Ocean Energy

 

Portugal's perspectives for ocean energy focus on wave energy through the development of technology, at an academic and industrial level, and the implementation of power plants (EI-ERO, PNEC2030). These activities constitute another economic vector linked to the sea and a contribution to the decarbonization of the energy system.

 

In addition to licensing power plants, the General Directorate of Energy and Geology, in its function of supporting the elaboration of public policies, monitors the progression of the sector through participation in working groups and projects, at national and international level.

 

Resource and Technology

 

Portugal has mainly a resource in terms of wave energy. The greatest potential is located on the continent on the NW coast and center, off localities such as Aljezur, Sines, Cascais, Peniche, Nazaré, Figueira da Foz, Aveiro, Leixões and Viana do Castelo. The waves in the northern region have a higher maximum energy than in the central region, but in the former the energy differs more between summer and winter than in the latter, where the swell is more constant throughout the year. At 50 m depth the morphology of the coast gives the greatest potential to the central zone, followed by the northern region and then areas to the south. The archipelagos of the Azores and Madeira have the greatest potential, especially on the west coast of the islands.

 

In addition to wave energy, ocean energy comprises energy from ocean and tidal currents, tidal amplitude, and salinity and thermal gradients at depth. It is considered that, in Portugal, the resource is weak in terms of amplitude and tidal currents (exploited in regions with a funneled coast) and zero in terms of thermal gradient (only in tropical areas) and salinity (potential in large estuaries).

 

The 'wave energy' corresponds to the kinetic energy of the vertical and horizontal oscillations produced in the waves, or to the gravitational potential energy of water columns formed by rising and/or leveling up in reservoirs. Several technologies have been developed to convert these forms of energy into electricity, with a relatively wide variety of devices persisting, determined by the sea and coast conditions at the site of deployment.

 

These devices can be installed on the coast or at different distances from it. Away from shore the waves have more energy, but extreme conditions increase the likelihood of damage. They can also be located on the surface of the water, submerged near it, or a little deeper, as long as energy is available. Depending on the technology and location, the devices can be anchored or based on the seabed by the action of the force of gravity or with foundations.

 

The configuration of the electrical connection system depends on the distance to the coast and the number of devices. In experimental plants with relatively low power, the alternating current produced is transmitted to earth in this form, without too much loss, directly from the device. Since there are several devices, the cables are connected to a feeder and, from this collector point, other cables with greater capacity make the transmission to a substation on land.

 

Uses

 

To date, the electricity produced by wave energy conversion devices or ocean currents that is injected into the distribution network is not enough to compensate for the high costs of developing technology, equipment and their installation, operation and maintenance at sea. However, given the advantages that wave and ocean current energy can offer, it remains a fairly active sector. Indeed, as it is possible to anticipate, with reasonable accuracy and in advance, the swell and sea currents, the amount of electricity generated can be predicted and this characteristic is important in the context of the country's energy system, contributing to reduce dependence on dispatchable sources and storage.

 

Wave energy also lends itself to introducing electricity into isolated systems offshore or offshore. For example, offshore electricity production makes it possible to provide energy, without transport costs, to activities such as aquaculture, underwater mining, maritime observation and surveillance platforms or hydrogen production. It is also planned to integrate wave energy and offshore wind into hybrid plants that generate electricity with less variability. On the coast, wave plants can provide electricity to local networks to support port areas, air conditioning buildings or desalination. Wave energy can play, in particular, an important role in the energy system of island regions, where the space available for onshore renewable power plants is relatively scarce.