5.2 Tidal Stream Energy Conversion Principles
4 min read•august 7, 2024
harnesses the power of moving water in . This renewable energy source uses turbines and other devices to transform the of predictable tidal flows into electricity.
Various technologies exist for tidal stream energy, including horizontal and , , and . Each type has unique advantages and is suited to different tidal conditions and locations.
Tidal Current Turbines
Harnessing Tidal Currents for Energy
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- Tidal current turbines convert the kinetic energy of moving water in tidal currents into electrical energy
- Tidal currents are caused by the gravitational pull of the moon and sun on the Earth's oceans, creating predictable and reliable
- Tidal current turbines are typically installed in areas with strong tidal currents, such as narrow channels or straits between islands or coastal areas (, Scotland)
- The velocity of tidal currents varies throughout the tidal cycle, with occurring during and lower velocities during
Types of Tidal Current Turbines
- are the most common type of tidal current turbine and resemble wind turbines with their blades rotating around a horizontal axis
- Horizontal axis turbines are typically mounted on the seabed or a floating platform and face the direction of the tidal current
- Examples of horizontal axis tidal turbines include the SeaGen turbine in , Northern Ireland and the turbine in Norway
- Vertical axis turbines have their blades rotating around a vertical axis and can operate in any direction of tidal current
- Vertical axis turbines are less common than horizontal axis turbines but offer some advantages, such as the ability to operate in shallower waters and easier maintenance access
- Examples of vertical axis tidal turbines include the and the (Uldolmok Tidal Power Station, South Korea)
Alternative Tidal Stream Devices
Oscillating Hydrofoils
- Oscillating hydrofoils are a type of tidal stream device that uses the lift force generated by a hydrofoil in a tidal current to drive a and generate electricity
- The hydrofoil is mounted on an arm that oscillates up and down as the tidal current flows past, creating a pumping action in the hydraulic system
- The hydraulic system drives a generator to produce electricity
- Oscillating hydrofoils have the advantage of being able to operate in slower tidal currents than tidal current turbines and can be designed to have a lower environmental impact (, UK)
Venturi Effect Devices
- Venturi effect devices use the Venturi principle to accelerate the tidal current through a constricted channel, creating a pressure difference that drives a turbine
- The tidal current enters a wide inlet and is funneled through a narrow channel, increasing its velocity and creating a low-pressure zone
- The pressure difference drives a turbine, which is connected to a generator to produce electricity
- Venturi effect devices have the advantage of being able to operate in slower tidal currents than tidal current turbines and can be designed to have a lower visual impact (, UK)
Tidal Stream Energy Metrics
Power Density
- is a measure of the amount of power that can be extracted from a given volume of tidal current
- Power density is calculated as the power available per unit area of the tidal current and is typically expressed in watts per square meter (W/m²)
- The power density of a tidal current depends on its velocity, with higher velocities resulting in higher power densities
- Tidal stream sites with high power densities are more attractive for development as they can generate more electricity from a smaller area, reducing the overall cost of the project (Pentland Firth, Scotland has a power density of up to 8 kW/m²)
Cut-in Speed
- is the minimum velocity of the tidal current at which a tidal stream device starts to generate electricity
- Tidal stream devices are designed to have a specific cut-in speed based on the characteristics of the tidal current at the site and the efficiency of the device
- Tidal current turbines typically have a cut-in speed of around 0.5 to 1 meter per second, while oscillating hydrofoils and Venturi effect devices can operate at lower velocities
- The cut-in speed of a tidal stream device affects its , which is the ratio of its actual energy output to its maximum possible output over a given period (SeaGen tidal turbine has a cut-in speed of 0.7 m/s)
Key Terms to Review (33)
Andritz Hydro Hammerfest: Andritz Hydro Hammerfest is a leading company in the field of marine renewable energy, specifically focused on the development and deployment of tidal stream energy technology. This company is known for its innovative tidal turbines and solutions that convert kinetic energy from tidal currents into electricity, playing a vital role in advancing sustainable energy production from water sources. Their contributions are crucial for understanding the principles of converting tidal stream energy into usable power.
Capacity Factor: The capacity factor is a measure of how effectively an energy generation system produces electricity compared to its maximum potential output over a specific period. It reflects the actual energy output relative to the maximum possible output if the system operated at full capacity continuously, which is essential for understanding the efficiency and reliability of energy systems, especially in the context of renewable sources like ocean energy.
Cut-in speed: Cut-in speed is the minimum velocity of water flow required for a tidal stream turbine to start generating power. This is a critical parameter in the design and efficiency of energy conversion systems, as it determines the threshold at which the turbine begins to harness kinetic energy from tidal currents. Understanding cut-in speed helps in optimizing turbine performance and ensuring reliable energy production.
Darrieus Turbine: A Darrieus turbine is a type of vertical axis wind turbine that harnesses kinetic energy from fluid flows, particularly in tidal and wave energy applications. Its unique curved blade design allows it to efficiently capture energy from water currents regardless of the flow direction, making it suitable for variable tidal stream environments. This design can maximize energy conversion while minimizing the structural complexity and maintenance requirements.
Ecological footprint: An ecological footprint measures the environmental impact of an individual, community, or organization in terms of the amount of natural resources consumed and waste produced, expressed in global hectares. It reflects how much land and water area is needed to sustain a certain lifestyle while providing insights into the sustainability of energy systems and resource management practices.
Efficiency rating: Efficiency rating refers to the measurement of how effectively a system converts available energy into usable power. In the context of tidal stream energy conversion, it quantifies the effectiveness of turbines or generators in harnessing the kinetic energy of moving water into electrical energy. A higher efficiency rating indicates that a larger proportion of the energy from tidal streams is converted into usable electricity, which is crucial for optimizing energy output and ensuring the viability of tidal energy systems.
Flow Patterns: Flow patterns refer to the organized movement of water within a body of water, particularly in relation to tidal streams. Understanding these patterns is crucial for optimizing energy conversion in tidal stream energy systems, as they influence the speed and direction of water flow, which directly affects the efficiency of energy capture by turbines and other devices.
Gorlov Helical Turbine: The Gorlov Helical Turbine is a type of turbine specifically designed for harnessing kinetic energy from flowing water, particularly in tidal stream applications. Its unique helical blade design allows it to operate efficiently in various flow conditions, maximizing energy capture while minimizing drag. This turbine is significant for its ability to generate power with lower start-up speeds, making it suitable for environments where tidal currents may not be strong enough for traditional turbines.
Habitat disruption: Habitat disruption refers to the alteration or destruction of natural environments that affects the organisms living within those ecosystems. This can occur due to human activities, such as energy production, and has significant implications for biodiversity and ecological balance.
Hales Tidal Venturi: The Hales Tidal Venturi is a type of tidal energy converter that uses a venturi effect to harness the kinetic energy from tidal streams. By narrowing the flow area, it increases the velocity of the water, allowing for more efficient energy extraction as the tidal currents pass through the device. This innovative design capitalizes on the natural movement of water, optimizing the conversion process and enhancing overall energy output.
Horizontal Axis Turbines: Horizontal axis turbines are a type of turbine that features blades mounted on a horizontal shaft, which rotates in the plane of the wind or water flow. These turbines are commonly used in various renewable energy applications, including tidal stream energy, where they convert kinetic energy from flowing water into mechanical energy. Their design allows for efficient energy capture and power generation in tidal environments, significantly contributing to sustainable energy solutions.
Hydraulic efficiency: Hydraulic efficiency refers to the effectiveness of a hydraulic system in converting hydraulic energy into useful mechanical work or output. In the context of energy conversion systems, it is crucial for determining how well the system utilizes the available fluid energy, minimizing losses due to friction, turbulence, and other factors. High hydraulic efficiency indicates that most of the input energy is effectively transformed into work, which is essential for optimizing performance and reducing operational costs.
Hydraulic system: A hydraulic system is a technology that uses pressurized fluid to transmit power and control movements in various applications. It operates based on the principles of fluid mechanics, allowing for efficient energy transfer and mechanical motion. In renewable energy contexts, hydraulic systems play a crucial role in converting kinetic energy from water movement into usable power, making them essential for devices like turbines and wave energy converters.
IEC 62600: IEC 62600 is an international standard that provides a framework for the assessment of the energy performance of marine energy systems, particularly tidal and wave energy converters. This standard helps ensure consistency and reliability in the testing and evaluation of these systems, enabling better comparisons and advancements in technology within the marine energy sector.
ISO 19364: ISO 19364 is an international standard that provides guidelines for the evaluation of tidal stream energy resources. This standard is critical for ensuring that tidal energy projects are assessed consistently and effectively, which helps in optimizing energy conversion from tidal streams. By following this standard, engineers can accurately evaluate potential sites for tidal stream energy generation, considering factors like hydrodynamics, environmental impact, and energy yield.
Kinetic Energy: Kinetic energy is the energy that an object possesses due to its motion, defined mathematically as $$KE = \frac{1}{2} mv^2$$, where m is the mass and v is the velocity of the object. In the context of ocean energy, this form of energy is crucial for understanding how water movement can be harnessed for power generation. The kinetic energy of moving water can be converted into mechanical energy and then into electrical energy, illustrating its potential in renewable energy applications.
Neap Tides: Neap tides are the smaller tidal ranges that occur when the sun and moon are at right angles to each other, resulting in lower high tides and higher low tides. This phenomenon is important in understanding tidal energy because it affects the flow and speed of water currents, which are critical for the efficiency of tidal stream energy conversion systems.
Numerical Modeling: Numerical modeling is a computational technique used to simulate and analyze physical phenomena by representing them with mathematical equations and algorithms. In the context of energy conversion, it helps in predicting how tidal and wave systems behave under various conditions, allowing engineers to optimize designs and assess energy potential effectively.
Oscillating hydrofoils: Oscillating hydrofoils are devices designed to convert kinetic energy from water currents into usable mechanical energy by utilizing the lift generated as they move up and down in the water. This movement mimics the flapping motion of wings, allowing these hydrofoils to efficiently capture energy from tidal streams and waves. They are significant in energy conversion systems because they can operate effectively at various speeds and conditions, making them versatile components in renewable energy applications.
Peak Velocities: Peak velocities refer to the maximum speed of tidal currents as they flow through a given area, critical for harnessing tidal stream energy. Understanding peak velocities helps in designing efficient tidal turbines, as these turbines must be optimized to operate effectively at these speeds to maximize energy conversion. The relationship between peak velocities and the overall energy potential of tidal streams is crucial for assessing site feasibility for tidal energy projects.
Pentland Firth: The Pentland Firth is a body of water located between the northern coast of Scotland and the Orkney Islands, known for its strong tidal currents and significant energy potential. This area is a key site for tidal stream energy development due to the powerful tidal flows created by the difference in sea level between the Atlantic Ocean and the North Sea. The unique geography and hydrodynamics of the Pentland Firth make it an ideal location for harnessing tidal energy, thereby connecting it to broader discussions of energy conversion principles and current patterns.
Power Density: Power density is a measure of the amount of power (energy per unit time) generated or received per unit area. It is crucial in understanding how efficiently energy can be harvested from tidal and wave sources, influencing the design and placement of energy conversion systems. High power density indicates that a given area can produce more energy, making it a key factor in evaluating the viability of energy projects in marine environments.
Power take-off system: A power take-off system is a crucial component in energy conversion devices that captures and converts mechanical energy from a moving medium, such as waves or tidal currents, into electrical energy. This system is essential for efficiently transferring the harvested energy to the grid or storage systems, optimizing the performance of various energy converters, including wave energy converters and tidal stream systems.
Site Assessment: Site assessment is the process of evaluating a location for the feasibility of energy projects, particularly focusing on tidal and wave energy systems. This assessment involves analyzing environmental conditions, oceanographic data, and site characteristics to determine if the area is suitable for energy generation. Effective site assessment is crucial for optimizing energy production while minimizing environmental impact.
Spring tides: Spring tides are the higher than average tidal conditions that occur when the Earth, Moon, and Sun are aligned during full and new moons. This alignment creates a stronger gravitational pull, leading to more extreme high and low tides, which can significantly impact tidal stream energy conversion systems and their efficiency.
Stingray Tidal Energy Device: The stingray tidal energy device is an innovative technology designed to harness the kinetic energy from tidal streams. Resembling a manta ray, this device utilizes flexible wings that move with the water currents, converting the energy of tidal movements into electricity efficiently. Its unique shape and operational principles enable it to operate effectively in various tidal environments, making it a promising solution for renewable energy generation.
Strangford Lough: Strangford Lough is a large sea lough located in County Down, Northern Ireland, known for its strong tidal currents and rich marine biodiversity. The lough is significant for its potential as a site for tidal stream energy generation due to the fast-flowing water created by the tides, making it an ideal location to explore the principles of energy conversion from tidal streams.
Tidal currents: Tidal currents are the horizontal movement of water generated by the gravitational pull of the moon and sun, resulting in the periodic rise and fall of sea levels. These currents are essential for understanding how energy is distributed in oceans and can be harnessed for tidal energy generation. They play a crucial role in shaping marine ecosystems and influence coastal processes.
Tidal stream energy conversion: Tidal stream energy conversion is the process of harnessing the kinetic energy of moving water in tidal streams to generate electricity. This technology captures the natural flow of tidal currents, using underwater turbines or similar devices to convert this mechanical energy into electrical power. The approach is considered a sustainable form of renewable energy, with minimal environmental impact compared to fossil fuels.
Tidal stream generator: A tidal stream generator is a device designed to harness the kinetic energy of moving water in tidal currents to produce electricity. These generators operate similarly to underwater wind turbines, converting the energy from fast-flowing tides into usable electrical power, and are an essential component of tidal energy conversion principles.
Turbine design: Turbine design refers to the engineering process of creating turbines that convert kinetic energy from fluids, such as water or air, into mechanical energy for power generation. Effective turbine design is crucial for maximizing energy conversion efficiency and involves considerations like blade shape, size, materials, and operational conditions. This impacts energy conversion systems and presents various challenges that engineers must address to enhance performance and durability.
Venturi Effect Devices: Venturi effect devices are instruments that utilize the principle of the Venturi effect to harness kinetic energy from fluid flow. This effect occurs when a fluid flows through a constricted section of pipe, resulting in a decrease in pressure and an increase in fluid velocity. In the context of tidal stream energy conversion, these devices can effectively channel and accelerate water flow to optimize energy extraction from tidal currents.
Vertical Axis Turbines: Vertical axis turbines are a type of wind turbine where the main rotor shaft is set vertically, allowing the turbine to capture wind from any direction. These turbines can operate efficiently in turbulent wind conditions and are often used in urban settings or offshore environments where space is limited. Their design offers advantages in terms of stability and ease of maintenance, which are important when considering energy conversion from tidal streams.