Ask the Expert

Professor Jacobson says: If we built and installed enough turbines to harvest every last watt of wind power out of the air at fast-wind sites over land worldwide, we estimate we’d get at least 72 trillion watts a year, or enough electricity to light up 720 billion 100-watt light bulbs. Put another way, this is about five times the current total energy need of the world’s population (about 12-14 trillion watts). It’s unlikely we’ll harvest trillions of watts of wind power any time soon, but there is certainly a lot of potential to get much more of our electricity from the wind. Right now only 1 percent of U.S. electric power demand and 2 percent of California electric power demand is supplied by wind.

How did we come up with our total energy estimate? A few years ago my former student Christina Archer analyzed data from more than 8,000 sites around the world where wind-speed is measured near the Earth’s surface, and 900 “sounding” sites where wind speed is measured above the surface, including near the hub height of a modern wind power turbine (about 80 meters, or 250 feet). Wind speed at the hub height is often faster than the speed at the surface, so she combined vertical profiles from the “sounding” data with the surface data to estimate wind speeds up in the air above the other 8,000 surface sites. All these data, combined with equations describing how wind turbines convert moving air into electricity, and some other mathematical estimations, allowed her to determine approximately how much power is available from the wind around the world.

Of course, there are a lot of practical considerations that must be addressed before even a small fraction of that power can be harvested. We’d need more than a few tens of million 5 megawatt turbines (a megawatt is a million watts) to capture all the power in the wind worldwide. But, if we deployed about 100,000 such turbines, we would generate enough energy to power all the cars in the United States if they were all electric. That number may seem to be a lot, but when you consider that the country produced about 300,000 airplanes during World War II, it doesn’t seem so unattainable.

It’s also worth noting that properly spaced, those wind turbines would take up only 1-2 square kilometers of footprint on the ground and about 0.5% of the area of U.S. in order to separate the turbines to prevent interference with one another. The spacing area is 30 times less than the land needed for corn to run all vehicles in the U.S. on corn ethanol.

Harvesting wind energy is not as simple as erecting turbines on a windy patch in the Great Plains, or along the West Coast, however. To be useful, the power has to be transmitted, and so we’d need to make a considerable investment in transmission lines.

Also, if wind power is to take on a significant share of the power generation load, perhaps about 20 percent or more, we’ll need to overcome the problem of intermittency. This refers to the common-sense observation that while sometimes the wind blows very hard, sometimes it doesn’t blow much at all. One group of turbines, sometimes called a “wind farm,” might not generate any power on a still, quiet afternoon.

There are several things we can do to solve that problem. One is that we can link far-away wind farms together via the power grid so that no one depends solely on just one wind farm. The other thing we can do is to combine wind power with other clean, natural sources such as geothermal power, hydroelectricity, solar, wave, and tidal power to ensure that there is always a few sources of energy available at any given time. My research group just finished a study in which we found that combining just four of these sources to provide 80 percent of California’s electric power demand would allow people to satisfy their power needs as reliably as they do today. Storing energy in batteries or hydrogen is another option for reducing intermittency.

Developing new energy sources takes a lot of effort and investment, but the difference between wind and the predominant energy sources of today is that wind power involves extremely little greenhouse gas or air pollution emissions. Ultimately the degree to which we adopt wind power may depend more on the proverbial “political winds” than on the technical feasibility of harvesting it.