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Sustainable development: the hydroelectric energy.

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The wind energy
Wind energy is the result of the conversion of wind kinetic energy into electric energy. It is the most important renewable energy because of price/production comparison and it has also been the first source of energy used by man.

Its use, very simple and not much expensive, is carried on by aeolian machines, which can be divided into two different groups:

This kind of energy is thought to consider both a centralized production insystems to be built in high and windy spots, and a possible energetic decentralization. As far as the decentralization is concerned each town is equipped with small power systems made up of few vanes (1-3 vanes of 3-4 megawatt). They produce energy which is used by inhabitants. You don’t need long to install this kind of systems. You have to fix the aeolian vanes into the ground after studying the wind speed and how much electric energy you can produce. On the contrary you need more than 4 years to plan and build other kind of systems (like hydroelectric or thermoelectric generating stations).

Systems

Nowadays installation cost in Italy varies between 850 and 1300 ¤/kW if you refer to systems with more than 600 kW of potential energy. Of course the price varies according to the complex ground orography where you have to install the system. A 10 MW generating station linked to the net in AT would cost between 8-13 million euros, while a generating station linked to the net of MT(3-4 MW) would cost between 0.9 and 1.2 million euros per MW. For small house systems the price is little higher and it varies between 1000-1500 ¤/KB because the market of these kind of systems hasn’t developped yet. This happens also because some rules discourage their use, following the widespread thought of the past years according to which wind energy was a big problem for the environment. The same thing hasn’t happened for solar energy generators systems.

Efficiency

The highest quantity of electric energy you can produce can be calculated using Betz’s Law which shows how the highest quantity of energy of every generator ( for example an aeolian vane ) is the 59.3 % of the wind energy which flows through it. It is very difficult to reach this kind of energy. An aergenerator with an efficiency between 40 % and 50% is very good.

Aeolian generators

Horizontal axle aeolian generators are placed in Varese Ligure (SP); they produce 3 GWh each year.

In the last twenty years aeolian generators have largely improved their efficiency, dimensions and prices: that’s why the given data are to be considered temporary this kind of generators have been able to move from a little kilowatt energy production to a 3 Megawatt production for the most efficient ones and to a production of the present market of 1.5 MW, with a wind speed of 3-4 m/s. Considering that the highest energy delivered to house usage is of 3 kilowarr, one vane can satisfy the energetic need of about 1000 house users, corresponding to 4000-4500 people ( if we consider 4 average inhabitants for each family) and to the averagedimensions of an Italian town council. These levels are reached both by horizontal and vertical aergenerators. Both a vertical and horizontal axle generator requires the least wind speed of 3-5 meters/sec and it delivers energy at a wind speed of 12 - 14 meters/sec. At high speed (20/25 meters/sec) the aergenerator is stopped by a braking system due to safety reasons.It is possible to find movable vane generators which follow the wind direction, without changing the amount of electricity produced by the aergenerator, and double vane generators to double the electric power produced. There are also silent generators; the main problem is the vane size and the lack of microvane generators which cannot be seen with the naked eye. They would solve the negative impact on the landscape.