The top-six and seven of the top-10 best non-leveraged sector ETFs in terms of year-to-date performance have something in common: Exposure to alternative energy stocks. Whether it is wind or solar, or some of combination of multiple clean energy themes, non-traditional energy ETFs have soared this year.

The First Trust NASDAQ Clean Edge Green Energy Index Fund (NasdaqGS: QCLN) is one of those funds. Unheralded compared to some of the other high-flying sub-sector ETFs, QCLN has been a star performer in its own right with a year-to-date gain of nearly 50%. [Clean Energy ETFs Are Cleaning Up]

Clean energy ETFs have been bolstered by a variety of factors, including President Obama’s Climate Change Action Plan. High oil prices along with issues surrounding global warming and high levels of carbon and greenhouse gas emissions have continued to boost the sector. Then there is a favorable long-term outlook that implies new annual investment in renewable power capacity will rise 2.5 to 4.5 times more between now and 2030.

It is fair to say those have been among the fundamental factors that have helped lift QCLN this year. At a more tangible level, investors can point to a few of the ETF’s 36 holdings that have been significant contributors to the fund’s 2013 upside. A prime example is Elon Musk’s electric car maker Tesla (NasdaqGM: TSLA). QCLN has an 11.4% weight to that soaring stock, one of the largest allocations to Tesla of any ETF. [Musk’s Rises Jolts These Small ETFs]

QCLN status as a “Tesla ETF” has helped the fund attract assets. When we highlighted the fund in late May, it had about $42 million in AUM, 20% of which had been poured into the fund in the previous 60 days. QCLN had $61.1 million in assets as of August 15, according to First Trust data.

Solar stocks have also been important contributors to QCLN’s upside as that group represents over 20% of the ETF’s weight. First Solar (NasdaqGM: FSLR) and SunPower (NasdaqGM: SPWR) are both top-10 holdings in QCLN, combing for 10.4% of the ETF’s weight.