Tall Tales

Humans considered storms to be a sign of nature’s fury. While we have gained some bit of understanding of the science behind hurricanes, cyclones, typhoons and gales their destructive potential has remained the same.

This is not to say that winds are a scourge of nature-sailboats and windmills were two very useful inventions that were crucial to the progress of human civilization. But the fact remains that if you got caught in a storm while  you were at sea, in nine cases out of ten you were likely to meet your maker.In the recent years, as science gained a slight understanding of these complex weather systems the damage caused by storms has been somewhat limited, as early warning systems prevents ships from going out in choppy seas. But there can be no avoiding the massive destruction caused by strong winds when they hit land and cross habitable areas. Case in point is Hurricane Katrina; even after four years (it struck in Aug 2005) the rebuilding of New Orleans is still continuing while the government risks being slapped with claims for billions of dollars in damages.

Anatomy of a hurricane

Inspite of the complexity of hurricanes (and also typhoons, tornadoes, cyclones,twisters), they can be thought of as a heat engine, transferring energy from one part of the earth’s surface to another. They need a source of heat to form. As they move onwards they encounter cooler temperatures and expend their stored energy mainly as kinetic energy (strong winds) and condensation (rains). This is a very simplistic explanation- check out the animation below for  a better idea.

This animation is courtesy BBC’s weather guides

Harnessing hurricanes

Hurricanes are a storehouse of enormous amounts of energy. A Category 5 hurricane like  Gustav released energy equivalent to 11.000 Hiroshima type atomic bombs. Of course, most of this energy is dissipated by friction, shear strain, atmospheric turbulence and heating. This energy is also dissipated over a much larger area (typically thousands of square kilometers ) and spread over an extended period of time (weeks). But even with such losses there is enough energy to go around, as any of the thousands of videos of hurricanes in action reveal.

A natural hurricane is impossible to control and utilize. But that does not prevent us from running with the concept and creating an artificial hurricane to convert the energy from the turbulence into electricity. There is a  theory, called CAPE (Convective Available Potential Energy)  that a unit mass of air gains energy as it rises through the warmer lower levels to the cooler upper levels of the atmosphere. Solar chimneys have already put this theory in action where warm air, heated by sun rises through a chimney and in the process drives wind turbines, thereby generating electricity.

Atmospheric Vortex Engines

A Canadian engineer named Louis Michaud has proposed a concept named Atmospheric Vortex Engine where the walls of the solar chimney are replaced by cooler layers of surrounding air and  solar radiation as heat source  by waste industrial heat in the form of steam.  At the base, the AVE will have a cylindrical structure, open at the top and with inlets at an angle all around the base.

The heated and moist air will be introduced into the cylinder tangentially and will rise up in the form of a vortex. A low pressure system will be created and more air will be sucked in, while depending on initial  heat energy supplied the top of the vortex can rise up to an altitude of around 10 kms. Since the pressure and temperature at such altitudes is very low the  spin cycle will be maintained and the vortex will continue operating in a self sustained manner, unless it is stopped. Wind turbines at the base near the air intakes will convert the energy of the incoming winds into electricity.

Calculations show that that an AVE station can produce up to 200 MW power and will need to have a base cylindrical structure of diameter 400m and  a height of 100m. At the base the vortex will have a diameter of 50 m and will extend to an altitude of 20 km.Some probable designs can be seen here.

Safety issues and challenges

Is there any chance of this vortex going rogue, gaining energy and becoming a threat? According to the inventor stopping the vortex is as simple as introducing cold and dry air and reversing the  angle of ingress . However the sustainability of the process might be disrupted due to weather events like high winds and cold weather that might intensify or stifle the process. For now, tests on miniature models have borne out the theory but there is no saying how things will work in the scales that will be needed for cost economic functioning. There are a whole lot of variables involved, many of them not under human control and plenty of research needs to be done before the technology can be deployed in real world.

As the world moves towards an increasingly energy constrained future we need to think creatively to meet our energy needs. AVE is just one of the many promising concepts which need to be looked into thoroughly. If things work according to plan hurricanes may be one of the numerous sources powering a brave new world.