You can't really complain about the returns in any clean energy ETF over the past few months...

A quick quarterly calculation of QCLN, PBD, PBW, GEX, FAN, and TAN—all exchange-traded funds comprised of U.S. and foreign-listed clean energy stocks—shows that each and every one of those tickers has returned better than 40%.

That's compared to just around 18% for the Dow. Again, that's nothing to sneeze at if you're into broader market index ETFs.

But it's not the best you could do, either.

For the best of the international clean energy ETF world right now, you've got to look at one of the specific sector ETFs that have popped up in recent years.

As different clean energy technologies gain steam, companies go public, and volume accumulates.

The Claymore/MAC Global Solar Index ETF (NYSE:TAN) has used robust average volume of over 500,000 to boost its share value to nearly $9.60, up from a March 9 low of just $4.68.

Being a global fund, TAN holds not only American market cap giant First Solar (NASDAQ:FSLR) but also Germany's Q-Cells (FRA:QCE), which operates in the low-cost eastern German manufacturing base and supplies modules all over Europe and the world.

TAN gained 75% in the three months through May 26.

-Sam Hopkins