The Swansea tidal lagoon has been cancelled, revived, cancelled again, and now, in March 2026, it is back once more. Swansea Council has signed a partnership agreement with Batri, a renewable energy developer that is part of DST Innovations, to lay the groundwork for what could become one of the UK’s first tidal energy projects at commercial scale. The plan begins modestly, with a solar farm on the contaminated Tir John landfill site, but the stated ambition is far larger: a tidal lagoon in Swansea Bay, a data centre, a battery manufacturing plant, floating solar installations, and a renewable energy transport hub. “This is where the overall Swansea project starts to become real on the ground,” said Stephen Hughes, Batri’s chief technology officer, as reported by New Civil Engineer.
The original Swansea tidal lagoon received a development consent order in 2015 for a 320-megawatt project with 16 turbines, but ministers declined to underwrite the costs, judging it poor value for money compared to other renewables. Planning permission lapsed in 2022 when construction had not begun. This new iteration takes a different approach. Rather than waiting for a single massive infrastructure commitment, Batri plans to build incrementally, starting with the 3-megawatt-peak solar farm, which already has planning permission and a grid connection offer. Revenue from the solar farm, privately funded with no capital required from the council or central government, will help finance subsequent phases.
How a Swansea tidal lagoon would generate power
A tidal lagoon is, at its simplest, a large enclosed area of sea. A curved seawall, or impoundment, stretches out from the coast and back again, creating an artificial bay. Inside the wall, turbines sit in housings at or near the base. As the tide rises, water flows through the turbines into the lagoon, spinning them to generate electricity. As the tide falls, the process reverses: water flows back out through the turbines, generating power again. Unlike wind and solar, tidal power is almost perfectly predictable. The moon’s gravitational pull follows a known cycle, so engineers can forecast tidal generation years in advance, down to the minute. Swansea Bay has a tidal range of about 8.5 metres, one of the highest in the world, which makes it a natural candidate for this technology.
Council leader Rob Stewart described the ambition plainly: “Our ambition is to become one of the leading renewable energy regions in Europe.” The economic case rests on jobs as much as energy. The original 2015 proposal promised thousands of construction and manufacturing roles. The new partnership makes similar claims, though detailed projections and timelines for the lagoon itself have not yet been disclosed.
Engineering Deep Dive: The Engineering Behind a Swansea Tidal Lagoon
The impoundment wall is the defining structure. In the original Swansea design, it would have extended roughly 9.5 kilometres into the bay, enclosing an area of about 11.5 square kilometres. The wall must withstand wave loads, tidal currents, and the hydrostatic pressure difference between the water level inside and outside the lagoon. This is a direct application of the hydrostatic pressure equation, p = rho g h, covered in A-level Physics. When the lagoon is full and the external tide is low, the pressure difference across the base of the wall can be substantial, requiring a structure massive enough to resist overturning and sliding.
The turbines are a variant of bulb turbines, a type of low-head hydroelectric machine designed for high flow rates and modest pressure differences. Each turbine sits inside a concrete housing within the impoundment wall. Water enters through a bell-mouth intake, accelerates through a constriction, passes over the turbine runner, and exits through a draft tube. The runner blades are adjustable, pivoting to optimise the angle of attack as the head, the difference in water level across the turbine, changes throughout the tidal cycle. This is the same aerodynamic principle that governs the pitch of propeller blades and wind turbine rotors. Bulb turbines can also operate in reverse, generating power on both the incoming and outgoing tide, a feature called bi-directional generation that roughly doubles the energy capture compared to a single-direction scheme.
Sluice gates, large openings in the wall that can be opened or closed, allow water to pass freely without generating power. Operators use these strategically to maximise the head difference before opening the turbines. For example, as the tide rises, the sluice gates might remain closed to keep the lagoon level low, increasing the pressure difference when the turbines are finally engaged. This is analogous to charging a capacitor before discharging it through a circuit, a comparison that might appeal to A-level Physics students studying electrical energy storage.
Environmental engineering is inseparable from the structural design. Enclosing part of a bay changes water circulation, sediment transport, and ecology. The original Swansea proposal required extensive environmental impact assessments. Fish passage is one concern: turbines can injure or kill fish that pass through them. Mitigation measures include fish-friendly turbine designs with slower blade-tip speeds, acoustic deterrents, and dedicated fish passes in the impoundment wall. Sediment dynamics are another: changing the flow patterns can cause accretion in some areas and erosion in others, affecting beaches, navigation channels, and habitats. Computational fluid dynamics (CFD) models simulate these effects before construction begins, solving the Navier-Stokes equations across the entire bay to predict how water will move around and through the lagoon.
The structural longevity of a tidal lagoon is one of its strongest arguments. Proponents claim a design life of 120 years or more, far beyond the 25-year lifespan of a typical wind turbine. The main structure is reinforced concrete and rock armour, materials with well-understood long-term durability in marine environments. Turbine runners and generators would need periodic replacement, perhaps every 30 to 40 years, but the impoundment itself is essentially permanent. Over a 120-year horizon, the levelised cost of energy, the total cost divided by total energy produced, could become competitive even if the upfront construction cost is high.
The starting point for this new phase, the Tir John solar farm, is a piece of engineering in its own right. Building a solar farm on a former landfill site requires careful management of ground conditions. Landfill caps must not be punctured by foundations, which rules out traditional driven piles. Engineers typically use ballasted mounting systems, where the solar panels sit on weighted frames resting on the capped surface, or shallow screw piles that anchor into stable ground above the waste layer. Gas management is also necessary, as decomposing waste produces methane that must be vented safely. These are the kinds of practical constraints that make real engineering more complex, and more interesting, than textbook problems.
Whether the Swansea tidal lagoon reaches construction remains uncertain. The project has been here before, with ambitions announced and then deferred. What has changed is the approach: starting small, building a revenue base, and scaling up rather than seeking a single transformative investment. The tidal range in Swansea Bay is not going anywhere. The engineering question is whether the economics and the politics can finally catch up with the physics.
Swansea Council signed a partnership with Batri to revive the tidal lagoon. The plan starts with a 3MWp solar farm before scaling up. Swansea Bay has an 8.5-metre tidal range ideal for tidal power.
