▁several ▁hundred ▁kil og rams ▁of ▁rare - ear th ▁content ▁per ▁meg aw att , ▁as ▁ne od ym ium ▁content ▁is ▁estimated ▁to ▁be ▁ 3 1 % ▁of ▁magnet ▁weight . ▁Hy brid ▁driv etra ins ▁( inter mediate ▁between ▁direct ▁drive ▁and ▁traditional ▁ge ared ) ▁use ▁significantly ▁less ▁rare - ear th ▁materials . ▁While ▁permanent ▁magnet ▁wind ▁tur b ines ▁only ▁account ▁for ▁about ▁ 5 % ▁of ▁the ▁market ▁outside ▁of ▁China , ▁their ▁market ▁share ▁inside ▁of ▁China ▁is ▁estimated ▁at ▁ 2 5 % ▁or ▁higher . ▁In ▁ 2 0 1 1 , ▁demand ▁for ▁ne od ym ium ▁in ▁wind ▁tur b ines ▁was ▁estimated ▁to ▁be ▁ 1 / 5 ▁of ▁that ▁in ▁electric ▁vehicles . ▁ ▁Bl ades ▁ ▁Bla de ▁design ▁▁ ▁The ▁ratio ▁between ▁the ▁speed ▁of ▁the ▁bla de ▁tips ▁and ▁the ▁speed ▁of ▁the ▁wind ▁is ▁called ▁tip ▁speed ▁ratio . ▁High ▁efficiency ▁ 3 - bla de - t urb ines ▁have ▁tip ▁speed / wind ▁speed ▁r ati os ▁of ▁ 6 ▁to ▁ 7 . ▁Modern ▁wind ▁tur b ines ▁are ▁designed ▁to ▁spin ▁at ▁varying ▁spe eds ▁( a ▁consequence ▁of ▁their ▁generator ▁design , ▁see ▁above ). ▁Use ▁of ▁al umin um ▁and ▁composite ▁materials ▁in ▁their ▁bl ades ▁has ▁contributed ▁to ▁low ▁rot ational ▁in ert ia , ▁which ▁means ▁that ▁newer ▁wind ▁tur b ines ▁can ▁acceler ate ▁quickly ▁if ▁the ▁wind s ▁pick ▁up , ▁keeping ▁the ▁tip