By reporter Marjorie Sun.

I got interested in this story after hearing Silicon Valley venture capitalist Vinod Khosla speak at a conference this fall in Sausalito. He explained how he decides where to invest in green tech and it was fascinating. He and other top venture capitalists think they can help stop global warming and make a ton of money at the same time. You can listen to Khosla's talk on a webcast and listen to all sorts of entrepreneurs and v.c.'s talk about the latest renewable energy projects.

Khosla says to achieve a huge reduction in greenhouse gas emissions fast, we have to think about solutions that make big cuts in emissions and will be widely adopted. Buying a Prius is fine, he says, but it's really just "fashion." We need solutions that people in India and China will buy, Khosla says. To him, the key issues that guide his investments are cost, scale, and adoption. If a renewable solution isn't cheaper than coal, forget it, he says. Geothermal "is nice, but it doesn't scale."

Same with wind. It's "a great technology, but it's a toy." As for hydrogen fuel, the adoption risk is too high. Again, forget it, he says. The focus should be a war on coal, oil, and the manufacturing of cement and steel, which are huge emitters of carbon dioxide. (He's a major investor in Calera, an alternative cement maker in Silicon Valley.)

One more area for potentially huge gains is to improve energy efficiency, such as lighting. Another legendary venture capital company, Kleiner Perkins, is also racing to develop renewable energy solutions and make a fortune. (Khosla is a former partner there.) Kleiner's efforts were profiled in a cover story in The New York Times Sunday Magazine recently

With the Obama administration, it will be interesting to see what new federal policies– tax, economic and regulatory– will be adopted to accelerate solutions and spur more investment during a double whammy of crises: the economic meltdown and climate change.

Listen to the Building Blocks Go Green radio report online.

You may listen to the "Cement – A Dirty Business" Radio report online, as well as find additional links and resources. Also don't miss our behind-the-scenes photos for this story.

Amy Standen is a Reporter for QUEST and Radio News at KQED-FM.