ANALYSIS - Onshore wind turbine tech to top out in 10 yrs

Does the world really need bigger onshore wind turbines? According to Philip Totaro, CEO of Totaro & Associates, in the next decade the wind energy industry could reach an upper limit to onshore turbine technology development.

In 10 years offshore turbines of 12 MW - 15 MW nameplate rating should be fairly common, but can we really expect onshore turbines to approach 10 MW? As we continue to push the boundaries of product and technology development, we are likely to find that physical size limits, as well as the limits of the "square-cube" law, put large onshore with turbines at a commercially competitive disadvantage.

The square-cube law is the notion that turbine costs and component mass increases (approximately) with the cube of the rotor diameter, but the nameplate rating of the turbine increases roughly as the square of the diameter.

While the industry has overcome these limits before with the introduction of carbon fiber blades, and other light-weight, cost-saving measures, technological innovation is not going to be enough in the near future. We must also consider sheer size limitations, commercial acceptance and the implications of a push up to and beyond the 5.0 MW nameplate rating for onshore turbines.

For example, a 5.5 MW onshore turbine with a power density of approximately 500 W/sq m would have a rotor diameter of ~118.4 m. However, for that same 5.5 MW turbine with a power density of approximately 200 W/sq m, the rotor diameter would necessarily have to be ~187 m. While weight and size limitations on transportability can be easily overcome through component segmentation (blades and towers), there is another question beyond technological feasibility which must be asked and answered... commercial viability.

The industry has had an unfortunate perception regarding this difference between technological feasibility and commercial viability for many years, leading to the wasted expenditure of millions in R&D dollars on the exploration of many conceptual ideas. While technologically feasible and could be made to function, the "bankability" is largely not considered when laying out the R&D budget and putting together the new technology introduction (NTI) project portfolio. Just because something could be built, doesn't mean that it should.

Even with broad-based support for wind energy around the world, turbines with a 210 m hub height and 450 m tip height are likely to push the limits of what could be considered commercially accepted. That is not to say that onshore turbines of at least 5.5 MW with a 187 m rotor are not technologically viable, but the industry has to tread carefully with ongoing market acceptance.

Twenty five years ago, when the industry struggled to push into the MW range, there was a fear that transportation limits would be exceeded. But the inevitable response was a technological solution in blade and tower transport trailers to accommodate a growing appetite for size and power increases. This was facilitated by the economies of scale associated with increased manufacturing and supply volumes coupled with the cost efficiencies of financing a larger project size.

At this point in the industry's development, most markets are moving to exploit lower power density range winds in close proximity to existing or planned transmission.

While these seemingly finite limits of our current market acceptance could change over time to accommodate 10 MW - 15 MW onshore turbines, the economic trade offs need to be considered. Offshore wind resource is co-located with population centers in many parts of the world, and with continually declining costs, is opening up more opportunities for project site development around the world.

Additionally, the emerging trend around re-powering of sites could actually lead to a relatively new concept in turbine technology development. Site setbacks and tip height restrictions may prove to be problematic to many wind park owners and developers who would like to deploy the latest, and largest turbines.

For a project site of 49.5 MW which comprises 33, 1.5-MW turbines based on 2002 technology, there are a few repowering options, but mainly centered around a larger turbine with a comparable power density (i.e. a site with 1.5-MW turbines at 400 W/sq m could not maximize power output with a 3.5-MW turbine designed for a 280 W/sq m project site).

But instead of deploying a brand new, gleaming 4.8-MW turbine, what about repowering the project site with a more efficient and reliable next gen 1.5-MW turbine? With blades comprised of lighter weight (possibly hybrid) materials which also have a higher Cp and give the turbine a better capacity factor, coupled with an IoT-enabled control and sensor systems, these new turbines could serve to leverage the latest industry innovations packaged into a product and sizing that has already been proven.

As many try to liken the wind energy sector to automotive, the corollary of a new model year product in each class is more likely to become the norm. For the wind energy industry, that means a 1.5MW platform, a 2.XMW platform, a 3.XMW platform and a 4.X MW platform could all become part of the ongoing product mix.

The market dynamics and economics have changed. It's certainly easier to replace a thousand Kenetech VS 33's with a hundred 3.0-MW turbines than trying to push through thirty, behemoth 10-MW turbines in an onshore market which simply isn't ready for them.

With solar costs continuing to decline, the emergence of distributed energy resources (DERs) as a market requirement, and butting up against the physical limits of onshore technology, the industry needs to think about the future and adapt to the emerging market conditions.

As the wind energy industry hopes to capture more mainstream interest of utilities and oil majors around the world, it behooves us to focus and channel our resources into commercially viable solutions in order to secure the long-term success of the industry.

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