Wind turbines don't necessarily run all the time - they only run when there's a demand for the electricity they produce (which is in turn influenced by the price of electricity they produce; it can be higher than fossil based kilowatts)

My BCO also claims turbines are sometimes used as motors to soak up excess power in the grid, so it might not even be the case that the ones you see moving are producing power!

I did read that the electronics are/can be used for grid balancing, but not read anything about it for years, so may have been a pipe dream from some installer.

Two small (50kW) turbines near me seems to have one down most of the time, and have noticed that a few further west have not been running. I suspect that this is a maintenance issue as there are not enough large ones in Penwith to affect the grid significantly. I think there is only a couple of companies locally that maintain them, and both are small.
The one at the 'Great WOW' or Heartlands I have not seen turning for years, but then it is a VAWT. The one at the EA office is working again, it is an old 15kW Proven.

Posted By: Ed DaviesAIUI, reasons for not running a turbine are:

1) It's broken.
2) Not enough wind.
3) Too much wind.
4) Local grid doesn't have the capacity to take the power.

Or:

5) Scheduled maintenance

Posted By: Triassicor:
6) they have been paid not to produce electricity.

Isn't that 4), seen from a different angle (& depending on contracts)?

or:
7) wet leaves on the track

Posted By: cjardMy BCO also claims turbines are sometimes used as motors to soak up excess power in the grid, so it might not even be the case that the ones you see moving are producing power!

I wonder what makes people thinks the grid has such a requirement of turbines, & if there is such a requirement how do they think the grid used to cope with it before it had turbines to 'turn' to?

Posted By: snyggapa: “In the same way that I believe we in effect subsidise the scots when the English and Scottish grids were unified - without enough capacity to move all of the wind production out of Scotland, the payments to Scottish generators to not run ran into, I believe, tens or hundreds of millions of poonds.”

Definitely not hundreds of millions of pounds. Maybe tens of millions though windfarms off the south coast of England got quite a lot and the total for all windfarms is only £34 million (which is, in turn, only 10% of the total amount of constraint payments to all types of generators). Note also that there's a new link being built to improve transmission from the Scottish parts of the grid to the English and Welsh parts so any such “subsidy” should be short lived.

http://www.carbonbrief.org/blog/2013/03/why-windfarms-get-paid-to-switch-off

“Windfarms and constraint payments

Between 2011 and 2012, National Grid says constraint payments to windfarms were just over ten per cent of the total amount paid to all generators - about £34 million.

Windfarms produce less than five per cent of our electricity so the payments they are getting are out of proportion to the amount of electricity they generate.

This is because the grid relies on old infrastructure which absorbs electricity from coal and gas plants more easily than from wind, according to renewables supplier Good Energy. This makes it easier to switch off the wind supply and keep the grid functioning rather than reducing electricity supply from coal or gas.

This makes windfarms a better choice for National Grid when choosing which power plants to turn off when there is oversupply - and renewables trade association Renewable UK says this means they get proportionately more constraint payments.”

When Brazil and China are now transmitting large quantities of electricity getting on for 3000 km from generation to consumption, it seems rather poor that we're struggling to connect Scotland and England!