Kate Mackenzie Turbines in the sky

Magenn's MARS prototype

Wired takes a look at several companies working on high altitude wind turbines: ranging from floating, kite-like devices tethered to long power cables to quaint-looking power-generating flying machines.

The devices are very diverse. Magenn‘s helium-filled devices resemble floating kites; Sky Windpower has a ‘controlled helicopter’ with four rotary blades keeping it suspended. Kite Gen’s devices describe a figure eight in the air.

There’s no doubt the wind is stronger at high altitudes, and the devices would take up less ground space, perhaps avoiding one key objection to wind turbines. The attractions are many:

Wind’s power — energy which can be used to do work like spinning magnets to generate electricity — varies with the cube of its speed. So, a small increase in wind speed can lead to a big increase in the amount of mechanical energy you can harvest. High-altitude wind blows fast, is spread nicely across the globe, and is easier to predict than terrestrial wind.

Companies also claim the devices would pose less of a threat to avian life, and emit lower noise pollution than regular wind turbines.

But they’re not without drawbacks.

High-altitude winds, although they are far stronger than terrestrial winds, don’t offer any solution to the ‘baseload’ problem, the inconsistency of supply affecting many renewables. In a article in Energies journal:

Because jet streams vary locally and seasonally, however, the high-altitude wind power resource is less steady than needed for baseload power without large amounts of storage or continental-scale transmission grids, due to the meandering and unsteady nature of the jet streams.

Magenn for example says target markets for its high altitude turbines are developing countries with off-grid or ‘mini-grid’ environmental, and would supplement diesel generators with a cheaper energy source.

The report also suggested that at a very high density, such turbines could affect the climate. However the report’s lead author Cristina Archer has a measure of optimism about the technology, telling Wired “It’s not going to be the silver bullet that will solve all of our energy problems, but it will have a role.”

And then there’s actually getting them off the ground. To say it’s embryonic is no exaggeration; Magenn plans to ship a ‘test product’ late this year and to sell 2 to 4 next year; full production they say will begin in 2010 or 2011. Kite Gen is honing its technology and carried out a test in 2007 at an airport.

Air and terrorism

Sky Windpower’s frankly titled page on ‘Tethers, Airplanes, Safety and Terrorism’ points out that tethered ‘aerostat’ radar systems have been used for decades in the US to detect drug-smuggling activity.  There is some more information on the Federation of American Scientists’ website, which points out that these systems are ‘fair weather friends’ and uptime is not particularly high.

Sky Windpower concedes that “However, inevitably, crashes will occur, just as airplane crashes do occur,” but also points out that they would be less attractive as terrorist targets than nuclear reactors.

Related links:

Magenn’s FAQ
Kite Gen’s FAQ
Sky Windpower
Windmills in the sky (Wired, 2005)