something else. DAN LASHOF, Natural Resources Defense Council: They're not going to all be in one place. They're going to be spread around. So the wind may not blow in North Dakota, but it'll blow in northern California. And that's when it will start to become predictable, as the utilities get more experience with it. ALEXANDRA McPHERSON: The experts that we have been working with have quoted that South Dakota, North Dakota and Texas have enough wind power annually to meet the United States' electricity demands. Now, if the wind starts blowing, then we would have, you know, back up resources, you know, solar energy. NARRATOR: In business for 15 years, Sunray, in southern California, is one of the longest-running solar plants in the world. Its 30-acre field of mirrors captures the energy of the sun and turns it into electricity without emitting greenhouse gases. But it can only generate power when the sun shines. BRETT HOOVER, Sunray Energy, Inc.: The coal plant can generate year 'round, 24 hours a day. You know, here, you know,, we can just kind of run when the sun's out, which is out quite a bit. You know, we get about 265 days of sunshine here. But if you get any kind of high stratus clouds or anything like that, you'll see your power just go right off the grid. NARRATOR: When the sun's out, Sunray produces 30 megawatts of electricity. While impressive, it can't yet compete with the coal plant next door, which