8.10 Potential And Challenges Of Marine Energy

Introduction

Marine energy refers to technologies that capture energy from the oceans, including tides, waves, ocean currents, temperature differences, and sometimes salinity gradients. This chapter focuses on what makes marine energy promising for the future energy mix and what specific challenges currently limit its widespread deployment. It builds on earlier explanations of tidal, wave, and ocean thermal energy conversion, and concentrates on the bigger picture of potential, constraints, and future prospects.

Types Of Marine Energy And Their Global Potential

Marine energy is not a single technology but a family of different concepts. The most developed categories are tidal range, tidal stream, wave energy, and ocean thermal energy conversion. Each of these has a distinct resource potential and geographical distribution.

Tidal range projects harness the difference in water levels between high tide and low tide. This resource is concentrated in estuaries and bays with large tidal ranges, often greater than 5 meters. Although the total global tidal range potential is relatively modest compared with solar or wind, in some regions it can cover a meaningful share of electricity demand and provide predictable power.

Tidal stream devices extract energy from fast moving tidal currents, usually in narrow channels or straits. Their global technical potential is significantly larger than tidal range, due to the widespread occurrence of strong currents in coastal regions and between islands. The usable resource is limited by environmental constraints and navigational needs, but in some countries it could provide several percent of national electricity.

Wave energy uses the oscillating motion of the sea surface. The wave resource is high in mid to high latitudes on the western coasts of continents and around many islands, especially in the North Atlantic and southern oceans. When expressed as average power per meter of wave front, some locations reach values of tens of kilowatts per meter. Integrated globally, the theoretical wave resource is very large, although only a fraction is economically and environmentally feasible to use.

Ocean thermal energy conversion, often abbreviated as OTEC, uses the temperature difference between warm surface waters and cold deep waters. Its potential is located in tropical and subtropical regions where this temperature difference is large enough year round. Although the total theoretical resource is large, practical deployment is still at an early stage and constrained by technical and economic factors.

Key Advantages Of Marine Energy

Marine energy offers several unique benefits that can complement other renewable sources. One important advantage is predictability, particularly for tidal energy. Tides follow gravitational cycles of the Earth, Moon, and Sun, so their timing and magnitude can be forecast with high accuracy many years in advance. This predictability reduces uncertainty for grid operators and supports planning of other power plants and storage.

Another potential benefit is resource concentration. Waves and tidal currents can deliver a high power density compared with some land based resources. In suitable sites, a relatively small area can generate significant power, which is attractive for countries with limited land. Coasts with strong wave climates or tidal currents can host compact marine energy projects close to existing load centers.

Marine energy can also offer temporal complementarity with other renewables. In many regions, wave energy remains available during cloudy or low wind periods, and tidal cycles do not align exactly with solar peaks. Combined portfolios of solar, wind, and marine energy can smooth overall generation profiles and reduce reliance on storage or backup fossil generators.

In addition, certain marine energy systems may create co benefits when integrated with other marine or coastal uses. Examples include multi use platforms that combine marine energy with aquaculture, or OTEC plants that supply not only electricity but also cooling, desalinated water, or nutrient rich water for mariculture. These linkages can improve the overall economics of marine projects.

Technical Challenges And Engineering Constraints

Despite the promising resource, marine energy technologies face demanding technical conditions. Devices must operate in a harsh environment characterized by saltwater corrosion, strong currents, biofouling from marine organisms, and frequent storms. Designing components that can survive for decades while maintaining performance is a major engineering challenge.

For wave and tidal stream devices, mechanical loads are complex and highly variable. Equipment must withstand extreme events, such as storms or rogue waves, which impose large forces on structures. Structural design must balance strength and durability against cost and maintainability. This often results in high upfront capital costs and a need for extensive testing in real sea conditions to validate designs.

Access for installation and maintenance is also difficult. Many promising sites are located in rough seas or strong currents, where safe access windows are limited. This complicates logistics, raises costs for vessels and crews, and lengthens repair times. The result is that availability, which is the fraction of time a plant is able to produce power, can suffer if maintenance concepts are not carefully planned.

Power take off systems, which convert mechanical motion into electricity, must perform efficiently under variable and sometimes irregular inputs. For wave energy, capture of energy across a range of wave heights and periods is particularly challenging. Control strategies that adjust device behavior dynamically are critical, but they require sophisticated sensors, algorithms, and reliable actuators that can operate underwater.

Finally, the grid integration of marine energy involves its own technical considerations. Although tidal energy is predictable, it still varies over the day with the tidal cycle and may peak at times that do not correspond to demand peaks. Many high potential sites are also far from strong grid infrastructure, often in remote coastal or island regions. This requires submarine cables and potentially new substations, which add complexity and cost.

Economic Barriers And Cost Competitiveness

At present, marine energy is generally more expensive than mature renewables such as solar photovoltaics and onshore wind. The levelized cost of energy for most wave and tidal technologies remains high because projects are small, at early stages of learning, and carry considerable perceived risk.

The levelized cost of energy can be expressed in simplified form as

$$LCOE = \frac{\text{Total Lifetime Costs}}{\text{Total Lifetime Energy Output}}$$

Total costs include capital expenditure, operation and maintenance, financing, and decommissioning. Since marine devices are often prototypes or pre commercial arrays, they lack economies of scale in manufacturing and deployment. Operation and maintenance expenses are significant due to offshore conditions and specialized vessels.

Financing is another economic hurdle. Investors often perceive marine projects as high risk because technologies are not yet fully proven over long lifetimes. This leads to higher costs of capital or difficulty in securing loans. Insurance can also be costly when failure probabilities are uncertain. These financial aspects directly affect the LCOE and slow down deployment.

Infrastructure requirements add further costs. Subsea cabling, foundations, moorings, and grid connections can represent a substantial portion of project expenditure, especially for remote or deep water sites. Shared infrastructure and clustering of multiple projects could reduce these costs over time, but this requires coordinated planning and greater market maturity.

Nevertheless, there is potential for cost reduction through technological learning, standardization, and volume manufacturing. As more devices are installed and operated, designers can refine components, simplify installation and maintenance, and optimize array layouts. Policy support, demonstration programs, and targeted research can accelerate the journey from prototypes to competitive commercial systems.

Environmental And Social Considerations

Marine energy interacts with complex marine ecosystems and human uses of the sea. While its overall environmental footprint can be lower than that of many conventional energy sources, there are important site specific issues that must be carefully assessed and managed.

One of the main ecological concerns is the potential for collision or disturbance of marine animals, including fish, marine mammals, and seabirds. Rotating components of tidal stream devices and moving parts of wave converters can create risks for certain species. In practice, the actual level of risk depends on device design, local species behavior, and density of installations. Robust environmental monitoring and adaptive management are essential during early deployments.

Noise is another consideration. Installation activities, such as pile driving, and the operation of turbines or pumps can introduce underwater noise that may influence sensitive species. There can also be changes in sediment transport, flow patterns, or wave regimes around devices and arrays, which might affect habitats.

For tidal range projects that rely on barrages, the environmental impacts can be significant. Alterations in tidal amplitude, water levels, and salinity can affect intertidal zones, wetlands, and migratory bird habitats. These changes can also influence fisheries and coastal erosion. Mitigation measures and alternative designs such as tidal lagoons may reduce some of these impacts, but trade offs remain.

On the social side, the sea is already used for shipping, fishing, tourism, and in some regions, cultural or spiritual practices. Marine energy installations may conflict with navigation routes, fishing grounds, or recreational areas. Long term exclusion zones around structures may limit access for local communities. Transparent planning, early consultation with stakeholders, and fair benefit sharing mechanisms are essential for social acceptance.

Visual impact can be a concern for some technologies that protrude above the surface, like certain wave devices or tidal range structures, particularly in scenic coastal areas. Although most tidal stream devices remain submerged, onshore infrastructure such as substations and cables still require land and can raise local concerns.

Regulatory, Planning, And Governance Challenges

Governance of marine space is often complex, involving multiple jurisdictions and overlapping regulations. Marine energy projects typically need approvals from several authorities that govern navigation, fisheries, environmental protection, coastal planning, and grid connection. The permitting process can be lengthy, uncertain, and expensive.

Spatial planning for marine areas, sometimes known as marine spatial planning, is an emerging tool that can help coordinate different uses. Incorporating marine energy into such plans requires good quality data on resources, environmental sensitivities, and existing activities. In many regions, these data are incomplete, which makes planning more difficult and riskier.

Licensing regimes for marine energy can either facilitate or hinder development. Where regulations are unclear or not adapted to emerging technologies, project developers may face delays and legal uncertainties. Conversely, well designed frameworks that include clear environmental safeguards, predictable timelines, and adaptive management provisions can support innovation while protecting ecosystems.

International aspects add another layer of complexity. Some high potential resources lie in or near international waters or along shared coasts. Cooperation between neighboring countries may be necessary for joint developments, shared infrastructure, or harmonized standards. Coordination at this level is still limited for most marine energy applications.

Innovation Pathways And Future Prospects

Marine energy technology is still in a relatively early phase compared with solar or wind power. This creates opportunities for significant innovation in device concepts, materials, control systems, and systems integration. Many different designs for wave and tidal devices are under development, and the sector is still converging toward preferred configurations.

Digital technologies can support improved performance and reliability. Advanced sensors, data analytics, and remote monitoring make it possible to detect faults early, optimize control strategies in real time, and schedule maintenance more efficiently. Numerical modeling and physical testing in wave tanks and tidal flumes help refine designs before full scale deployment at sea.

Hybrid approaches that combine marine energy with other renewables or uses of the marine space are also promising. Co locating wave or tidal devices with offshore wind farms can allow shared cables, substations, and maintenance vessels, which reduces overall costs. Marine energy can also power offshore facilities, such as aquaculture operations or surveillance systems, independent of onshore grids.

In small island states and remote coastal communities, marine energy may play a special role. These locations often have good marine resources, high dependence on imported fossil fuels, and limited land area. Even if costs remain higher than large scale renewables elsewhere, local benefits such as enhanced energy security, reduced fuel imports, and job creation can justify targeted support.

In the longer term, if costs fall substantially, marine energy could make a notable contribution to global low carbon electricity supply, especially in coastal regions. Its predictable and complementary nature would enhance the resilience and flexibility of power systems that already rely heavily on variable solar and wind energy.

Balancing Potential And Challenges

Marine energy stands at an interesting crossroads. The theoretical and technical potential is large, particularly for wave and tidal stream resources, and many countries with extensive coastlines could benefit from a diversified renewable portfolio that includes marine sources. However, the sector must overcome substantial technical, economic, environmental, and regulatory challenges before large scale deployment becomes commonplace.

For beginners in the field of renewable energies and sustainability, it is important to understand that marine energy is neither a guaranteed solution nor an insignificant niche. Instead, it is a promising but still emerging option that requires thoughtful research, careful environmental assessment, supportive policy frameworks, and open engagement with coastal communities.

Future progress will likely be incremental, through demonstration projects, learning by doing, and gradual cost reductions. Decisions taken today about where and how to develop marine energy will shape not only its contribution to low carbon energy systems, but also its relationship with the oceans and the people who depend on them.