The challenge | The teams | The designs | The test | The demolition

The Demolition Day teams face an electrifying challenge this week: they have to build a wind turbine. It may be no larger than 4 metres wide at the base, and the support tower must be at least 6 metres high. On top of the tower a 600-watt turbine generator will be installed.

For the test, each wind turbine will be wired up to a bank of lights. If the rotors can manage 250 revolutions per minute and handle the 0.5 tonnes of force produced by that amount of spin, they should be able to spark up all the lights. As ever, the best test result gets first choice of the demolition tools on Demolition Day.
 

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Hard As Nails
Karen Baker: Engineer
Karen is a qualified civil engineer and has over 14 years experience of both engineering and site management. Her current job involves construction training so she knows a good job when she sees one.

Bernie Sketchley: Builder
With over 30 years experience of the building trade, not much can faze Bernie. He's done everything from bricklaying and plastering to roofing and groundwork.

Jay Preece: Demolition
Jay is a demolition foreman for Downfast Demolition and Salvage Ltd. He has over 14 years experience of carefully destroying things, and can't wait to get going on the opposition's creation.

Structural Survivors
Neil Telfer: Engineer
Neil works as a Senior Project Engineer for Bullen Consultants. He has a BSc in civil engineering and is currently working towards his MSc in bridge engineering. He also works with Demolition Day team-mate Miltos.

Miltos Divanis: Builder
Miltos works as a graduate engineer for Bullen Consultants. He's a qualified civil engineer with a masters degree in structural steel design, and has worked on building sites since he was a small child in Greece, helping his dad.

Tim Philpott: Demolition
Tim has run his own demolition company for nearly 25 years. During that time he has taken down just about every kind of building and even has his own robotic tracked concrete crusher – the only one in Norfolk!

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Good wind turbines need to run efficiently to harvest the best of the wind. As well as being strong enough to stand up to gale force winds, they also need to look good because they are often sited right in the middle of the countryside. Another key factor is in the rotor blades, which need to be carefully shaped and tapered to the tip to gain maximum speed and reduce inherent drag.
 

Hard As Nails' wind turbine
Hard As Nails base their design on a cardboard tube tripod which is anchored in cable drums and rock baskets filled with stone and concrete. A central telegraph pole adds stability and the whole bottom half of the structure is encased in shuttering so the opposing team can't see how it is constructed. A timber and concrete box placed at the top acts as a secure platform for the turbine. The team also correctly base their rotors on an aircraft wing profile.

Structural Survivors's wind turbine
Structural Survivors are big on their foundations. They create a massive timber framed box some 3m high, filled with soil wrapped in geotextile. After running out of the this manufactured wrapping, they fill the top half of the box with polystyrene, soil and another plywood box insert, again filled with soil. This massive foundation half of the structure contains nearly 60 tonnes of material. A telegraph pole supported by cable drums and oil drums acts as their main turbine support post. This is braced in place by steel cables to the four corners of their foundation. The team base their rotors on simple plywood paddles.

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The judge for this programme is Dale Vince, managing director of Ecotricity and a UK leader in wind turbine design. He's checking whether the teams will create 600 watts of power and also a nice looking design.

The test involves a massive electric fan, which is capable of creating 60mph winds, blowing full on at the teams' rotors. If they can withstand the pressure, and make 250 revolutions per minute, they should be able to illuminate the complete bank of lights. First up, the structure built by Hard As Nails gets blasted. Their tripod tower holds up to the wind but their rotors just aren't big enough. With just one bulb flickering it looks as if they manage just a handful of watts. They have failed.

Structural Survivors are next. Their wind turbine with its paddle rotors is flying under the 60mph wind but they can only manage three dim bulbs. Another failure. Who can win the test stage? It looks as though it's going to be down to design – and Structural Survivors' tower isn't pretty.

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After careful consideration, Judge Dale awards the win to Hard As Nails because their tower looks the better of the two. That means Jay Preece gets first choice of the demolition tools. After checking out each others' structures, the two demolition men take their pick. Jay goes for the Grapple while Structural Survivors' Tim Philpott opts for the PD15 Steel Shears.

At the claxon bark, the quick and versatile Grapple takes out the Structural Survivors' tower in one swoop. Then the side of the box foundation is ripped open and the soil within spills out over the arena. Meanwhile, Tim has the shears gnashing away at the Hard As Nails cardboard tubing. Soon he has the cladding off and the base is ripped apart.

Now both teams are trying to flatten the mangled wrecks to less than one metre above the ground. The Grapple sways across the soil; the Shears track over the tangle of tubes and reinforcing bar. Finally, with one soil-flattening sway, the Grapple claims victory for Hard As Nails. Structural Survivors are just behind with one re-bar above the line. Another close finish on Demolition Day.

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