Jet stream winds are not an ideal source of renewable energy, scientists now claim. Some experts have previously believed the winds in the upper atmosphere might provide an abundant supply of renewable energy.
But studies conducted at Germany's Max Planck Institute for Biogeochemistry in Jena suggest they would generate around 200-times less power than previously thought and have a dramatic impact on weather and temperature.
Axel Kleidon, head of the Max Planck Research Group on Biospheric Theory and Modelling, says, "Our investigations show that the potential of the jet streams as a source of renewable energy was overestimated. It is incumbent on us to carefully study the global impact of renewable energy technologies that seem environmentally sound."
Scientists have claimed the high speeds of the jet stream winds, from 7-16km up in the air, could drive rotary wind turbines hanging in the air like kites.
Rotary wind turbines could hang like kites in the upper atmosphere where the jet streams blow. This photomontage shows what they might look like; © Lee Miller
But the Max Planck researchers say the wind speed comes from the fact that there is hardly any friction in the upper atmosphere, rather than powerful propulsion. In addition, simulation tests show the climate might undergo significant changes if an enormous amount of energy was removed from the jet streams.
The geostrophic jet stream winds constantly move at more than 90km an hour and much work has gone into developing technologies to generate renewable power.
The streams themselves are created as radiation from the sun warms the tropics more than the poles. The difference in temperature in the atmosphere produced a reduction in air pressure, which drives the winds. This limits the wind strength and the amount of wind energy that can be taken from the jet stream.
The rising effect of changes in pressure and the Coriolis force from the rotation of the earth create the power and direction. Winds are forced to the right in the northern hemisphere and to the left in the southern hemisphere.
The streams travel quickly because they originate in the upper atmosphere, far away from the earth and any friction, so little energy is needed to create and maintain the wind flow.
Axel Kleidon explains, "It is precisely this low energy requirement that limits the potential for using the jet streams as a source of renewable energy."
A high level of kinetic energy does not necessarily mean that it can be used in wind power stations. Top: A model simulation of kinetic energy transport. Bottom: The maximum extraction rate. The transport of kinetic energy is often wrongly seen as a measure of wind output, whereas it merely reflects high transport in the near absence of friction. This is why the extraction rate (bottom) is several orders of magnitude lower; © Lee Miller / MPI for Biogeochemistry
After carrying out atmospheric tests and climate simulations, the group says the maximum output of energy from the jet stream winds in 7.5terawatts (7.5million megawatts). This is 200-times less usable wind energy than detailed in earlier studies and around 40% of half of mankind's primary energy requirements.
Wind turbines create a resistance to convert wind energy to power and if energy was taken from the jet stream, it would upset the balance of jet stream forces in a major way, slowing the climate system and wiping out the temperature differentials between the equator and the poles, the group claims.
Lead author, Lee Miller, says, "If we used wind turbines to take 7.5 terawatts out of the atmosphere at the level of the jet streams, about 300 terawatts less energy would be generated in the atmosphere as a whole. This would have a drastic impact on temperature and weather."