Capacity factor

Capacity factor is the single number most often quoted to describe how hard a wind asset is working. It is actual energy produced divided by the theoretical maximum over the same period, expressed as a percentage. A modern onshore site commonly sits in the thirties and a good offshore site considerably higher, because the wind offshore is both stronger and steadier.

The denominator is rated power multiplied by the hours in the period, which is what makes the figure so easy to compute and so easy to misread. Two turbines with identical hardware and identical maintenance will report different capacity factors purely because one of them stands in a windier place.

The number is useful for comparing sites and dangerous for judging machines. Capacity factor is dominated by the wind resource, so a turbine in a poor location will report a lower figure than a worse-maintained turbine somewhere windy. It tells you what the site yielded, not whether the equipment did its job. For that you need a comparison against the conditions the machine actually saw, which is what a power curve provides and what availability partially controls for.

This is why OpenTurbine does not rank turbines on capacity factor. A per-turbine model built from matched conditions asks a different and more useful question: given the wind this specific machine experienced, did it produce what it should have? That question is the basis of loss attribution, and it is the only version of the comparison that survives a mixed fleet.