24 Mar 2021
Value in nature – the remarkable reel of the tides
In this week's blog entry, Harold discusses the role of tidal power in the UK's energy awakening.
Today, an example of an overlooked gift from nature – the power of tides, where magic lies in the unique gravitational dance of the earth, moon, and sun. The tides around the UK are genuine tidal waves, unlike tsunamis which are mistakenly called tidal waves but have nothing to do with tides (they are caused by underwater landslides or earthquakes).
The average incoming power of the regular Atlantic tidal waves off our western shores is an enormous 250GW. Consecutive crests and troughs are separated by just over 6 hours, reeling their way around our islands, potentially providing highly predictable and well-diversified renewable energy for millions of years to come.
This power can be harnessed in various ways, with established technologies (barrages, lagoons and tidal farms). Barrages and lagoons are essentially "offshore hydro", driven by the vertical height distance between high and low tides. A tidal farm, by contrast, is like a set of underwater wind turbines, capturing kinetic energy from currents during the transition between high to low tides.
Tidal streams provide interesting options to help meet the UK’s complex energy needs. With some scale, there is more than a fair chance that costs can follow the favourable trend for other similar-tech renewables, especially given the UK’s general offshore expertise and experience with hydro and wind.
So why have we not developed our tidal resources? Especially as an HMG Green Paper in 1978 estimated that tidal could reach up to 80TWh/y by 2000, more than the potential estimated at the time for wind (64TWh/y). Initial focus centred on a huge 8.6GW tidal barrage in the Severn Estuary – the idea was not new in the Bristol area – in fact, an embryonic scheme had been proposed in Victorian times. Alas, by the mid-1990s a DTI review considered the prospects for tidal barrages "unpromising". This judgement was also delivered down to offshore wind, hydrogen by electrolysis and nuclear fusion, something of an irony given where we stand today. A later Swansea lagoon project failed to find sufficient government support in 2018.
More recently, attention has turned to tidal streams. The density of water is nearly 1000 times that of air, so the power of water flow is nearly 1000 times greater than the power of the flow of air, at the same speed, allowing turbines below the sea to be much smaller. Moreover, as the underwater world is relatively peaceful compared to that above it, engineers need not worry about freak storms, although sub-surface engineering obviously presents its own challenges. There are already operational projects in the UK – MeyGen in the Pentland Firth and, further north, the Shetland Array.
In my view, tidal streams provide interesting options to help meet the UK’s complex energy needs. With some scale, there is more than a fair chance that costs can follow the favourable trend for other similar-tech renewables, especially given the UK’s general offshore expertise and experience with hydro and wind. In any case, I have argued in previous posts that the concept of economic costs is ambiguous – in a societal context, it needs to be interpreted from a long-term systems standpoint, with sustainability as an anchor. Moreover, diversification is a critical concept in any energy nexus, a consequence of the principles of risk management. Tidal fits well on all these criteria.
Not to develop our tidal resources smacks of a failing in our collective imagination, an example of the "tragedy of the horizon" emphasized in Mark Carney’s recent Reith Lectures. A far-sighted perspective is something we desperately need in UK energy policy. For now, as Brutus might have put it: "we must take the current when it serves, or lose our ventures." This is particularly true in politics and in energy.
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