Generation of electricity from tidal lagoon project was miscalculated

THE chorus of recrimination from much of the Welsh establishment following the UK Government decision not to support the Swansea Bay Tidal Lagoon electricity-generating scheme is totally misplaced.

The justification for this project was that it would be a pathfinder for an array of such lagoons around the UK’s western coastline.

However, some reasonably straightforward considerations and calculations should have shown that an array of tidal lagoons distributed along the UK’s western coast was a non-starter as a substantial and gridcompatible source of electricity for the demand foreseen in the year 2050.

Such an array would have produced on average three to four gigawatts of expensive electricity, some 7%-10% of today’s electricity demand in the UK and 4.5%-6% of the demand in 2050 as foreseen by the National Grid.

A single lagoon’s electricity output occurs in four daily periods of three hours, separated by four periods of no generation.

The combined output from the six lagoons on the western coast of the UK still exhibit this behaviour, although there is some generation at nearly all times

“Smoothing” this strongly variable output is extremely difficult to do. (Hopes that arrays along the north Wales/north-west of England coast would fully compensate arrays in the Severn estuary have proved illusory.)

Furthermore during the lunar month of 29 days and 13 hours, two spring and two neap tides occur.

From spring to neap tide, the electricity output varies by a factor of five, so that at spring tide the average output is five gigawatts falling to one gigawatt some seven days and nine hours later at neap tide, and then rising again to five at the second spring tide 14 days and 18 hours from the first.

There has been a failure to discuss in qualitative and in particular quantitative detail the amount and nature of the electricity produced by such an array of lagoons following the path proposed by the late lamented Professor David JC McKay (19692017) in his masterpiece Sustainable Energy – Without the Hot Air.

Such calculations are certainly within the grasp of A-level physics students and Economy Secretary Ken Skates is proud of his achievement in physics and mathematics at A-level.

It is a matter of great surprise to me that various Welsh Government and other Welsh agencies’ reports, and certainly the 150 pages and more of the Hendry report, do not follow this approach.

Indeed, they are largely devoid of relevant quantitative arguments.

This is not quite “a great opportunity for long-term, predictable and reliable energy generation, and an important role in the UK’s low-carbon electricity mix”, as claimed by the Institution of Mechanical and Civil Engineering, supported by the Learned Society of Wales.