What are they

Hydropower is obtained from the potential energy of a body of water and can be converted into mechanical energy (by the rotation of an axis) through hydraulic turbines. In turn these can generate electricity, as it happens in the hydroelectric uses. Generally the hydroelectric uses comprise dams, in order to retain water in the form of potential energy. The water is then released from the reservoir flowing through turbines at a lower elevation, and by means of generators the turbine's mechanical energy is converted into electrical energy.

Hydroelectric power plants are classified for use as watercourse plants or plants with regularization. Water power plants do not have the capacity to store water. Thus, if the volume exceeds the limits for which they were sized, the water is turbid or discharged. Regular plants have storage capacity and can regulate water flows so that they can be used when it is most convenient. In fact, these plants store water in the reservoirs during the winter, so that they can supply energy during periods of less rainfall. Since the beginning of the 20th century, this type of energy use has become one of the privileged forms of electric energy production. In fact, in the 1950s and 1960s in Portugal, almost all of the consumption was assured by hydroelectric plants using only thermal power stations for support during periods of drought.

Wind energy, commonly known as wind, is caused by differences in pressure along the Earth's surface due to the solar radiation received on Earth being greater in equatorial areas than in polar areas. The wind has already been used to move sailboats, grind grain or raise water from wells. Currently wind energy is seen as one of the most promising renewable sources of energy and is characterized as a mature technology that can contribute to the security of energy supply, environmental sustainability and economic viability of the system. Wind power plants have wind turbines whose blades rotate with the force of the wind, rotating the axis of the generator, which produces electricity. In addition to onshore facilities, wind power plants can also be installed offshore. In Portugal, the best places to use wind energy are located along the west coast, in the central zone, and in some regions of the northern interior. Generally, in these places the wind speeds are between 6 and 7 m/s.

Biomass is all organic matter of vegetable or animal origin capable of regenerating in a short time and in a sustainable way. Biomass comprises the by-products of the forest, agriculture, livestock and urban solid organic waste. Proper management and exploitation of biomass dramatically reduces the likelihood of forest fires, as it contributes to the clearing of forests, pastures and forest resources. In forest biomass power plants, electricity is produced through the direct burning of the biomass in order to obtain heat energy that transforms the water in to steam, which in turn will move turbines and trigger electric generators. Although this process releases carbon dioxide into the atmosphere, the CO2 emissions balance is zero, since the plants that gave rise to the fuel during its life cycle absorb amounts of CO2 that offset the emissions. Bioenergy is the term used to designate the energy generated by the conversion of biomass, which can be both electricity and liquid and gaseous fuels.

Solar energy is the name given to radiation from the sun and is one of the most important aspects of renewable energy. The use of this energy source serves to illuminate interior spaces of buildings, heating sanitary waters, or producing electricity. The production of electricity of solar origin is possible through photovoltaic solar panels or solar thermal panels. In the first case, when solar radiation hits the photovoltaic cells, the absorbed light is converted into electric energy through the photovoltaic effect. In the second case, mirrors are used to concentrate sunlight to heat a fluid, generating steam that rotates the blades of a turbine, creating a rotation movement of the generator's axis that produces electricity. In Portugal the availability of the energy resource is high, as well as the potential of exploitation, not only due to the geographic location of the privileged country, but also because the production occurs mainly during the day hours of greater consumption of electricity, adapting to the profile of the diagram, as an essential complement to the generation technologies present in the national electric mix.

There are numerous sources of energy in the ocean that can be used to generate electricity. The main sources of ocean energy include wave motion, thermal gradient, salt gradient, and tidal currents. The equipment for conversion of this renewable energy into electricity is still under development, seeking to improve its performance and its resistance to the maritime environment. However, Portugal has been among the pioneers in Europe since 1978, studying the potential of wave energy and working intensively with the European Union. The country participated in the creation of the European Atlas of Wave Energy and, with an European support ,installed one of the first world centers of oscillating water column on the island of Pico, Azores. It has a good command of the technology of the systems in the coast, a great interest of foreign companies, by the good natural conditions, and even a growing interest on the part of some Portuguese companies. In this context, in 2008, in order to ensure the promotion of the development of the use of the energy of the sea waves, the Pilot Zone of São Pedro de Moel was created. This exclusive zone intends to foster technological development and the installation, in the pre-commercial or commercial concept demonstration regimes, of equipment for the exploitation of wave energy, attracting promoters and producers of technology to the country.

Geothermal energy is the energy obtained from the heat that comes from the interior of the Earth. Due to the high temperatures, the magmatic intrusions and other places with volcanic activity are zones with high geothermal potential. This type of energy can be used in thermal plants, through a turbine whose blades are moved by the water vapor produced by the Earth's heat. This rotation movement is transmitted to the axis of generators, producing electricity. In Portugal, in the Autonomous Region of the Azores, there are units of electricity production using geothermal energy. In addition to being used for the production of electricity, geothermal energy is also used as a heat source for greenhouses or heat pumps, for thermal or industrial purposes, and for heating or cooling buildings.