Neodymium is element number 60 on the periodic table with an atomic weight of 144, and it is one of the "rare earth" group of elements.
And there is literally a ton of neodymium in every wind turbine, from Denmark to Kodiak Island. Published estimates vary, but between 500 pounds to 2000 pounds of neodymium are needed for every megawatt of wind power. The USGS estimates that the United States will need 380 metric tonnes of neodymium annually to provide 20% of our electrical power by 2030. My calculations show that we need more -- a minimum of 3100 metric tonnes of neodymium per year. The availability of so much neodymium is in doubt, and may limit the growth of wind power in the United States.
Part I of this post, "Limits on the Growth of Wind and Solar Power, Part I -- Area"
can be found here: