Wind Turbines on Wind Farms?

Is there any reason they would turn off wind turbines in a wind field due to efficiency? I know the fans are braked if winds exceed a certain velocity and possibly due to energy needs they may stop some of them. However in a debate with a friend he argued that it would be more efficient and produce more energy to have fewer running versus more. This is counter intuitive can someone shead some light on this topic. I refuse to accept my friend logic.
In response to answer number two...its a wind mill u dont use energy to run it u gain...so y would u ever want them not moving or "shut them down.'' Even if u had 1 rotation per hour u'd be gaining more energy than 0 rotations. Further my friend argued that the first turbine in a row would run slower if the one behind it were running. This I know is false. And my friend has no reliable source or literature to prove his point.

The annual electrical energy demand is 300,000,000 KWh. Is it possible to build a wind farm that could provide electricity throughout the year? If so, how many wind mills will be required to build the wind farm. Average wind speed is 15 mph. A state-of-the-art windmill has a rotor blade length of 75 m and the practical efficiency of a wind mill is 40%.

how to make a simple wind mill or wind engine that can produce energy, specifically a simple LED light?

is for a school project...

link that has step-by-step instructions please

for a science project i have to make a wind mill or wind turbine ( a small one no taller than a foot long) and then i have to measure which shape of the blade creates the most amps..how should i connect it to an amp meter and where can i get materials to make one?
how should i get the wind turbine to connect to the generator and the meter..do u know anywhere to buy pre made small windmilll/windturbines to hook up to generators

How much will it cost for a working solar panel and working wind mill?

I have land on a hill over looking the sea and I was wondering if when I build on this land, would a modern wind mill would be practical.

I mean,one price and includes instalation of ALL compoents, wireing to code, trenching, location, and erecting the wind mill it self.

  
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