With the term “renewable energies” we mean the energies generated by sources that by their intrinsic characteristic are regenerable or they are not "exhaustible", and whose use does not affect natural resources for future generations. These are forms of energy that are alternative to traditional fossil sources, having the peculiarity of being also clean energy, or not to introduce harmful substances and / or climate-altering substances such as CO2 into the atmosphere. Therefore they are at the basis of the so called “green economy”, investing in their development means guaranteeing a sustainable future to our planet.
In a context of strong economic dependence from fossil fuels, renewable energies represent the ideal tool for reducing greenhouse gas emissions.
The technology in this field has increasingly developed, and today we can find different types of renewable energies such as wind, solar, hydroelectric, marine, geotermic, biomass and biofuels.
Currently, the new Renewable Energy Directive of the European Union (D. 2009/28/EC) has established that a mandatory 20% share of EU energy consumption must come from renewable sources by 2020.
Furthermore, all the member states are required to derive 10% of the fuels used for transport from renewable sources by 2020. A total decarbonisation is expected by 2050.
The solar energy is an inexhaustible source continuously generated by nuclear reactions within the sun. This incredible amount of energy reaches our planet in the form of electromagnetic radiation able to cross the earth's atmosphere and reach the ground: it is estimated that it is equal to 15,000 times the world energy needs.
In Italy, the average annual irradiation varies from 3.6 kWh/m2/day in the Po Valley to 5.4 kWh/m2/day in Sicily: in practice, the sun provides an amount of energy equal to the annual electric consumption of a medium family (about 3,000 kwh).
A considerable part of this energy can be used by photovoltaic or solar thermal installations for the production of electricity or hot water.
Photovoltaic systems make it possible to transform solar radiation into electricity by exploiting the properties of some semiconductor materials, like silicon, suitably treated to generate electricity when affected by solar radiation. The energy produced can be stored in batteries, which make it always available, or can be used immediately by users thanks to the direct connection to the electricity grid.
Solar thermal systems use solar radiation to produce heat. The main sector of application is the production of hot water at low temperatures (up to 80-90 degrees) for sanitary uses and for the heating of private homes.
In countries with strong solar radiation it is also possible to produce electricity, through high temperature systems (600 degrees and above) obtained with more sophisticated technologies, able to reach the potentiality of real thermo-electric power plants; in this case, we speak of "solar thermodynamic".
The wind energy is a technology transforming the energy released by the wind into mechanical energy through wind power plants, which reproduce the functioning of old windmills. The rotation produced by the pressure exerted by the wind on the blades is thus used to operate the aerogenerators (electric) or aeromotor systems (pump devices). The wind power installed in Europe is the largest in the world: Germany, Denmark, Holland, Spain, Portugal, countries where windiness maintains constant and continuous levels, are among the most active in the use of this source.
The wind power installed in Europe is the largest in the world: Germany, Denmark, Holland, Spain, Portugal, countries where windiness maintains constant and continuous levels, are among the most active in the use of this source.
When a mass of water moves, it carries with it an enormous amount of energy that can be used by man: hydraulic energy is the force of water movement.
Running water is a very important source of energy that man has exploited since ancient times. Together with the windmill, the water mill was the first source of non-animal mechanical energy for humans.
Among renewable sources, water energy is the most used because it is based on a well-known technology and with a very high yield. In the nineteenth century this principle was also used for the production of electricity, leading to the birth of hydroelectric energy.
The main sources of hydraulic energy are the natural cycle of water, waves and tides. To this end, various technologies exist to recover energy from water, river currents, marine currents and tides, as well as from waves.
It is energy generated by geological sources of heat and can be considered a form of renewable energy. It is based precisely on the principles of geothermal energy, or on the exploitation of the natural heat of the Earth due to the thermal energy released by the processes of nuclear decay of radioactive elements such as uranium, thorium and potassium, naturally contained within the Earth.
This type of energy was used for the first time in Italy, in 1904, by the Prince Piero Ginori Conti, who experimented with the first geothermal generator in Lardello, in Tuscany.
Thanks to the peculiarity of geothermal energy, the energy obtained can be used both as a source of electricity and as a source of heat. However, to date in Italy geothermal energy constitutes less than 1% of global energy production.
Wave energy is a source of energy that consists in exploiting the kinetic energy contained in the wave motion, from which it takes its name. There are various techniques of exploitation of the wave motion and the transformation of the energy of the waves into electric energy is the subject of various studies and realizations.
There are many islands in the world that are focusing on renewables, from the Pacific to the Atlantic, from the North Seas to Australia, but also Portugal, Greece and Spain. We cite the most virtuous examples of islands that have already achieved total energy independence.
The world record as the first island to have achieved energy self-sufficiency is the island of El Hierro, in Spain. Belonging to the Canary archipelago, it is an island of volcanic nature of 268.71 km2, recognized by UNESCO in 2000 as a 'Biosphere Reserve'. Since 2014, 10,162 residents have been using a hydroelectric plant for the production of electricity, composed of two water basins with a difference in height of 682m and a capacity of 700 thousand m3 of water and a pumping station of 6 MW, and wind plants with 5 turbines for a total of 11.5 MW, integrated together.
The operation involves the passage of water with the consequent activation of hydraulic turbines, such as to generate electricity, driven by the energy produced by wind turbines fed continuously by the trade winds always present on the Canary Islands.
In the Pacific Ocean, we find another island that has reached the 100% renewable target, ie the island of Kodiak, located in the Gulf of Alaska, which with its 8,975 km2 and 15,000 residents is the 80th island largest in the world and the second largest in the United States. Since 1985 there is an 11.5 MW hydroelectric plant on the island; however, it was not sufficient to meet the island's energy needs, so that more than 66,000 liters of diesel fuel / year were imported at a cost of over 7 million dollars.
Since 2008, the Kodiak Electric Association, the managing body of the electricity grid, has chosen to reduce the dependence on diesel, aiming for 95% of energy production from renewable sources by 2020. The good news is that the target was reached in 2016, four years in advance, with the demand requirement met to 99.7%.
To achieve this objective, six 1.5 MW wind turbines were purchased (with zero interest rate financing by the Government); moreover, an aerogenerator has been installed in combination with a 3 MW battery which, if the wind is low, enters into operation for the period of time necessary for the hydroelectric plant to get to work at full capacity. The payback times have been calculated in just 9 years.
Pre-existing diesel plants have not yet been dismantled, but are closed and put into operation only for maintenance.
Another example of a virtuous island is from the Brass Strait, off the north-western tip of Tasmania, where King Island is present. Since 2013, the island guarantees 65% of its energy needs thanks to renewable sources, and in the days of intense wind it reaches 100%.
It is a plant that has often allowed to reach more than 33 hours of autonomy with zero diesel operation and with the supply of diesel completely switched off and replaced by renewable energy. Cost 46 million dollars, the project involves a combination of technologies such as 6 MW of wind energy, 12 GW of solar photovoltaic and storage systems to guarantee the use of energy even at night.
In addition, the battery systems use the most advanced lead technology, and have a capacity of 34 MW / 1.6 MWh: this is the largest type of storage ever installed in Australia, which makes it possible to gradually set aside the diesel plants, currently not yet completely abandoned in order to take over rare cases of greater energy demand at night, especially during the period of major tourism on the island.
Back in Europe, in Denmark, 150km west of Copenhagen, is the island of Samso, 112 km2 of land for 3,860 residents. The project is made up of 11 onshore and 10 offshore wind turbines, for a total of 34 MW.
The peculiarity of this plant is that the wind turbines were purchased from different companies on the island, or from the local municipality, farmers and an investment company. We are facing a 'bottom up' approach, where the full involvement of the local population has been significant for the success of the project.
Currently, the wind turbine system helps to avoid the release into the atmosphere of about 12 tons of CO2 / inhabitant, considering that each MW covers the needs of about 630 homes. Furthermore, in 2005 a district heating network was built, consisting of four plants (three of which fed straw and one with wood waste) combined with solar panels.
Another European virtuous reality is constituted by the small island Eigg, belonging to the British archipelago of the Hebrides, in Scotland, 30.49 km2 of surface with a population of 83 inhabitants.
The island community has chosen not to invest resources in a long and expensive submarine cable that would have connected it to the mainland, but rather to enhance the energy potential from renewable sources.
Therefore, the 45 families living on the island are energetically self-sufficient thanks to the plants present, from which they get the daily 5 kW of electricity self-imposed by the inhabitants as a limit for consumption, 10 kW for the 20 industrial companies. Famous their motto "We can only use what we make".
Eigg Electric is the community-owned company that supplies electricity to all residents of the island through: 3 hydroelectric plants (the largest of 100 kW in the western part of the island and two smaller ones of 5-6 Kw; 4 wind turbines of 6 kW; 50 kW of photovoltaic panels.