A quick check on wind turbine design for power generation [1] confirms to my satisfaction that all wind turbines should be throttable down to zero electrical output and then with good mechanical brakes [2] taking away the remaining kinetic energy sufficient to stop then lock the rotor. I've read elsewhere (sorry, no reference) that stopping the rotor can be necessary in emergency windspeed conditions. Per [2]:
> Let’s compare the emergency braking requirements of a
>1.5 MW wind turbine under maximum wind conditions with
>those of a 40-ton mining truck. Imagine driving a
>fully loaded truck down a steep gradient of 25% (1:4)
>at 85 mph when a road sign warns of a cliff a quarter
>mile ahead. The engineering required for effective
>braking in both cases is much the same. Braking for
>the wind turbine is, in fact, more demanding.
Beyond mechanical brakes, the available control strategies and actuators normally applied toward maximizing power output per [1] can instead be applied toward bringing the power output to zero and the rotor to a halt, such as:
* Apply generator torque control (dumping power to the grid) sufficient to slow the blades down to near zero
* Then or as the blades slow down, stall or furl the blades using pitch control
* Apply the brakes to lock the rotor
* Yaw the whole machine 90 degrees off the wind
OK so if they're stoppable, what is up here?
Others more familiar with Danish market, operators and regulatory conditions might speak better to this, but I'll surmise that the turbine operators get paid when they produce energy, whether Denmark needs it or not. So the turbine operators never stop their turbines, night nor day.
When that creates an excess of energy the grid engineers must do something. The article mentioned slowing hydro output elsewhere and heating the water used locally for district heating.
This creates an environment where there should be a financial incentive to create technologies for storage or highly variable use of this nightime and other times highly variable excess electrical energy.
Hundred-megawatt data centers [3] with quickly variable compute capability come to mind, but making stored hot water hotter (the district heating 'dummy load' approach) seems to me a lot simpler, cheaper and immediately practical, if a bit wasteful of the low-entropy energy that electricity is.
* Apply generator torque control (dumping power to the grid) sufficient to slow the blades down to near zero
* Then or as the blades slow down, stall or furl the blades using pitch control
* Apply the brakes to lock the rotor
* Yaw the whole machine 90 degrees off the wind
OK so if they're stoppable, what is up here?
Others more familiar with Danish market, operators and regulatory conditions might speak better to this, but I'll surmise that the turbine operators get paid when they produce energy, whether Denmark needs it or not. So the turbine operators never stop their turbines, night nor day.
When that creates an excess of energy the grid engineers must do something. The article mentioned slowing hydro output elsewhere and heating the water used locally for district heating.
This creates an environment where there should be a financial incentive to create technologies for storage or highly variable use of this nightime and other times highly variable excess electrical energy.
Hundred-megawatt data centers [3] with quickly variable compute capability come to mind, but making stored hot water hotter (the district heating 'dummy load' approach) seems to me a lot simpler, cheaper and immediately practical, if a bit wasteful of the low-entropy energy that electricity is.
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[1] https://en.wikipedia.org/wiki/Wind_turbine_design
[2] http://news.altramotion.com/?p=242
[3] http://gigaom.com/2012/01/31/the-era-of-the-100-mw-data-cent...