SAN FRANCISCO (MarketWatch) — Solar power could be the world’s largest source of electricity by 2050, eclipsing fossil fuels and other clean-energy sources, the International Energy Agency said in a report Monday.

The IEA, an energy watchdog for mostly developed countries, added that solar-panel systems and concentrated solar power plants combined could generate 16% and 11% of the world’s electricity by then.

“The rapid cost decrease of photovoltaic modules and systems in the last few years has opened new perspectives for using solar energy as a major source of electricity in the coming years and decades,” IEA executive director Maria van der Hoeven said in a statement.

Both technologies, however, are capital intensive, with most of their expenses made upfront. Lowering the cost of capital for solar enterprises is key, the agency said.

The IEA, which said its report spelled out a roadmap for solar power, but not a prediction, called on governments and policy makers to strive for consistent policies to support solar. They would thus lower the risks for potential investors in solar and inspire confidence about it in the capital markets, the IEA said.

Meanwhile, shares of solar companies were mostly mixed on Monday in New York. Top decliners included U.S.-listed shares of Trina Solar Ltd. US:TSL, a China-based solar-panel maker.

Solar installer SolarCity Corp. SCTY, +7.36% shares declined 2.1%. Shares of SunPower Corp. SPWR, +2.22% , a solar-power developer, were off 1.2%.

Shares of developer SunEdison Inc. US:SUNE bucked the trend to rise 2%.

SunEdison said Monday it had filed a draft registration statement to launch a new “yieldco,” or a spinoff that acts as a holding company for existing and new solar projects, in emerging markets, primarily in Asia and Africa.

The news comes after SunEdison’s successful initial public offering of its TerraForm Power Inc. US:TERP yieldco in July. Terraform shares soared 35% on their debut on the Nasdaq.