Why turbines are growing in height and size?

Wind turbines are getting bigger

Wind turbines are increasingly viewed as an integral part of a carbon-free futuristic grid. Ever since its modest beginnings, manufacturers have ramped up turbine rated power for the past 30 years. This has mainly been achieved through building higher rotor hubs and larger turbine blades. The graph below shows the evolution of average rated power, diameter and hub height for wind turbines for the past 30 years.

This explosive race to build bigger and higher turbines wouldn’t seem to slow down anytime soon, which would then bring the question: What are the limits to the size of a wind turbine and what stops us from building a turbine as high as Burj Khalifa? Even predictions about size limitations have been changing throughout the years. A Dutch journal set 500kW as the limit for wind turbines way back in the 70s. A German magazine on the other handset 70-80m range as the limit for rotor diameter in 1998 (Sun & Wind Energy, 2018). Just roughly two decades later, the Haliade-X is in operation with almost thrice the rotor diameter, pushing the definition of what’s plausible even further.

To answer this question one has to first understand why turbines are growing in height and size. Bigger turbines have a larger surface area and can “capture” more wind. In theory, turbines with twice the radius (or blade length in this case) would result in a quadrupling of rated power. Higher hubs on the other hand allow the turbine to access a steadier flow of wind due to the lack of ground obstacles which slow it down (surface friction). Wind speeds as a result tend to increase with height (The HOMER Pro, n.d.). Hub height indirectly influences the capacity factor of turbines, a measure to indicate how often a plant is running at maximum power. Offshore turbines remove the need to build at extreme heights due to the absence of ground obstacles.

Theoretically, there are no limits to how high a turbine can be built. Practically, one might be surprised at the problems usually encountered when building at such heights. Legal compliance is one such issue as in the case of onshore turbines in the US, where researchers found turbine average height to be converging on roughly 152m (499 feet). This was because of the extra work required by the Federal Aviation Administration during the approval process for turbines beyond that height (Roberts, 2019).

Turbine manufacturers are turning to build bigger turbines for offshore parks

For onshore turbines at least, the shadow and noise produced by larger wind turbines is another key point to be considered. In this case, social acceptance is more likely to be the hindering factor rather than a technical one from the customer’s perspective (Lee, 2020).

From a techno-economic point of view, the transportation of wind turbines to the installation site is currently the biggest obstacle facing manufacturers when building gargantuan blades. Turbine blades are not modular and have to be built and transported as a single solid piece. Transporting these pieces on winding roads is an extremely challenging task and can quickly drive up costs.

Lifting the heavy blades onto the hub, a whopping 55 tons each in the instance of the Haliade-X, is another expensive routine that must be considered when planning these turbines (WeMake Consulting, 2021). Advances in material sciences have partly helped solve this problem. As turbines grow in length, manufacturers are using carbon fiber instead of glass fibers in select structural parts of the blades. The former is significantly lighter and more robust but also comes with an additional upfront cost. Using composite solutions, allows them to increase blade length without any significant change in weight. The additional cost of carbon fibre is offset by lower overall system costs because of the lighter weight (Composites World, 2012).

For now, at least, manufacturers have chosen to tackle the problems mentioned by building larger turbines for offshore parks instead. For instance, the transportation problem can be solved by building manufacturing plants directly on-site (harbour) and the blades can then be transported to the installation site using ships. As previously mentioned, offshore turbines are also lower in height thanks to lower surface friction. The steadier flow of wind on the offshore sites also contributes to a higher capacity factor; as high as 60% in some cases. For comparison, capacity factors of onshore turbines typically range between 26-52%. Building larger turbines for offshore parks comes with the added advantage of getting to reduce the total number of turbines needed to reach the same total rated capacity. This is essential to keep maintenance costs low, which can be extremely high for offshore turbines.

To conclude, it is difficult to set a limit on how high or big wind turbines can get in the future. As long as the engineering, as well as logistic problems mentioned above, can be solved economically, one cannot argue against turbines growing even larger than they already are! At Proxima Solutions, we are looking forward to helping wind park asset managers to have better oversight to optimize energy production, making key metrics such as rated and actual power, as well as a capacity factor, monitorable at any time with live data (30 seconds). Let's start doing things together, pushing the boundaries of your operation and discovering your wind farms’ hidden potential.

About us:

Proxima Solutions is a German Company founded in 2018 to provide a digital platform for the asset management of renewable energy plants. Combining artificial and human intelligence, data science and renewable energy expertise, we offer a suite of software tools that enables asset owners and asset managers to increase energy production from their wind and hydro energy plants. We can also support our customers with a set of services (plant supervision, predictive diagnostics, asset management) where we optimize asset performance and preserve asset lifetime by implementing the recommendations from our advanced analytics and AI predictive algorithms.



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