NEW YORK ( TheStreet) -- ETFs that invest in alternative energy have been crushed. During the past three years, Market Vectors Solar Energy ( KWT) fell 38.4% annually, while First Trust Global Wind Energy ( FAN) fell 17.2%, according to Morningstar. Producers of solar panels and wind turbines struggled to match cheap competition from China and other countries, triggering much of the collapse. In addition, low natural gas prices have made consumers less eager to adopt alternative energy.Can wind and solar stocks revive anytime soon? Maybe not. Many companies remain on shaky ground. Hundreds of alternative energy companies have shuttered their doors in the past year, and more are likely to follow. But there is a steadier way to bet on greener technologies: PowerShares WilderHill Progressive Energy Portfolio ( PUW). The PowerShares ETF does not hold solar or wind businesses. Instead, it focuses on companies that are working to make traditional energy systems more efficient. Holdings include companies that reduce coal emissions and produce efficient cars.