Tidal Energy

Question 1

How are the tides created.

Answer 1

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

Question 2

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

Answer 2

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.)

Question 3

Is tidal energy a renewable energy?

Answer 3

see explenation on slide 107.

Question 4

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

Answer 4

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

Question 5

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

Answer 5

see slide 109.

Question 6

How is the power density defines and quantified?

Answer 6

PD=0,5rhoc^3

Question 7

What is the M2 wave?

Answer 7

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

Question 8

What is the principle of a tidal barrage?

Answer 8

see slide 115

Question 9

What is the principle of a twin basin plant?

Answer 9

slide 116.

Question 10

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

Answer 10

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.

Question 11

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

Answer 11

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

values

Question 12

What are som beneficiary side effects of a tidal barrage?

Answer 12

+ Benefits transportation
+ protection against flood
+ some ecological benefits

Question 13

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

Answer 13

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

Question 14

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

Answer 14

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

Question 15

Explain how a tidal lagoon works.

Answer 15

see slide 122.

Question 16

What is the basid principle of a tidal stream generator?

Answer 16

see slide 123

Question 17

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

Answer 17

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

Question 18

How does tidal stream generators compare to wind turbines?

Answer 18

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

Question 19

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

Answer 19

see slide 125

Question 20

SeaflowMCT

Answer 20

yes

Question 21

SeaGen MCT

Answer 21

double seaflow

Question 22

Voith Siemens Hydro

Answer 22

Korea

Question 23

EvoPod

Answer 23

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

Question 24

Hammerfest Strøm, HS300

Answer 24

Tested in Finland, three pitch adjustable blades

Question 25

Sound of Islay

Answer 25

10 Hammerfest strøm

Question 26

Open Hydro

Answer 26

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

Question 27

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

Answer 27

straight blades on tidal stream instead of parabolic

Question 28

Gorlov Turbine

Answer 28

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

Question 29

Advantages with the gorloc turbine patent

Answer 29

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

Question 30

How do oscillating hydrofoils work?

Answer 30

see slide 137

Question 31

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

Answer 31

see slide 137

Question 32

Stingray

Answer 32

Oscillating single blade

Question 33

The pulse device

Answer 33

Two single blades, oscillating, advantages in shallow waters

Question 34

Tonchev's Rotojet

Answer 34

Combinaton of Darrious and Savonious | Claimed to be self startign

Question 35

Minesto "Deep Green" an underwater kite

Answer 35

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

Question 36

What is a tidal fence?

Answer 36

see slide 142

Question 37

What is the principal of Dynamic Tidal Power (DTP)

Answer 37

see slide 143

Question 38

Advantages of DTP

Answer 38

+ 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

Question 39

Disadvantages of DTP

Answer 39

- generation capacity is proportional to square of dam lenght - > 30km needed

Question 40

Where are the best locations for DTP?

Answer 40

Places where the tidal wave is parallell to the coast line. | Celtic Sea, Northern sea, and yellow sea along the chinese coastline.

Question 41

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

Answer 41

Coastal currents, Ocean gyres and deep ocean currents

Question 42

What creates the Ocean gyres?

Answer 42

Hadley cell winds

Question 43

We have mainly 5 steady ocean gyres. Name them

Answer 43

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

Question 44

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

Answer 44

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

Question 45

General about ocean current potential and turbine type

Answer 45

See slide 147