Wave and Tidal Power: Technologies and Methods
Wave Power Systems
Tapered Channel (TAPCHAN)
The Tapered Channel, or TAPCHAN, is used to divert water into a reservoir. It is generally constructed on a cliff, providing a higher water head. Electricity is generated with the help of a Kaplan turbine placed in the tank that receives the water. The narrowing of the channel increases the wave amplitude, causing it to spill over the walls of the channel and into the reservoir.
Advantages:
- Low maintenance costs
- Reliability
- Use for peak load supply
Disadvantages:
- The need for locations with consistent waves
- A water head of at least 1 meter
- A suitable location for a reservoir
Oscillating Water Column (OWC)
The Oscillating Water Column, or OWC, operates perpendicular to the direction of wave travel to capture the wave’s power. They are typically installed onshore or nearshore. Water enters through a subsurface opening into a chamber containing a column of air above a column of water. The wave causes the captured water to rise and fall, which in turn compresses and decompresses the air column. This trapped air flows through a turbine, causing it to rotate and generate electricity. The turbine works in both directions, thereby increasing power production. Importantly, the turbine must rotate in the same direction irrespective of the airflow direction.
Point Absorber
A Point Absorber is a floating device in which a floating buoy moves inside a fixed cylinder due to wave action. The relative motion is used to drive electromechanical or hydraulic energy converters. It is the most widely used system in the USA. The buoy or piston movement must be in resonance with the waves to maximize energy capture. Also, the piston movement must be limited to keep it within the fixed cylinder. It uses a bidirectional turbine.
Attenuator
An Attenuator is a long, multi-segment floating device that works parallel to the wave direction and effectively rides the waves. Movements are selectively constrained to produce energy. The power conversion module is located inside the device.
Overtopping Devices
Overtopping Devices have reservoirs that are filled with water by incoming waves to levels above the average surrounding ocean. The water is then released and allowed to fall under gravity through hydro-turbines. The energy of the falling water is used to generate electricity.
Tidal Power Technologies
Tidal Barrage Method
The Tidal Barrage Method is used to force water into a reservoir during high tide. When the tides produce an adequate difference in water level, the gates are opened, allowing the water to flow out and generate power.
Tidal Turbine Method
This technology is at an early stage of development. The main issue with the tidal current system is the design of the turbine. Submerged tide turbines capture energy through the processes of hydrodynamic lift or drag, rather than aerodynamic lift or drag like wind turbines.
Four types of turbines have been explored:
- Horizontal Axis Turbine: The power output depends on the rotor diameter.
- Vertical Axis Turbine: The water stream flow is perpendicular to the rotational axis of the turbine.
- Tidal Lift Mechanism: A large wing moves up and down in a linear motion, compressing oil to run a hydraulic power converter.
- Venturi-Based Systems: A Venturi tube is used to accelerate water flow. A pressure drop is generated in the tube due to the narrowing of the section, and an increase in speed occurs.