The electric system at mid-century will have a lot more renewable energy than it does today, but coal and nuclear power together will still supply two-thirds of the energy, according to a new study from the Electric Power Research Institute, a consortium supported by both government- and investor-owned utilities.

Coal-fired plants will likely be capturing and storing their carbon dioxide — so-called “clean coal” — and the exact mix between coal and nuclear will depend on construction and carbon sequestration costs, according to the study.

Wind and biomass, meanwhile, will supply about a quarter of the electricity, while solar power will not play a significant role, the study predicts. “It just doesn’t enter into our equation,” said Revis W. James, the director of the institute’s Energy Technology Assessment Center.

Of course, as the physicist Niels Bohr famously observed, “Prediction is very difficult, especially about the future.” Last year the Energy Department produced a report that said that wind alone could produce 20 percent of the country’s energy by 2030. And various advocates say a substantial share could come from solar photovoltaic cells, which make electricity directly from light, or solar thermal systems, which gather the sun’s heat to boil water. Geothermal energy and energy from ocean waves or temperature differences are also candidates.

But wind and biomass are the only ones likely to have a cost low enough to compete — at least in the near term, Mr. James said.

The institute is pushing for a broad research program to lower the costs of carbon capture and of low-carbon energy production, and has published two reports — one on where costs stand now, and another on how the mix would vary under various cost levels for carbon storage and for reactor construction.

One way that power plants are compared is by price per kilowatt of generating capacity — roughly the amount needed to run a window air-conditioner.

For nuclear power, the institute has been using $4,000 a kilowatt, but Mr. James noted that Moody’s, the debt-rating agency, recently predicted $6,000. At the lower construction price, the cost per kilowatt-hour (the amount that the window air-conditioner would consume running for an hour on a hot day) is about 6.4 cents. At the higher price it is 9.4 cents. (For comparison, in 2007 the average generating cost for the United States was 6.6 cents.)

But $6,000 a kilowatt is hardly a ceiling. The institute notes that some reactors built in the 1980s came in even higher. So the study also models the results at $8,700 a kilowatt of capacity, which would mean 12.2 cents a kilowatt-hour.

For coal, the cost to sequester carbon dioxide is likely to be determined by the number of places approved for underground storage of that compound — and how much it would cost to build a pipeline to pump the material to those sites.

Costs could be lower if the carbon dioxide could be sold to oil producers, who already use it for oil production (they pump it underground in old oil fields to force out oil that cannot be recovered by conventional means).

But, said Mr. James, that financial advantage might not be around very long because the volumes carbon dioxide from power plants would be so large they would quickly depress the market.

And, of course, the relative competitiveness of any future energy resource will depend on another uncertain factor: How much it will cost to emit carbon dioxide into the atmosphere. Congress will soon consider putting a cap on emissions and making industries buy the right to emit, but the dollar price that would result from any particular cap are highly uncertain.