🌊Tidal and Wave Energy Engineering Unit 5 – Tidal Energy Conversion Fundamentals

Key Concepts and Terminology

• Tidal energy harnesses the power of the rise and fall of ocean tides caused by the gravitational pull of the moon and sun
• Tidal range refers to the vertical difference between high tide and low tide water levels
• Tidal current is the horizontal flow of water resulting from the rise and fall of tides
• Tidal barrage is a dam-like structure built across an estuary or bay to capture tidal energy using turbines
• Tidal stream generators are underwater turbines that extract energy from tidal currents
• Tidal lagoon is a man-made enclosure that captures tidal water and releases it through turbines to generate electricity
• Tidal fence is a row of vertical axis turbines placed in a channel to capture tidal current energy
• Tidal prism is the volume of water that flows into and out of an estuary or bay during a tidal cycle

Tidal Energy Basics

• Tides are caused by the gravitational interaction between the Earth, moon, and sun
• The moon's gravitational pull is the primary driver of tides due to its proximity to Earth
• Tidal forces cause the ocean to bulge toward and away from the moon, creating high and low tides
• The Earth's rotation and the moon's orbital motion result in two high tides and two low tides each lunar day (24 hours and 50 minutes)
• Tidal range varies depending on the location and the alignment of the Earth, moon, and sun
  • Spring tides occur during new and full moons when the Earth, moon, and sun are aligned, resulting in higher tidal ranges
  • Neap tides occur during the first and third quarter moons when the Earth, moon, and sun form a right angle, resulting in lower tidal ranges
• Tidal energy is a renewable and predictable source of energy as tides are well-understood and can be forecasted accurately

Types of Tidal Energy Systems

• Tidal barrage systems utilize a dam-like structure to capture tidal energy in estuaries or bays
  • Water is allowed to flow through turbines in the barrage during high tide, generating electricity
  • During low tide, water is released back to the sea through the turbines, generating electricity again
• Tidal stream generators are underwater turbines that extract kinetic energy from tidal currents
  • These turbines can be mounted on the seafloor or suspended in the water column
  • Tidal stream generators are less disruptive to the environment compared to tidal barrages
• Tidal lagoons are man-made enclosures that capture tidal water and release it through turbines to generate electricity
  • Tidal lagoons can be constructed offshore or along the coastline
  • They have a smaller environmental impact compared to tidal barrages as they do not block entire estuaries or bays
• Tidal fences are rows of vertical axis turbines placed in channels to capture tidal current energy
  • Tidal fences have a lower environmental impact compared to tidal barrages
  • They allow for the passage of marine life and sediment through the spaces between the turbines
• Hybrid systems combine multiple tidal energy technologies or integrate tidal energy with other renewable sources (wind or solar) to optimize power generation

Tidal Energy Resource Assessment

• Tidal energy resource assessment involves evaluating the potential of a site for tidal energy development
• Factors considered in tidal energy resource assessment include tidal range, tidal current velocity, bathymetry, and site accessibility
• Tidal range is a key factor in determining the potential energy that can be harnessed at a site
  • Sites with a tidal range of at least 5 meters are considered suitable for tidal barrage or lagoon development
• Tidal current velocity determines the kinetic energy available for extraction by tidal stream generators or tidal fences
  • Current velocities of 2 m/s or higher are considered economically viable for tidal current energy projects
• Bathymetry, which is the underwater equivalent of topography, influences the design and placement of tidal energy devices
• Site accessibility, grid connection, and proximity to energy demand centers are important considerations for tidal energy development
• Numerical modeling and field measurements are used to assess tidal energy resources and predict power output
• Geographic Information Systems (GIS) are employed to analyze and visualize tidal energy resource data

Environmental Considerations

• Tidal energy development can have both positive and negative environmental impacts
• Tidal barrages can alter the natural tidal regime, affecting sediment transport and water quality in estuaries and bays
  • Changes in sediment transport can lead to erosion or accretion in nearby coastal areas
  • Altered water quality can impact marine ecosystems and biodiversity
• Tidal stream generators and tidal fences may pose risks to marine life through collision, entanglement, or changes in hydrodynamics
  • Careful site selection and design can minimize these risks
• Tidal energy infrastructure may affect the visual aesthetics of coastal landscapes and create noise pollution
• Positive environmental impacts of tidal energy include the reduction of greenhouse gas emissions and the potential for coastal protection
  • Tidal lagoons can provide a barrier against coastal flooding and erosion
• Environmental Impact Assessments (EIAs) are conducted to evaluate the potential effects of tidal energy projects on marine ecosystems and local communities
• Adaptive management strategies are employed to monitor and mitigate the environmental impacts of tidal energy development over time

Tidal Energy Conversion Technologies

• Tidal energy conversion technologies transform the kinetic and potential energy of tides into electrical energy
• Tidal barrage systems use bulb turbines, which are similar to hydroelectric turbines, to generate electricity
  • Bulb turbines are housed in a bulb-shaped casing and can generate power during both ebb and flood tides
• Tidal stream generators employ various turbine designs, including horizontal axis, vertical axis, and cross-flow turbines
  • Horizontal axis turbines resemble wind turbines and are the most common type used in tidal current energy projects
  • Vertical axis turbines have a cylindrical rotor that rotates perpendicular to the tidal current
  • Cross-flow turbines have a rectangular or cylindrical rotor that rotates parallel to the tidal current
• Tidal lagoon systems can use bulb turbines or other low-head hydroelectric turbines to generate electricity
• Tidal fences utilize vertical axis turbines arranged in a row to capture tidal current energy
• Power take-off systems, such as gearboxes and generators, convert the mechanical energy from the turbines into electrical energy
• Advancements in materials, such as composite blades and corrosion-resistant coatings, improve the efficiency and durability of tidal energy conversion technologies

Challenges and Limitations

• Tidal energy development faces several challenges and limitations that hinder its widespread adoption
• High capital costs associated with the construction and installation of tidal energy infrastructure
  • Tidal barrages and lagoons require significant upfront investments in civil works and turbine technology
  • Tidal stream generators and fences have lower capital costs but still face challenges in terms of economies of scale
• Environmental concerns, such as the impact on marine ecosystems and coastal geomorphology, can lead to public opposition and regulatory hurdles
• Limited number of suitable sites with sufficient tidal range or current velocity for economically viable tidal energy development
• Intermittency of tidal energy output due to the cyclical nature of tides
  • Tidal energy generation is predictable but not continuous, requiring energy storage or grid integration solutions
• Maintenance and accessibility challenges for tidal energy devices operating in harsh marine environments
  • Corrosion, biofouling, and debris accumulation can affect the performance and longevity of tidal energy systems
• Lack of a well-established supply chain and limited operational experience compared to other renewable energy technologies
• Potential conflicts with other marine users, such as shipping, fishing, and recreational activities
• Need for further research and development to optimize tidal energy conversion technologies and reduce costs

Future Developments and Potential

• Tidal energy has significant potential to contribute to the global renewable energy mix, particularly in coastal regions with suitable tidal resources
• Ongoing research and development efforts focus on improving the efficiency, reliability, and cost-effectiveness of tidal energy technologies
  • Advancements in turbine design, materials, and power take-off systems can increase energy capture and reduce maintenance requirements
  • Numerical modeling and site characterization techniques are being refined to optimize tidal energy project design and performance
• Integration of tidal energy with other renewable sources, such as wind and solar, can provide a more stable and dispatchable power supply
• Development of energy storage solutions, such as batteries or hydrogen production, can help mitigate the intermittency of tidal energy output
• Establishment of international standards and best practices for tidal energy development can facilitate the growth of the industry and ensure environmental sustainability
• Collaborative efforts among industry, academia, and government can accelerate the commercialization and deployment of tidal energy technologies
• Tidal energy can contribute to energy security, economic development, and the decarbonization of the power sector in coastal communities worldwide
• Successful demonstration projects, such as the MeyGen tidal array in Scotland and the Sihwa Lake Tidal Power Station in South Korea, showcase the potential of tidal energy and provide valuable operational experience