Wind Energy Can Meet Global Demands Without Damaging The Climate
02 October, 2012
Though there is enough power in the earth's winds to be a primary source of near-zero emission electric power for the world, large-scale high altitude wind power generation is unlikely to substantially affect climate. Scientists at the Lawrence Livermore National Laboratory made the claim. The scientists studied the geophysical limits to global wind power. The study has been presented in an essay in the Sept. 9 edition of the journal Nature Climate Change .
Anne M Stark for LLNL News reported :
"The future of wind energy is likely to be determined by economic, political and technical constraints rather than geophysical limits," said Kate Marvel, lead author of the paper and a scientist in the Laboratory's Program for Climate Model Diagnosis and Intercomparison.
Airborne turbines that convert steadier and faster high-altitude winds into energy could generate even more power than ground- and ocean-based units. The study examined the limits of the amount of power that could be harvested from winds, as well as the effects high-altitude wind power could have on the climate as a whole.
Turbines create drag, or resistance, which removes momentum from the winds and tends to slow them. As the number of wind turbines increases, the amount of energy that is generated increases. But at some point, the winds would be slowed so much that adding more turbines will not generate more electricity. This study focused on finding the point at which energy generation is highest.
Using a climate model, Marvel, along with Ben Kravitz and Ken Caldeira of the Carnegie Institution Department of Global Ecology, estimated the amount of power than can be produced from both near-surface and high-altitude winds.
The group found that wind turbines placed on the earth's surface could extract kinetic energy at a rate of at least 400 terawatts, while high-altitude wind power could extract more than 1800 terawatts. Current total global power demand is about 18 terawatts.
At maximum levels of power generation, there would be substantial climate effects from 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 0.2 degrees Fahrenheit and affect precipitation by about 1 percent. Overall, the environmental impacts would not be substantial.
Another study on wind energy  by researchers at Stanford University's School of Engineering and the University of Delaware said: Not only is there plenty of wind over land and near to shore to provide half the world's power, but there is enough to exceed total demand by several times if need be, even after accounting for reductions in wind speed caused by turbines.
The findings were published in the Proceedings of the National Academy of Sciences (PNAS) by Mark Z. Jacobson, a professor of civil and environmental engineering at Stanford and Cristina Archer, an associate professor of geography and physical ocean science and engineering at the University of Delaware .
Jacobson and Archer adapted the three-dimensional, atmosphere-ocean-land computer model known as GATOR-GCMOM to calculate the theoretical maximum wind power potential on the planet taking into account wind reduction by turbines. Their model assumed wind turbines could be installed anywhere and everywhere, without regard to societal, environmental, climatic, or economic considerations.
The new paper contradicts two earlier studies that said wind potential falls far short of the aggressive goal because each turbine steals too much wind energy from other turbines, and that turbines introduce harmful climate consequences that would negate some of the positive aspects of renewable wind energy.
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.
Among the most promising things the researchers learned is that there is a lot of potential in the wind - hundreds of terawatts. At some point, however, the return on building new turbines plateaus, reaching a level in which no additional energy can be extracted even with the installation of more turbines.
"Each turbine reduces the amount of energy available for others," Archer said. The reduction, however, becomes significant only when large numbers of turbines are installed, many more than would ever be needed.
"And that's the point that was very important for us to find," Archer said.
The researchers have dubbed this point the saturation wind power potential. The saturation potential, they say, is more than 250 terawatts if we could place an army of 100-meter-tall wind turbines across the entire land and water of planet Earth. Alternatively, if we place them only on land (minus Antarctica ) and along the coastal ocean there is still some 80 terawatts available - about seven times the total power demand of all civilization. Hypothetical turbines operating in the jet streams six miles up in the atmosphere could extract as much as an additional 380 terawatts.
"We're not saying, 'Put turbines everywhere,' but we have shown that there is no fundamental barrier to obtaining half or even several times the world's all-purpose power from wind by 2030. The potential is there, if we can build enough turbines," said Jacobson.
Archer and Jacobson showed that four million, five-megawatt turbines operating at a height of 100 meters could supply as much 7.5 terawatts of power - well more than half the world's all-purpose power demand - without significant negative affect on the climate.
In terms of surface area, Jacobson and Archer would site half 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 sitting 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."
UPI reported :
Jacobson said: "Today, we have installed a little over 1 percent of the wind power needed."
Wind power can play a greater role than currently supported in meeting most or bulk of global energy demand, said the study report.
Scientists used a sophisticated climate model to argue that wind as an energy resource can satisfy "half to several times" the world's total energy needs within the next two decades.
Wind farms have drawn criticism worldwide for being cost-inefficient, eyesores on pristine rural or seaside landscapes and noisy. Supporters of wind energy's greater use contest most of those criticisms.
"If the world is to shift to clean energy, electricity generated by the wind will play a major role and there is more than enough wind for that," Andrew Myers, a spokesman for the Stanford University School of Engineering said.
 Wind Daily , “Sufficient wind energy available to meet global demands without damaging climate”, Sep 13, 2012 , Livermore CA , SPX , http://www.winddaily.com/reports/Sufficient_wind_energy_available
 Wind Daily , “Wind could meet many times world's total power demand by 2030”, Stanford CA, SPX , Sept. 13, 2012, http://www.winddaily.com/reports/Wind_could_meet_many_
 Wind Daily , “Report backs greater role for wind energy”, Stanford , Calif. , UPI, Sept. 13, 2012 , http://www.winddaily.com/reports/Report_backs_greater_role_for_wind_energy_999.html
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