Venture capital investing in clean energy grew by almost 70 percent in 2006, to $18 billion, according to research firm New Energy Finance. And more than $10 billion was invested in companies and projects in the first half of 2007.

The group tracked more than 1,800 investors worldwide and recorded 193 funds that invest in clean energy.

Investment was highest in North America, with most of it going toward biofuels. In Europe private equity investment growth was strong, and in Asia investment was driven by pre-IPO investments in Chinese solar companies

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Indonesia's biofuels program makes use of palm oil.

Looking at various industries, the investments broke down into $8.4 billion for wind, $4.7 for biofuels and $2.3 billion for solar, which together made up 86 percent of the total venture capital / private equity investment.

The report is available on New Energy Finance's website. It's called "Cleaning Up 2007."