Earth Day may be one day a year, but for some funds it's been Earth Day all year.

Anyone not convinced that environmental green can equate to monetary green should take a look at the top of the open-end equity mutual fund performance rankings for the first quarter of this year.

The top-performing fund for the first three months of 2007 was the

(GAAEX) - Get Guinness Atkinson Alternat Energy Report

Guinness Atkinson Alternative Energy Fund (GAAEX) with a blistering gain of 14.46% for the period. The sixth spot was captured by the

(NALFX) - Get New Alternatives Fund A Report

New Alternatives Fund (NALFX), another fund largely committed to alternative energy which rewarded its holders with an early Earth Day present of an 11.89% first-quarter return.

Alternative energy sources include those using solar, wind, hydroelectric, tidal wave, geothermal biomass or biofuels to generate power. In addition, other technologies have become an important weapon in achieving energy efficiency.

In order to see how other U.S. open-end funds are participating in the alternative energy sector, we searched TheSteet.com Ratings database to examine portfolio holdings in selected alternative energy stocks. The stocks we chose are the eight with the highest domestic weightings in the WilderHill New Energy Global Innovation Index. The components of the index are primarily international, with only a few U.S. constituents.

The selected alternative energy stocks, along with summaries of holdings by U.S. open-end funds, appears in the table below. Fund holdings of the eight companies rank from a low of 6.2% of the shares in

First Solar

(FSLR) - Get First Solar, Inc. Report

to a high of 22.6% in

Energy Conversion Devices'

(ENER)

outstanding shares.

While larger companies may have divisional activities in alternative energy, the funds in the table, in the opinion of the WilderHill New Energy Global Innovation Index, are most heavily dedicated to that singular effort.

The open-end list of funds are ranked by return performance for the first quarter of 2007. A total of 598 funds have positions in at least one of the eight firms, with the

(THCGX) - Get Thornburg Core Growth A Report

Thornburg Core Growth Fund (THCGX) having the biggest commitment, a total of 6.7% of its portfolio in two of the eight stocks.

Aggregate holdings of U.S. funds in the eight stocks amounts to $446 billion, which amounts to 15.2% of the group's aggregate market value of $29.27 billion.

Because technology is an inherent component in the development of alternative energy --

Energy Conversion Devices

TheStreet Recommends

(ENER)

being a prime example -- four technology funds are among the top-20 top percentage holders of the eight stocks.

Even though the Guinness fund holds only two of the domestic alternative energy stocks amounting to 3.62% of its portfolio, it is the purest play for that sector of all current open-end funds. Its total portfolio holdings are spread among 14 countries, with only 21.12% of its portfolio invested in U.S. stocks.

Like the Guinness fund, the New Alternatives Fund is largely international in focus; this helps explain why it holds only two of the domestic stocks in the table.

In addition, two alternative energy exchange-traded funds are the

PowerShares WilderHill Clean Energy Portfolio

(PBW) - Get Invesco WilderHill Clean Energy ETF Report

and the

PowerShares WilderHill Progressive Energy Portfolio

.

(PUW)

The former focuses on clean energy, while the latter invests in a basket of stocks that focus in "transitional energy bridge technologies, with an emphasis on improving the use of fossil fuels."

The PowerShares WilderHill Clean Energy Portfolio, which has been around since March of 2005, ranked 16th out of 377 ETFs during the first quarter of 2007, with a total return of 9.06% for the period. The portfolio, which debuted in October of 2006, returned 4.34% during the first quarter. Its portfolio includes

Tenneco

(TEN) - Get Tenneco Inc. Class A Report

,

Toyota

(TM) - Get Toyota Motor Corp. Sponsored ADR Report

and

Honda

(HMC) - Get Honda Motor Co., Ltd. Sponsored ADR Report

.

Richard Widows is a financial analyst for TheStreet.com Ratings. Prior to joining TheStreet.com, Widows was senior product manager for quantitative analytics at Thomson Financial. After receiving an M.B.A. from Santa Clara University in California, his career included development of investment information systems at data firms, including the Lipper division of Reuters. His international experience includes assignments in the U.K. and East Asia.