Swansea Bay Tidal Lagoon: The Plan to Power 155,000 Homes and Its Fate

Juice Architects

Tidal power for 155,000 homes

While the power plant above looks more like a gorgeous get-away than a solution to man’s energy needs, its benefits extend far beyond its beauty. As Reconstruct reports, the Swansea Bay Tidal Lagoon was projected to use the rise and fall of ocean tides to generate enough renewable electricity to power 155,000 homes for 120 years!

The original proposal projected enough annual electricity to displace more than a quarter million barrels of oil each year – according to the historical projection; a full carbon assessment would also need to include construction and operation.

The Swansea proposal concerned a tidal lagoon: an enclosed area of seawater used to create a water-level difference across generating equipment. The 2015 article noted that power plants had been generating electricity from the tides since 1966 (La Rance in Brittany, France, opened that year with 240 MW) and presented Swansea as the first to use a radically new method; a lagoon is a different design from La Rance’s estuary barrage, but this description does not by itself establish a worldwide first.

How does it work?

The archived design described a nearly six-mile-long barrier wall intended to enclose a huge amount of water in an artificial “tidal lagoon”. In the proposed design, the lagoon would capture and hold seawater at high tide. As the tide goes out, water in the 4.5 square mile lagoon was projected to be as much as 27 feet higher than the water outside its walls. The design proposed routing the resulting flow through 26 turbines, flooding out to sea until the water level equalizes on both sides of the lagoon.

The design also described reversing flow at high tide, keeping the sea out of the lagoon until it reaches maximum height. Then water is let go, so it may rush through the turbines until it again fills up the lagoon.

To put it into perspective, the amount of water rushing through the turbines would fill 100,000 Olympic swimming pools each day!

The Swansea Bay Tidal Lagoon was proposed to generate electricity as well as to provide a sports arena, aquaculture farm, and seaside sculpture garden, reports GoodNewsNetwork. Its proposed aquaculture farm was intended to grow oysters, kelp, and other local sea crops.

In addition, the lagoon can be used as a giant arena for sailing and cycling sports.

The designers of the proposed structure planned to implement sculptures that appear to disappear into the water or rise out of it as the tides roll in and out.

Swansea Bay Tidal Lagoon: The Plan to Power 155,000 Homes and Its Fate

Juice Architects
The 2015 coverage said Swansea, Wales was chosen because it has some of the highest tide differences in the U.K. The archived account gave a projected annual generation of 420 gigawatt-hours; this is a design estimate, not a measured operating result.

Plans for the structure were approved by the UK Energy Ministry in June, and the 2015 article forecast construction beginning in 2017; this was a forecast, not a record of completed work.

The 2015 coverage described the developers as negotiating to exchange the $1.5 billion price tag (subsidized by the government for 35 years) for approval on two more tidal lagoon plants at Cardiff and Newport.

Source: True Activist

More from the archive:

The proposal needs its later decision attached

The construction expectations in the 2015 article were forecasts, not confirmation that the lagoon was completed. On June 25, 2018, the UK government published its statement on the proposed Swansea Bay tidal lagoon. It concluded that the proposal and wider lagoon programme did not meet its value-for-money requirements and that public funding could not be justified on the terms assessed. That is a specific historical decision about a proposal, not a verdict that every tidal-energy scheme is impossible.

The associated assessment documents provide the context for that decision. They should be read as a dated evaluation, with assumptions and comparisons made at the time, rather than as a current price list for renewable electricity.

Predictable tides do not mean uninterrupted generation

The lagoon concept depends on a difference in water level across a barrier. The timetable of tides can be predictable while the available generating conditions still vary. A statement about annual electricity therefore says something different from a promise to deliver the same power at every moment. The government's 2018 statement explicitly distinguished variable generation from a constant supply.

A “homes powered” figure also depends on the assumed annual use per home. It is a way of expressing an energy quantity, not proof that a particular set of houses receives electricity exclusively from the project. Keep the annual generation estimate beside that comparison so readers can understand what the headline translates.

Compare like with like

For any revised tidal proposal, identify which design is being discussed and the date of its estimate. Construction cost, operating life, annual energy, financing and grid connection should refer to the same version. Combining the most attractive number from several proposals can create a project that nobody actually proposed.

The renderings remain useful illustrations of the original ambition. They show how energy infrastructure and public space were imagined together. Their value is as design communication; they do not document an operating power station or establish the environmental outcome of building one.