As the Climate Change talks get underway in Copenhagen this week, there is much attention focused on alternative energy sources that produce little or no greenhouse gas pollution.  Some of these energy sources - like wind, solar, biomass and geothermal - are also attractive because they are renewable and offset the need for imported oil, gas or coal.  But, it will be a long time before any of these energy sources will be a large-scale alternative to fossil fuels.

Most analysts regard non-fossil fuel-based energies as a supplement rather than as an alternative to traditional energy sources.  Even though their development is expanding rapidly, they provide less than one percent of energy needs.

At a recent talk at the James A. Baker Institute for Public Policy at Rice University in Houston, Ambassador Richard Jones, Deputy Executive Director of the International Energy Agency, assessed future energy supplies and demand.

"Modern renewable energy technologies grow," said Richard Jones. "In fact, they see the fastest rate of increase.  But their share of total energy use is so small today that even by 2030, they are only taking about [providing] two percent [of the energy consumed worldwide]."

But in some green communities around the world, eco-friendly energies are beginning to replace fossil fuels.  In Austin, the capital of Texas, renewable energies are having a major impact.  This fast-growing city gets about a tenth of its electrical power from wind turbines in the western part of the state.

Roger Duncan is General Manager of the electrical utility, Austin Energy.

"We get somewhere between 10 and 12 percent of our energy from renewable energy and the remainder from coal, nuclear and gas," said Roger Duncan. "We have plans going forward to get 30 percent of our energy from renewables by the year 2020."

Most power generation in Austin will depend on fossil fuels like coal and natural gas for decades to come. But Duncan says that as those fuels become more expensive, the outlook for renewables improves.

"Fossil fuels are cheap today, but rising in cost," he said. "And we expect them to rise further in the future because of carbon constraints.  Some of the renewables are expensive today, but are dropping in cost.  And we expect in a few years, or a decade at least, for them to drop substantially in cost."

But at least some of the cost of renewables today is offset by government subsidies that are far higher as a percentage for each unit of energy produced than subsidies for oil, gas and coal.

But Baker Institute energy economist Ken Medlock says the public needs to understand that development of alternative energy through government programs is not free.

"It is going to cost something to do this," said Ken Medlock. "And at the end of the day, if you push too hard, the cost only rises.  And who ends up paying for that?  Well, it is you and me."

Medlock says development of renewable sources of energy makes sense because fossil fuels will not last forever.  But he adds that government should take a different approach.

"If we were to target funds at R&D - basic research and development - rather than implementation of technology that is not quite there yet, I think in the long run we would be much more successful," he said.

In the coming decades, Medlock says, the United States can use as a transitional fuel abundant natural gas that burns 50 percent cleaner than coal.  But, he says, rapid advances in the effectiveness of technologies such as solar energy could shorten that time frame.

"At some point, it becomes commercially competitive," said Medlock. "And when that happens, we do not need policy to pick solar versus something else because solar will win out."

Medlock and other experts say there is a major alternative to both fossil fuels and renewables - the conservation of energy through more efficient vehicles, better constructed homes and office buildings, and better methods for monitoring energy use.