Net capacity factor is a way of describing a power plant or other kind of energy generator. It looks at how much energy the generator can produce compared to how much energy it could produce if it was working at its maximum level at all times.
For example, if a power plant could produce 100 units of energy, but for some reason it only produces 75 units of energy, we would say that its net capacity factor is 75%. That means that it can produce 75% as much energy as it could if it worked at its maximum capacity all the time.