Tidal power – Tidal stream generation

A relatively new technology, tidal stream generators draw energy from currents in much the same way as wind turbines. The best way to understand the mechanism of the generator is to think of it is an underwater windmill. The higher density of water, 832 times the density of air, means that a single generator can provide significant power at low tidal current velocities (compared with wind speed).

The advantage of this kind of source is its predictability (predictable as the phases of the moon).

Tidal stream power systems need to be located in areas with fast currents where natural flows are concentrated between obstructions, for example at the entrances to bays and rivers, around rocky points, headlands, or between islands or other land masses.[1]

First tidal power turbine got plugged to the network[2]

An underwater turbine that generates electricity from tidal streams was plugged into the UK's national grid on the 17th of July 2008. It marked the start of a new source of renewable energy for the UK.

Tidal streams are seen by many as a plentiful and predictable supply of clean energy. The most conservative estimates suggest there are at least five gigawatts of power in tidal flows around UK, but there could be as much as 15GW.
The trial at Strangford Lough, in Northern Ireland, uses a device called SeaGen (www.seageneration.co.uk). During the testing phase its power is limited up to 300kW. However, when it will eventually run at full power the turbine is expected to generate 1.2 MW.

SeaGen was designed and built by the Bristol-based tidal energy company Marine Current Turbines (MCT).

The cost of installing the marine turbines is £3m for every megawatt they eventually generate, which compares to £2.3m per megawatt for offshore wind. The costs will drop if the technology is more widely adopted.
After SeaGen will start to operate at full capacity the plans of MCT is to build a farm of turbines before 2011. Their next site will be off the coast of Anglesey and the initial farm will be about 10.5MW. It seams that the resource up there is around 350MW."

The Pentland Firth, the Channel Islands and the Severn estuary are also other potential hotspots for tidal energy in UK.

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Tidal Power in the waters of the East River off Roosevelt Island[3]

At the other side of the Atlantic Ocean, near by New York, other people are also working to similar installations.

A third generation of experimental turbines has been installed by Verdant Power (www.verdantpower.com) in the waters of the East River off Roosevelt Island. The East River is not a real river, but a tidal strait connecting Long Island Sound to Upper New York Bay.

The first two generations of turbines were installed in late 2006 and early 2007 and the company gained a lot of knowledge from their breakdown and trouble shooting.
These kinds of generators have been designed so that they are automatically swung by the tidal currents and always face the right direction of the current. They sit on piles drilled into the riverbed and at low tide are six feet below the surface. Underwater power cable links the generator to Roosevelt Island.

The original turbine blades were fiberglass stretched over a steel skeleton, but apparently they broke on the first deployment. Thus, new blades were fabricated from aluminum magnesium, and they held up well, but the flowing water found the next weak point in the machines, along the rotors, or hubs. These snapped within two months. Now, the new generation is provided with new aluminum alloy blades fixed to hub.

In my personal opinion this kind of energy, if applied in the right places, could be another good example of renewable energy and could make a massive contribution to Britain, and to other countries with similar resources, cutting CO2 and fuel consumption. The main issue is that there are few places in the world where this kind of technology can be properly applied. My hoping is that tidal stream generation, like wind, will become a significant reality and contributor to the future mix of energy.


Posted by Filippo

Resources:
[1]: Wikipedia – accessed on September 3, 08
[2]: Guardian magazine, UK - Thursday July 17 2008
[3]: New York Times, USA - Thursday August 23, 2008