Investors pumped more than €2 billion into green energy companies in Europe and the US last year, a new study says.

The report says clean energy projects in the US, Europe and Israel attracted $3.1 billion (€2.3 billion) from venture capitalists and other investors in 2006.

This was almost 30 per cent ahead of the $2.3 billion that was invested in the sector in 2005.

The report, produced by Cleantech Network, a US-based organisation of investment houses, venture capital funds and industry players, says solar power attracted $452 million from investors, while biofuels accounted for more than $800 million.

Cleantech also mentions Irish wind energy company Airtricity, which it said raised $290 million in "follow-on finance" investments last year.

However, Airtricity, headed by businessman Eddie O'Connor, said yesterday that it could not reconcile the figure with numbers published in its 2006 annual report.

That document states that the company raised €310 million in equity and €151 million in debt last year.

The cash will be used to fund wind farms, which generate electricity from wind turbines.

Cleantech says the UK and California are hubs for green energy investment. Most of the development activity took place in western Europe and on the west coast of the US.

A total of 53 clean technology companies held initial public offerings (IPOs) and floated on stock markets during the year.

"London's Alternative Investment Market led the exchanges with 21 offerings. Nasdaq floated 10 IPOs and Frankfurt eight," the report says.

According to earlier reports from the same organisation, a number of big US pension funds, key players in American and world markets, have begun investing large sums of money in the clean technology and green energy sectors.

The California Public Employees Retirement System has invested $700 million in these industries and the California State Teachers Retirement System has placed $188 million.

Similar funds from New York and Oregon have also increased their exposure to these businesses.

Cleantech recently produced estimates showing that the level of investment in these sectors in the US alone could hit $17 billion by 2009.

The organisation said more state pension providers were planning to start allocating some of their funds to clean technology.

Cleantech's members are largely drawn from the venture capital, fund management and advisory industries.