1. 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 45.000 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.
2. 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
3. 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.
4. 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
5. 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 30-40 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
6. 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 400.000 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
7. 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.
8. 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.
9. 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.
10. 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.
