The fate of a pioneering £1.3 billion proposal to build a tidal power lagoon on the UK coast at Swansea . Green energy supporters around the world have championed it as a trailblazer for a massive untapped source of dependable, renewable energy, calling on the UK government to commit to it.
However, tidal energy is not the saviour many people imagine it to be. The oceans have always created the impression of infinite potential, for example in terms of food resources and waste disposal, which we now know to be an illusion. In the same vein, a lot of people see the oceans as an attractive source of huge amounts of sustainable energy, including tidal power. Again, this is wrong.
In practice, tides can supply only relatively small amounts of energy. And while the environment impact of tidal energy varies depending on how we extract it (tidal lagoons are better than most), it will damage ecosystems.
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Earth’s tides, created by the tug of the moon and sun, hold about 3.5 terawatts of power. That sounds promising, but it is only about 20 per cent of the world’s power demand. And only a fraction of that 3.5 terawatts can be harnessed: we need water currents with a minimum speed of 1.2 metres per second to turn a turbine. This rules out the vast majority of tidal energy resources because they are in the open ocean where tidal currents are too weak, generally moving at less than 0.1 metres per second.
Viable currents (or sufficient tidal ranges to generate them from water trapped behind barriers or in lagoons) are only found in shallower waters around the perimeter of oceans. There are , although the UK has more than its fair share of them. These include , the north of Scotland, and the Severn estuary. The last of those has been the subject of tidal energy proposals for a century.
Strong tides also mean rich marine life
Unfortunately, such sites are often in extraordinarily rich and ecologically fragile straits and estuaries that are vital spawning grounds for marine life. Strong tides are what make these waters so productive: their turbulence stirs up nutrients necessary for life. What’s more, turbines can kill fish passing through them.
The reality is that in total, could be generated by suitable sites globally, and it is doubtful whether even this can ever be extracted efficiently.
There is evidence . They could obstruct a quarter of the area through which the tide flows, and this will change currents so much that the potential power can no longer be extracted efficiently. Because of this, permanently exploitable tidal power is reduced to a few tens of gigawatts.
Tides are crucial for life in shallow seas. Without them, marine life would come to a halt due to a lack of turbulence. Tidal energy extraction may seem attractive, but in practice there is little to be had – and it comes at an ecological cost. It seems alluring, but tidal power is not the global saviour it seems.
