"Renewable fuels and clean energy, a sector beaten down hard since last fall, are now primed for a major comeback," says Eric Roseman, editor of The Commodity Trend Alert. Here's his top ETF play on the sector.

"With every passing day the price of crude oil rises, the secular trend to alternative energy becomes even more powerful. Consumers, companies and governments are now sick and tired of soaring energy prices.

"The long-term solution is to obviously reduce our dependence on oil and increase our consumption of renewable fuels like wind, solar, and nuclear energy.

"The bull market in alternative energy began in 2005 when a host of companies in this thriving sector went public, supported by government subsidies, especially in Germany and Spain. Interestingly, Germany and Spain have just reduced solar energy subsidies this spring.

"In my view, those subsidy cuts don't matter at this stage. When companies in the solar sector are making money, why should governments continue subsidizing them?

"For those who want to 'go green' there are new opportunities to tap the environmental trend by adding cutting edge, alternative energy ETFs to your portfolio," says Doug Fabian, editor of Successful Investing.

"ETF providers are starting to latch onto the green theme. Two fund families, PowerShares and Market Vectors, have created their own classes of clean energy ETFs. A pair of ETFs has been launched in the narrow but potentially profitable niche of solar energy.

"The Claymore/MAC Global Solar Energy Index ETF (NYSE: TAN) is designed to track 25 companies in the solar power industry. Sectors included in the ETF are equipment producers, companies that concentrate on selling electricity, and suppliers of materials or services, installation, integration or finance. TAN currently invests in companies such as MEMC Electronic Materials, Suntech Power Holdings, and LDK Solar Co. Ltd.

"Van Eck Global launched the Solar Energy ETF (ASE: KWT). That solar energy ETF seeks to replicate the price and yield performance of the Ardour Solar Energy Index, which includes companies that generate at least 66% of their revenues from solar energy. The four top holdings are First Solar, Germany's Q-Cells and Solarworld AG, and Norway's Renewable Energy.