Exchange traded funds that track the solar industry experienced another quarter of robust returns, building upon their first quarter outperformance after years of lagging behind the overall markets.

The Guggenheim Solar ETF (NYSEArca: TAN) surged 44.9% since the start of April, and the Market Vectors Solar Energy (NYSEArca: KWT) gained 27.9% in the second quarter.

Solar ETFs are generating high returns as the industry outshines expectations that a string of negative factors would weigh on solar stocks. Top solar panel producers have provided better-than-expected guidance for the rest of the year. [Solar ETF Rallies Over 50% in a Month]

Looking ahead, the International Energy Agency recently stated that renewable energy could generate more electricity than nuclear reactors and natural gas powered utilities by 2016, reports Ehren Goossens for Bloomberg.

The IEA projects that wind, solar, bioenergy and geothermal power could expand 40% over the next five years, or double the 20% growth in 2011.

“Renewable power sources are increasingly standing on their own merits versus new fossil-fuel generation,” IEA Executive Director Maria van der Hoeven said, in the article. “Many renewables no longer require high economic incentives.”