Wind and solar power could produce 40 percent of the world's electricity by 2050, but only if government subsidies are secured for the next two decades, scientists said on Wednesday.

The technologies will each need global support totaling 10 billion to 20 billion euros ($12.76 billion to $25.51 billion) per year, said Peter Lund, professor in advanced energy systems at Helsinki University of Technology.

Without financial and political support, he said wind and solar power would only account for less than 15 percent of the world's energy output.

With favorable conditions, solar and wind energy could be replacing coal, which is the worst enemy for us. We have to give them political preference, as it used to be done for nuclear energy in the 1970s, Lund told the International Scientific Congress on Climate Change in Copenhagen.

He said with a strong deployment programme and supportive policies, wind power could break even between 2020 and 2025, while solar power could break even closer to 2030.

In November, the International Energy Agency said if the world managed to limit global warming to 2 degrees Celsius by 2030 -- a scenario many scientists already see as hopeless -- renewable sources of energy would account for 40 percent of global electricity generation.

To limit warming to 3 degrees, renewables would make up 23 percent of global power generation.

Scientists said intermittent electricity such as that from wind is now still 50 percent more expensive compared to baseload electricity from coal or nuclear.

We need policies that promote investment in supply chains to avoid long waiting times and price spikes, said Anthony Patt, a researcher at the International Institute for Applied Systems Analysis in Laxenburg, Austria.

To fully exploit the potential of wind and solar power, electricity grids will have to be modernized and national electricity markets will have to be integrated, scientists said.

We have a huge challenge ahead of us in integrating different sources of intermittent power, said Poul Erik Morthorst, a scientist at the National Laboratory for Sustainable Energy in Riso, Denmark.

Eventually, the subsidies will lead to cheaper electricity when wind and solar power become commercially viable, Lund said.

We could have 25 percent of our power come from wind and 15 percent from solar, he said. Without support, by 2050 we will only have 10 percent from wind and 5 percent from solar, which means that these technologies will be fully marginalized.

(Editing by Katie Nguyen)

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