The West Somerset Lagoon is a large tidal lagoon power generation project planned for the southwestern coast of the UK, situated between Minehead and Watchet along the Bristol Channel. The concept involves constructing a curved breakwater near the shore to enclose a body of water, utilizing the difference in water levels between the lagoon and the open sea during tidal changes to drive turbines for electricity generation. It falls under tidal range generation rather than tidal stream generation, relying on sea level fluctuations rather than water flow speed. The project’s proponents have attached an appealing label: an installed capacity of approximately 2.5 GW, an annual generation of about 6.5 TWh, zero carbon emissions, and independence from weather conditions, with a theoretical lifespan exceeding a century.
Such claims resonate because they hit the pain points of the UK’s energy transition. As the proportion of wind and solar power continues to rise, the grid is becoming increasingly unstable; the greatest strength of tidal energy is its high predictability. Tidal changes are determined by astronomical factors, allowing generation periods to be scheduled years in advance, unaffected by calm winds or cloudy days. For a grid that requires long-term planning for backup capacity, this certainty is inherently valuable.
However, when one examines the physical realities, the project’s role becomes clearer and less ideal. Tides do not follow a daily cycle but rather a semi-diurnal pattern, with a cycle of approximately 12 hours and 25 minutes. The lagoon generates electricity for about 10 to 14 hours each day, but not continuously; instead, it is divided into four segments and shifts backward each day. Today, it may generate in the evening, but a few days later, it may shift to late at night. This means it cannot naturally align with human peak electricity usage times, remaining fundamentally a high-quality but rhythmically fixed intermittent power source.
Some have suggested that by integrating battery storage, this rhythm could be ‘smoothed out’, making tidal power as stable as nuclear energy. While this is not impossible from an engineering perspective, it is economically prohibitive. To convert the lagoon’s output into nearly round-the-clock supply would require tens of GWh of storage, and batteries have a lifespan of only about ten years, far short of the lagoon’s claimed lifespan of 120 years. The result would be an already capital-intensive project compounded by another capital black hole that requires frequent replacements.
What truly weighs down this proposal is its financial structure. The characteristics of a tidal lagoon involve extremely high upfront costs, a long construction period, and indivisibility. This means it is nearly impossible to finance through competitive Contracts for Difference (CfD) and must rely on a Regulated Asset Base (RAB) model, which incorporates some construction risks into electricity prices to secure lower financing costs. In institutional terms, it resembles nuclear power rather than typical renewable energy projects. Discussions inevitably turn to Sizewell C, as both share similar risk-bearing mechanisms.
However, the key difference lies in necessity. The government’s decision to advance Sizewell C stems from the current scarcity of low-carbon power sources that do not rely on weather or storage and can provide long-term continuous supply. Nuclear power is not an ideal solution but is viewed as temporarily indispensable. In contrast, the Somerset tidal lagoon offers predictable intermittency, a function that could theoretically be replaced by a combination of offshore wind, storage, demand management, and transmission upgrades. This is not a matter of technical superiority but rather a question of policy prioritization.
Adding to this are considerations of environmental impact and irreversibility, making the issue even sharper. Once the lagoon is constructed, there is virtually no turning back. The impacts on sediment, ecology, and coastal dynamics must be rigorously verified in advance, rather than remedied afterward. The true risk of such projects has never been about whether they will generate power, but rather whether the costs of a mistaken judgment are bearable.
Therefore, the Somerset tidal lagoon is neither a castle in the air nor a panacea. It possesses unique value, but only if positioned correctly as a piece of the energy grid puzzle, rather than being expected to serve as a substitute for nuclear power. The energy transition has never been about choosing the most appealing narrative, but rather about selecting the least bad order under real-world conditions. If the tidal lagoon is to endure, it must first be viewed with a clear and rational perspective.
