Energy derived from the tides. The tides mainly gain their potential energy from the gravitational forces acting between the Earth and the Moon. Tidal energy comes from the gravitational energy of water as it flows from high tide to low tide.  This energy can be captured by closing a bay with a dam. As the tide rises, the bay fills with water.  At high tide, the dam is closed to hold the water in the bay. At low tide, the stored water is released through a turbine in order to generate electricity. 

The largest tidal power station in the world (and the only one in Europe) is in the Rance estuary in northern France. It was built in 1966.

A major drawback of tidal power stations is that they the plants can be built in few places and can only generate when the tide is flowing in or out - in other words, only for 10 hours each day. However, tides are totally predictable, so we can plan to have other power stations generating at those times when the tidal station is out of action.

• Additional advantages of tidal current power generation

Like the ocean dam models of France, Canada and Russia, vertical and horizontal axis tidal current energy generators are fueled by the renewable and free forces of the tides, and produce no pollution or greenhouse gas emissions. As an improvement on ocean dam models, however, the new models offer many additional advantages:

- because the new tidal current models do not require the construction of a dam, they are considered much less costly. 

- because the new tidal current models do not require the construction of a dam, they are considered much more environmentally-friendly.

- because the new tidal current models do not require the construction of a dam, further cost-reductions are realized from not having to dredge a catchments area.

- tidal current generators are also considered more efficient because they can produce electricity while tides are ebbing (going out) and surging (coming in), whereas barrage-style structures only generate electricity while the tide is ebbing.

- Vertical-axis tidal generators may be stacked and joined together in series to span a passage of water such as a fiord and offer a transportation corridor (bridge), essentially providing two infrastructure services for the price of one.

- Vertical-axis tidal generators may be joined together in series to create a ‘tidalfence’ capable of generating electricity on a scale comparable to the largest existing fossil fuel-based, hydroelectric and nuclear energy generation facilities.

- Tidal current energy, though intermittent, is predictable with exceptional accuracy many years in advance. In other words, power suppliers will easily be able to schedule the integration of tidal energy with backup sources well in advance of requirements. Thus, among the emerging renewable energy field, tidal energy represents a much more reliable energy source than wind, solar and wave, which are not predictable.

- present tidal current, or tidal stream technologies are capable of exploiting and generating renewable energy in many marine environments that exist worldwide. Canada and the US, by virtue of the very significant tidal current regimes on its Atlantic and Pacific coastlines – proximal to existing, significant electro transportation infrastructure - is blessed with exceptional opportunities to generate large-scale, renewable energy for domestic use and export. 

• Life-cycle Assessment

1. Construction of components, including thin-shelled (reinforced concrete) marine caissons, durable steel turbines, electrical generation equipment, electrical transmission cables, other infrastructure)

2. Transportation, assembly and installation of energy generation system

3. Operation and maintenance of energy generation system

4. Removal, disassembly and recycling of components

• Environmental Signature

- expected long-life of components (thin-shelled marine caissons, durable steel turbines, electrical generating equipment, electrical transmission cables)

- requires no fuel

- produces no emissions

- produces no waste products during operation

- little or no situation expected during operation

- open sluice, slow-rotor design allows for easy passage of fish and marine invertebrates

- minimal noise expected during operation

- minimal EMF (Electro-Magnetic Field) expected during operation

• Main Environmental Concerns

- impact on fish and marine mammal movement and/or migration rotors

Mitigation: rotors stop at slack tide, protective barriers, sensory braking tech., acoustical tracking technology to guide fish and mammals

- deflection of local energy regime (as energy is removed by turbines)

Response: energy displacement is NOT expected to be significant

- marine fouling (encrustation) of energy system components by algae and invertebrates

Mitigation: use of non-toxic, anti-fouling materials

- noise and/or Electro-Magnetic Fields (EMFs) in marine environment

Response: noise and/or EMF from operation expected to be minimal