4.1 Fundamental Wave Energy Conversion Concepts

Wave energy conversion devices harness ocean waves to generate electricity. From oscillating water columns to point absorbers, these technologies tap into a renewable resource with high energy density. However, challenges like harsh marine environments and variable wave conditions must be overcome.

Power take-off systems are crucial for turning mechanical energy into electricity. Efficiency metrics like wave-to-wire efficiency and capture width ratio help evaluate device performance. Optimizing these factors, along with resonance and hydrodynamic response, is key to making wave energy economically viable.

Wave Energy Conversion Devices

Types of Wave Energy Conversion Devices

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  Frontiers | Scaling Orchestration in Physical Model Test of Oscillating Buoy Wave Energy Converter View original

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  MS - Design and performance analysis of wave linear generator with parallel mechanism View original

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  Frontiers | Frequency Domain Modeling of a Halbach PM Linear Generator Based Two-Body Point ... View original

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• Wave energy conversion devices harness the kinetic and potential energy of ocean waves to generate electricity
• Oscillating water column devices use the rise and fall of waves to compress air in a chamber, driving an air turbine connected to a generator
• Point absorber devices typically consist of a buoy that moves up and down with the waves, driving a linear generator or hydraulic system
• Attenuator devices are long, snake-like structures that are oriented parallel to the direction of wave propagation and generate electricity from the relative motion of their segments (Pelamis)
• Overtopping devices allow waves to spill over into a reservoir above sea level, and the water is then released back to the sea through a turbine (Wave Dragon)

Advantages and Challenges of Wave Energy

• Wave energy is a renewable and abundant resource with high energy density compared to other renewable sources
• Wave energy conversion devices can be located offshore, reducing visual impact and conflicts with other coastal activities
• Challenges in wave energy development include the harsh marine environment, which requires robust and reliable designs
• Variability in wave conditions and the need for efficient power take-off systems are also significant hurdles in wave energy conversion

Power Generation and Efficiency

Power Take-Off Systems

• Power take-off (PTO) systems convert the mechanical energy captured by wave energy devices into electrical energy
• PTO systems can be based on hydraulics, air turbines, or direct drive linear generators, depending on the type of wave energy device
• Efficient PTO systems are crucial for maximizing the overall performance of wave energy conversion devices
• Hydraulic PTO systems use hydraulic fluid and accumulators to smooth out power fluctuations and drive a hydraulic motor connected to a generator

Efficiency Metrics

• Wave-to-wire efficiency represents the ratio of the electrical power output to the available wave power and is a key indicator of a device's performance
• Capture width ratio is the ratio of the absorbed wave power to the available wave power in a width equal to the device's characteristic dimension
• Optimizing wave-to-wire efficiency and capture width ratio is essential for the economic viability of wave energy projects
• Factors affecting efficiency include the device's hydrodynamic performance, PTO efficiency, and transmission losses

Device Performance Factors

Resonance and Hydrodynamic Response

• Resonance occurs when the natural frequency of a wave energy device matches the frequency of the incoming waves, leading to increased energy capture
• Designing devices to achieve resonance across a wide range of wave frequencies is challenging but can significantly enhance performance
• Hydrodynamic response refers to how a device interacts with and extracts energy from the surrounding water
• Factors influencing hydrodynamic response include the device's shape, size, and motion characteristics (heave, pitch, surge)

Optimizing Device Performance

• Numerical modeling and wave tank testing are used to optimize the design of wave energy devices for improved performance
• Control strategies, such as latching and declutching, can be employed to maximize energy capture by adjusting the device's response to incoming waves
• Material selection and structural design play a crucial role in ensuring the durability and survivability of wave energy devices in extreme wave conditions
• Site-specific optimization, considering local wave climate and bathymetry, is necessary for deploying wave energy devices in the most suitable locations