Renewable energies such as wind or solar power are set to surge by 2050 and expected advances in technology will bring significant cost cuts, a draft United Nations report showed on Wednesday.

The most comprehensive UN overview of the sector to date said renewables excluding bioenergy, which is mainly firewood burnt in developing nations, could expand by three to 20 times by mid-century.

"The cost of most renewable energy technologies has declined and significant additional technical advancements are expected," the Intergovernmental Panel on Climate Change (IPCC) said, based on a review of 164 expert scenarios.

"Further cost reductions are expected, resulting in greater potential for climate change mitigation and reducing the need for policy measures to ensure rapid deployment," the draft said.

It said most scenarios pointed to a "substantial increase in the deployment of renewable energy by 2030, 2050 and beyond."

No one single technology was likely to come to dominate and the expansion was likely to continue even without new measures to promote a shift from fossil fuels as part of a U.N.-led fight against climate change, it said.

UN talks on a new deal to combat global warming have made little progress. A summit in Copenhagen in 2009 failed to agree a binding treaty to combat global warming, blamed by the IPCC mainly on emissions from burning fossil fuels.

A copy of the summary for policymakers, obtained by Reuters, will be edited at an IPCC meeting in Abu Dhabi starting on Friday and published on May 9. It is based on a 900-page IPCC Special Report on Renewable Energy Sources.

The summary for policymakers is due to guide governments, investors and companies in coming years.

The draft, written by some of the world's leading experts before Japan's nuclear disaster, also said that renewables were likely to have a bigger share of the world's low-carbon energies by 2050 than nuclear power and fossil fuels from which greenhouse gases were captured and buried. – Reuters