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15-07-2015

Tidal Lagoon Swansea Bay

Tidal Lagoon Swansea Bay
The principle that the gravitational force of the moon is responsible for the tides is well known.

The moon and the tides

Tides on earth result from a balance from gravitational and centrifugal forces. The principle that the gravitational force of the moon is responsible for the tides is well known. In addition to this force of attraction, the rotation force of the earth-moon system around an axis has an impact on the tides as well.
These forces are highly predictable and therefore the tides can be computed with precision. They are a reliable source of sustainable and renewable energy.
Most of the suitable places for tidal energy are located in the United Kingdom. Therefore, it is not surprising that the UK is a key player in this field. Currently a tidal power plant of complete new dimensions is under development at the Swansea Bay.

With the second highest tidal range in the world, 7 to 9 meters difference between low and high tide, a peak power output of 320 MW can be theoretically extracted. This power is reachable using a 9.5 km long breakwater wall holding a basin with an area of 11.5 km2.

How does it work?

Tidal power plants use the different potential energy between the basin and the sea. This difference is also called head difference. Here the cycle of operating points is shown. Assuming a cycle starts with a head difference through a higher water level in the basin, water flows through the turbine into the sea until the difference is insufficient for energy harvesting purpose. At this point a valve is closed. Whereas the head of the basin is maintained low, the sea level rises through the tide. If a sufficient head difference is reached, the valve is opened and water flows through the turbine from the sea into the basin. As soon as the basin is filled, a valve is closed. Again, while the head of the basin is maintained constant, the sea level decreases due to the tide. As soon as a sufficient head difference is reached, the valve is opened and the cycle of operating points is closed, as it repeats itself from here onwards. Each time water flows between the basin and the sea, electricity is generated by up to 26 low head bulb turbines. Bulb turbines are so called “double regulated” turbines because as well the blades as the stator angle can be varied during operation regarding optimal running points. 

Still, one remaining challenge in the design of the bulb turbines is to optimize their behavior for a flow in both directions. Similar to oscillating water column wave energy converters like the Pico Plant or the Sparboy, most power is lost due to the inefficient conversion of the inversed flow. The varying water level due to wave motion causes a bidirectional airflow through the turbine. The turbines from the tidal power plant and the Pico Plant differ in the flowing fluid but are facing both the challenge of a bidirectional flow design.

Sustainability

An interdisciplinary way of thinking and working makes a project sustainable. NGOs like WWT or RSPB welcome this project and see it as a chance “to learn as much as possible from what would be the first tidal lagoon”.
This project differs to other tidal plants as the development is based on a broader picture than just energy production. It includes sport opportunities like sailing, diving or surfing in the basin, cycling and running on the breakwater wall. Furthermore implementing art figures on the wall shall inspire the cultural life. Another benefit is tourism. One of the mayor focus points is to protect sea life and environment by implementing a mariculture farm and promoting a green eco system generation. 

Overall one can see a good project in the right direction.