Wind's footprint: It's all relative

Building wind turbines is a very energy-intensive process, especially the production of the steel towers and the concrete foundations.

According to the German Environment Agency (Umweltbundesamt, UBA), wind power plants take between 2 1/2 to 11 months to generate the amount of energy that was needed for their construction.

On average, wind turbines are operated for about 25 years. During this time, they generate 40 times more energy compared to the energy required for the production, operation and the disposal of a wind power plant.

So-called upstream emissions, generated mostly through the production of carbon-intensive steel and cement, are included in the overall carbon balance of a wind turbine's life cycle.

An onshore wind turbine that is newly built today produces around 9 grams of CO2 for every kilowatt hour (kWh) it generates, according to according to the UBA. A new offshore plant in the sea emits 7 grams of CO2 per kWh.

Compared with other technologies, wind power does well in terms of carbon emissions. By comparison, solar power plants emit 33 grams CO2 for every kWh generated. Meanwhile, power generated from natural gas produces 442 grams CO2 per kWh, power from hard coal 864 grams, and power from lignite, or brown coal, 1,034 grams.

According to a study commissioned by the global anti-nuclear movement WISE, nuclear energy accounts for about 117 grams of CO2 per kWh, considering the emissions caused by uranium mining and the construction and operation of nuclear reactors.

What can be recycled?

In the last three decades, wind power has grown exponentially. In 1991, 50 wind turbines with a capacity of 100 kilowatts were built in Germany. By 2001, another 2,000 turbines had been added to the grid with a capacity of 1,300 kilowatts.

When maintained well, these small-scale plants can operate for more than 30 years and can now be found in many countries.

Due to their long lifetime, only a few old plants have so far been decommissioned. But by 2050, up to 50,000 wind farms will need to be shut down and replaced by newer and much more efficient wind power technology.

This will require the disposal of much of the concrete found in the foundation, steel in the tower and the gear box and a compound of plastic with glass or carbon fiber used in the rotor blades.

The concrete can be crushed and used in roadworks, and the precious steel can be recycled into new steel. Other valuable metals such as copper and aluminum can be reused.