Dec. 13 (Bloomberg) -- Iberdrola Renovables SA, the world's biggest owner of wind-driven power plants, fell on its trading debut in Madrid after the 4.1 billion-euro ($6 billion) initial public offering was completed at the low end of a price range.

The stock lost as much as 33 cents, or 6.2 percent, to 4.97 euros in the first six minutes of trading. Parent company Iberdrola SA, Spain's second-largest electricity generator, sold 18.2 percent of its Renovables unit two days ago for 5.30 euros apiece, compared with a maximum suggested price of 7 euros.

``The IPO was done at the bottom of the range, and that wiped out the euphoria surrounding the company's debut,'' Enrique Soldevila, an analyst at BPI in Madrid, said by phone today. The shares pared their loss and closed at 5.15 euros, down 2.8 percent.

International fund managers ordered 1.6 times the stock reserved for them in Spain's largest IPO. Investors have sought utilities that can generate power without releasing carbon dioxide, a gas blamed for global warming. Countries including the U.S. and China have stepped up aid to generators that harness the sun, wind and other renewable sources of energy.

Rising global demand for electricity through 2030 can only be supplied with $11.6 trillion of new power plants, the International Energy Agency estimated. Bilbao-based Iberdrola plans to grab its share of the construction contracts.

Wind Parks, Hydro

Renovables owns wind parks and small hydroelectric plants from Hungary to the U.S. that can produce more than 7,300 megawatts of power. By 2010, it aims to have generators running on renewable energy that can produce 13,600 megawatts of power, enough to supply about 27 million average European homes, up 77 percent from 7,700 megawatts this year.

Iberdrola Chairman Ignacio Sanchez Galan this year pledged to spend more than a third of a 24 billion-euro investment program through 2010 on renewable power. He wants to consolidate the company's position as a world leader in wind energy and center growth in the U.S.

``This about more than just one day's trading, it's about a company that has tremendous potential,'' said Galan today in an interview.

He said Iberdrola will install about 2,000 megawatts-worth of new capacity every year through 2015.

Installed wind-power capacity rose 32 percent globally in 2006 to 74,223 megawatts, the European Wind Energy Association said in its annual report. The U.S. installed the most new wind turbines, followed by Germany, India, Spain and China. The five countries accounted for two-thirds of the total new capacity.

Investor Thermometer

Iberdrola sold 768 million shares in Renovables, which means renewables in Spanish, and banks may buy an extra 1.8 percent stake, the so-called greenshoe option, if demand is strong.

``This is the first really big renewables company that comes to market, so it's acting as a thermometer to gauge investor interest,'' Soldevila said.

Iberdrola bought three wind-park developers in the U.S. last year. It added the renewable power assets of Scottish Power Plc after acquiring the Glasgow-based utility this year, and plans to conclude the purchase of Maine-based Energy East Corp. in the first half.

Wind mills use breezes to drive a turbine that produces electricity. On average they operate about 3,000 hours a year, or a third of the time. Countries including Sweden and Spain are building wind parks offshore where wind is usually stronger and more constant.

To contact the reporter on this story: Kristian Rix in Madrid at krix@bloomberg.net

Last Updated: December 13, 2007 12:09 EST