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examBoard: Cambridge
examType: IGCSE
lessonTitle: Tidal and Wave Power Generation
Our oceans cover more than 70% of Earth's surface and contain enormous energy potential. Tidal and wave power harness the natural movements of seawater to generate clean, renewable electricity. Unlike solar or wind power, ocean energy is highly predictable and consistent, making it an attractive renewable energy source.
Key Definitions:
Tidal power works by capturing energy from the predictable daily cycle of rising and falling sea levels. The Moon's gravitational pull is the primary force creating tides, with the Sun also playing a role. Locations with large tidal ranges (typically >5m) are most suitable for tidal power generation. The UK has some of the world's best tidal resources, particularly in the Severn Estuary, Pentland Firth and around the Orkney Islands.
Wave power harnesses energy from surface waves created when wind blows across the ocean. The energy in waves is concentrated near the water surface and can be captured by various devices. Wave power is most effective in locations with consistent, powerful wave activity, such as the western coasts of Europe, North America and Australia. The UK's Atlantic coastline has excellent wave energy potential.
There are three main approaches to generating electricity from tides, each with distinct characteristics and environmental considerations:
Tidal barrages are dam-like structures built across estuaries or bays. They generate electricity using the height difference between high and low tides.
As the tide rises, water flows through sluice gates into a basin. At high tide, the gates close, trapping water. When the sea level drops, water is released through turbines, generating electricity similar to hydroelectric dams but using tidal flows instead of rivers.
Highly predictable energy generation, long operational lifespan (100+ years), can double as transport links across estuaries and may provide flood protection benefits.
High construction costs, significant environmental impact on estuarine ecosystems, changes to sediment patterns and affects marine organism migration.
Tidal lagoons are artificial pools created by enclosing a coastal area with walls. They work on similar principles to barrages but are built out from the coastline rather than spanning entire estuaries.
Lagoons create an artificial basin that fills and empties with the tides. Turbines in the walls generate electricity as water flows in and out. Some designs can generate power during both incoming and outgoing tides (bi-directional generation).
Lagoons typically have less environmental impact than barrages as they don't block entire estuaries. They can create new marine habitats around their structures and have less effect on fish migration. However, they still alter local currents and sediment patterns.
Tidal stream generators work like underwater wind turbines, capturing energy from flowing tidal currents rather than from the rise and fall of water levels.
These include horizontal axis turbines (similar to wind turbines), vertical axis turbines, oscillating hydrofoils (which move up and down like a whale's tail) and venturi effect devices (which accelerate water flow through a constricted channel).
Tidal stream systems have minimal visual impact as they're mostly underwater, can be installed in arrays (like wind farms), have lower environmental impact than barrages and can be deployed incrementally, reducing initial investment costs.
Wave energy converters (WECs) come in various designs, each suited to different marine environments and wave conditions:
Floating structures that absorb energy from waves in all directions. They typically use the up and down motion of waves to drive hydraulic systems or linear generators. Examples include the PowerBuoy and Wavebob.
Long, snake-like structures aligned parallel to wave direction. They flex with wave motion and this movement drives hydraulic pumps to generate electricity. The Pelamis Wave Energy Converter is a famous example.
Partially submerged structures with an air chamber above the water. As waves enter, they push air through a turbine. When waves retreat, air is drawn back through the turbine, generating electricity in both directions.
These capture water from waves in elevated reservoirs, then release it through turbines similar to mini hydroelectric plants. The Wave Dragon is an example of this technology.
These harness wave energy near the shore using paddle-like flaps that move back and forth with wave surges. The Oyster device developed by Aquamarine Power uses this principle.
Located in the Pentland Firth between mainland Scotland and the Orkney Islands, MeyGen is the world's largest operational tidal stream project. The site experiences some of the fastest tidal flows in the UK (up to 5 metres per second). Phase 1A of the project has installed four 1.5 MW turbines on the seabed, powering approximately 2,600 homes. The turbines look like underwater wind turbines with 16-metre diameter rotors. The project demonstrates how tidal stream technology can work at commercial scale with minimal visual impact. Future phases aim to expand capacity to 398 MW, potentially powering 175,000 homes.
While tidal and wave power are renewable energy sources, they still have environmental effects that must be carefully managed:
Located in South Korea, the Sihwa Lake Tidal Power Station is currently the world's largest tidal power plant with a capacity of 254 MW. Interestingly, it was built into a seawall that was originally constructed in 1994 for flood protection and agricultural purposes. The power station began operating in 2011 and generates enough electricity for 500,000 people. What makes this case study particularly notable is that the tidal power plant actually improved water quality in Sihwa Lake, which had become heavily polluted after the original seawall restricted water exchange with the sea. The power station increased water circulation, helping to restore the marine environment while generating clean energy.
Tidal and wave power technologies are still developing compared to other renewables like wind and solar. Here's what the future might hold:
Emerging technologies include flexible membranes that generate electricity when deformed by waves, improved materials that can withstand harsh marine environments and hybrid systems that combine different types of ocean energy. Floating platforms that can harness both wind and wave energy are also being developed to maximize energy capture from a single location.
The high cost of marine energy remains a significant barrier. Initial capital costs are high and maintenance in marine environments is expensive and challenging. However, costs are expected to fall as technology matures and more projects are deployed. Government support through subsidies and research funding is crucial for continued development.
Tidal and wave power have enormous potential to contribute to our renewable energy mix. While they currently provide only a tiny fraction of global electricity, their predictability and high energy density make them valuable complements to intermittent renewables like wind and solar. With continued technological development and appropriate environmental safeguards, these ocean energy sources could become important components of a sustainable energy future.
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