Curtailment

Curtailment is production a site chose not to make. The reasons are commercial or regulatory rather than technical: the grid cannot take the power, prices have gone negative, a noise limit applies at night, or a shutdown protocol is in force to protect birds or bats. The turbine is healthy and the wind is there; the machine is being held back on purpose.

For performance analysis, curtailed periods have to be identified and excluded before anything is judged. A curtailed hour looks exactly like severe underperformance in the raw record - output far below what the wind implies - and if it is left in, it contaminates the baseline. That corrupts the expectation the model builds and buries real faults underneath an apparent problem that is not one.

Handled properly, curtailment is also worth measuring in its own right. Knowing how much energy a site gives up to grid constraints versus to equipment issues separates a problem you solve with an interconnection conversation from one you solve with predictive maintenance, and only the second is affected by how well the fleet is run. It also keeps availability figures honest.