World's richest green billionaires 2011

Being green and making money don't always go hand in hand, but these ten billionaires have tapped global demand for solar and wind power and gotten very rich from it. To make this list, billionaires were measured on the size of their "green" net worth - for the most part, the value of a stake in a publicly traded wind or solar company (two of the 10 have private holdings; I consulted others to come up with an estimate of those values).

The four Chinese billionaires in the top ten illustrate that China really has become the hot spot for solar and wind manufacturing.

The added boost came from a booming IPO market in the country over the past year.

Christy Walton Her late husband John was an early investor in thin-film solar company First Solar (FSLR), which now leads that segment of the solar market and has a market capitalization of $12 billion. The company went public in 2006.

Aloys Wobben German engineer founded wind turbine maker Enercon in 1984. Now it has $4.3 billion in revenue and turbines installed in 30 countries.

Zhu Gongshan Chairs polysilicon maker GCL-Poly Energy, which is listed on the Hong Kong stock exchange. Polysilicon is a key material in traditional solar panels. Shares doubled in value over the past year.

His net worth has climbed from $2.4 billion in mid-February to a recent $3.3 billion on the back of GCL-Poly Energy's rising stock price.

Wang Chuanfu Chairman of battery maker BYD gets his green cred from his company's efforts to produce batteries for electric vehicles. BYD has had execution problems. It but got a PR boost from an investment that Warren Buffett's Berkshire Hathaway made in 2008.

Rubens Ometto Silveira Mello The world's first ethanol billionaire.

Brazilian entrepreneur turned his chaotic family-owned sugarcane mills into Cosan (CZZ), a leading processor of sugarcane in Brazil. Last year the company inked a large joint venture deal with Shell. Read my colleague Keren Blankfeld's smart March 2011 profile of Ometto here.

Han Junliang China's first wind power billionaire chairs Sinovel Wind Group, which went public on the Shanghai Stock Exchange in January 2011. But the company appears to be having troubles.

My colleague Eric Savitz reports here that American Superconductor issued a profit warning because Sinovel Wind refused to accept shipments of wind turbine components.

Wu Jianlong This 44-year-old Hong Kong resident chairs solar cell maker Zhejiang Sunflower Light Energy. The company had its initial public offering on the Shenzhen Stock Exchange in August 2010. Thanks to the surging value of his company's stock, Wu's net worth is up $200 million since he debuted on Forbes' World Billionaires list in March.

The company is located in the eastern Chinese province of Zhejiang.

Adi Godrej The Indian billionaire owns 1,750 acres of land that he and his family have turned into the Soonabai Pirojsha Marine Ecology Center, where visitors can take a guided tour through the mangroves, visit a marine aquarium, and learn about biodiversity conservation.

Vinod Khosla Through his venture capital firm Khosla Ventures, he has invested in upwards of 40 companies across the spectrum of clean energy and materials.

One solar thermal company, Ausra, was sold to French nuclear power giant Areva in 2010. Biofuels company Amyris (AMRS) went public in late 2010; Kior, a company that aims to turn wood chips into diesel and gasoline, recently filed to go public.