High oil prices and an array of government incentives are leading to soaring rates of investment in renewable energy, according to the United Nations' annual "Global Trends in Sustainable Energy Investment" report.

The UN report calculates global investment capital flows into renewable energy companies reached $100 billion for the first time in history last year. More than $30 billion of the total was the result of mergers and acquisitions led by investment banks such as JP Morgan and Goldman Sachs.

"The finance community has been investing at levels that imply disruptive change is now inevitable in the energy sector," says Eric Usher, Head of the Energy Finance Unit at the UN. Usher said the UN's "report puts full stop to the idea of renewable energy being a fringe interest of environmentalists. It is now a mainstream commercial interest to investors and bankers alike."

The huge investment flows mean that IPO's, largely dormant since the heady days of the technology boom nearly a decade ago, are now re-emerging. A trio of solar companies went public with impressive returns in 2007, including JA Solar (NASDAQ:JASO) , Trina Solar (NYSE:TSL) and Solarfun Power Holdings (NASDAQ:SOLF) .

In the wind power sector, regular CNBC guest analyst and IPO expert Francis Gaskins was the first to cover Nacel Energy (BULLETIN BOARD: NCEN) which has seen its stock soar more than 250% since IPO. Last month, Nacel Energy unveiled a major 80-megawatt wind energy expansion, including two new projects in Texas. Gaskins currently has $4 target on the company (Nacel Energy closed Friday at $2.79).