Today (October 15, 2007) is Blog Action Day and upwards of 15,000 bloggers will cover subjects related to the environment. The aim is to raise awareness of environmental issues – this post is my contribution to the cause. Environmentally friendly, renewable energy generation is a theme I've covered in a number of previous posts ranging from wave energy to horizontal, vertical and micro wind turbines. Continuing this theme today I'm going to cover flying wind turbines.

Background

Ground- and sea-based, horizontal-axis wind turbines are currently the most efficient means by which wind energy is converted into electricity. However, such wind turbines suffer from being within the relatively slow moving and unreliable (turbulent) wind found in the Earth's planetary boundary layer (PBL). The PBL height varies according to season and terrain but typical heights are 457m for large cities, 366m for suburbs, 274m for open terrain, and 213m for open sea. Clearly, if wind turbines could be located above the PBL then they would be exposed to more reliable, high-speed wind.

Flying (or airborne) wind turbines, while still at the concept design phase, are being proposed and developed that would position themselves above the PBL. Such a location would, in theory, allow higher efficiency electricity generation than current ground- and sea-based wind turbines.

Inflatable Wind Turbine

Lighter-than-air vehicles (hot air balloons) gave humans their first taste of flight and inspired Magenn Power to develop a tethered, inflatable wind turbine.

The helium-filled balloon-like device rotates around its horizontal axis using a drag capture rotor, much like a vertical-axis wind turbine. The rotation also helps maintain its altitude by contributing additional lift force due to the Magnus effect – the same effect that accounts for curve balls in sports such as baseball. The electrical generators are mounted on the ends of the rotor. A tether holds the device in position and also carries electrical current to the ground.

Kite-Based Wind Turbine

Another age old flying device, the humble kite, has been proposed as a platform to carry small horizontal-axis wind turbines aloft. One company rumored to be working on such a concept is Makani Power, though information on their website is sketchy. Makani are noteworthy because they employ Pete Lynn – a renowned expert and proponent of kite-based devices – and they received $10 million of venture capital funding from Google.

Computer Aided Engineering

Both of these companies I mentioned that are developing flying wind turbines also make extensive use of Computer Aided Engineering (CAE) tools. A primary tool for fluid flow simulation is Computational Fluid Dynamics (CFD) which can perform virtual tests at high altitudes that are both costly and dangerous to perform in reality. Nearly all environmentally friendly power generation, with the exception of solar power and ethanol, is concerned with fluid flow, whether it be air or water, and so the trend of using CFD to analyze innovative devices is likely to continue.