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Ocean & Wind Energy > Tidal Energy > Flashcards

Tidal Energy Flashcards

1
Q

How are the tides created.

A

Lunar (and solar) gravity pull on the earths water, and the centrifugal force from the earths rotation.

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2
Q

How much do the different constituents contribute to the tides? Is this a local or global value?

A

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.)

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3
Q

Is tidal energy a renewable energy?

A

see explenation on slide 107.

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4
Q

What are the three main categories in utilizing tidal energy potentials?

A

Tidal barrages, Tidal Stream Generators (TSG), and Dynamic Tidal Power (DTP).

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5
Q

How does the tidal energy potential apply to the different means/types of utilization?

A

see slide 109.

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6
Q

How is the power density defines and quantified?

A

PD=0,5rhoc^3

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7
Q

What is the M2 wave?

A

The principle lunar semidurnal. Its period is 12 hours and 25,2 min, exactly half a tidal lunar day.

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8
Q

What is the principle of a tidal barrage?

A

see slide 115

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9
Q

What is the principle of a twin basin plant?

A

slide 116.

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10
Q

Define the energy available from a tidal barrage scheme with a formula

A

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.

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11
Q

Cost effectiveness is measured by the Gibralt ratio. What does it say/measure?

A

Rg = dam length[m]/yearly production [GWh]

values

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12
Q

What are som beneficiary side effects of a tidal barrage?

A

+ Benefits transportation
+ protection against flood
+ some ecological benefits

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13
Q

What needs to be considered (ecologically) in tidal barrages?

A

less variations in tidal range
lower flow velocity -> less turbidity - clearer water, more light -> more life
accumulation of silt
impedded fish passage

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14
Q

Ecological evaluation of La Rance project after 40 years of operation.

A
  • slightly increased accumulation of fine sediments
  • invertebrate fauna more prolific
  • shorebird population increased
  • fish fauna more abundant
  • fish turbine massacre.
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15
Q

Explain how a tidal lagoon works.

A

see slide 122.

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16
Q

What is the basid principle of a tidal stream generator?

A

see slide 123

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17
Q

Name 3 types of classes of wave turbines. Are there others as well?

A
  1. horizontal axis
  2. vertical axis
  3. Oscillating plates
  4. yes, som other exotic devices like resistance runners and kites.
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18
Q

How does tidal stream generators compare to wind turbines?

A

Much higher energy density.
Lower velocities.
Boundary layer at ground level.
Flow velocities are completely predictable(!)

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19
Q

What are the adv. and disadv. of floating or seabed mounted stream turbines?

A

see slide 125

20
Q

SeaflowMCT

A

yes

21
Q

SeaGen MCT

A

double seaflow

22
Q

Voith Siemens Hydro

A

Korea

23
Q

EvoPod

A

floating, four-blade, leeside rotor,
moored to the ground
tested in Strangford Lough

24
Q

Hammerfest Strøm, HS300

A

Tested in Finland, three pitch adjustable blades

25
Q

Sound of Islay

A

10 Hammerfest strøm

26
Q

Open Hydro

A

Extremely low specific speed turbine
rim generator with water lubricated bearings
Bay of FUndy

27
Q

What is the difference between a vertical axis Darrious rotor for wind and tidal stream?

A

straight blades on tidal stream instead of parabolic

28
Q

Gorlov Turbine

A

Twisted helically blades, vertical axis - fish friendly due to low specific speeds
can be combined to long tubes

29
Q

Advantages with the gorloc turbine patent

A

Accessible technology, 90% of tide energy stations can be built from locally available labour, materials and equipment
Only the blades themselves are outside components

30
Q

How do oscillating hydrofoils work?

A

see slide 137

31
Q

What is the difference between an oscillating hydrofoil and a rotating foil machine?

A

see slide 137

32
Q

Stingray

A

Oscillating single blade

33
Q

The pulse device

A

Two single blades, oscillating, advantages in shallow waters

34
Q

Tonchev’s Rotojet

A

Combinaton of Darrious and Savonious

Claimed to be self startign

35
Q

Minesto “Deep Green” an underwater kite

A

claimed to achieve velocities up to 10 times the free stream velocities –> 1000times the energy from the given rotor size

36
Q

What is a tidal fence?

A

see slide 142

37
Q

What is the principal of Dynamic Tidal Power (DTP)

A

see slide 143

38
Q

Advantages of DTP

A

+ 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

39
Q

Disadvantages of DTP

A
  • generation capacity is proportional to square of dam lenght
  • > 30km needed
40
Q

Where are the best locations for DTP?

A

Places where the tidal wave is parallell to the coast line.

Celtic Sea, Northern sea, and yellow sea along the chinese coastline.

41
Q

What kind of ocean currents do we have here on earth?

A

Coastal currents, Ocean gyres and deep ocean currents

42
Q

What creates the Ocean gyres?

A

Hadley cell winds

43
Q

We have mainly 5 steady ocean gyres. Name them

A

a. North pacific gyre
b. South pacific gyre
c. North atlantic gyre
d. South atlantic gyre
e. Indian ocean gyre

44
Q

Which 4 parts can the european North atlantic gyre be divided to?

A

Gulf stream, North equatorial current, North atlantic current, Canary Current

45
Q

General about ocean current potential and turbine type

A

See slide 147

Ocean & Wind Energy (3 decks)

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