With the iShares Dow Jones U.S. Industrials ( IYJ) up about 5% this year, it makes sense for PUW to be up as well, given that it owns industrials that are also found in IYJ. Unfortunately for investors looking to invest in this alternative energy leader, PUW has meager volume of about 10,000 shares per day. Therefore, while PUW looks to be the best of the alt-energy bunch right now, eager investors should be wary of the fund's low liquidity, as during the "flash crash" this past May, PUW briefly plummeted to 14 cents per share. For now, better bets may be found in the natural gas sector , which is considered by many to be a bridge fuel. Overall, with potential federal legislation hanging over the sector, alternative energy ETFs look to be a murky area of investment in the near future. -- Written by Don Dion in Williamstown, Mass.