Optimal offshore wind turbine size: is it time to standardise?

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TKI Wind op Zee
TKI Urban Energy

Is it time to standardise the size of offshore wind turbines? On 17 May, TKI Wind op Zee will organize its 10th webinar to present and discuss the outcome of a recent study on optimal offshore turbine size and standardisation. The question is if bigger is better and necessary for our renewable energy production.

Over the past decade, the cost of offshore wind energy has fallen sharply due to a combination of economies of scale, innovation, and an increase in the capacity of wind turbines, which in itself is also a major innovation. Where we installed 4 MW turbines offshore in 2013, we are currently installing turbines of 14 to 15 MW. 

How far the industry can push this increase in the capacity of wind turbines is unknown. What we do know is that we have already surpassed what we considered to be the limit. Although the electricity production of the turbines is increasing, the costs of the turbine, the blades, the tower, and the costs of transport and installation are also increasing. It is conceivable that at a certain point the additional returns from the increase in capacity do not outweigh the additional costs in the entire value chain. Additionally, the advantages and disadvantages of continuously scaling up wind turbines are being brought up for discussion within the sector itself.  

Secondly, the question about the potential for standardisation and industrialisation of the wind turbines and the supply chain involved in manufacturing, transport, and installation arises. As long as the capacity of turbines continues to change, it will be difficult to achieve economies of scale through standardization of the design and the components for wind turbines, support structures, installation equipment, etc. This means that the trend towards the decrease of costs by the increase in turbine capacity is accompanied by cost disadvantages because of missed standardisation and industrialisation in the wider supply chain, including the Operations and Maintenance phase.

For these reasons, TKI Wind op Zee was interested in shedding some light on the matter at hand. The main conclusions of the study conducted by DNV are the following:  

  1. The rapid growth in the size of offshore Wind Turbine Generator (WTG) is expected to slow down in the coming years. 
  2. DNV does not see any technical limitation for WTGs to grow beyond the current largest offshore WTG designs. However, analysis shows that further growth does not necessarily result in a lower Levelised Cost of Energy (LCoE). A direct cost reduction has more potential.  
  3. In the current fast-growing offshore wind market, increasing WTG production numbers offers the opportunity to reduce costs. Larger production numbers generally allow for larger investment in product and production optimisation, and larger production numbers offer benefits in economies of scale.  
  4. The cost of energy is found to increase with WTG rating. Lower rated turbines, 12-15MW, with high specific power densities (400-450W/m2) are found to be the most cost-optimal. For high specific power densities, the LCoE is found to show no significant variation with respect to WTG rating in the range of 12-20 MW.  
  5. This indicates that the choice of optimal turbine configuration is not straightforward and may depend on parameters other than WTG rating and rotor diameter.  
  6. It is found that site conditions and discount rates have a strong influence on the cost of energy. Turbine design choices like design tip speed ratio and drivetrain configuration impact the LCoE to a lesser but still significant extent. The LCoE is also sensitive to O&M modelling assumptions.  
  7. Based on the performed assessments, DNV expects that up to 2030-2035 leading offshore WTG manufacturers will mainly focus on their current largest design WTG platforms and future upgrades that enable small growth steps. It is expected that the platform lifecycle ends with 14-18MW range platforms carrying rotors with diameters in the range of 230-250m. After 2030-2035, it is expected that next-generation WTG platforms will be introduced with a limited increase in size compared to the platforms they replace. These new WTG platforms will however be highly cost optimised, feature many new technologies and will be operated and maintained following new strategies. WTG sizes are expected to go up to 18-24MW with rotor diameters in the range of 250-265m. 
  8. LCoE values are sensitive to several influential factors for which best estimates were made but could change over time. Examples of these are the cost price of raw materials and labour, discount rates and Operational Expenditures (OpEx). Significant future changes in any of these factors can influence conclusions on optimal WTG size. 

Want to know more? Read here the full report and sign up for our webinar on the standardisation of wind turbines on 17 May.