Clean tech has become a major destination for investors, from venture capital firms to ordinary shareholders. The large and diverse sector, which covers everything from energy to transportation to construction, touches all sorts of industries and often blurs with other areas. Clean tech, like green, was once closely associated with the socially responsible investing movement, but its sheer size today has created a wealth of investment vehicles in alternative, as well as concepts such as energy efficiency and storage.

Here’s a look at the largest funds, based on market capitalization. (Data is from Morningstar).

Not surprisingly, many of the select, top holdings include clean-tech industries such as solar, global water resources, fossil fuels alternatives, wind energy, global warming and carbon emissions. The timing couldn’t be better as some analysts forecast $5 retail gasoline by the summer, as crude oil prices remain well over $100 a barrel.

But because clean-tech investing can be volatile, investment strategists generally advise dipping into this space as part of a larger, diversified portfolio plan.

Click ahead to see 10 select, large ETFs with a strong focus on clean-tech holdings. The data are based on one-year trailing returns as of Jan. 31.

By Heesun Wee
Posted 01 March 2012

Fund size: $908.8 million
1-year trailing total return: -3.4 percent
5-year trailing total return: 0.83 percent
Select top holdings: Pentair, Calgon Carbon, Pall

Fund size: $256.1 million
1-year trailing total return: -9 percent
5-year trailing total return: NA
Select top holdings: Hyflux, Arcadis, Kurita Water Industries

Fund size: $218.1 million
1-year trailing total return: - 43.5 percent
5-year trailing total return: - 19.9 percent
Select top holdings: Suntech Power Holdings, JA Solar Holdings, AMSC, STR Holdings

Fund size: $193 million
1-year trailing total return: +1.6 percent
5-year trailing total return: NA
Select top holdings: Geberit AG, United Utilities Group, Severn Trent, American Water Works

Fund size: $107.7 million
1-year trailing total return: -13.2 percent
5-year trailing total return: -1.5 percent
Select top holdings: Schneider Electric, Pall, First Solar

Fund size: $90.2 million
1-year trailing total return: - 61.8 percent
5-year trailing total return: NA
Select top holdings: GCL-Poly Energy Holdings, First Solar, GT Advance Technologies

Fund size: $89.8 million
1-year trailing total return: - 33.9 percent
5-year trailing total return: NA
Select top holdings: LSB Industries, Renewable Energy, First Solar

Fund size: $66.6 million
1-year trailing total return: +3.5 percent
5-year trailing total return: NA
Select top holdings: Basic Sanitation Company of the State of Sao Paulo (Brazil), Mueller Water Products, American Water Works

Fund size: $63.8 million
1-year trailing total return: -40.2 percent
5-year trailing total return: NA
Select top holdings: Cooper Industries, Kurita Water Industries, Enel Green Power

Fund size: $29.3 million
1-year trailing total return: - 21 percent
5-year trailing total return: NA
Select top holdings: Vestas Wind Systems, Greentech Energy Systems, China WindPower