Lo, a smart grid! The Left's energy miracle turns out not to be that.(president Barack Obama's policy on renewable energy)

'WE will build the roads and bridges, the electric grids and digital lines that feed our commerce and bind us together," President Obama promised in his inaugural address. "We will harness the sun and the winds and the soil to fuel our cars and run our factories."

He wasn't kidding. The stimulus package adopted last week included: $8 billion in loan guarantees for wind and solar projects, $4.5 billion for "smart grid" upgrades, $6.5 billion to help the Bonneville and Western Area Power Administrations upgrade their grid to ferry renewable energy from remote regions, and $600 million to help the Department of Defense convert facilities to wind and solar. We're on our way.

Modernizing our electric grid to accommodate a future built on "renewable" energy has become a favorite cause of environmentalists. Al Gore's "Repower America" plan says the key to creating a "green America" will be a "unified national smart grid" that will enable "clean electricity generated anywhere in America [to] power homes and businesses across the nation." In his current bestseller, Hot, Flat, and Crowded, Thomas Friedman longingly imagines that, 20 years from now, grid updates in California will have "made large-scale renewable energy practical for the first time ever.... Southern California Edison [will derive] more than half of its power from two vast renewable energy sources--wind and solar."

Environmentalists are right that there are problems with our current grid, and not just in terms of delivering wind and solar electricity. But they often misrepresent what it would take to solve the problems. They speak of the "smart grid" as if it were a panacea, but it will only install computers in every home to measure electricity use, the better to match supply with demand. Several additional technologies would be required to make large-scale wind and solar energy a reality, not to mention investments in the windmills and sunlight collectors themselves. Once all of these costs are taken into account, grid upgrades are much less attractive--and nuclear energy, coupled with some solar power, looks like a much more reasonable cure for the nation's energy ailments.

The first problem with the current grid is that it cannot balance the intermittent power supply from wind and solar energy with Americans' shifting electricity demands. A grid is not a machine for cranking out electricity, but a highly tuned instrument; because electricity travels at the speed of light, it must be consumed as it is generated. If electricity drops more than 5 percent, brownouts or blackouts may occur. If it surges by an equal amount, it can damage electrical equipment. (That's why you have a "surge protector" between the wall outlet and your computer.)

On the supply side, the wind doesn't blow all the time, and the sun doesn't shine all the time. On the demand side, people need different amounts of electricity depending on the time of day and the weather. This mismatch wreaks havoc on the system, and that's why Friedman's "half" figure is sheer fantasy: The best estimates are that the grid can tolerate no more than 20 percent wind without becoming overwhelmed by fluctuations. Solar, at best, could handle another 10 percent of our consumption.

The second problem stems from the fact that wind and solar facilities--because of their staggering land requirements--are best located in remote places. The upper Midwest is being billed the "Saudi Arabia of wind." Huge solar installations are planned for southwestern deserts. This means the grid has to ferry electricity over long distances to urban centers, which our current setup cannot do efficiently.