The analysis has highlighted the main design, economical and technical issues related to the XL monopile technology, which are summarized below:

  • XL monopiles offer a considerable design and cost advantage when deployed with higher capacity turbines.
  • Usage of the higher capacity turbines supported on XL monopiles results in lower material usage and therefore foundation cost, in comparison with lower capacity OWTs supported on monopiles.
  • LCOE for wind farms using high capacity OWTs may be lower than for low capacity OWTs supported on monopiles (over full operational life).
  • Design limitations impose a highly constrained operating envelope for XL monopiles (localized buckling, natural frequency, toe-kick deflection).
  • 8.0MW turbines achieve the same ratio of weight per MW of rated power at deeper waters as 3.3MW OWTs, which indicates the possibility of future developments at great water depths.
  • The breaking point for XL monopiles, using higher capacity OWTs, is 40 m. Over 40m jacket foundations become more competitive.
  • Storage, manufacturing, transport and installation bottlenecks have delayed the wider usage of the technology.
  • Transport and installation cost will be the determining factors in any future XL monopile deployment.
  • XL monopiles have several cost related limitations that could be potentially lifted during the next 15-20 years.
  • New emerging foundation technologies could potentially challenge the design benefits obtained with XL monopiles.