Oceans cover over two thirds of our planet’s surface. The energy contained in the oceans has tremendous potential, including in the form of waves and tides. These sources have an estimated 337 GW. New technologies and projects represent a significant opportunity for renewable energy development in several countries.
The basics of tidal energy:
Tidal power is created using a head difference between two bodies of water. To create this difference, a wall separates the two water bodies. As the tide flows in or out, the wall blocks the flow of the tide and generates this head difference. When the head difference has reached the optimum design level, the water is forced to pass through holes in the wall, where turbines are placed to generate power. Since two tidal cycles occur per day, this head difference develops four times each day (in one cycle, the tide comes in and out).
Turbines convert the water energy into mechanical energy, and then into electricity by means of an electric generator as seen in the video below.
Since tidal head differences generally measure a few meters, typical turbines include water wheels, Archimedes screws and bulb turbines. One other way to generate power from tides uses turbines on the seabed, driven by the kinetic energy of the moving tidal flow, similar to wind turbines in airflows.
Tidal power projects exist in France, South Korea, Russia, the UK and China, among other places. Research suggests that in the UK over 20% of the national energy demand could be satisfied by exploiting tidal and wave energy sites around the country. Famous tidal power plants include:
- La Rance in France (240 MW)
- Lake Sihwa in South Korea (254 MW)
- Annapolis in Canada (20 MW)
- Jiangxia in China (3.9 MW)
The latest projects and innovations in tidal energy:
Tidal energy offers a long-term, predictable form of clean energy. Ongoing projects like the Swansea Bay tidal lagoon in the UK (320 MW) has generated positive interest from local people and government institutions. New tidal projects are under consideration throughout the world, including locations that were until now considered unsuitable. Some tidal plants under construction include the Meygen Tidal Project (398 MW) in the UK, while others are in development in Russia, South Korea, India and the Philippines.
To support these projects, tidal power engineers are refining existing technologies, with a special focus on the improvement of turbines. Modified bulb turbines with an additional set of guide vanes allow better management and control of the flow through the turbine. Bulb turbines can reach very high power output. Two examples include:
- The 7 meter diameter bulb turbines in the Swansea Bay tidal lagoon that can produce 16 MW.
- The innovative Straflo turbines can reach values of 20 MW, as in the Annapolis plant.
Archimedes screws could be employed as a fully submerged tidal stream device, or they can be enclosed in a pipe system. Archimedes screws also have the additional advantage of “fish friendliness”. Finally, water wheels under testing use inflow hydraulic structures to better control flow and power.
The future of tidal energy:
In the short term, tidal energy will likely represent a small share of total renewable energy. But these projects and new technologies demonstrate its growing relevance in specific locations, complementing more traditional sources like wind and solar.
