Image caption Each of Britannia's turbine blades will weigh more than 30 tonnes

Huge wind turbines with a span rivalling that of the London Eye could form part of the UK's energy future.

The first giant offshore turbine, named Britannia, will be complete by 2012.

It will tower 574ft (175m) above the North Sea, with blades that sweep a circle more than 100ft (30m) wider than the diameter of the London landmark.

Lead engineer Bill Grainger thinks future turbines will be even bigger, saying: "There isn't a technical issue that screams out size limit."

Offshore turbines are commonly capable of generating either 2.5 or five megawatts of power, but the Britannia will produce 10 megawatts.

That translates into enough electricity to power about 10,000 homes, and replace some two million barrels of oil during its lifetime.

Risk of failure

Mr Grainger thinks Britannia is only the start of a trend towards a new generation of giant turbines, producing more power, more cost-effectively.

He told The Engineer magazine: "There might be a limit to the size that people want to put into the field; if a 20 megawatt turbine failed, that's a big chunk of electricity to lose.

"But then, if a power station goes off-line you've lost 300 megawatts, so I don't think that's a limit either.

You have to make changes as you get bigger. Blades get floppier, for example Bill Grainger, Clipper Windpower Marine

"They'll get bigger than 10 megawatts, is my feeling. How much bigger? I don't know."

Mr Grainger is engineering manager at Clipper Windpower Marine, the UK arm of the US company in charge of the £44m Britannia build.

Each of its blades will be 236ft (72m) long and will weigh more than 30 tonnes.

It is the enormous stress placed on these metal structures as they rotate that presents one of the biggest engineering challenges to increased turbine size.

Mr Grainger said: "You have to make changes as you get bigger.

"Blades get floppier, for example, so you have to put more carbon in, but we aren't anywhere near 100% carbon yet."

Britannia is being built at Blyth, in Northumberland, and is most likely to be placed on Dogger Bank, off the north-east coast of England.