▁tur b ines ▁are ▁often ▁heav ier ▁than ▁g ear - based ▁wind ▁tur b ines . ▁A ▁study ▁by ▁the ▁EU ▁called ▁" Rel ia wind " ▁based ▁on ▁the ▁largest ▁sample ▁size ▁of ▁tur b ines ▁has ▁shown ▁that ▁the ▁reli ability ▁of ▁g ear box es ▁is ▁not ▁the ▁main ▁problem ▁in ▁wind ▁tur b ines . ▁The ▁reli ability ▁of ▁direct ▁drive ▁tur b ines ▁off sh ore ▁is ▁still ▁not ▁known , ▁since ▁the ▁sample ▁size ▁is ▁so ▁small . ▁ ▁Exper ts ▁from ▁Techn ical ▁University ▁of ▁Den mark ▁estimate ▁that ▁a ▁ge ared ▁generator ▁with ▁permanent ▁magnet s ▁may ▁use ▁ 2 5   kg / MW ▁of ▁the ▁rare - ear th ▁element ▁Ne od ym ium , ▁while ▁a ▁g ear less ▁may ▁use ▁ 2 5 0   kg / MW . ▁ ▁In ▁December ▁ 2 0 1 1 , ▁the ▁US ▁Department ▁of ▁Energy ▁published ▁a ▁report ▁stating ▁critical ▁short age ▁of ▁rare - ear th ▁elements ▁such ▁as ▁ne od ym ium ▁used ▁in ▁large ▁quantities ▁for ▁permanent ▁magnet s ▁in ▁g ear less ▁wind ▁tur b ines . ▁China ▁produces ▁more ▁than ▁ 9 5 % ▁of ▁rare - ear th ▁elements , ▁while ▁Hit achi ▁holds ▁more ▁than ▁ 6 0 0 ▁pat ents ▁covering ▁Ne od ym ium ▁magnet s . ▁Direct - drive ▁tur b ines ▁require ▁ 6 0 0   kg ▁of ▁permanent ▁magnet ▁material ▁per ▁meg aw att , ▁which ▁transl ates ▁to