What is... Tidal Energy?

The energy associated with Waves and Tides comes in two forms, Kinetic and Potential. Ocean waves contain Kinetic energy through water motion, and potential energy due to the elevation of water as the waves crest. It is a similar situation for tidal energy, the question is, how do we harness this energy?

In this post, we are going to discuss the two main types of Tidal Technology.


For an overview of both Tidal Energy and Wave Energy and where they fit in the Energy Transition, read our earlier blog: What is... Wave and Tidal Energy?

Tidal Range

There are two main categories of tidal technology. The most common is “Tidal Range” or “Tidal Barrage” which takes advantage of the high and low tides using a barrier (barrage). The turbines are situated within the barrage, when there is a difference in tide from one side of the barrier to the other, the water will flow through the turbines. This takes advantage of the gravitational potential energy of tides.

Tidal Stream

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The second energy type uses natural water currents (kinetic energy), primarily in the sea but can also use areas of strong currents in rivers and lakes. The example to the right shows a horizontal axis turbine. Small scale deployment of this technology has been achieved, next is the deployment of turbine arrays. Companies like Alstom and Andritz Hydro have already launched arrays in test sites around the world.


The graphics below show other ways in which we can generate Tidal Stream energy:


Venturi Effect Devices Reciprocating Hydrofoils


















Archimedes Screw Tidal Kite


















Vertical Axis Turbine


Conclusion

As discussed in last weeks blog (What is.... Wave & Tidal Energy?) tidal energy has several advantages over the more commonplace renewable energies of wind and solar. One huge advantage is that the tides are predictable - we can accurately predict tides hundreds of years into the future (compare that to the accuracy of wind and sun forecasts for the weekend!). Also, as the Earth is 2/3 covered by water there are large areas where tidal power could be rolled out. Tidal power (in the form of Tidal Barrage) can also be designed to work as a flood defence, offering multiple benefits for a single installation. Finally, the power density (amount of power possible per square metre) is much greater than for wind/solar power due to the density of water compared to air.


Due to the advantages tidal power offers, in the coming years, as technology advances and costs fall, we can expect more and more of these schemes to be developed around our coastlines.


Next week we will describe different technologies used in Wave Energy.
This article is part of a series explaining some of the key technologies that are enabling the energy transition. Click Here to see the full series.

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