Developers and financiers will invest $1.9 trillion building clean-energy power plants worldwide from 2012 through 2018 as demand for electricity increases, according to The Pew Charitable Trusts.

Development costs for solar and wind farms and other types of renewable-energy plants will increase to $327 billion in 2018 from about $200 billion last year, according to a report posted on Pew’s website today.

Those figures may increase even more if governments establish national energy policies that include commitments for renewable power, Phyllis Cuttino, director of the Pew Clean Energy Program in Washington, said yesterday in a telephone interview. The incentives should have defined durations to give the industry clarity.

“Policy does matter,” she said. “You have to have a renewable-energy target or a standard. Or something in the tax code. Or eliminate market barriers. There are different policies you can use to get there, but you’ve got to do something. You can’t just have no national energy policy.”

Global energy consumption is expected to increase 47 percent from 2010 to 2035, and cumulative investment in the renewable-energy industry may approach a $5.9 trillion over the same period, according to the report, which was prepared by Pike Research LLC.

“Industry has said very clearly to us, ‘What we need is, we need to have certainty,’ ” Cuttino said. “There has been an unlevel playing field, tilted in favor of incumbent technologies. And we need to get over that hump.”

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