There are many ways to harness the renewable and emissions-free energy available from the Earth's oceans. The technologies include wave energy, tidal and current energy, and energy from thermal and salinity gradients. In addition, offshore wind energy and marine (floating) solar arrays offer a possibility to exploit vast resources that are far larger than those available onshore. The potential capacities range from many hundreds of gigawatts to terawatts of generation. These technologies could contribute a significant part of the global electricity demand; they are particularly suitable for providing sustainable power to marine regions and island communities and nations. This book brings together contributions from international experts with academic and industry backgrounds to provide a systematic overview of ocean energy technologies, their readiness and modelling, as well as installation and grid connection technologies.
Inspec keywords: wave power generation; wind power; tidal power stations; systems engineering; reviews; solar power; marine engineering; power grids; hydroelectric power; power generation planning; salinity (geophysical); offshore installations
Other keywords: system engineering analysis; oceans; tidal systems; grid connection; planning; gradient systems; storage; offshore wind; installation; wave systems; renewable energy resources; overview; ocean energy technologies; offshore solar; energy conversion
Subjects: Tidal and flow energy; Monographs, and collections; Wind power plants; Solar power stations and photovoltaic power systems; Energy extraction from the oceans; General electrical engineering topics; Wave power; Wind energy; Power system planning and layout; Tidal power stations and plants; Energy resources; Solar energy
The book chapter presents a review of ocean energy technologies. Areas covered include: wave energy; tidal and current energy; thermal and salinity gradient systems; offshore wind and marine solar energies.
The book chapter examines the various facets of wave energy, including resource quantification and wave measurement, the wide variety of onshore and offshore wave energy devices, the variety of power take-off (PTO) mechanisms which convert wave power into other useful forms and concluding with some insight to how wave energy devices are modelled and controlled.
The book chapter deals with both tidal rise and fall energy and hydrokinetic energy from tides, ocean currents and rivers. (River energy is included because the proposed technologies share some characteristics with those proposed for tidal currents.) Out of the many devices proposed, some have been built, but most of these have disappeared as a result of either lack of financial support, poor design or poor management. The aim of this chapter is not to catalogue every device past or present, but rather to summarize the main types of technology and the most interesting and promising.
The book chapter presents thermal and salinity gradient energy (SGE) systems. First, a description of both energy resources and the determination of energy potential is given. Then, power plants that convert the thermal gradient potential as well as the salinity gradient are discussed. Environmental and economic aspects associated with these technologies are also considered.
The book chapter reviews the development of offshore wind energy systems. The author primarily focuses on the technology innovations and its contribution as a driver of rapid cost reduction. Offshore wind power provides tangible evidence of ocean energies' ability to contribute to our future energy mix.
There are currently few of us working on systems at sea, but the number is growing. It is very probable that systems will continue to be installed bycompanies at sea in niche markets where the cost of electricity is high and the sea conditions are benign. It would also not be a huge leap to install a large system in a large, sheltered bay or port where the only difference from current systems floating on lakes is the sea water instead of fresh water. These systems could even be based on Ciel et Terre or similar technology which is designed for ponds and reservoirs but there is no reason it would not work in a sheltered bay or port where waves would never reach significant wave heights, say higher than 1 m. While it is not entirely clear where the Solar-at-Sea farm will be launched, the Netherlands certainly has that potential of utilizing sheltered areas of the sea which would not be in competition with other activities such as shipping, leisure and fishing.
The load and response analysis discussed in this chapter largely focuses on the assessment of structural responses of installed ORE devices. There are also important design considerations which are related to marine operations (such as installation and maintenance) and to the calculation of the structural resistance. Installation methods and costs can have significant consequences on the design of ORE substructures. For example, optimization of the weight of components and how high they need to be lifted needed storage area in a shipyard, ability to fit within available dry docks, and possibility of using available vessels for installation work may be more important than substructure optimization with respect to steel weight. Over the lifetime of a substructure, the costs of access and maintenance may be significant, and designs which allow for easier inspection or require less maintenance may be favored over designs which are less expensive to construct but more difficult to maintain. With respect to structural resistance, it is important to note the particular challenges related to corrosion in the marine environment. Designers must account for possible reductions in steel thickness due to corrosion through structural design (cathodic protection or coatings). ORE devices with significant dynamic motions near the free surface-implying surfaces which are at times submerged, at times dry, and also subjected to sea spray-may experience different corrosion rates compared to more static offshore structures.
This chapter provides an overview on the main challenges encountered during the interconnection of marine energy farms to the onshore electric power system. It explains how less technologically mature marine energy converters (MECs), such as wave and tidal ones, are normally integrated into distribution systems, and potentially cause power quality problems. Then it shows how system level issues arise when larger offshore installations, such as offshore wind farms, are interconnected to power transmission systems. The presentation is complemented by illustrative test cases.
This chapter focuses on energy storage situated offshore. Large amounts have already been written on energy storage generally and there would be little value in adding to these outputs. However, there are good justifications in concentrating specifically on storing energy offshore. First, the environment is rather special and it provides resources that may be helpful for energy storage. These resources include (a) hydrostatic head between surface and seabed that may sometimes be large, (b) an effectively infinite amount of thermal ballast enabling a stable reference temperature to be maintained and (c) an unlimited supply of saltwater that may be useful for electrolysis to support hydrogen production. Second, energy storage at the site of renewable energy generation potentially makes better use of expensive electricity transmission lines joining the generation to consumption. Finally, there are opportunities for integrating storage with the primary harvesting of energy that can afford substantial effective reductions in cost and increases in effective performance.
A multipurpose platform is an offshore system designed to serve the purposes of more than one offshore industry. Indeed, a number of industries have expanded, or are expanding, from onshore to offshore locations, adapting to the harsh environment in order to extract energy (conventional or renewable) or useful materials (deep mining), to produce food (aquaculture), nutraceuticals, and pharmaceuticals (blue biotechnology), to expand the urban areas, or to simply develop the local tourism, to name a few. This process starts to appear like, and certainly has the potential to become, a further `agricultural/industrial revolution', characterised by: (a) a substantial shift from `gathering of resources where available' to the systematic, settled use of the resources offered by the ocean, (b) a shift from offshore facilities of a specific industry operating independently to an `ecosystem' of offshore industrial activities, and (c) the resulting development of new technologies. Expanding the above-mentioned industries towards this new frontier can help to respond to two of the main challenges facing mankind: the sustainable, safe, and reliable production of energy and food, driven by an increasing population and rising prosperity. For these reasons, and also due to the huge potential to create jobs and revenues, many countries around the world are proposing and implementing strategies to develop the so-called Blue Economy.
The chapter deals with the basic concepts of installation, operation and maintenance of offshore renewable energy systems. Whilst focus is given to the offshore wind industry, the extension to ocean energy (wave and tidal) offers a wider perspective on the major issues concerning the installation and maintenance. A reliability-based approach has been adopted for the analysis of the failures, providing an overview about the most common functional decomposition methodologies as well as logistic requirements for the different operations at the various stages of the lifetime of an offshore renewable project. The economic modelling of the operations, based on strategies for their planning, briefly completes the chapter.
As the preceding chapters have shown - the ocean energy technologies we are looking at today are all at very different points in their development pathways. Some technologies - notably offshore wind - are now commercial and evolving rapidly (albeit with some level of public subsidy), whilst others are still making their way out of their land-based laboratories and into the sea. What they all have in common is that each and every technology must make a journey through the technology readiness levels until we reach the Eureka moment of `it works'. For some technologists, this is the ultimate goal - to show simply that it can be done. This journey will involve a continual development and must address the actual practicalities of a myriad of elements including installation, reliability, operability, fatigue and mean time to fail of everything from components to systems to people. For ocean energy technologies, this will ultimately involve significant test and development in the real sea environment - at specialist facilities such as European Marine Energy Centre (EMEC) - where developers can discover the weak points in their design and then resolve them.
