What is the impact of wind energy on the environment?

Wind energy is non-polluting by nature. However, it does have some negative impacts on the environment. Wind farms consisting of hundreds of turbines take up significant amounts of land, and some people feel that these farms are eyesores. The moving blades in the wind turbines also create a risk to birds in the area.

The Altamont Pass near San Francisco, California, developed in the 1980s, began a huge environmental outcry against wind farms and gave wind farms a bad reputation. At least 22,000 birds, including some 400 golden eagles, were found to have collided with wind turbines (or been electrocuted by power lines) there. The problem was that no one performed a migratory bird study before the 5,400-turbine facility was built. Such a study, required today, would have shown that the Altamont Pass is an important migration route and wintering area for raptors.

Modern turbines, with slower rotating blades, coupled with better locations for wind farms have been very successful in reducing bird fatalities. When the Buena Vista Wind Energy Project at Altamont replaced 179 turbines with 38 taller ones in 2006, a local ecologist advised the company to avoid ridge saddles between hills and other hotspots for raptor traffic. Since then, golden eagle fatalities at Buena Vista have dropped by 50% and other raptor deaths by 75%.

The Altamont Pass Wind Farm continues to undergo significant changes that will help address its historical problem with bird fatalities. One operator has begun a major upgrade, and over the next decade one turbine will replace about 15 old ones while producing the same amount of power. Figure 1 illustrates the change in visual appearance after repowering. Another operator announced in October 2015 that it will shut down operations, which will affect about 800 turbines, with "the reduction of avian impacts" given as the primary reason for the decision.

Wind turbines have been found to be deadly to bats, too. in 2004 it was discovered that thousands of bats had died at wind farms in the mountains of West Virginia and Pennsylvania. Work is now under way to find a means to warn bats away from the rotating blades.

These efforts to make turbines safer for birds seem to be working. A 2003 study of 4,700 turbines located outside California found an average of 2.3 birds per year killed per turbine. That's a tiny number compared with the more than 4 million birds that collide annually with communication towers. In fact, bird fatalities from wind turbines are significantly lower than many human related "bird killers", as illustrated in Figure 2. Yet, there are still concerns that a number of particularly vulnerable groups, such as raptors, which are slow to reproduce and favor the wind corridors that are best suited for wind farms, are particularly vulnerable to getting killed by wind turbines.

The Royal Society for the Protection of Birds perhaps best sums up the situation with avian deaths from wind turbines when it says that it supports wind power - not because windfarms pose a lower risk to birds than other energy sources - but because in its view climate change poses the "single greatest long-term threat" to bird species.

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