Energy payback periods are differ widely between sources. In the case of wind, it also depends on the size of the turbine as efficiency increases with the square of the blade radius so the larger the blade, the quicker the payback. In theory. The figure used here in Ireland is less than 6 months also.

Nuclear payback periods are particularly problematical because it depends what you include/exclude from your calculations to make your case. Using high quality uranium and excluding reprocessing and waste management costs, the figures are much better than fossil fuel plants. However, if you have to process low quality uranium, you include the costs of cleanup after mining and an estimated figure for storage costs after use, the figures can be made to be negative, ie. it costs more energy than it produces.