🌊Tidal and Wave Energy Engineering Unit 7 – Tidal Barrage and Stream Technologies

Fundamentals of Tidal Energy

• Tidal energy harnesses the power of the ocean's tides, caused by the gravitational pull of the moon and sun
• Tides are predictable and reliable, making tidal energy a consistent and renewable source of power
• Two main types of tidal energy systems: tidal barrages and tidal stream generators
  • Tidal barrages use a dam-like structure to capture water during high tide and release it through turbines during low tide
  • Tidal stream generators utilize underwater turbines to capture the kinetic energy of moving water currents
• Tidal energy has the potential to provide a significant amount of clean, renewable electricity in coastal areas with high tidal ranges (Bay of Fundy, Canada)
• Tidal energy is not affected by weather conditions, unlike solar and wind power, providing a stable and predictable energy output
• The energy density of tidal currents is higher than wind or solar, allowing for more compact and efficient energy generation systems
• Tidal energy has a lower environmental impact compared to fossil fuels, as it does not produce greenhouse gas emissions or air pollutants

Tidal Barrage Systems Explained

• Tidal barrages are large-scale tidal energy systems that use a dam-like structure to capture and release water for power generation
• The barrage is built across an estuary or bay with a high tidal range, creating a reservoir behind the dam
• As the tide rises, water flows through sluice gates into the reservoir, and during low tide, the water is released through turbines to generate electricity
• Tidal barrages can generate power during both the incoming and outgoing tides, known as flood generation and ebb generation, respectively
  • Flood generation occurs when water flows into the reservoir through the turbines during high tide
  • Ebb generation occurs when water is released from the reservoir through the turbines during low tide
• The La Rance Tidal Power Plant in France, built in 1966, is the world's oldest and second-largest tidal barrage system
• Tidal barrages require a significant upfront investment and can have environmental impacts on the local ecosystem, such as changes in water salinity and sediment transport
• Proper site selection and environmental impact assessments are crucial for the successful implementation of tidal barrage systems

Stream Technology Basics

• Tidal stream technology harnesses the kinetic energy of moving water currents, similar to how wind turbines capture wind energy
• Underwater turbines are placed in areas with strong tidal currents, such as narrow channels or around headlands
• The flowing water rotates the turbine blades, which drive a generator to produce electricity
• Tidal stream generators can be either seabed-mounted or floating, depending on the water depth and site conditions
  • Seabed-mounted turbines are fixed to the ocean floor and are suitable for shallow waters
  • Floating turbines are tethered to the seabed and can be deployed in deeper waters
• Tidal stream technology has a lower environmental impact compared to tidal barrages, as it does not require the construction of large dam-like structures
• The SeaGen project in Strangford Lough, Northern Ireland, is an example of a successful tidal stream installation, with a peak output of 1.2 MW
• Tidal stream technology is still in the early stages of development, with ongoing research and pilot projects aimed at optimizing turbine design and improving efficiency

Key Components and Design

• Tidal turbines are the primary component of tidal stream systems, responsible for converting the kinetic energy of moving water into rotational energy
• Turbine blades are designed to optimize energy capture and minimize environmental impact, with considerations for marine life and corrosion resistance
  • Horizontal axis turbines have blades that rotate parallel to the water flow, similar to wind turbines
  • Vertical axis turbines have blades that rotate perpendicular to the water flow, and are less common in tidal stream applications
• Gearboxes and generators convert the rotational energy from the turbine into electrical energy, which is then transmitted to shore via underwater cables
• Foundations and support structures anchor the turbines to the seabed and provide stability in strong tidal currents
  • Gravity-based foundations rely on the weight of the structure to maintain stability
  • Pile-driven foundations use long steel piles driven into the seabed for anchoring
• Control systems and power electronics manage the turbine operation, optimize energy output, and ensure safe and reliable performance
• Tidal stream systems must be designed to withstand harsh marine environments, including corrosion, biofouling, and extreme weather events

Environmental Considerations

• Tidal energy projects must carefully consider and mitigate potential environmental impacts to ensure sustainable development
• Tidal barrages can alter the natural tidal regime and water flow patterns, affecting sediment transport and water quality
  • Changes in salinity and nutrient levels can impact aquatic habitats and biodiversity
  • Fish and marine mammal migration patterns may be disrupted by the presence of the barrage
• Tidal stream generators have a lower environmental impact compared to barrages, but still require careful site selection and monitoring
  • Underwater noise generated by the turbines can affect marine mammal communication and behavior
  • Turbine blades may pose a collision risk to fish and diving seabirds
• Proper site selection, environmental impact assessments, and ongoing monitoring are essential for minimizing negative effects on the marine ecosystem
• Tidal energy projects can also have positive environmental impacts, such as reducing greenhouse gas emissions and providing artificial reef habitats for marine life
• Engaging with local communities and stakeholders is crucial for addressing environmental concerns and ensuring public acceptance of tidal energy projects

Efficiency and Power Output

• The efficiency of tidal energy systems depends on various factors, including turbine design, site conditions, and operational strategies
• Tidal stream turbines can achieve efficiencies of up to 40-50%, which is higher than most wind turbines (30-40%)
  • The higher energy density of water compared to air contributes to the increased efficiency of tidal turbines
  • Advancements in turbine design, such as optimized blade shapes and materials, can further improve efficiency
• The power output of tidal energy systems varies depending on the tidal range, current velocity, and turbine size
  • Tidal barrages can generate significant amounts of power, with the Sihwa Lake Tidal Power Station in South Korea having a capacity of 254 MW
  • Tidal stream arrays, consisting of multiple turbines, can have a combined output in the range of several megawatts to tens of megawatts
• Capacity factors for tidal energy systems are typically higher than those for solar and wind power, due to the predictable nature of tides
• Optimizing turbine array layouts and using advanced control strategies can help maximize power output and efficiency
• As tidal energy technology matures and economies of scale are achieved, the cost of electricity generated from tidal sources is expected to decrease

Installation and Maintenance

• The installation of tidal energy systems requires specialized equipment and expertise due to the challenging marine environment
• Site preparation involves surveying the seabed, assessing environmental impacts, and obtaining necessary permits and approvals
• Tidal barrage construction requires extensive civil engineering works, including dams, sluice gates, and turbine housings
  • Cofferdams are often used to create temporary dry working areas for construction
  • The installation process can take several years and requires careful planning and coordination
• Tidal stream turbines are typically installed using specialized vessels and underwater equipment
  • Turbines and foundations are transported to the site and lowered onto the seabed using cranes or hydraulic systems
  • Underwater cables are laid to connect the turbines to onshore substations
• Regular maintenance is essential for ensuring the long-term reliability and performance of tidal energy systems
  • Turbine blades and components may require cleaning to remove biofouling and prevent corrosion
  • Underwater inspections and repairs may be necessary to address any structural or mechanical issues
• Remote monitoring systems can help detect and diagnose problems, reducing the need for on-site maintenance visits
• Decommissioning and removal of tidal energy systems at the end of their lifespan must be planned and executed responsibly to minimize environmental impacts

Real-World Applications and Case Studies

• Tidal energy projects have been implemented in various locations worldwide, demonstrating the potential for large-scale deployment
• The La Rance Tidal Power Plant in France, operational since 1966, has a capacity of 240 MW and generates around 500 GWh of electricity annually
  • The barrage is 750 meters long and uses 24 reversible bulb turbines for flood and ebb generation
  • The project has provided valuable insights into the long-term performance and environmental impacts of tidal barrages
• The MeyGen Tidal Energy Project in Scotland is one of the largest tidal stream arrays in the world, with a planned capacity of 398 MW
  • The first phase of the project, completed in 2017, consists of four 1.5 MW turbines and has generated over 30 GWh of electricity
  • The project demonstrates the feasibility of large-scale tidal stream energy and has attracted significant investment and interest
• The Sihwa Lake Tidal Power Station in South Korea, completed in 2011, is the world's largest tidal power plant, with a capacity of 254 MW
  • The project utilizes an existing seawall and generates electricity during the ebb tide
  • The power station has an annual output of 552 GWh and has helped reduce greenhouse gas emissions by over 300,000 tons per year
• Smaller-scale tidal energy projects, such as the Bluemull Sound Tidal Array in Shetland, UK, showcase the potential for community-scale tidal power generation
• Ongoing research and development efforts focus on improving turbine designs, reducing costs, and addressing environmental challenges to accelerate the deployment of tidal energy worldwide