If time and tide wait for no man, shouldn’t we be rushing to exploit tidal energy?
Thirty-eight feet. That’s around the height, from floor to rooftop, of a two-storey house. It’s also the tidal of the Bay of Fundy in Novia Scotia[1]. Think of the energy needed to shift that water, and imagine if it could be harnessed to produce electricity.
The technologies do of course exist. Barrages, or dams can exploit the tidal range (the amount by which the water level rises or falls). The barrage lets water into an inlet or lagoon through sluice gates, then releases it as the tide ebbs and the water flows back out. Turbines built into the barrage are turned as the water flows out of the dam, generating electricity. The other main technology is turbines (think of an underwater windmill), which are placed on the seabed and use the tidal stream (the flow of water which is produced as the water rises and falls) to generate electricity. Water is around 800 times denser than air, so the turbines generate much more energy per square metre of turbine area than a wind turbine.
Tidal energy has a distinct advantage over wind and solar. High and low tide times are entirely predictable – you can set your watch by them. So on the face of it, tidal energy sounds great – it’s predictable; the fuel (seawater) to drive the turbines is free; and plenty of energy is generated. What’s not to like?
For all its apparent advantages, tidal energy does have some serious drawbacks. Estimates for the number of suitable sites worldwide with a high tidal range for barrages are in the tens, not hundreds[2], and only a few sites are currently operational – at La Rance in France, Annapolis Royal in Nova Scotia, and Ansan in Korea. Initial construction costs are very high (although once operational they’re cheap to run) and barrages also affect the ecosystem by causing silt to build up. Turbines must be designed to operate in an extremely hostile environment and must be robust to cope with salt water throughout their working life.
Tidal energy undoubtedly has a strong future; tidal energy could become a major renewable energy source in the Northeast and Northwest part of the USA with some small-scale projects coming on line in 2011-2012[3], and the UK Government estimates that around 20 per cent of the UK’s energy needs could be met by tidal energy. Tidal energy won’t be the answer to all our energy problems but there’s no doubt it has an important part to play.
For other related articles, check out History of Tidal Energy.