Energy, all at sea

Floating wind turbines could capture the energy of higher wind speeds further out to sea and address some of the noise and unsightliness complained about by those with turbines closer to home.

Wind turbines represent one of the most reliable renewable energy solutions, along with solar power and tidal and hydroelectric power. As wind turbine designs increase their size they also get noisier and become more of an eyesore. The solution is either to site them remotely on dry land or to build them at sea with the tower embedded in the seabed of shallow waters, but this restricts them to near-shore waters with depths no greater than 50 metres, which means they cannot utilise the strong winds further out to sea.

Now, naval architect Dominique Roddier of Berkeley, California-based Marine Innovation & Technology has, together with his team, published a feasibility study of a novel platform design – WindFloat – that, as the name suggests uses floating wind turbines. The study is published in the Journal of Renewable and Sustainable Energy this month.

Floating wind turbines could use stronger offshore winds
Floating wind turbines could use stronger offshore winds (Credit: Roddier et al/JRSE/American Institute of Physics)

Roddier and colleagues, Christian Cermelli, Alexia Aubault, and Alla Weinstein, have tested a 1:65 scale model in a wave tank, which shows that a three-legged floating platform, based on existing gas and oil offshore platform designs. The team explains the main issue: “A floater supporting a large payload (wind turbine and nacelle) with large aerodynamic loads high above the water surface challenges basic naval architecture principles due to the raised centre of gravity and large overturning moment,” they say. In other words at first glance such a rig would capsize very easily. However, after several years work, their results show that the current design is stable enough to support a 5-megawatt wind turbine, the largest turbine that currently exists. These mammoth turbines are 70 metres tall and have rotors the size of a football field. Just one, Roddier says, produces enough energy “to support a small town.”

The next step is to continue construction of a prototype with electricity operator Energias de Portugal that will help the developers understand the life-cycle cost of such projects and to refine the economic model. The prototype will be tested in open water by the end of summer 2012, Roddier says. “The WindFloat [design] is envisioned to be located 15-20 km offshore so as to minimize risks/nuisance to the general public, and to mitigate the view impact from the coastline,” the team adds.

Links

J Renewable Sustainable Energy, 2010, 2, 3, 033104
Marine Innovation & Technology

Nitrogen-fixing aliens

Scientists hope that Titan, a moon of Saturn, with its nitrogen-rich atmosphere, could act as a model system for terrestrial chemistry before life began on our planet. Now, another step towards that goal has emerged as researchers at the University of Arizona have incorporated atmospheric nitrogen into organic macromolecules under conditions resembling those on Titan.

“Titan is so interesting because its nitrogen-dominated atmosphere and organic chemistry might give us a clue to the origin of life on our Earth,” explains Hiroshi Imanaka, who is an assistant research scientist in the UA’s Lunar and Planetary Laboratory. “Nitrogen is an essential element of life.” Titan looks orange through a telescope because its atmosphere is a rich smog of organic molecules. Particles in the smog could settle on the surface and be exposed to conditions that might eventually create life, said Imanaka.

Saturn's A and F rings, the small moon Epimetheus and the smog-enshrouded Titan, Saturn’s largest moon. (Credit: NASA/JPL/Space Science Institute)
Saturn's A and F rings, the small moon Epimetheus and the smog-enshrouded Titan, Saturn’s largest moon. (Credit: NASA/JPL/Space Science Institute)

Of course, nitrogen alone is not enough, nitrogen molecules must be converted to a chemically active form that can drive the necessary biochemical reactions that underpin biological systems.

Imanaka and Mark Smith converted a nitrogen-methane gas mixture similar to Titan’s atmosphere into a collection of nitrogen-containing organic molecules by irradiating the gas with high-energy ultraviolet light. The laboratory set-up was designed to mimic how solar radiation affects Titan’s atmosphere.

Most of the nitrogen simply formed solid compounds directly, rather than gaseous ones, explains Smith, whereas previous theories suggested that nitrogen would move from gaseous compounds to solid ones in stepwise process. But, those settling particles may not contain nitrogen at all. If some of the particles are the same nitrogen-containing organic molecules created by the UA team in the laboratory then it would suggest that conditions conducive to life might just exist on Titan, Smith says.

These and other laboratory observations help scientists planning future space missions to decide on what to look for on other worlds that might hint at life and what instruments should be developed to help in the search.

Links

Proc Natl Acad Sci, 2010, online
Mark A. Smith homepage
UA lunar and planetary laboratory

Tubes in space

Carbon nanotubes form in space but use a metal-free chemistry until now unavailable to chemists on Earth. The discovery is a surprising outcome of laboratory experiments designed by Joseph Nuth at NASA’s Goddard Space Flight Center, in Greenbelt, Maryland, and his colleagues. They were hoping to understand how carbon atoms are recycled in stellar nurseries, the regions of space where stars and planets are born, but the finding could have applications in nanotechnology, as well as help explain some characteristics of supernovae.

Writing in the journal Astrophys J Lett, Nuth and colleagues explain how astrochemistry makes carbon nanotubes without requiring a metal catalyst. Nanotubes are produced, they say, when graphite dust particles are exposed to a mixture of carbon monoxide and hydrogen gases, conditions that exist in interstellar space.

The finding corroborates the discovery of graphite whiskers, bigger than nano nanotubes, in three meteorites. The meteoric discovery hinted at why some supernovae appear dimmer and farther away than they ought to be based on calculations using current models. Nuth’s approach is a variation of a well-established way to produce gasoline or other liquid fuels from coal. It’s known as Fischer-Tropsch synthesis, and researchers suspect that it could have produced at least some of the simple carbon-based compounds in the early solar system. Nuth proposes that the nanotubes yielded by such reactions could be the key to the recycling of the carbon that gets released when carbon-rich grains are destroyed by supernova explosions.

Stellar Nursery
A stellar nursery could be home to carbon nanotube factories (Credit: NASA, http://apod.nasa.gov/apod/ap021102.html)

The structure of the carbon nanotubes produced by Nuth and colleagues was determined by materials scientist Yuki Kimura, of Tohoku University, Japan, using transmission electron microscopy. He observed particles on which the original smooth graphite gradually morphed into an unstructured region and finally to an area rich in tangled hair-like masses. A closer look with an even more powerful microscope showed that these tendrils were in fact cup-stacked carbon nanotubes, resembling a stack of disposable drinking cups with the bottoms removed. If further testing indicates that the new method is suitable for materials-science applications, it could supplement, or even replace, the familiar way of making nanotubes, explains Kimura.

Researchers might also now evaluate whether graphite whiskers absorb light. A positive result would lend credence to the proposition that the presence of these molecules in space affects the observations of some supernovae.

LINKS

Astrophys J Lett, 2010, 710, L98-L101

http://dx.doi.org/10.1088/2041-8205/710/1/L98