Wave n Tidal

Question 1

What are the three types of waves devices and describe them?

Answer 1

Passive - designed to guide the waves to spill over into elevated reservoirs which then drain through conventional low-head hydraulic turbines into the sea
Relative motion - between structural parts with the motion employed to transfer a working fluid around a circuit to drive a rotary machine
Oscillating water column - sea water is admitted into a chamber which is vented to the atmosphere

Question 2

Give examples of each of the 3 wave energy devices

Answer 2

Passive - Wave dragon
+ heavy and durable
~ lots of materials required

Relative motion - Pelamis
+ far offshore so more energy potential
~ far offshore so survivability hard

Oscillating water column - Limpet on Islay
+ shoreline so easy to maintain
~ less potential energy

Question 3

Describe the tidal barrage method?

Answer 3

• Basin is filled through the sluices until high tide, sluices are the closed
• Turbine gates close until sea level falls to create sufficient head across the barrage
• Gates open and turbines generate until head is low again
• Sluice opened, turbine disconnected and basin is filled again
  e.g. La Rance, France
  + more energy potential
  ~ greater impact on wildlife, can block off areas to certain wildlife and changes the diversity

Question 4

Describe tidal stream method and give an example?

Answer 4

• Extraction of energy from tidal flows around coastlines
• Three different design options: Horizontal-axis, vertical-axis, oscillating hydrofoils
  e.g. Stingrays
  + Cheaper and less ecologically damaging than other tidal methods
  ~ since underwater, sound and frequency generated by turbines might impact sea life who rely on echolocation)

Question 5

What are some of the challenges associated with tidal energy?

Answer 5

• reduce capital cost
• limit corrosion and abrasion
• Maintenance issues
• Power take off at low speeds
• Gearing reduction/elimination
• Power transmission/grid access
• Marine and aquatic life impact

Question 6

What are spring and neap tides?

Answer 6

Spring tides - higher high tides and lower low tides
Neap - lower high tides and higher low tides

Question 7

Describe three possible approaches to turbine sizing for power extraction from the phased operation of multiple sites over the lunar cycle?

Answer 7

• size turbines to restrict the maximum output to that experienced during neap tides
• size turbines for the average monthly output and introduce other sources of energy to meet the shortfall
• size turbines for the spring tide condition and introduce long term (weekly) energy storage so that the excess capacity during near-spring tides can be stored for later use.