Oceans as a Resource » Wave and Tidal Energy Potential

What you'll learn this session

Study time: 30 minutes

The principles behind wave and tidal energy generation
Different types of wave and tidal energy technologies
Global potential for wave and tidal energy resources
Environmental impacts of these technologies
Case studies of successful wave and tidal energy projects
Challenges and limitations facing wave and tidal energy development

Introduction to Wave and Tidal Energy

The oceans cover more than 70% of our planet's surface and contain enormous amounts of energy in the form of waves and tides. As we look for renewable alternatives to fossil fuels, these marine energy sources offer promising potential with minimal carbon emissions and reliable power generation patterns.

Key Definitions:

Wave energy: Energy captured from the surface motion of ocean waves, which are created by wind blowing across the sea.
Tidal energy: Energy derived from the natural rise and fall of ocean tides caused by the gravitational pull of the moon and sun.
Tidal range: The vertical difference between high tide and low tide.
Tidal stream: The horizontal flow of water as tides move in and out.

⊕ Wave Energy Basics

Waves are created when wind blows across the ocean surface. The energy in waves comes from the movement of water up and down (potential energy) and back and forth (kinetic energy). The amount of energy in a wave depends on:

Wave height
Wave speed
Wavelength
Water density

The best wave energy resources are found in areas with strong, consistent winds and deep water close to shore.

⊕ Tidal Energy Basics

Tidal energy comes from the gravitational pull of the moon and sun on Earth's oceans. Unlike waves, tides are highly predictable, making tidal energy a reliable renewable resource. Tidal energy can be harnessed in two main ways:

Tidal range technologies (using the difference between high and low tides)
Tidal stream technologies (using the flow of water during tidal movements)

The best tidal energy sites have a large tidal range or strong tidal currents.

Wave Energy Technologies

Engineers have developed several different devices to capture energy from waves. Each is designed for specific wave conditions and locations.

⧉ Point Absorbers

Floating structures that absorb energy from waves in all directions. They convert the up and down motion of waves into electricity using hydraulic systems or direct drive generators.

Example: PowerBuoy by Ocean Power Technologies

⧉ Attenuators

Long, snake-like structures that float parallel to wave direction. As waves pass, the different sections bend and flex, generating electricity.

Example: Pelamis Wave Energy Converter

⧉ Oscillating Wave Surge Converters

Hinged devices usually located near the shore that capture energy from wave surge and breaking waves.

Example: Oyster by Aquamarine Power

Tidal Energy Technologies

Tidal energy can be captured using various technologies, each suited to different coastal conditions.

⊕ Tidal Range Technologies

These systems use the difference in height between high and low tides:

Tidal barrages: Dam-like structures built across estuaries that generate electricity as water flows through turbines during incoming and outgoing tides.
Tidal lagoons: Artificial pools created along coastlines that fill and empty with the tides, driving turbines in the process.

The La Rance Tidal Barrage in France, operating since 1966, is the world's oldest tidal power station.

⊕ Tidal Stream Technologies

These devices capture energy from tidal currents:

Horizontal axis turbines: Similar to underwater wind turbines, these rotate as tidal currents flow past.
Vertical axis turbines: Rotate around a vertical axis regardless of current direction.
Oscillating hydrofoils: Use the lift created by tidal flows to drive a hydraulic system.

MeyGen in Scotland is the world's largest tidal stream project, with plans to install up to 398MW of capacity.

Global Potential for Wave and Tidal Energy

The theoretical global potential for wave and tidal energy is enormous, though only a fraction is technically recoverable with current technology.

⊕ Wave Energy Potential

The global wave energy potential is estimated at 29,500 TWh/year, equivalent to about 80% of current world electricity consumption. Regions with the highest wave energy potential include:

Western coasts of Europe (especially Scotland, Ireland, Portugal)
Western coast of North America (Alaska to California)
Southern coast of Australia and New Zealand
Southern tip of Africa
Southern coast of South America

These areas typically have strong, consistent winds that travel across large stretches of ocean.

⊕ Tidal Energy Potential

The global tidal energy potential is estimated at 1,200 TWh/year. The best locations for tidal energy have either:

Large tidal ranges (7+ metres) for tidal barrages
Fast tidal currents (2.5+ m/s) for tidal stream devices

Prime locations include:

Bay of Fundy (Canada) - world's highest tidal range at 16m
Severn Estuary (UK) - tidal range up to 14m
Pentland Firth (Scotland) - strong tidal currents
Cook Strait (New Zealand)
Kimberley Coast (Australia)

Case Study: MeyGen Tidal Stream Project, Scotland

The MeyGen project in the Pentland Firth, Scotland, is the world's largest operational tidal stream project. Located between mainland Scotland and the Orkney Islands, this area has some of the fastest-flowing tidal currents in the UK.

Key facts:

Phase 1A deployed four 1.5MW turbines (6MW total) in 2016-2017
The turbines are submerged on the seabed and connect to the national grid via undersea cables
Each turbine is 16m in diameter and stands 22.5m tall
The project has generated over 40 GWh of electricity for the grid
Future phases aim to expand capacity to 398MW

The MeyGen project demonstrates the commercial viability of tidal stream technology and provides valuable operational data for future developments.

Environmental Impacts of Wave and Tidal Energy

Like all energy sources, wave and tidal technologies have environmental impacts that must be carefully managed.

⊕ Positive Impacts

Low carbon emissions: Minimal greenhouse gas emissions during operation
Predictable energy: Especially tidal energy, which follows reliable patterns
Energy security: Reduces dependence on imported fossil fuels
Artificial reefs: Some structures can create new marine habitats
Coastal protection: Some wave devices may reduce coastal erosion

⊕ Negative Impacts

Habitat alteration: Changes to water flow, sediment transport and local ecosystems
Wildlife collisions: Risk to marine mammals, fish and birds from moving parts
Noise pollution: During construction and operation
Electromagnetic fields: From power cables, potentially affecting marine species
Visual impact: Some devices may affect coastal landscapes
Navigation hazards: Potential obstacles for shipping and fishing

Challenges and Future Outlook

Despite significant potential, wave and tidal energy face several challenges that have limited their widespread adoption.

⧉ Technical Challenges

The harsh marine environment presents significant engineering challenges:

Corrosion from saltwater
Structural damage from storms
Biofouling (growth of marine organisms)
Difficulty in maintenance
Grid connection from offshore locations

⧉ Economic Challenges

Financial barriers include:

High capital costs
Limited economies of scale
Competition from other renewables
Uncertain return on investment
Need for government support

⧉ Future Outlook

Promising developments include:

Improved materials and designs
Hybrid systems combining wave/tidal with other renewables
Smaller, modular devices
Integration with offshore wind farms
Growing government support in the UK, EU and elsewhere

Case Study: Sihwa Lake Tidal Power Station, South Korea

The Sihwa Lake Tidal Power Station is currently the world's largest tidal power plant, with a capacity of 254 MW. Built in 2011, it's an excellent example of how a project can serve multiple purposes.

Key features:

Uses a seawall originally built for flood protection and agricultural land reclamation
Generates electricity during incoming tides only
Improved water quality in Sihwa Lake by increasing seawater exchange
Produces about 552 GWh annually, enough for 500,000 people
Prevents the release of 315,000 tonnes of CO2 per year

This project demonstrates how tidal power can be integrated with existing infrastructure and provide multiple environmental benefits beyond clean energy.

Summary: The Future of Wave and Tidal Energy

Wave and tidal energy represent significant untapped renewable resources with enormous potential to contribute to our future energy mix. While these technologies are still developing and face challenges, they offer several unique advantages:

Predictability (especially tides) compared to wind and solar
High energy density
Minimal land use requirements
Reduced visual impact compared to onshore renewables

For the UK, with its extensive coastline and strong marine resources, wave and tidal energy could become an important part of achieving net-zero carbon emissions by 2050. Continued research, investment and policy support will be crucial in helping these promising technologies reach their full potential.

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