Alternative energy exchange traded funds, including the PowerShares WilderHill Clean Energy Portfolio (NYSEArca: PBW) and First Trust NASDAQ Clean Edge Green Energy Index Fund (NasdaqGS: QCLN), have struggled mightily this year against the backdrop of tumbling oil prices, but investors might want to revisit green energy funds.

The greater regulation on fossil-fuel power plants should be a boon for the alternative, clean energy industry. However, the continued weakness in green ETFs suggests that Wall Street believes poor fundamentals over the short-term currently outweigh the long-term benefits of the new proposal. Tighter fossil-fuel regulations could eventually work in favor of solar ETFs, including the Guggenheim Solar ETF (NYSEArca: TAN) and the Market Vectors Solar Energy ETF (NYSEArca: KWT).

Some market observers argue that the lighter wind should be a catalyst for renewable energy investors to gain exposure in diverse places. Investors should look beyond a single firm or region in the nascent industry. Investors, though, can instantly diversify across the clean energy space through a broad ETF. For instance, PBW and QCLN include a range of alternative energy companies, including those engaged in solar photovoltaics, biofuels and advanced batteries. [Renewable Energy ETFs Look Like a Good Long-Term Play]

“Green-energy prices have been falling rapidly, as well. The cost of the solar systems bought by consumers has declined 15% a year over the past eight years, and Deutsche Bank analysts expect costs to fall another 40% over the next four to five years. But while coal and natural-gas prices will rise again at some point, green energy is likely to just get cheaper,” reports Lewis Brahm for Barron’s.

Many firms have already been investing into clean energy projects in recent years. For instance, Citi wants to allocate $100 billion to environmental finance over the next 10 years and Wells Fargo has invested $52 billion in environmental efforts since 2005.