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Wind Power Has Lightest Footprint – Carbon and Otherwise

Wind power's tiny footprints don't stop at carbon emissions. A new analysis of the impacts of various energy sources on human health and the environment finds that wind also has the smallest imprint on another, rarely considered but important aspect: land.

Wind power's ecological footprint is so small — a million times smaller than ethanol's — that if all the cars driven in the United States were battery-electric, they could be fueled by wind turbines whose total land footprint, not counting spacing in between, takes up less than 1.2 square miles, Stanford University environmental engineering professor Mark Jacobson found.

To fuel the same number of battery-electric vehicles with cellulose ethanol would require an amount of land equivalent to eight Californias – literally a million times more land and equivalent to the amount of land harvested in the U.S. in 2003.

Jacobson hit upon the idea of measuring land footprint after hearing people talk a lot about how much land a certain technology required. He realized that what they actually meant was the overall spacing.

Some technologies like wind seem to take up a lot of space, because the turbines must be separated. However, if you look at the actual land they take up, it’s not very much. For wind in particular and also for tidal turbines, the actual physical land that they take up is much different from the spacing.

The land between wind turbines is free for other uses. In Iowa, the No. 2 wind power state in the country, wind turbines sprout from fallow areas of farm fields. Maine is building wind farms along its mountain ridges. A report released last week by the Land Policy Institute at MichiganState University suggested that if Michigan turned its unusable, industry-damaged brownfields into for wind farms, the energy generated could power almost half of Michigan’s homes.

By allowing grasses, shrubs and other plants to grow among the turbines' small bases (the bases rarely exceed 215 square feet — about the size of a standard parking space), wind power also reduces atmospheric carbon in another way, Jacobson realized:

It dawned on me that if you cover it with impermeable material like asphalt or cement, not only do you cut out the vegetation, but there’s also the carbon stored in the ground from vegetation that has died over the years.

Plants take in carbon dioxide and convert it into oxygen in photosynthesis. After plants die, the carbon stored in them stays in the ground, in the roots and in the actual plants dying over the winter and sinking into the ground. Bacteria eventually break down the plant material, but it releases the carbon dioxide back into the atmosphere over a long period time.

When land is paved over for sprawling nuclear or coal power plants, the overall amount of carbon that can be stored in the ground decreases.

Switching grassland to cornfields for ethanol production also decreases the amount of carbon stored by about a quarter. Cutting down forest for cornfields reduces the carbon storage by about 60 percent. At the same time, converting that land to ethanol production, nuclear plants and coal strip mines wipes out many animal habitats.

Although the amount of carbon storage lost is small, the impact on the ecosystem is important, said Mark Delucchi, a research scientist at the University of California-Davis’s Institute of Transportation Studies and a reviewer of the paper. "The use of land has direct effects on the ecosystems," he said. Changing the land use can alter the water cycle in the area, possibly creating problems with rain runoff, or change the surface reflectivity, which changes the amount of energy going into and out of the system.

That has economic impacts, as well, Delucchi said.

Jacobson didn’t weigh economic costs in his analysis because of the volatility of fossil-fuel prices and because the costs of technologies change over time. Instead, he analyzed 11 energy sources – renewables plus nuclear, coal with carbon capture and storage, corn-ethanol and cellulosic ethanol – and ranked each according to their impacts on the environment and social aspects, including carbon emissions, mortality, water consumption, effect on wildlife and other variables.

Wind was the best, not only in terms of land use, but in several areas, including carbon emissions, mortality, thermal pollution and chemical pollution. Jacobson determined that if the U.S. replaced all on-road vehicles with battery-electric vehicles powered by fewer than 150,000 five-megawatt wind turbines, the move would cut CO2 emissions by a third. He also found that wind would use only 2 billion gallons of water a year to power the U.S. vehicle fleet compared to the 170 trillion gallons needed to produce corn ethanol.

The argument that wind turbines endanger too many birds didn’t pan out, Jacobson found. The upper estimate of how many birds are killed by wind turbines is around 40,000 – a figure dwarfed by the 100 million to 1 billion birds killed by flying into windows. Even if enough wind turbines were installed to worldwide to eliminate all the carbon emissions generated by humans worldwide – an estimated 2.2 million to 3.6 million at 5MW each – the number of bird deaths at the arms of wind turbines would still be less than 1% the number currently killed by human activity.  

Jacobson said he was surprised to see how clearly his analysis showed certain energy solutions to be good for the environment and others bad. Even when he changed the weightings for various impacts, for example on water supply, climate change or pollution, the results were about the same:

If people had done this earlier, then we wouldn’t be trying these energy alternatives that aren’t so good

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