Magnets made of rare-earth metals like neodymium are commonly used in the generators found in offshore wind turbines. Turbines with neodymium magnets generally need less maintenance than those without them—an advantage when your turbine is a few miles out from land.

But neodymium is costly, it almost all comes from China (which has restricted export in the past to drive prices up), and the environmental impact of extracting it from the Earth is not super.

Although there are hardly any offshore wind turbines in US waters today, the US Department of Energy (DOE) in 2015 mapped out a plan to expand offshore wind to 86 gigawatts (GW) of capacity by 2050. If such a future comes to pass, the US will need to think about its supply of neodymium, especially if US government officials push for domestic offshore wind turbine manufacturing.

A pair of researchers from Yale and IDC Herzliya in Israel tried to quantify how much neodymium would be needed to reach DOE's 2050 turbine goal. The researchers concluded that, although the global neodymium supply could meet the projected demand, reusing or recycling the magnets could help out a lot.

The offshore wind turbines of today, for tomorrow

The researchers estimated offshore wind development over time in six regions of the United States: the Northeast, the Mid-Atlantic, the Southeast, the Great Lakes, the Gulf of Mexico, and the Pacific.

The Northeast has been the leader when it comes to offshore wind development in the United States, because state and local politics favor the development, and distant waters are still shallow enough to support early-stage wind projects. The region currently supports the US' only offshore wind installation, a 30 megawatt (MW) wind farm off Block Island, Rhode Island. An additional 1.2GW of offshore wind capacity contracts have been awarded to a variety of companies for projects in Northeast waters.

Accordingly, the researchers modeled a future in which capacity is built out quickly in the Northeast, followed by development in mid-Atlantic waters. The Southeast, the Gulf of Mexico, and the Great Lakes regions see sporadic growth, while development in the Pacific lags for years before a sudden boom in offshore wind turbines toward the end of the 30-year period.

The researchers assumed that offshore wind turbines installed closer to 2050 would be able to use less neodymium due to technological improvements. (Hints of these improvements can be seen in the electric vehicle industry today.)

All told, the US offshore wind industry would require 15.5 gigagrams (Gg) of neodymium between now and 2050 to make the DOE's vision of 86GW of offshore wind possible.

"This is enough to provide for 20 million hybrid and electric cars (which require on average 0.75 kg of neodymium per vehicle)," the paper notes. "While substantial, the United States imported nearly 2Gg of neodymium in various products and semi-manufactures in 2010 alone." The US is estimated to have imported more than 25Gg in recent years.

That the US is already importing substantial amounts of neodymium is something of a good sign from an economic perspective. Rare-earth metals aren't necessarily rare, despite their name, and strong demand suggests that more miners will get into the market to take advantage of healthy market conditions. While there will likely be enough neodymium in the world to satisfy offshore wind demand, there is some concern that turbine makers will end up competing with the electric vehicle market, which is also expected to grow out to 2050.

Reuse, reduce, recycle

Some of the pressure, the researchers say, can be alleviated by reusing neodymium magnets from wind turbines that have reached the end of their lives. Wind turbines generally have a lifespan of 20 years before they have to be recycled or repowered. The researchers argue that the likely staggered nature of offshore wind buildout means that neodymium magnets could be recycled or, better yet, reused for new turbines once the originals have worn out, as the magnets have much longer lifespans than the turbines they're housed in.

"If all outflow of permanent magnets in decommissioned capacity was recovered and reused, 3.5Gg of virgin neodymium demand could be avoided by 2050," the paper states. But this ideal situation will require policy to foster neodymium recycling and reuse. In 2011, just 1 percent of potential scrap neodymium was actually recovered, the paper notes.

Instead of re-processing the magnets, the researchers suggest that offshore wind turbines could be mandatorily designed in a modular way so that the large magnets can simply be removed and reinserted into a newer turbine.

"Such an initiative is urgent and should not be delayed, because the turbines that will be installed in the upcoming decade will be the first ones to reach their EOL [End of Life] and to therefore become a potential secondary source," the paper says. "Policy that factors in the reusable design of components should therefore be part of the approval processes of offshore wind farms."

Nature Sustainability, 2019. DOI: https://doi.org/10.1038/s41893-019-0252-z (About DOIs).