Tidal Energy

Periodic movement of the ocean water, cause by the moon and the sun

• rises and falls
• period of 12.5 hours

• flows and ebbs
• periodic horizontal movement of the water

bring the tide producing forces

• caused by surface winds
• period of about 6 seconds

• half-day cycle -> due to rotation of earth
• 14 day cycle -> due to moon and sun gravitational fields

Structure placed across a flowing body of water to stop the flow

basic concept of tidal power is derived from the tidal range

• 1. water is 800 times denser that air and has a much slower flow rate
•    -> The turbine experiences much bigger forces and moments

2. Water turbines have smaller diameters

• 1. Renewable source
• 2. Once dam is constructed, power is free
• 3. It needs no fuel
• 4. No greenhouse gases or other wastes
• 5. Not expensive to maintain
• 6. Tides are predictable

• 1. Expensive to build plant
• 2. Sea water is corrosive
• 3. Destruction to ecosystem
• 4. Appropriate waves and tides are location dependent

use stainless steel with a high chromium content and small content of molybdenum

use aluminum bronzes

• disrupts fish migration
• kills fish passing through the turbines

• 1. bulb turbine
• 2. Straflo turbine
• 3. Tubular turbines

• adv:
• very efficient in terms of space and size (no need for separate housing unit)

• dis:
• cannot be maintained without stopping the flow

• adv:
• the generator can be maintained easier

• dis:
• -sealing between the runner blades and radial generator causes problems

• -more delicate
•      -> harder to pump water through and regulate power produced

• blades can be adjusted (to meet energy demand)
•  -> allow turbine to move more efficiently, no excessive wear

harness the horizontal flow of the tidal currents and streams (KE of the tides)

• tidal fences
• tidal stream turbines
• tidal lagoons
• prototype tidal generator designs

Unlike tidal barrage power stations, tidal fences can be used unconfined basins. 

They do not require flooding of the basin and are cheaper to install.

Less environmental effect than equivalent-scale barrage. (Salinity does not change)

• Resembles horizontal axis wind turbine.
• Utilize tidal currents that are moving velocities 2 and 3 (m/s) to generate 4-13 kW/m2.

use a rubble mound impoundment structure and low-head hydroelectric generation equipment situated up to a mile or more offshore in a high tidal range area.

Tidal Lagoons are similar to barrages but do not take up as much room as they do. Also they have a lower cost and impact on the environment. This means that they can generate continuously.

• Stingray
• Gorlov Helical Rotor
• Verturi Tidal Turbine

Consists of a hydroplane that has an attack angle relative to the approaching water stream varied by a simple mechanism.

This causes the supporting arm to oscillate, which in turn forces hydraulic cylinders to extend and detract a cylinder, which produces high-pressure oil that drives a hydraulic motor that in turn drives an electric generator.

Gorlov's helical turbine is based on the Darrieus turbine. It could also work underwater to produce energy from currents.

Gorlov’s helical turbine has twisting blades in the shape of a helix, which is very efficient.

• Fast currents
• natural flows are concentrated between obstructions