As the water turns the turbines, electricity is generated. The water in the lagoon then returns to closely match the same level as the sea outside. We can hold the tide within the lagoon for approximately 2. As the tides rise and fall naturally, with no requirement for fuel, tidal power is truly renewable and, unlike other forms of renewable energy, is entirely predictable.
As there are always two high and two low tides every day, tidal lagoons will generate electricity over four periods a day, every day of the year. As we hold the tides for 2. The height and time of the tides can be predicted years in advance to a high degree of accuracy, allowing the precise operation of the lagoon on each tidal cycle to be optimised well in advance.
To achieve this, the wall is required to have a very low permeability leakage rate to prevent the tide from escaping through the wall rather than flowing through the turbines. By constructing the central portion of the wall from a dense sand or gravel, and protecting it against the incoming waves and weather degradation with large armour rock, the wall will function as intended.
Another important characteristic of a stream is that the horizontal speeds of the current exist at an almost identical rate throughout the entire depth of the water. Tidal streams, however, are still not the best option for tidal energy.
While the nature of a stream allows for some placement flexibility, streams are often high-traffic bodies of water for both sea life and ships. Placing turbines in these areas can kill sea creatures and disrupt migration patterns. Utilizing tidal streams is less harmful than building barrages, but the energy output is not as powerful and the number of viable sites is limited.
A lagoon is a body of water partly enclosed by any barrier. Lagoons operate similarly to barrages but present fewer environmental complications.
Lagoons can easily be constructed out of natural materials and are built along the coastline. Barriers would keep out sea creatures too large to swim into the lagoon, while the smaller animals would be able to enter and exit easily. The biggest drawback of a lagoon is its relatively limited potential to produce energy based off of a relatively slow flow rate. A closer look at the data, however, suggests that this analysis is too simplistic. The tidal lagoon scheme is very similar to the tidal barrage method of using tides to generate power.
In fact, the only real difference between the two is that the tidal lagoon does not block off an entire estuary, but rather makes use of only part of it. The concept is relatively simple. A large enclosed structure is built in the estuary or anywhere that tidal forces are adequate. This means the Swansea lagoon will be generating electricity for 14 hours out of 24, according to the company.
The tide flows in and out in a predictable pattern, so the energy it generates is reliable. The Severn Estuary has the second highest tidal range in the world, so it would be surprising if a government keen to bump up its power production from renewables ignored it entirely. An argument raged until just a few months ago over another proposal, known as the Severn Barrage.
Under this idea, an artificial barrier stretching from shore to shore across the Severn Estuary could have been used to impound a large area of water much further up the estuary:. Simplified map of the proposed Severn Barrage, which would have been situated much further up the Severn estuary. Created by Friends of the Earth pdf. There were several proposals for barrages in different places, but the basic idea was again that they would generate electricity as the tide drove the water through turbines embedded in the structure.
However, the barrage was opposed by some green groups on the grounds that it would be environmentally damaging.
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