I do not have access (yet) to the original work, but John Hopkins University reports at http://gazette.jhu.edu/2011/01/18/new-study-yields-better-turbine-spacing-for-large-wind-farms/
Large wind farms are being built around the world as a cleaner way to generate electricity, but operators are still searching for the most cost-effective and efficient way to arrange the massive turbines that turn moving air into power.
Based on wind tunnel work, they found that 300-ft diameter turbines are now spaced at seven rotor diameters apart and that by moving them to 15 rotors diameters apart results in more cost-efficient power generation. What is not reported is if the total power output of squashed machine, at lower cost efficiency is more or less than more widely spaced but more cost-efficient.
No matter what the results of this question is, there are many other questions this study raises.