August may not be the month when investors finally reach consensus that "green" investments are for real. But the gains enjoyed in August by a half dozen alternative energy exchange-traded funds might attract some converts to the notion that they could one day be a permanent part of the investment landscape. While the Standard & Poor's 500 struggled to hold onto a gain of 1.2% in August and the only traditional energy funds that advanced were of the "inverse" variety, the six alternative energy funds in the accompanying table enjoyed gains of at least double the magnitude of the S&P. The advances in August of the alt-energy ETFs represented major reversals from setbacks the group had suffered earlier this year. The stated objective of the Claymore/MAC Global Solar Index ETF ( TAN) is that it "seeks investment results before fees and expense that correspond generally to performance of the MAC Global Solar Energy Index, which comprises 25 stocks selected based on the relative importance of solar power." It was one of two ETFs that turned negative performances from earlier months into double-digit gains in August. The First Trust NASDAQ Clean Edge U.S. Liquid ETF ( QCLN) "seeks investment results that correspond generally to the price and yield of an equity index called the NASDAQ Clean Edge U.S. Liquid Series Index before fees and expenses the fund." The gauge is designed to track the performance of companies that are primarily manufacturers, developers, distributors, or installers of clean-energy technologies. The iPath Barclay Capital Global Carbon Total Return ETF ( GRN) is "designed to measure the performance of the most liquid carbon-related credit plans and is designed to be an industry benchmark for carbon investors." Each carbon-related credit plan included in the Barclays Capital Global Carbon Index Total Return is represented by the most liquid instrument available in the marketplace.