New Insights into Marine Renewable Energy Technologies

Dear Colleagues,

It is frequently assumed that the objective of marine energy conversion is to develop the most efficient device for harvesting and converting marine energy into electricity, which can then be delivered to the end user. Although this has considerable accuracy, such a reductionist view results in significant uncertainty, which is a major barrier to the development of a marine renewable electricity industry. Consequently, from a technical standpoint, the incorporation of marine energy necessitates a trajectory that ensures each phase offers sufficient confidence for subsequent stages. As a preliminary proposal, the following milestones in technological development are put forth. It is important to note that these milestones are not intended to represent a linear and progressive process; rather, they are to be viewed as occurring simultaneously and in a feedback loop.

It is crucial to gain a comprehensive understanding of the energy source in order to develop successful power plants that offer competitive efficiency and attractive costs. Marine energy sources can be classified according to their predictability. Those with high predictability, such as tides or ocean currents, offer a relatively stable and permanent energy source. In contrast, sources with strong randomness, such as wind or waves, exhibit greater variability and are less predictable. Furthermore, sources such as ocean thermals or saline gradients can be considered to have a relatively constant presence. Consequently, the intrinsic frequencies of each source, along with their spatial and temporal variability, and the capacity to represent and predict them mathematically will influence the level of interest they generate among different types of investors. In turn, the characterisation of sources from an availability perspective will determine the sector of the energy market in which each source can be inserted. In other words, sources that are available on a continuous basis may be used to generate baseload power, while highly predictable sources may be employed to meet peak demand, and sources that are more variable may be used for distributed generation or self-consumption. Concurrently, the implementation of storage and modulation strategies is vital for the success of this industry.

The development of energy capture devices represents a central aspect of marine energy harvesting. The technologies themselves, including the proposed concepts and operating principles, form the foundation of this field of study. As previously stated, the concept must align with the characteristics of the source, which will result in many technologies being site-specific. In terms of technology development, it is advisable to adhere to a defined objective criterion for assessing progress. A frequently employed scale is the TRL (Technology Readiness Level), which assesses the maturity of a concept in terms of its commercial viability. Nevertheless, this may prove inadequate for emerging technologies that are expected to be significant in scale and costly. In order to reduce the number of concepts that fail to reach high TRL levels, it is possible to conduct life cycle and levelised cost of energy assessments in conjunction with the development process. This allows for the identification and rectification of potential weaknesses in the technologies at an early stage.

The marine environment is one of the most extreme on the planet. A number of threats are present, including high humidity, salinity, drying and wetting cycles, freezing and thawing, atmospheric phenomena and biofouling. In some cases, these occur simultaneously. This condition gives rise to a number of technological challenges, the most significant of which is the need to ensure that the materials used can withstand the conditions they will encounter and provide a sufficient lifetime for the investment to offer a reasonable return. Consequently, the devices must be furnished with robust mechanical designs capable of withstanding the rigours of extreme marine conditions and incorporate mechanical fuses that ensure their resilience in exceptional circumstances. It is also worth noting that arrays of devices, occupying a significant marine area, have the potential to disrupt energy flow patterns, posing an additional threat. Therefore, it is essential to ensure an appropriate distribution and placement of these arrays. Additionally, ancillary installations, such as buoys, cable infrastructure, anchorage points and other similar structures, must also be designed in accordance with appropriate standards. The optimal situation would be one in which the designer has complete control over all components and is fully aware of the critical role each plays in the overall system.

The issue of demand and massification is a contentious one in the context of large-scale electricity projects worldwide. It is often observed that such projects do not necessarily lead to an improvement in electricity coverage in the surrounding areas, given that they are connected to a grid that distributes power across an entire region or country. In the context of marine renewable energies, it is important to ensure that coastal communities that will be affected by the construction of power plants do not remain unbenefited. An increasingly common practice in this regard is to identify demand poles that coincide with sites of high availability, with the aim of encouraging production close to centres of consumption. Furthermore, it is essential to develop the capacity to determine not only the available and usable energy, but also to define the maximum thresholds of energy that can be extracted or transformed from the marine environment. The consequences of failing to anticipate the effects of mass production have been witnessed by humanity on numerous occasions. It is imperative that such a mistake is not repeated.

As has been previously observed, the technological challenges associated with the integration of marine energy remain substantial and intricate. A number of issues require discussion and the foundations of numerous agreements and best practices must be established with the requisite scientific and technical rigour, given the implications of intervening in the oceans with power plants of various kinds. It is evident that a necessary companion to the transition to renewables in the electricity sector is a paradigm shift in the use, misuse and waste of energy that is prevalent in today's society.

Dr. Edgar Gerardo Mendoza-Baldwin
Guest Editor

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• estimation of available marine energy
• wave energy technologies and conversion
• ocean current energy technologies and conversion
• tidal energy technologies and conversion
• saline gradient technologies and conversion
• ocean thermal energy conversion and technologies
• marine energy integration in electricity networks
• levelized cost of energy
• hybrid technologies
• materials and corrosion
• marine energy environmental impact assessment