method change this energy into electric current. This units are based on the movement of water that turns a turbine which brings in operation a generator. Most hydroelectric units use a dam which retains a big quantity of water creating thus a big reservoir. Certain doors in the dam open and because of the gravity the water passes in a driver which leads it to a turbine. As it passes from the driver it creates a big pressure. The water falls on the propeller s of a turbine and makes it turn. This movement is transported in the generator which is connected with the turbine with an axis.

The most usual type of turbine for hydroelectric units is the turbine Francis which resembles to a big disk with convex. Such a turbine can weigh up to 172 tons and make 90 rotations per minute. While the propellers of the turbine are turning, the magnets of the generator are turned round an inductor placing in movement electrons and creating the alternating electric current. The transformer takes the alternating current and changes it into current of high potential. Outside each hydroelectric unit exist four cables: the three phases of current that are created simultaneously plus the neutral for the three.

Most hydroelectric units function in this way. However,another type of hydroelectric unit exists. In a conventional hydroelectric unit the water from the reservoir passes from the turbine and leads again to the river. The new hydroelectric units use two reservoirs. The higher reservoir which assembles the water that retains the dam and is used for the production of electric current. The lower reservoir which assembles the water that leaves from the turbines, send it behind in the river. A reverse turbine channels this water again behind in the higher reservoir. Returning the water behind the unit has more water for use in periods of peak.