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.


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

13.73 Billion years BCE

Science doesn’t have a lot to say about what happened before the Big Bang, but researchers have now developed microwave detectors that will let them take a look at the first trillionth of a trillionth of a trillionth of a second after that primordial cosmic event.

A collaboration between scientists at the National Institute of Standards and Technology (NIST), Princeton University, the University of Colorado at Boulder, and the University of Chicago has yielded super-sensitive microwave detectors that were revealed at the American Physical Society (APS) April meeting held in Denver during May.

Cosmic microwave temperature fluctuations fill the sky and are an echo of the first moment after the Big Bang (Credit: NASA/WMAP Science Team)

Cosmic microwave temperature fluctuations fill the sky and are an echo of the first moment after the Big Bang (Credit: NASA/WMAP Science Team)

The cosmic microwave background (CMB) is often referred to as the afterglow of creation. This remnant, or echo of the Big Bang fills the universe and various projects have obtained snapshots of the CMB stretching back closer and closer to the Big Bang. The new project will use a large array of the sensors mounted on a telescope mounted in the Chilean desert. They will look for subtle fingerprints of the CMB from primordial gravitational waves, ripples in the fabric of the spacetime continuum. Theory has it that these waves will have left an imprint on the direction of the CMB’s electric field, called the B-mode polarization.

This is one of the great measurement challenges facing the scientific community over the next twenty years, and one of the most exciting ones as well, says Kent Irwin, the NIST physicist leading the project.

Prototype NIST detector that will be used to spot signature of rapid inflation immediately after the Big Bang. (Credit: NIST)

Prototype NIST detector that will be used to spot signature of rapid inflation immediately after the Big Bang. (Credit: NIST)

If found, these waves would be the clearest evidence yet in support of the inflation theory, which suggests that all of the currently observable universe expanded rapidly (within the first tiny fraction of a second) from a subatomic volume, leaving in its wake the telltale cosmic background of gravitational waves.

The B-mode polarization is the most significant piece of evidence related to inflation that has yet to be observed, explained NIST’s Ki Won Yoon, at the APS meeting. A detection of primordial gravitational waves through CMB polarization would go a long way toward putting the inflation theory on firm ground.

These types of experiments can only be done by treating the universe as a whole as a cosmic laboratory. The particles and electromagnetic fields that exist immediately after the Big Bang are billions of times more energetic than those available even with the most powerful particle colliders on Earth today. On this energy scale, three of the fundamental forces of nature but excluding gravity, are predicted to merge into a single unified force.

At the energy scale at which inflation occurred, which is the GUT or Grand Unified Theory energy scale, only 3 out of the 4 fundamental forces are predicted to merge into a single unified force – electromagnetism, the strong nuclear force, and the weak nuclear force, Irwin told Spotlight.

The final force of nature, gravity, is not predicted to merge with the other three until a much higher energy scale referred to as the Planck scale, which would have occurred before inflation, and would not have been related to the primordial gravity waves. A theory that correctly incorporates gravity into a unified field is humorously referred to as a TOE or Theory of Everything, he adds.

Further reading

APS April 2009 Meeting

National Institute of Standards and Technology homepage

Suggested searches

Big Bang
cosmic microwave background

Musing on supermassive black holes

New observations from a collection of powerful telescopes have allowed astronomers from Germany and the US to settle a paradox regarding the behaviour of merging elliptical galaxies. The team has revealed evidence that the largest, most massive galaxies in the universe and the supermassive black holes at their cores grow together rather than one leading to the other, which explains the fluffy nature of their central regions.

Astronomers have known for many years that galaxies, containing billions of stars can grow as they absorb and merge with their neighbours. What was unclear though was the relationship between the supermassive black hole at the core of elliptical galaxies, and the growth of such a galaxy.

The elliptical galaxy NGC 4621 (Credit: WikiSky/SDSS)

The elliptical galaxy NGC 4621 (Credit: WikiSky/SDSS)

Initially, astronomers assumed that the huge gravitational fields of such black holes would greedily pull all galactic matter in towards them creating a relatively small, dense cluster at the centre. In the 1980s observations revealed the opposite. The biggest galaxies have huge fluffy, low-density centres.

The best theory to explain this contrary behaviour of supermassive binary black holes was the slingshot effect now observed by Kormendy and Bender. The popular theory of such galactic mergers and acquisitions has it that as two supermassive galaxies collide, their central black holes begin orbiting each other, whisking up the cores of the merged galaxy and flinging stars out of the central region. As the black hole pair sinks to the centre of the merger to form an even more supermassive black hole, the local region should appear depleted of stars.

John Kormendy

John Kormendy

Now, Ralf Bender of Germany’s Max-Planck-Institute for Extraterrestrial Physics and Ludwig Maximilians University Observatory together with John Kormendy of the University of Texas at Austin, have published details of their findings in the latest issue of Astrophysical Journal Letters. The team analysed data from Austin’s McDonald Observatory, the Hubble Space Telescope and many other telescopes around the world for 11 supermassive elliptical galaxies in the Virgo Cluster. They measured the dimming of the galactic core due to the stellar depletion, the so-called light deficit.

Ralf Bender

Ralf Bender

Finding evidence for light deficits in galactic cores is quite surprising, despite being founded on recent decades of new theory and observation by many astronomers, including Kormendy and Bender. The biggest elliptical galaxies contain enormous black holes with masses a billion or more times the mass of our Sun.

Our new observations are a strong and direct link between black holes and galaxy central properties, Kormendy explains, They are a ‘smoking gun’ that connects black holes with the formation of the surprisingly fluffy centres of giant elliptical galaxies.

The fluffiness also increases in lockstep with another galaxy property that is known to be tied directly to black holes, namely the speeds at which stars move far out in the galaxy where they cannot feel the black hole’s gravity.

Astronomers love tight correlations, Bender says. They tell us what is connected with what. The new observations give us much stronger evidence that black holes control galaxy formation, at least at their centres.

Further reading

Astrophys. J. Lett., 2009, in press

John Kormendy homepage

McDonald Observatory

Suggested searches

black holes