Why do wind turbines stand still?
For several quite different reasons, and "there is no wind" is only one of them — the others are more interesting and are routinely misread as evidence that the technology does not work.
The reasons, in rough order of frequency:
Too little wind. Turbines need a minimum cut-in speed, typically around 3 to 4 metres per second, below which the energy available cannot overcome losses.
Too much wind. Above a cut-out speed, commonly around 25 metres per second, turbines shut down deliberately to avoid structural damage. A stationary turbine in a gale is protecting itself, not failing.
Maintenance, scheduled and unscheduled. Turbines are serviced regularly, and one stopped while others turn usually means a technician is there.
Curtailment — this is the important one. The grid sometimes cannot accept the power: demand is low, or the transmission capacity between the wind farm and the demand is insufficient. Operators are instructed to reduce output, and are frequently compensated for doing so, which generates recurring and misleading headlines about paying wind farms to switch off. The underlying problem is insufficient transmission and storage, not excess wind.
Grid stability requirements, where a minimum of other generation is needed.
Commissioning, where a new farm is built but not yet connected — a wait that can run to years in congested networks.
Noise or shadow flicker limits at certain times, and bat and bird protection, where turbines are curtailed at low wind speeds during migration or at dusk in summer, which measurably reduces bat mortality.
Grid frequency response, where some turbines are deliberately held slightly below maximum so they can increase output instantly if needed.
What the availability figures actually show. Modern turbines are available well over 95% of the time. Capacity factor — the proportion of theoretical maximum actually generated, typically around 30–40% onshore and higher offshore — is not a measure of reliability but of how the wind blows, and is accounted for in planning.