Tidal Energy Flashcards
How are the tides created.
Lunar (and solar) gravity pull on the earths water, and the centrifugal force from the earths rotation.
How much do the different constituents contribute to the tides? Is this a local or global value?
Effect of lunar gravity: 27cm
Effect of solar gravity: 12cm
Real tides/local tides differ greatly due to resonance effects and local amplifications due to flow contraints (islands etc.)
Is tidal energy a renewable energy?
see explenation on slide 107.
What are the three main categories in utilizing tidal energy potentials?
Tidal barrages, Tidal Stream Generators (TSG), and Dynamic Tidal Power (DTP).
How does the tidal energy potential apply to the different means/types of utilization?
see slide 109.
How is the power density defines and quantified?
PD=0,5rhoc^3
What is the M2 wave?
The principle lunar semidurnal. Its period is 12 hours and 25,2 min, exactly half a tidal lunar day.
What is the principle of a tidal barrage?
see slide 115
What is the principle of a twin basin plant?
slide 116.
Define the energy available from a tidal barrage scheme with a formula
slide 120.
The energy is proportional to the difference in tidal hights and the Volume of storage. The volume of storage is again proportional to the dam length.
Cost effectiveness is measured by the Gibralt ratio. What does it say/measure?
Rg = dam length[m]/yearly production [GWh]
values
What are som beneficiary side effects of a tidal barrage?
+ Benefits transportation
+ protection against flood
+ some ecological benefits
What needs to be considered (ecologically) in tidal barrages?
less variations in tidal range
lower flow velocity -> less turbidity - clearer water, more light -> more life
accumulation of silt
impedded fish passage
Ecological evaluation of La Rance project after 40 years of operation.
- slightly increased accumulation of fine sediments
- invertebrate fauna more prolific
- shorebird population increased
- fish fauna more abundant
- fish turbine massacre.
Explain how a tidal lagoon works.
see slide 122.
What is the basid principle of a tidal stream generator?
see slide 123
Name 3 types of classes of wave turbines. Are there others as well?
- horizontal axis
- vertical axis
- Oscillating plates
- yes, som other exotic devices like resistance runners and kites.
How does tidal stream generators compare to wind turbines?
Much higher energy density.
Lower velocities.
Boundary layer at ground level.
Flow velocities are completely predictable(!)
What are the adv. and disadv. of floating or seabed mounted stream turbines?
see slide 125
SeaflowMCT
yes
SeaGen MCT
double seaflow
Voith Siemens Hydro
Korea
EvoPod
floating, four-blade, leeside rotor,
moored to the ground
tested in Strangford Lough
Hammerfest Strøm, HS300
Tested in Finland, three pitch adjustable blades
Sound of Islay
10 Hammerfest strøm
Open Hydro
Extremely low specific speed turbine
rim generator with water lubricated bearings
Bay of FUndy
What is the difference between a vertical axis Darrious rotor for wind and tidal stream?
straight blades on tidal stream instead of parabolic
Gorlov Turbine
Twisted helically blades, vertical axis - fish friendly due to low specific speeds
can be combined to long tubes
Advantages with the gorloc turbine patent
Accessible technology, 90% of tide energy stations can be built from locally available labour, materials and equipment
Only the blades themselves are outside components
How do oscillating hydrofoils work?
see slide 137
What is the difference between an oscillating hydrofoil and a rotating foil machine?
see slide 137
Stingray
Oscillating single blade
The pulse device
Two single blades, oscillating, advantages in shallow waters
Tonchev’s Rotojet
Combinaton of Darrious and Savonious
Claimed to be self startign
Minesto “Deep Green” an underwater kite
claimed to achieve velocities up to 10 times the free stream velocities –> 1000times the energy from the given rotor size
What is a tidal fence?
see slide 142
What is the principal of Dynamic Tidal Power (DTP)
see slide 143
Advantages of DTP
+ can be built in areas with relatively low tidal ranges
+ ecological much lower than barrages
+ due to static head, less turbines are needed compared to tidal stream
Disadvantages of DTP
- generation capacity is proportional to square of dam lenght
- > 30km needed
Where are the best locations for DTP?
Places where the tidal wave is parallell to the coast line.
Celtic Sea, Northern sea, and yellow sea along the chinese coastline.
What kind of ocean currents do we have here on earth?
Coastal currents, Ocean gyres and deep ocean currents
What creates the Ocean gyres?
Hadley cell winds
We have mainly 5 steady ocean gyres. Name them
a. North pacific gyre
b. South pacific gyre
c. North atlantic gyre
d. South atlantic gyre
e. Indian ocean gyre
Which 4 parts can the european North atlantic gyre be divided to?
Gulf stream, North equatorial current, North atlantic current, Canary Current
General about ocean current potential and turbine type
See slide 147
