Yesterday, Al Gore said that the United States should produce all of its electricity from carbon-free, renewable energy within 10 years. Although he didn’t lay out specifics, he seems to want to do it with wind, solar, and geothermal, although it’s not clear from his speech whether nuclear would be acceptable. Can it be done? It isn’t likely.

To get a sense of the scale of the problem, consider: last year, wind, solar, and geothermal power accounted for an impressive-sounding 48 million megawatt-hours of electricity. (I rounded up. If I had rounded down, it would have obliterated the contribution from solar, since it is such a small part of the total.)

But in 2006, the most recent year with complete figures, four billion megawatt-hours of electricity were produced in the United States. Eventually, wind, solar, and geothermal power could cover this. But right now, they account for a little more than 1 percent of the total. Going from 1 to 100 percent will require not only building the wind turbines and solar panels and steam turbines for harvesting geothermal energy: it will also require massive new transmission infrastructure for distributing this power, from the deserts or windy plains, where much of this energy can be found, to the coasts, where people actually live. And it will require massive amounts of energy storage, since solar power doesn’t work well at night, and wind power is erratic.

In light of this scale, even some truly ambitious schemes seem like a drop in the bucket. Over the past couple of weeks, T. Boone Pickens, an oil tycoon, has been using some of his billions to run television ads supporting his personal energy plan for the United States. Part of that plan is his project to build what seems to be the biggest wind farm in the country. It would nearly double the amount of wind produced in the state of Texas, the state with by far the most wind power. But that project will only produce 4,000 megawatts of power. (Total electricity generating capacity in the United States is about 1 million megawatts.) And it won’t be cheap. To cover transmission-line costs alone for that and other proposed wind projects, the state of Texas plans to spend about $5 billion.

Al Gore is right, of course, that the country needs to turn to renewable energy. And it’s frustrating how slowly the change is coming. But as we’ve recently seen with biofuels and food prices, scaling up a new source of energy can bring unanticipated consequences. Careful planning is required. We need some realistic plans for making the switch to renewable electricity, not empty rhetoric with unachievable goals.