The growth of wind energy -- about 30% per year since 2005 -- is well documented. Less well known are wind's maintenance headaches. Wind turbines are big, complex mechanical systems. Wind components operate under demanding conditions. The gearbox must convert rotor speeds of 20 rpm to 25 rpm into 1,200 rpm to 1,800 rpm to drive the generator. According to SKF Group's national wind energy accountants manager Kevin George, wind produces variable speeds, sudden stops and starts, and sometimes extreme loads that lead to transient misalignments that reduce gearbox life.