With the aid of a diagram, explain the operation of a single effect tidal barrage power station.
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
Describe three possible approaches to turbine sizing for power extraction from the phased operation of multiple sites over the lunar cycle.
○ 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
List some of the challenges facing tidal stream energy conversion devices.
- Reduce capital cost
- Limit corrosion and abrasion
- Maintenance and safety issues
- Power take-off at low rotation speed
- Gearing reduction/elimination
- Power transmission/grid access
- Land access and use
- Phased operation of different sites
- Maritime and aquaculture impact
- Overcome vested interest
List three examples of power extraction technologies, briefly explain how they work and give an advantage and limitation of each.
- 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-bladed horizontal axis. Advantage: Easily adjusted to stay in path of strongest current. Limitation: No electrical connection to shore.
- 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.
