((9/13.41)^3 x 3959) / 1.14 = 1049.6 kw. and 892 / 1049.6 = about the same 85%.

This, though, is applicable to "near-perfect conditions". Anything less or more than 9 meters/second and it falls off. Remember that I said "at rated power". On the ridges here in Tehachapi the winds go from nothing to 20 meters/second in no time at all and in remembering all of this, take a look at perhaps an older (possibly out-of-date) production curve of the 1.5 MW sl from the GE website (with my own notations including the Betz energy curve added):



Meanwhile one BTU - the heat equivalent of burning one match stick - is 778 foot pounds or raising 778 pounds off the floor one foot. One pound of lignite (low BTU) coal has about 7000 BTUs in it. One pound. Thermodynamic efficiencies are only about 30% for burning coal as such but even the air in just a cubic yard of volume has a mass weight of two pounds.

It is in the big picture where efficiency differences become important. Back in the Minnesota farm country where land goes by square mile sections, visualizing the wind at 30 mph entering one side of such an area up to an elevation of 1000 feet results in a Betz-adjusted total energy potential of 429.9 MWs. Remember that the air enclosed in a square mile of surface area up to this elevation has a mass of over one million tons, about the same as the displacement weight of all ten of the U.S. Navy's mighty nuclear powered aircraft carriers (one more is being built). One square mile.

Even just this 100% - 85% = 15% energy inefficiency deficit applied to 429.9 MWs is 64.5 MWs. How many 1.5 MW turbines is this again on just one square mile? I am using the optimum performance criterion established above for the Enercon.

The other part of the problem is where does the energy in this energy deficit of 15% go? Likely most of it currently goes into the parasitic drag of the blades and creating the "whoosh" sound from them. What isn't no doubt escapes downwind due to a missing blade or two that would be there if it weren't for the parasitic drag thereby added.

It is easy to go on like this and I am sure not very welcome, even a little off-topic. At this time of the close of the year before the start of the next, it might be appropriate to reflect on these thoughts. Wind energy has embraced many euphemisms about how well it is doing - the number of homes serviced, etc. - but knuckling down to some of the hard facts of the details of blade performance over hard won land areas available to it also needs to be considered.