challengesforengineers.com

QR5

Siborg — Sun, 18 May 2008 14:39:47 +0000

The QR5 is a 5kW VAWT from Quiet Revolution, the advantage of it being vertical axis over the more traditional horizontal axis, windmill type, turbine is that it is better able to respond to changes in wind direction. This is because it isn’t having to yaw round to get the turbine blades facing in the direction that the wind is blowing from. This ability to swiftly respond to variations in the wind direction really comes in to it’s own in the urban environment where the wind characteristics can be highly variable in nature. If you have a good wind, consistent in direction and speed, blowing on to a major city by the time you get to the city center speed and direction and will be seriously variable!

Another innovative feature of the QR5 is the active control system, where the variation in wind speed is measured, by an ultar-sonic anemometer, and used to quantify the ‘gustiness’ of the wind. This data is used by some clever control algoirithms, to get the turbine tip speed ratio (the ratio of tip speed to wind speed) close to its optimum for power generation.

Business is good for Quiet Revolution with full order books and customers waiting up to a year to get one of their elegant turbines. A recent high profile project was an installation of 3 turbines at Kings Arena Waterfront development for Liverpool County Council. Unfortunately, the aesthetic appeal, rather than the functionality, of the turbines has dominated the choice of wind turbine placement with them being placed in front a large curvilinear building. Having them in front of the building means that they won’t be able to take best advantage of the regular sea breezes that occur mornings and evenings due to a temperature differential between the land and sea, this differential causes convection currents in the movement of air to happen. According to Sander Mertens, previously of Delft University, the turbines would have been ideallly placed in the centre of the building on 7m masts, this would have meant that turbines would have been able to take advantage of speed-up of the wind as it was forced up over the building as well as the daily land and sea breezes.

By Simon Catmull

Energy Storage

Siborg — Mon, 21 Apr 2008 16:40:28 +0000

Energy storage devices that have big enough energy densities are a vital component of sustainable generation. They would enable the naturally variable renewable energy generated (wind, wave, solar etc) to meet the roughly predictable energy demand of the consumers (that’s you & I bud!). They would also revolutionise personal transport, making electric vehicles a practical reality (Apologies Mr. Sinclair but your C5 just never cut it) with good top speeds and ranges.

Unfortunately energy storage technologies are several decades behind in terms of their development when compared to the efforts that have gone into the development of other technologies i.e. cramming more processing power on to computer chips, packing more and more gadgets into the ubiquitous mobile phone and lets not forget the razor wars and the never ending quest for the ‘ultimate shaving experience’ by packing more blades and widgets into a razor than you’d find on your average Swiss army knife! In the preceeding decades there had been little improvment on the metal acid battery that has been knocking about for thousands of years if the Baghdad Battery is to be believed.
Never fear though, work is under way to remedy this situation and in this category we shall be discussing the latest in energy storage technologies from Ultra capacitors to fly wheels spinning at supersonic speeds.

By Simon Catmull

Archimedes Wave Swing

Siborg — Sat, 29 Mar 2008 17:51:58 +0000

The AWS is comprised of a submerged cylinder fixed to the sea bed and an upper casing (called the floater) that surrounds the cylinder and is free to move. The action of the waves passing above the device cause pressure changes in the gas contained between the cylinder and floater. When the wave above the AWS is at a peak the gas is compressed and when the wave is in a trough the gas expands. This creates a relative motion between the 2 cylinders where power may be taken off via a hydraulic system and then converted into electricity.

AWS is at an exciting time in their pre-commercial development in 2004 they successfully tested a pilot plant off the coast of Portugal achieving a peak power of 1.5MW and now have plans to install a 250kW device at the European Marine Energy Centre (EMEC) for further testing sometime this year. According to their news page they are aiming for full commercial development by 2011, and with investment and funding in excess of £8 million from the likes of; Shell, Tudor, The Carbon Trust, The Scottish Executive and RAB Investment, they are looking well set to achieving their targets.

By Simon Catmull

Bouncing Buoy

Tjerk de Graaff — Tue, 18 Mar 2008 21:55:29 +0000

This is a relatively simple method of extracting energy from waves, by using the vertical motion of the waves to move either a set of permanent magnets inside a buoy and generate electricity or to pump water. CETO is a system that does just that, it is a water pump that is attached to the sea floor and a air bag that hovers just below the water level. when a wave passes the airbag it pulls it up and along. This movement causes the pump to push sea water trough a pipeline to the shore, where it can either be used to generate electrical energy or a high enough pressure to pass through a revere osmosis device and generate fresh water.

By Tjerk

Wave Dragon

Tjerk de Graaff — Tue, 18 Mar 2008 21:36:10 +0000

Wave Dragon receives waves with open arms. Its a device that is specifically designed to guide waves to a central point where it imitates a beach, and so lets the waves roll up the beach into a reservoir. The sea level in this reservoir is higher than the real sea level, and hence there is potential energy. This energy is converted into Electric power by bleeding the reservoir trough turbines back to the sea. The device is made of metal box sections containing air. This gives the platform its rigidity and buoyancy. The only moving parts are the turbines, which are standard off the self parts. Testing is in the summer of 2008.

By Tjerk

Anaconda ‘Another Sea Snake’

Tjerk de Graaff — Mon, 10 Mar 2008 11:10:03 +0000

How do you overcome offshore structures from breaking up due to the forces that the oceans trow at them? This question is traditionally answered by engineers through the designing of strong, stiff structures made of steal. The problem with these structures is that they are designed for a maximum stress and their life is determined by the stress cycle. Now what would happen if you design something that is flexible? Something that flexes with the waves? Something that experiences (to an extent) no fatigue cracking.

This is what the guys at MED have done. Instead of using a metal structure to extract energy from waves they are using rubber, Yes the stuff car tires are made of. The system works by submerging a flexible rubber tube filled with water under the waves. hold on to one end of the tube and when a wave passes over the tube the pressure wave along the tube causes a higher pressure inside the tube at the end. This pressure can then be used to drive a turbine to generate electricity.

By Tjerk

Pelamis ‘Sea Snake’

Siborg — Sat, 08 Mar 2008 15:06:11 +0000

The Pelamis ‘Sea Snake’ is an offshore wave energy capture device. It is a 150m long by 3.5m diameter tube articulated at several points that rests on the sea surface. The wave motion forces the articulations to bend allowing power to be taken off by hydraulic piston about the joints at each of the articulations. The hydraulic system feeds to a swash plate hydraulic motor which is then coupled to an asynchronous generator. The Hydraulic system has the advantge of being an extrremely high density power take-off that is well able to deal with the tremoundous forces that will be experienced by devices at sea as well as having components that have been widely adopted in a variety of industries and are now available ‘off the shelf’.

By Simon Catmull