Italian utility giant Enel is considering spinning off 40 percent of its clean-energy business in a public offering next year, according to research firm New Energy Finance (via Clean Edge).

The news comes a few days after U.S. wind-power company Noble Environmental Power filed to sell 23.4 million shares in an initial public offering – despite an ongoing investigation from New York's attorney general.

Enel and Noble are the latest in a series of greentech companies that have been pushing toward IPOs in the last two months.

Energy Recovery and GT Solar had their public debuts in July, while STR Holdings, GCL Silicon Technology Holdings, First Wind Holdings Inc., A123Systems, Changing World Technologies and Schott are planning IPOs (see GT Solar Goes Public, GT Solar Sinks on LDK News, GT Solar IPO Attracts Class-Action Suits and Angling for IPOs in Tough Times).

But not all of these plans will necessarily materialize into public offerings, industry watchers said last week. The punishing climate for greentech companies that have already gone public this year, combined with the rocky economy will keep some greentech companies from actually going public in 2008, they said.

For example, Enel hasn't ruled out other options, such as a private selling of the stake. If it goes public, the new company will be called Enel GreenPower, according to New Energy Finance.

Enel produces and sells a variety of renewable energies such as wind, solar and geothermal, and the company has over 19 gigawatts of installed renewable capacity in countries like Italy, the United States, Canada and Spain, the company said on its Web site.

Last month, Enel said it had agreed to buy electricity from eight wind-power projects that is being built in Brazil by an affiliate of the German company SoWiTec International. Enel will also have the option to buy the plants, which will have a total capacity of up to 1 gigawatt.

Essex, Conn.-based Noble Environmental Power, which develops, constructs and operates wind parks in the United States, set the number of shares it plans to sell 23.4 million shares when it goes public on the Nasdaq Stock Exchange, according to a Friday filing with the U.S. Securities and Exchange Commission.

The company, which aims to raise up to $375 million, hasn't listed a price range for the shares.

Noble Environmental Power operates 282 megawatts of wind generating capacity. The company also plans on adding an additional 950 megawatts of capacity to its portfolio by the end of 2009. Founded in 2004, Noble began operating its first wind parks in March.

The company is planning its public offering while facing an investigation by the New York State Attorney Generation Andrew Cuomo. Cuomo is investigating whether the company, along with Newton, Mass.-based wind power developer First Wind, has improperly influenced local officials in exchange for approval of land-use agreements, engaged in anti-competitive practices and committed other violations.

According to Noble Environmental Power's latest SEC filing, the investigation is still in its early stage, and the company is unable to foresee when it might be resolved.