Wind contributes less than 1% to the world’s energy. The planned buildup in wind power will have to use mostly fossil fuel energy and thus contribute to CO2 emis­sions. Fortunately, wind is one renewable energy source that can payback this energy in months instead of years. Careful analyses of energy use in wind energy generation have been made by Vestas Wind Systems in 199720 and 2006.21 Vestas is a large Danish manufacturer that has installed 38,000 turbines, about half the world’s total. The bottom line is that the fossil energy used can be recovered in about four months for a 600-kW turbine in 1997 and in about 6.8 months for an off­shore 3-MW turbine in 2006.

These so-called life-cycle analyses are interesting because they give a good idea of all that is involved in building a wind farm. We’ll take the 2006 study as an example. The study begins with the description of a fictitious power plant to be built.21 This plant will consist of 100 Vestas V90-3.0MW turbines built 14 km (9 miles) offshore in water 6.5-13.5 m (about 33 feet) deep. Each turbine will pro­duce 14 GWh/year for a total of 1,400 GWh/year for the whole plant. That’s 1.4 billion kWh/year of electricity, compared to the 2,300 kWh that an average Danish household uses per year. That is enough power for 600,000 homes! It turns out that large plants require less energy per kilowatt produced than small ones.

The energy used to build this plant is divided into four parts: (1) manufacture of the components, (2) transport, construction, and installation of the turbines, (3) their operation and maintenance, and (4) their dismantling and disposal at the end of life. The lifespan is assumed to be a conservative 20 years. The compo­nents consist of the foundations, the towers, the nacelles, the blades, the trans­former station, the transmission lines up to the grid, and even the boat dock for offshore plants. The foundation if offshore would be a steel tube 30 m long 4 m in diameter, and 40 cm thick. The transition piece to the tower is of concrete. The tower is made of steel, and all the energy used in making the steel from ore, fabricating the tower, and sandblasting and painting the surface is counted. The nacelles contain the gearbox, the generator, the transformer, a switchboard, a yaw system, a hydraulic system, and the cover. When these components are made by subcontractors, all the energy used in those factories is accounted for. The blades are made of 60% fiberglass and 40% epoxy, and the spinner on which they are mounted is plastic.

Transporting these components to the site by truck or boat uses gasoline or die­sel, and the large cranes used for installation use more fuel. A transformer station for the offshore plant is to be built on three concrete piles 14 m above the water. The steel structure is 20 m x 28 m in size and 7 m high, with a helicopter platform on top. To carry the power to land, two 150-kV underwater cables are used up to a cable transition station 20 km away. From there, 34 more kilometers of dry cables carry the power to land. For maintenance, it is assumed that half the gearboxes and generators in the station will have to be replaced or repaired during the 20-year life cycle. Each turbine will be inspected four times a year, and the energy used to transport the inspectors by car, helicopter, and boat is also counted. A resource one usually does not know about is the use of sacrificial aluminum anodes for cathodic protection against the attack of parts by salt water. Since the aluminum cannot be reclaimed, the energy in mining is lost.

At the end of life, the turbines, towers, and foundations have to be dismantled and disposed of. Metals can be 100% recycled, with 90% recovery, and 10% going to landfill. Materials like fiberglass, plastics, and rubber can be burned; and the heat can be captured for use. Energy is actually recovered in the dismantling stage. When all this is added up, each turbine’s energy cost over 20 years is 8.1 million kWh, while it is producing 14.2 million kWh/year. Dividing these two numbers gives the 0.57-year or 6.8-month energy payback time quoted above. This is for an offshore plant. An onshore plant produces only half as much energy, but it also takes half as much energy to build and maintain. Amazingly, the energy recovery time is almost the same, at 6.6 months. As for the carbon footprint, such a plant generates about 5 g of CO2 for every kilowatt-hour (kWh) of electricity generated. By comparison, normal European power plants emit 548 g/kWh. Wind is indeed a very clean way to generate energy, but it has other problems.