My guesses (as an ME): poor engineering, inability to account for dynamic loads and vibrations, poor welds, materials defects, poor quality materials, improper inspections, insufficient safety margins, blades failing causing huge imbalances on the rotor which are transferred to the tower, blades striking the tower after blade failure. I’m no expert, but those are somewhat informed educated guesses.
Interesting tidbit. My dad was the program manager at GE for the very first multimegawatt wind turbines they developed. He had a team of dynamicists working for him. I was in ME school at the time. I remember him telling me how extremely difficult the dynamic analysis was and how the problems his team faced were almost intractable. This was back in ‘75 or so — over 40 years ago (I’ve got a great pic I took of Dad in front of the assembled test turbine on the shop floor).
It’s interesting how big of a problem tower collapse still is today. It’s really the dirty secret of the industry, IMO. The first power generation company I worked for out of school (Babcock & Wilcox) go at into wind energy and recently had a huge collapse of a tower in the UK. It’s all very hush-hush and not much has leaked out about it.
So you seem to actually know a decent bit about the wind turbines. Why do they require so much more copper and rare-earths than other power sources? Wouldn’t the majority of the structure be the same? The only big difference is that it’s wind/blades turning the turbine, instead of water flow or steam? Sure, the structure needs to hold up, but that’s not a rare-earths usage, and the only thing I can think of for copper is just in the cabling? Since each tower is so spaced out?