Joules (or watts) is a measure of capacity. Electricity generating capacity, especially with intermittent sources like wind is almost meaningless. Who cares about capacity if the actual generation is zero.
Watt-hours, Megawatt-hours, and terawatt-hours are used because that's the descriptive term of energy actually produced.
I understand the number is an ideal, maximum number, but I'm talking about the units. Are you saying power should be reported in megawatt-hours per year? That might be convenient, but it's the same as megawatt-years per year, which reduces to megawatts which is what I said.
MW tells us the scale of the plant. TWh/year tells us the production of the plant.
I've got a good gut sense for what a 3 MW wind turbine looks like, so when I read "50 MW Plant" - I can already envision about how large, and about how many turbines it will have (approx 15-30).
TWh/year doesn't tell me as much, because the plant might be located in a very windy place. Or maybe not in a windy place at all - the data is still useful, but I prefer MW when people are talking about a plant's "physicality".