Submarine interconnections that respect the sea that hosts them

PalmToday, the Balearic Islands are connected to each other and to the Peninsula by submarine electrical interconnections. This has been a huge step forward in ensuring the security of the electricity supply on our islands and, in turn, is key to the energy transition because these links provide us with energy that is mostly from renewable sources.

This is the present: the current interconnections in operation (the Peninsula-Mallorca, Mallorca-Menorca, Mallorca-Ibiza, and Ibiza-Formentera links), together with local renewable energy production, are allowing us to move towards a model that is gradually abandoning fossil fuels.

The short-term future will consolidate this path taken with a second link with the Peninsula—already in the pipeline—and a new interconnection between Mallorca and Menorca. Two new links that will reinforce—along with other elements of the energy transmission network, such as the batteries under construction in Menorca and Ibiza—the benefits of safety and savings in costs and CO2 emissions (until 2009).

But let's go back a little further. A few years before the present of the current interconnections and that future that has been in the works for some time now. Red Eléctrica, the Redeia company responsible for the operation and transmission of the Spanish electricity system, is the one designing these infrastructures, managing their construction, and commissioning, operating, and maintaining them.

Long before the project for each submarine interconnection is drawn up—and obviously, before the process begins—Red Eléctrica thoroughly studies the area—both on land and at sea—in which this infrastructure will be installed.

The objective is clear: detailed knowledge that allows for the most environmentally friendly project to be supported and, in turn, guarantees the integrity and safety—the technical feasibility—of an infrastructure as important and complex as an interconnection that travels kilometers of sea transporting energy. The approach is resounding: the best alternative will always be the one in which the impact is as small as possible and that allows for the correction or compensation of any possible impact by adopting all relevant measures during the execution of the works.

Submarine electrical interconnection projects always require the results of studies on land and at sea to get started. The information provided by these studies is what underpins the various alternatives that will be proposed to ultimately specify—in a process in which dialogue with the institutions and citizens of the area where the infrastructure will be developed is also essential—the best alternative from all points of view: environmental, technical, social, and regulatory.

On the land side, a territorial diagnosis is made and fieldwork is carried out to complete the environmental inventory on which the Environmental Impact Study that will accompany the project will be based. This preliminary phase on the land side may not differ much from that of other types of projects, although the transition from sea to land of the link requires addressing specific issues of great technical complexity.

It is undoubtedly in the marine area where these preliminary studies (which are also key to the EIA) have the greatest scope and are very specific to this type of infrastructure.

Two types of studies are carried out. First, an environmental marine survey is carried out in shallower waters. Then, detailed sampling is carried out, which incorporates the entire scope of the project, including the deepest waters.

For the future second link between the Peninsula and the Balearic Islands—a project that already has a consensus land route finalized last July and which enters the land from the sea in the Herradura area, in Alcudia—in 2019-2020, the sea route of the Castellón interconnection was already underway, extending to its landing in Mallorca. Up to 13 alternatives for the interconnection's arrival were studied—based on the data obtained.

It should also be said that regarding the future second link between Mallorca and Menorca, Red Eléctrica began its studies in December 2021 (on land) and at sea in March 2022, and today they are already completed, so the project can be accelerated when it is included in the energy planning by the state government.

And what is analyzed in each of these preliminary studies?

The marine environmental campaign includes studies of the seabed (topo-bathymetry, morphology, slopes); metocean (analysis of currents, wave regime, coastal dynamics) and water quality, as well as granulometric and chemical characterization of marine sediments.

A comprehensive biocenosis study is also carried out, identifying and locating the different marine biological communities within the study area (Posidonia oceanica, Cimodocea, coral reefs, cetaceans, sea turtles, among others). The existence of fishing grounds is also analyzed (type of fishing vessels, frequency of work, gear used) and anchoring points are identified.

A study of underwater archaeological heritage is also carried out, through a prior analysis of marine archaeological charts, as well as through dives and surveys during the study process.

The data generated by all these studies are processed and serve as a reference for addressing the second part of the marine environmental analysis and characterization phase.

The following detailed technical campaign repeats some of the studies already carried out in the previous phase, but in this case they are undertaken in the deepest zone (for example, a geophysical/geotechnical survey, current, wave, and sediment studies, among others). In addition, this second campaign incorporates new analyses and studies such as the detection of explosive devices and a detailed assessment of the physical characteristics of the seabed, conditions, and risks for burying the cable (depth, optimal type of protection, existence of marine currents, among other aspects). Studies are also being carried out on other existing infrastructure along the route, such as other links, such as telecommunications and gas pipelines.