Peak wind

From The Register:

Both these assertions, however, have been called into doubt - and the first one, that there's plenty of wind power to meet all human demands, is particularly shaky as it ignores the thorny issue of cost. McElroy, Jacobson and their allies tend to make wild assumptions - for instance that it would be feasible to distribute massive wind turbines across most or even all of the planet's surface.

Professor Keith has some scathing criticism for these ideas. To start with, he says that most large-scale wind potential calculations thus far have simply ignored the problem that the possible massive wind farms of the future are going to result in much less powerful winds for long distances behind them. He and Professor Adams write:

"Estimates of global wind resource that ignore the impact of wind turbines on slowing the winds may substantially overestimate the total resource. In particular, the results from three studies that estimated wind power capacities of 56, 72 and 148 TW respectively appear to be substantial overestimates given the comparison between model results and the assumptions these studies made about power production densities...

To cite a specific example, Archer and Jacobson assumed a power production density of 4.3 W m-2... production densities are not likely to substantially exceed 1 W m-2 implying that Archer and Jacobson may overestimate capacity by roughly a factor of four."

I'd always wondered about that, by how much does a wind turbine slow down the wind.