Tidal Power

Tidal Power, often referred to as tidal energy, is achieved through capturing energy created as water moves in ocean currents and tides. Some of the oldest technologies for using ocean energy have utilized the power of ocean tides.

Every coastal area consistently experiences two high and two low tides over a period slightly greater than every 24 hours. These tides can be utilized or harnessed to generate electricity using two different methods:

1.) Kinetic Energy - Kinetic energy is the energy that is created from water moving in rivers and the regular incoming/outgoing ocean tides. For this, underwater tidal generators must be built or submerged to allow the currents created by the moving tides to power underwater turbines that power electric generators.

2.) Potential Energy - Potential energy in tides comes from the differences in water height between low and high tides. This is often referred to (or termed) “head” or “head differentiation”. To harness those tidal differences into electricity, the difference between the high and low tides must be at least five meters, or at least 16 feet. There are really only about 40 sites on the Earth with tidal ranges of this magnitude. So, this energy production method is limited to only certain areas.

* A third type of water power is wave power. Wave power is not exactly the same as tidal power, but it can be used to create a significant amount of electric power for those living on or close to coast-lines. Click here to read more about wave power and the future for this technology.

Types of Tidal Power

• Tidal Barrages - Barrages allow tidal waters to fill an estuary via sluices and to empty through turbines. Traditional tidal electricity generation involves the construction of a barrage across an estuary to block the incoming and outgoing tide. The dam includes a sluice that is opened to allow the tide to flow into the basin; the sluice is then closed, and as the sea level drops, the head of water (elevated water in the basin) using traditional hydropower technology, drives turbines to generate electricity. Barrages can be designed to generate electricity on the ebb side, or flood side, or both.


• Tidal Fences - Tidal fences look like giant turnstiles. They can reach across channels between small islands or across straits between the mainland and an island. The turnstiles spin via tidal currents typical of coastal waters. Some of these currents run at 5–8 knots (5.6–9 miles per hour) and generate as much energy as winds of much higher velocity. Because seawater has a much higher density than air, ocean currents carry significantly more energy than air currents (wind).


• Tidal Turbines - Tidal turbines look like wind turbines. They are arrayed underwater in rows, as in some wind farms. The turbines function best where coastal currents run at between 3.6 and 4.9 knots (4 and 5.5 mph).

  In currents of that speed, a 15-meter (49.2-feet) diameter tidal turbine can generate as much energy as a 60-meter (197-feet) diameter wind turbine. Ideal locations for tidal turbine farms are close to shore in water depths of 20–30 meters (65.5–98.5 feet).

Since water has such high density – nearly one thousand times as dense as air – there is a lot of energy to extract from ocean or marine currents. This is true even when those currents are moving at low velocity. Experts predict that some day soon, it will be possible to produce energy in marine currents at velocities as low as 0.5 meters per second.

Benefits of Tidal Power

Tidal currents are created by the movement of the earth, the sun, and the moon. This makes them very predictable and repeating on a regular basis. This predictability is favorable for maintenance and production, as there are no factors that would interfere with this everyday process.

There are no tidal power plants in the United States (currently). But, the conditions are very good for tidal energy production in the Pacific Northwest and the Atlantic Northeast regions of the country. And, as mentioned above, there are an estimated 40 locations on our planet that could be very favorable for this type of alternative energy production.

This form of energy production may not benefit every one of us, but for those living in these predicted locations and coastal communities, the future looks bright for reducing dependence on fossil fuel electricity production.

Current Working Projects

A company called Statkraft is currently in the process of developing and testing a tidal power plant which they plan as an anchored steel structure that generates electricity using four large turbines held in place under the water line in the marine currents. These turbines can easily be brought to the surface for maintenance.

Since this power plant is a floating plant, no disturbance will be done to the sea floor, and environmental impact will be minimal (if any). The entire plant can also easily be moved or removed if necessary.

Another facility – the La Rance station in France – currently generates up to 240 megawatts of power. It is a barrage type of set up. Right now, France is the only country that successfully uses this type of power source.

Harmful Factors

In considering setups like the La Rance station in France, French engineers have stated that if this same type of tidal power were used at high enough levels on a global level, the Earth could slow its rotation speed by an estimated 24 hours every 2,000 years.

Aside from the long-term detrimental aspects, the more short-term concerns for tidal energy production are for the environmental impact(s) on the actual tidal basins themselves. Setups like the barrage system can significantly reduce tidal flow and cause silt buildup. This and the possible effects upon sea life are the primary concerns

Return from Tidal Power to Water Power

Return from Tidal Power to Home Page