September 11, 2012
There Is Enough Wind To Go Around
April Flowers for redOrbit.com - Your Universe Online
Researchers at Lawrence Livermore National Laboratory and the Carnegie Institution for Science report that there is enough energy available in winds to meet all of the world's demand, especially through the use of atmospheric turbines. Atmospheric units convert steadier and faster high-altitude winds into energy, creating even more power than ground and ocean based units.
The study, published in Nature Climate Change, examines the limits of the amount of power that could be harvested from winds, as well as the effects that high-altitude wind power would have on the climate as a whole. The team used models to quantify the amount of power that could be generated by both surface and atmospheric winds. Surface winds were defined as those that can be accessed by turbines supported by towers on land or rising out of the sea. High-altitude winds were defined as those that can be accessed by technology merging turbines and kites.
The study was confined to the geophysical limitations of these techniques; it did not include technical or economic factors.
Turbines slow winds by creating resistance, or drag. As the number of turbines increases, so does the amount of energy extracted. At some point, however, the winds will be slowed so much that adding new turbines will not generate more electricity. The research team focused on finding that tipping point. They used models to determine that more than 400 terawatts of power could be extracted from surface winds and more than 1,800 terawatts from atmospheric winds.
Currently, global consumption is around 18 TW of power. Near-surface winds could provide more than 20 times today's global power demand. Wind turbines on kites could potentially capture 100 times the current global demand.
At maximum levels of power extraction, there would be substantial climate effects to wind harvesting. But the study found that the climate effects of extracting wind energy at the level of current global demand would be small, as long as the turbines were spread out and not clustered in just a few regions. At the level of global energy demand, wind turbines might affect surface temperatures by about 0.1 degree Celsius and affect precipitation by about 1%. Overall, the environmental impacts would not be substantial.
"Looking at the big picture, it is more likely that economic, technological or political factors will determine the growth of wind power around the world, rather than geophysical limitations," Ken Caldeira of the Carnegie Institution said.
In a separate study conducted by the University of Delaware and Stanford University, scientists calculated the maximum energy potential from wind sources along with the climatic impacts of harnessing the energy. Their results were published in the Proceedings of the National Academy of Sciences.
Their results, slightly different from those of LNL, suggest that a full half of the world's future energy demands could be met by wind power with minimal environmental impact. They arrived at this determination by calculating the maximum theoretical potential of wind power worldwide, taking into account the effects that numerous wind turbines would have on surface temperatures, water vapor, atmospheric circulation and other climatic considerations.
"Wind power is very safe from the climate point of view," said Cristina Archer, associate professor of geography and physical ocean science and engineering at the University of Delaware.
The team identified the maximum wind power potential by finding the saturation point where adding more turbines would fail to increase energy input. This is the same tipping point the earlier study was searching for, the point of diminishing returns.
This "saturation wind power potential" is reached when too many turbines leave too little wind left behind to extract, interfering with the climate and leveling off the total energy output.
"They reduce the amount of energy available for others," Archer said. "And that's the point that was very important for us to find."
This study concluded that the saturation wind power potential is greater than 250 TW globally and 80 TW over land and coastal ocean areas at 100 meters in the air, the height of most modern wind turbines. These figures far exceed current global energy demands. Hypothetical turbines operating in the jet stream six miles up in the atmosphere could extract as much as an additional 380 terawatts. (Still a bit of a disparity between the first study and this one.)
"The result of this study suggests that there is no fundamental barrier to obtaining many times the world power demand for all purposes in a clean-energy economy from wind," Stanford's Marc Jacobson said.
The team cautions that this saturation wind potential is a theoretical calculation and propose a "fixed wind power potential" for more practical applications. This fixed potential is the maximum power that can be extracted by a given number of wind turbines as they are spread apart over increasingly larger areas.
They suggest that installing 4 million turbines would yield up to 7.5 TW, more than enough to supply half the world's power demand in 2030, which the study estimates to be around 11.5 TW every year. Spreading wind farms out worldwide in windy locations would increase efficiency, as well as minimize costs and reduce overall impacts on the environment when compared with packing the same 4 million turbines in a few spots.
"We have a long way to go. Today, we have installed a little over one percent of the wind power needed," said Jacobson.
In terms of surface area, Jacobson and Archer would place half of the four million turbines over water. The remaining two million would require a little more than one-half of one percent of the Earth's land surface – about half the area of the State of Alaska. However, virtually none of this area would be used solely for wind, but could serve dual purposes as open space, farmland, ranchland, or wildlife preserve.
Rather than put all the turbines in a single location, Archer and Jacobson say it is best and most efficient to spread out wind farms in high-wind sites across the globe – the Gobi Desert, the American plains and the Sahara for example.
"The careful siting of wind farms will minimize costs and the overall impacts of a global wind infrastructure on the environment," said Jacobson. "But, as these results suggest, the saturation of wind power availability will not limit a clean-energy economy."
This study contradicts earlier claims that the wind resource is small and damaging to the climate. Last year, German researchers from the Max Planck Institute for Biogeochemistry reported there to be a very low potential for wind with harmful effects similar in magnitude to doubling atmospheric carbon dioxide.
Puzzled by their conclusions, Archer and Jacobson set out to determine the resource at a global scale using a physical model to thoroughly address the many factors at play. They used a 3D atmosphere-ocean-land coupled model (GATOR-GCMOM) that extracts energy where the turbines would actually be located 100 m off the ground, instead of at the surface like the German study. Their high-resolution model addresses numerous factors, such as chemistry and water vapor content.
"The model is very complex and sophisticated," Archer said. "It's very, very reliable."
The new model provides a more sophisticated look than previously possible by separating winds in the atmosphere into hypothetical boxes stacked atop and beside one another. Each box has its own wind speed and weather. In their model, Jacobson and Archer exposed individual turbines to winds from several boxes at once, a degree of resolution earlier global models did not match.
"Modeling the climate consequences of wind turbines is complex science," said Jacobson. "This software allows that level of detail for the first time."
With a single model, the researchers were able to calculate the exposure of each wind turbine in the model to winds that vary in space and time. Additionally, the model extracts the correct amount of energy from the wind that gets claimed by the turbines, reducing the wind speed accordingly while conserving energy. It then calculates the effect of these wind speed changes on global temperatures, moisture, clouds and climate.
The new findings confirm that wind power is a viable component of a clean-energy economy. Wind power does alter the atmosphere when extracted at massive scales by decreasing wind speed at hub height and to a lesser extent at the surface, reducing the amount of water vapor and cooling the planet. However, the study finds the impacts are negligible at more practical scales of extraction, such as 7.5 TW. At any scale, wind extraction impacts are less than damage from heat-generating combustion and nuclear reaction from fossil and fissile fuels. Wind turbines generate no significant heat, pollutants, soot or ozone.
"Everything comes at a price, but the price of wind power comes at a low cost in terms of climate impacts," Archer said.
Researchers at Near Zero, a non-profit organization founded to improve dialogue between energy experts and policy makers, conducted a survey of experts which shows the promise of high-altitude wind energy and the barriers to harnessing it.
Airborne wind energy, according to the survey, could scale up fairly quickly if given significant government support for research and development.
Surface winds are already being harnessed to generate substantial amounts of electricity, however, higher in the sky winds tend to be stronger and steadier, making them an even larger source of energy. Unfortunately, these winds are higher than any turbines currently in production can reach. According to studies like those above, the energy potential from these winds is enormous, but the field of airborne wind energy is still in its infancy. There are many challenges to face before it becomes commercially competitive.
Near Zero conducted both an informal discussion and a formal survey to find out what technologies are most advanced, which have the best potential, and how best government could jumpstart the development of the airborne wind energy industry. Thirty-one experts completed the formal survey, identifying technological, engineering, and regulatory barriers to testing airborne wind energy technologies and bringing the industry to large scale.
With a boost from the government, the airborne wind energy industry could grow very quickly. During this initial stage, funding of $10 million per year could cut many years off how long it takes to reach significant scale, and $100 million per year would further accelerate the deployment of high-altitude wind generators.
There are many barriers facing such technology, according to the experts. The primary barrier seems to be reliability of the technologies, since airborne wind energy systems would have to remain aloft for long periods of time in shifting winds and changing weather.
A secondary barrier is the body of existing regulations, posing challenges for both testing prototypes and for large-scale implementation in coming years. Thus regulations pose a challenge for rapid testing of various prototypes, to see which may be commercially viable.
The experts favored particular types of systems – those using rigid wings – and argued against putting large funding toward approaches using balloons. Some experts also suggested installing airborne wind energy systems offshore, in part because of the large wind resource available, and because regulatory and safety issues may be easier to resolve than for land-based systems.
In Germany, a 200-meter high wind measuring mast has been erected to deliver precise data that will be used to forecast energy yields.
The German government has decided to transform their energy system, partially by phasing out nuclear energy and dramatically expanding wind energy production, both onshore and off.
“There is still immense potential inland that remains to be tapped, such as in the low mountain ranges,” says Tobias Klaas, scientist at the Fraunhofer Institute for Wind Energy and Energy System Technology IWES in Kassel.
To run a wind farm efficiently, planners must know in advance precisely what wind speed predominates at the site, and what kind of turbulence to expect.
“With conventional methods, it is almost impossible, or possible only at great effort and expense, to measure projected power when planning modern, large-scale facilities,” says Klaas. Moreover, forests and hills hamper the analysis of wind conditions. Experts refer to this aspect as “complex terrain,” where topography influences wind conditions, even at great heights.
To combat these problems, IWES erected a 200-meter tall wind measuring mast, which has been operating on a hill not far from Kassel since January taking measurements of wind speeds, turbulence and meteorological data. It is Europe's tallest measuring mast for wind energy, as conventional masts are only about 100 meters in height. Scientists know little about wind dynamics at the 200-meter level.
“Indeed, there are theories about how wind speed increases with height, yet these no longer apply at such great heights. Hence, actual measurement values are needed to further develop the models,” explains Klaas.
For instance, trees decelerate ground-level winds and create turbulence, and it was not possible to draw conclusions about the conditions at the upper regions based on these data. Using ultrasound anemometers (special wind gauges), the new mast records, in spatial terms, how fast and in which direction the wind is blowing, thereby rendering a precise depiction of the turbulence. Conventional vane anemometers moreover establish wind speed and direction at various heights. They additionally measure other meteorological factors, like air pressure, humidity and temperature. The figures on precipitation amounts and the duration of sunshine complete the data set.
“We have achieved a unique sensory device that allows us to determine the impact of these parameters on wind conditions,” says Klaas.
These measurements help in determining the optimal alignment of wind turbines and the appropriate dimensions of new turbines, which will help save on expenses. It should also be possible to develop standards for LIDAR (light detecting and ranging), the new ground based remote measurement process which is considered to be key to wind profile measurements up to several hundred meters. Due to the lack of standards, LIDAR remains unapproved as the sole measurement process for expert reports on wind, which are the basis for yield calculations. If successfully granted one day, thanks to the Fraunhofer measuring mast, then such approval would make expert reports on wind superfluous, because LIDAR would render measuring masts obsolete.