The greenback has been in freefall over the past several months, as low interest rates and rumors of international reserve fund diversification drew confidence away from the U.S. currency. We see the PowerShares DB US Dollar Index Bullish ETF (NYSE:UUP) sagging steadily towards a 10% 3-month decline in the chart below.

Oil, which is traded in US dollars, has wobbled in the meantime, as reflected by the United States Oil Fund ETF (NYSE:USO). 

What's especially interesting in this index race right now is the neck-and-neck coupling of the PowerShares Wilder Hill Clean Energy ETF (NYSE:PBW) with the broad S&P 500.

The S&P has roared upward on economic optimism and relatively strong earnings from industrial titans like Alcoa.

And both the S&P and PBW have drawn serious market premiums above USO since early September.

Should oil rise further on increased demand expectations, expect to see renewed separation of renewable energy ETFs from the U.S. benchmark.

As for the dollar's impact on clean energy funds, more investors are turning to international companies that do business in euros, yen and yuan to pad their energy portfolios agains the bottoming buck.

-Sam Hopkins