Research Projects and Publications

Futureproof Offshore Wind Turbine Foundations – Reducing LCOE and Environmental Impacts through Repowering Focused Selection

Wind Energy Research

Author: Mary Boylan Hassan
Year: 2020
Supervisors: Ármann Gylfason, Elsa Joao, Edward Hart, and Rebecca Hall


Offshore wind energy production has grown exponentially since its beginning in the early 1990s. Since earlier installations had low power output (less than 1 MW) and low capacity factors (less than 30%), the farms offshore were significantly less impactful than their onshore counterparts. In the UK, however, increased government funding and support has paved the way for greater presence of offshore wind farms in their electric grid infrastructure. Now that the UK has become the leader in offshore wind energy, many sites in English and Scottish waters are being examined for their potential large-scale installations (up to 1000 MW of installed power) while current installations are considerably greater than even a decade prior.

With this expansion in both turbine and farm size, the end of life scenarios for offshore wind turbines become an increasingly critical analysis to make. All farms must eventually be decommissioned, but little is known about the ramifications to a project's cost and the impact to the grid when a farm is taken offline. Instead of the traditional method of decommissioning a farm after a 20-25 year lifetime, farms may benefit from a partial or full repowering through turbine part replacements.

Depending on the type of foundation chosen, costs and efficiencies can drastically change for a farm. Since foundations can account for roughly a quarter to a third of the project's overall upfront costs, the selection for the right type of foundation is crucial for financial success. Foundation design and cost can drastically change depending upon the depth, bathymetry, sea conditions, and many other factors; the key to successful design lies in how to extract the most energy while contending with high installation costs. Using the levelized cost of energy over various lifetime scenarios for different foundation types and analyzing vessel fuel usage, this thesis identifies why partial repowering could be a wise choice for future large-scale installations, due to its low LCOE and moderate CO2 impact.

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