Proponents of alternative energy and energy efficiency were elated on Thursday by President-elect Barack Obama's economic stimulus speech, but some analysts warned his energy agenda could hit turbulence in Congress or from the slow economy.

Mr Obama asked Congress "to act without delay" to pass legislation that included doubling alternative energy production in the next three years and building a new electricity "smart grid."

He said he also planned to modernise 75 per cent of federal buildings and improve energy efficiency in two million homes to save consumers billions of dollars on energy bills.

Billionaire oil investor T. Boone Pickens said Mr Obama's plan would help kickstart the slow economy.

"Investing in alternative energy, focusing on conservation and rebuilding our power grid to deliver that energy to every corner of our country are critical components of this effort," said Mr Pickens.

"President-elect Mr Obama's prescriptions will address the twin challenges of an ailing economy and the threat of global warming," the League of Conservation Voters said.

Some analysts questioned Mr Obama's ability to boost spending on higher-cost renewable fuels during a recession.

"It will be more difficult to meet the alternative fuel goals if oil prices keep falling and we are in a recession," said Phil Flynn, oil analyst with Alaron Trading in Chicago.

It will take political finesse to implement the plan, said Tim Evans, an energy analyst at Citigroup in New York. Solar stocks climbed after Mr Obama said his economic recovery plan would result in more jobs building solar panels.

The solar industry is ready to create jobs as soon as funding from the stimulus plan comes through - in hard-hit manufacturing areas like Ohio and Michigan, said Rhone Resch, president of the Solar Energy Industries Association.

Not everyone cheered Mr Obama's plan. Private companies could use domestic energy resources like oil and coal to create jobs without the hefty price tag for taxpayers, said Thomas Pyle of the Institute for Energy Research, in a statement.

"The road to economic recovery will be paved with private sector investment, not government-sponsored asphalt," he said.

Factbox - What is a smart grid?

"Smart grid" describes a more efficient, cost-saving method of moving electricity along major long-distance transmission lines to local distribution power lines and disparate end-users in homes, businesses and schools.

Smart grid advocates say utilities and customers will realise cost savings in the long run, despite the high roll-out costs.

In a smart grid, computers and sensors, installed at power plants, substations and along power lines, would signal control centres that would better manage the flow of electricity. For instance, computers would detect transmission bottlenecks and direct power around them.

Power outages are now monitored as customers call local utilities to report them. Smart grid computers would discover outages automatically.

"Smart meters" would be installed to replace conventional electricity meters. Cutting demand during peak hours would reduce the need for capital spending on more power plants, substations and power lines.

The meters combined with smart appliances would make it possible to control and regulate appliances remotely.

Proponents say "smart" technology also will help renewable power sources like solar panels and solar power plants and wind farms integrate into the overall transmission system.

Conventional power grids have difficulty with the intermittent nature of solar and wind power.

After year-long study of smart grid technologies in the Pacific Northwest, US officials and IBM estimated customers saved 10 per cent on monthly power bills and cut power use by 15 per cent.

If those figures could be realised nationwide, it could save between €51 billion and €88 billion in spending on new power plants and transmission lines, the study found.