Foundation Considerations for Larger Wind Turbines

Today's wind turbines are significantly larger than earlier models introduced during the infancy of the wind industry. Foundations supporting modern wind turbines require more materials with higher required strengths resulting in unique construction challenges. Increased heat generation during the concrete curing process and congestion of reinforcement are two issues which require special attention during the design and construction of wind turbine foundations. In addition, specified design strength of grout, concrete, and steel reinforcement are approaching the limit of commercially available products on the market.

The average rotor diameter, hub height, and capacity of land-based wind turbines have increased 173%, 73%, and 350% respectively between the years of 1999 and 2020. The trend of increasing turbine size is expected to continue. According to FAA data, the average “tip height” (from ground to blade tip extended directly overhead) among projects that came online in 2022 was 164 meters. The same dataset indicates an average tip height of 195 meters among the “proposed” turbines in the FAA permitting process. While larger turbines are an overall positive development in the industry in terms of a decreased levelized cost of energy, they pose design, delivery logistics, and construction challenges which need to be addressed proactively. 

The talk will cover specific aspects in the design and construction of land-based wind turbine foundation which require special attention due to increasing turbine sizes. These include mass concrete temperature control, material strength limitations, and foundation constructability issues. An overview of these topics is provided below.

Mass concrete temperature control - What is a mass concrete temperature control plan and why is it important? What are typical concrete temperature limits during foundation concrete curing? What happens when measured concrete temperatures exceed these limits during construction? Anecdotal feedback on the increase of concrete curing temperatures which exceed acceptable limits, due to increases in foundation concrete volume, will be provided.

Grout and concrete material strength - Discussion of foundation materials (e.g., concrete, grout, anchor bolts) which may approach their maximum achievable design capacity based on commercially available products as foundation size increases over time. Discussion of innovative solutions implemented on projects to address this issue (e.g. load spreader plates to distribute loads at the bottom tower flange to grout interface).

Foundation constructability - Discussion of potential construction challenges (e.g., reinforcement congestion) resulting from larger foundations. Discussion of solutions incorporated over time to address these challenges (e.g., new reinforcement layout patterns).