A windmill in the ocean is twice the cost on land. Land based on $2500 per KW, in the water that is $5000.
The concrete and cabling costs are also multiples of a gas plant.
The ironic part is that all windmills shut down when the wind speed is above 35mph or else they will break apart. They cannot capture high speed wind energy. FloDesign is expected to do better since it is a radical new design, more like a jet turbine and no pin-wheel, but they do not yet have a working model.
If you have a windmill that takes decades to achieve break-even, it means you have a windmill that will not achieve break-even within its operational lifetime.
Similar deal with solar power. Making square miles of solar panels will involve huge amounts of pollution. Then you have solar panels that need to be kept clean (they don't work when encrusted with dirt and bird poop), using water and detergent. And by the time the solar panels have paid for themselves, they need to be replaced.