Tidal Energy

Question 1

With the aid of a diagram, explain the operation of a single effect tidal barrage power station.

Answer 1

Basin is filled through the sluices until high tide; sluice gates are closed
● There may be pumping using grid electricity to raise the level further
● Turbine gates closed until the sea level falls to create sufficient head across the barrage
● Gates opened and turbines generate until the head is again low
● Sluices are opened, turbines disconnected and the basin is again filled

Question 2

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

Answer 2

○ 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 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

Question 3

List some of the challenges facing tidal stream energy conversion devices.

Answer 3

1. Reduce capital cost
2. Limit corrosion and abrasion
3. Maintenance and safety issues
4. Power take-off at low rotation speed
5. Gearing reduction/elimination
6. Power transmission/grid access
7. Land access and use
8. Phased operation of different sites
9. Maritime and aquaculture impact
10. Overcome vested interest

Question 4

List three examples of power extraction technologies, briefly explain how they work and give an advantage and limitation of each.

Answer 4

1. Stingray: Oscillating hydrofoil, imitates the tail swinging of organic organisms to extract energy from the tidal stream. Advantage: Simpler geometry and easier to produce than rotor blades. Limitation: Close to seabed means more friction.
2. 2-bladed horizontal axis. Advantage: Easily adjusted to stay in path of strongest current. Limitation: No electrical connection to shore.
3. CoRMaT: (Contra Rotating Marine Turbine). Advantage: Suitable for deployment in water depths from 8-500m where max tidal energy harvest is likely. Limitation: Tethered so no direct onshore energy transportation.