ALOK JHA, Guardian UK, January 5, 2009
Propellers on ships have been tried and tested for centuries in the rough and unforgiving environment of the sea: now this long-proven technology will be used in reverse to harness clean energy from the UK’s powerful tides.
The tides that surge around the UK’s coasts could provide up to a quarter of the nation’s electricity, without any carbon emissions. But life in the stormy seas is harsh and existing equipment – long-bladed underwater wind turbines – is prone to failure. A Welsh renewable energy company has teamed up with ship propulsion experts to design a new marine turbine which they believe is far more robust.
Cardiff-based Tidal Energy Limited will test a 1MW tidal turbine off the Pembrokeshire coast at Ramsey Sound, big enough to supply around 1,000 homes. Their DeltaStream device, invented by marine engineer Richard Ayre while he was installing buoys in the marine nature reserve near Pembrokeshire, will be the first tidal device in Wales and become fully operational in 2010.
To ensure the propeller and electricity generation systems were as tough as possible, the tidal turbine’s designers worked with Converteam, a company renowned for designing propulsion systems for ships. “They’ve put them on the bottom of the Queen Mary … and done work for highly efficient destroyers, which is exactly the same technology that we’re looking at here,” said Chris Williams, development director of DeltaStream.
DeltaStream’s propellers work in reverse to a ship’s propulsion system – the water turns the blades to generate electricity – but the underlying connections between blades and power systems are identical to those on the ship.
Tidal streams are seen as a plentiful and predictable supply of clean energy, as the UK tries to reduce its greenhouse gas emissions. Conservative estimates suggest there is at least 5GW of power, but there could be as much as 15GW – 25% of current national demand.
A single DeltaStream unit has three propeller-driven generators that sit on a triangular frame. It weighs 250 tonnes, but is relatively light compared with other tidal systems which can be several times heavier. The unit is simple to install and can be used in closely packed units at depths of at least 20m. Unlike other tidal turbine systems, which must be anchored to the sea floor using piles bored into the seabed, DeltaStream’s triangular structure simply sits on the sea floor.
Duncan Ayling, head of offshore at the British Wind Energy Association and a former UK government adviser on marine energy, said that one of the biggest issues facing all tidal-stream developers is ease of installation and maintenance of their underwater device. “Anything you put under the water becomes expensive to get to and service. The really good bit of the DeltaStream is that they can just plonk it in the water and it just sits there.”
Another issue that has plagued proposed tidal projects is concern that the whirling blades could kill marine life. But Williams said: “The blades themselves are thick and slow moving in comparison to other devices, so minimising the chance of impact on marine life.”
The device also has a fail-safe feature when the water currents become too powerful and threaten to destroy the turbines by dragging them across the sea floor – the propellers automatically tilt their orientation to shed the extra energy.
Pembrokeshire businessman and sustainability consultant Andy Middleton said: “People are increasingly recognising how serious global warming really is, and in St David’s we are keen to embrace our responsibility to minimise climate change. DeltaStream is developing into a perfect example of the technology that fills the need for green energy and has the added benefit of being invisible and reliable.”
The country’s first experimental tidal turbine began generating electricity in Strangford Lough, Northern Ireland last year, built by Bristol-based company Marine Current Turbines. SeaGen began at about 150kW, enough for around 100 homes, but has now reached 1,200kW in testing. It had a setback early in its test phase, with the tidal streams breaking one of the blades in July.