The four-day symposium, one of the most ambitious meetings ever held on wind, solar, hydro, biofuels and hydrogen, wraps up on Friday with a political declaration by ministers and senior officials from more than 150 countries.
There will also be a bulky "action plan" in which participants spell out their vision for increasing renewables' share of the world energy mix.
But ecologists said that behind-the-scenes haggling could dangerously water down these documents, ruining the best political opportunity in a generation to help wean the world off oil, a vulnerable commodity that on Tuesday spiked to a new record high.
The United States, supported also by Japan, France and Brazil, was trying to dilute terminology in the draft political statement about the commitment to renewables, one source said.
A similar row dogged the 2002 World Summit for Sustainable Development in Johannesburg, where the United States also pushed through a conservative energy agenda that rooted out any reference to timetables or market percentages.
As for the action plan, "we are seeing weak political commitment from the EU," WWF International spokeswoman Mitzi Borromeo told AFP.
"It looks as if the EU is failing in its commitment to go beyond 2010," she said, referring to the European Union's current goal of having renewables meet more than 22 percent of its energy needs by the end of the decade.
"The way things look at the moment, Asia could overtake Europe on its commitment to renewable energies."
She singled out China for praise, noting that Beijing is proposing a new law that would "practically double" renewables' share of the national energy supplies, which are heavily dependent on coal, and increasingly, on oil.
The Bonn conference gathers more than 3,000 representatives from corporations, consumers, environmental groups as well as policymakers.
Renewables account for just a tiny part -- only five percent -- of world energy supplies, according to International Energy Agency (IEA) figures for
That compares with 38 percent for oil, 50 percent for coal and gas, and seven percent for nuclear.
On current trends, the shares will be almost unchanged by 2030, even though fossil fuels have been condemned for driving climate change through carbon pollution.
One reason for this is that fossil fuels are well entrenched in the global economy. They can only be dethroned if oil prices remain high, giving the edge to renewable technologies that are still in their infancy and remain costly and relatively energy-inefficient.
The price of crude edged downwards in early London trading on Wednesday, with North Sea Brent swapping hands at 38.65 dollars a barrel for July delivery.
On Tuesday, Brent rocketed upwards by more than two dollars, smashing the 39-dollar mark for the first time since October 1990, in a movement driven by terror attacks in Saudi Arabia as well as the Iraq war and growing consumption by India and China.
In New York on Tuesday, crude surged 2.45 dollars to a record closing price of 42.33 dollars a barrel.