Marine Energy Flashcards
How do tidal currents occur?
The moon’s gravity causes high tide on the side closest to the moon and pulls the earth toward itself leaving the water behind. Low tides then occur between the two high tides.
How do ocean currents occur?
Ocean currents are driven by several processes such as wind, temperature and salinity differences.
How are ocean waves created?
Waves are created by the interaction of wind with the surface of the sea. The size of the waves is determined by the wind, the depths of the oceans (bathymetry) and ocean currents. The bathymetry can focus or disperse the energy of waves.
What does OTEC stands for?
Ocean Thermal Energy Conversion uses the temperature difference between cooler deep and warmer shallow or surface seawaters to run a heat engine and produce electricity. (min 20 degrees difference => typical in equatorial region)
How can power be generated using salinity gradient?
Salinity gradient technologies generate electricity from the chemical pressure differential created by differences in ionic concentration between freshwater and seawater. Seawater has a higher osmotic pressure than freshwater due to its high concentration of salt.
What are main challenges for salinity gradient energy production?
The membrane quality and scaling and low efficiency
What types of devices can generate power using tidal energy?
- Horizontal axis
- Vertical axis
- Perpendicular axis
=> with respect to the current direction
Further division can be made: - Seabed anchored
- Floating (attached with cables to the seabed)
In what two types can horizontal axis be divided?
- Ductless (zonder rand)
- Rimmed/ Ducted (met rand)
What are advantages of tidal energy?
- Seawater has a higher density than air (lower speed and smaller turbines for the same energy)
- Tidal current is fully predictable and reliable
- Relatively insensitive to weather conditions
- Minimal or zero visual impact
What challenges does tidal energy have?
- SItes with the largest potential for energy extraction are the ones normally avoided by divers
- Difficult to install devices and to keep them working under very harsh conditions
- Survivability: The device has to be robust enough to endure high loads during storms (High CAPEX)
- Harsh environment (highly corrosive, distance from shore, difficult O&M, electrics, access, …)
What challenges does tidal energy have?
- SItes with the largest potential for energy extraction are the ones normally avoided by divers
- Difficult to install devices and to keep them working under very harsh conditions
- Survivability: The device has to be robust enough to endure high loads during storms (High CAPEX)
- Harsh environment (highly corrosive, distance from shore, difficult O&M, electrics, access, …)
What is an example of wave energy technology?
Point absorbers
How do point absorbers work?
Point absorbers are normally heavy devices that exploit the relative motion between an oscillating body and a fixed structure or component, which can be either moored to the seabed or installed on the seabed through a large foundation mass. Point absorbers are normally smaller in dimension compared to other WEC’s (Wave Energy Converters). They are non- directional devices, as their performances are not affected by wave directionality.
How does an attenuator work?
Attenuators exploit the incoming wave power to generate an oscillatory motion between adjacent structural components. The resulting motion activates the power take-off (PTO = krachtafnemer), either by pumping high-pressure fluids through a hydraulic motor or by operating a direct drive generator. Attenuators are designed to operate offshore and are commonly surface floating, although fully submerged devices have been proposed.
How does an oscillating water column works (OWC)?
Oscillating water columns use the oscillatory motion of a mass of water induced by a wave in a chamber to compress air to drive an air turbine. The water column thus acts as a piston on the air volume, pushing it through the turbine as the waves increase the water level in the chamber and drawing it as the water level decreases. OWCs are one of the first types of wave energy converters developed and different operational ones are installed onshore in self-contained structures. Floating OWCs have been tested and are currently under development for offshore deployment.
