Ethical bank Triodos, a Netherlands-based bank with over 3.3 billion euros (US$5.2 billion) in assets, has been investing in wind projects since it turned against nuclear power after the 1986 Chernobyl power station disaster.

"The appetite is there, the market is there, the growth will be surprisingly fast," Triodos Renewables operations director Matthew Clayton said.

His fund hopes to raise 8.5 million pounds (US$16.6 million) through a prospective share issue, up to 20 percent of which will be invested in marine power and other fledgling sustainable energy projects, with the rest in wind.

"From the business plans and technology we have been reviewing, and given the learning the wind and hydro sectors can offer the marine technology sector, there is going to be a lot of leapfrogging," said Clayton.

"Marine power is a maximum of five years behind wind."

UK-based Triodos Renewables, which operates 24 MW of wind capacity in the UK, has looked at 30 wave and tidal investment opportunities in the past two years.

It invested 1.8 million pounds in Marine Current Turbines, which has created a tidal device that uses underwater blades similar to wind turbines.

"There will be 3-6 marine technologies that work and which will be there in the long-term, from the 30-40 currently, and that process of selection is happening," said Clayton.

Wave and tidal power will catch up with wind quickly because the UK government has promised to double financial support for marine power from April 2009, through its so-called Renewable Obligation Certificate system of guaranteed payments.

The government will give twice the financial support for each megawatt of marine electricity compared to onshore wind.

Triodos Renewables fund has delivered 7 percent returns to its shareholders, on a compound annual growth rate, since 2005.

Triodos's fund will use the money to develop and acquire at least 27 MW of extra electricity producing capacity, more than doubling its existing wind portfolio.

Marine Current Turbines (MCT) is presently testing a 1.3 MW tidal system in Northern Ireland's Strangford Narrows and hopes to have it supply electricity to the grid by July this year.

Stephanie Merry, a spokeswoman for the Renewable Energy Association, an industry group, said the sector was at the same stage of development as wind was in the early to mid-1980s -- but that did not mean marine was two decades behind wind.

With the first grid-connected projects coming on line soon -- such as MCT in Strangford Loch, Northern Ireland, Pelamis in Portugal, and OpenHydro at the European Marine Energy Centre off Orkney -- she believes it will be 10 years before marine systems have the same electricity-producing capacity as the current crop of wind systems. (Editing by David Cowell)