Gear or No Gear, Not a Battle
- Published: 13 February 2023 13 February 2023
Direct-drive wind turbines using a permanent magnet synchronous generator have been developed after observing the problems with the gearbox. Nonetheless, nothing is 100% perfect. Obviously, during recent decades there have been efforts to advance the technology, in all directions. That includes improving the performance of the gearbox. One advantage in removing the gearbox from the loop is a reduction in the tower top weight, but this is not always possible. In a recent article by van de Kaa et al. (2020), the subject of the comparison of direct-drive turbines and geared turbines has been systematically studied to determine which technology will become the dominant one in the future. This implies that in the future the other technology needs to switch. The final conclusion of this study is that cost of energy and reliability are the two most important factors, and both technologies still have equal chance of success.By Ahmad Hemami, McGill University, Montreal, Canada
For a comprehensive course in wind energy that I teach, I spend a lot of time updating the numbers for the cost of various turbine components and their percentage of the total cost, as well as the cost of wind farms, for which turbine prices are only one part. As many may know, this is not a straightforward process, since the expenses are case sensitive, and there are no clear-cut figures for this.
Any new concept in an established manufacturing process or engineering operation will be costly to implement. In most cases it requires research and development, the cost of which must be absorbed by the company behind it. If the concept sounds ‘revolutionary’, at first it might seem either difficult or impossible to achieve. On the other hand, in many industrial applications – out of necessity – research and development is a continuous endeavour to make a product more efficient, have improved performance, cheaper and so on.
A 2018 publication by Sandia National Laboratories (SNL) [1] indicates that an overall more economical choice of wind turbine for an offshore floating turbine is a vertical axis wind turbine (VAWT). SNL has performed a comprehensive and extensive simulation study using a variety of software for different aspects, from stresses in blades to the levelised cost of energy (LCOE). There are several aspects involved in the design and operation of a wind turbine and even more if it is on a free platform subject to wave forces. In this study, the point of emphasis is the lower LCOE, as a result of smaller platforms for a VAWT, mainly due to the lower centre of gravity compared with a horizontal axis wind turbine (HAWT). This study and others on VAWTs point to the direction of the technology for floating turbines. After all, if the cost of energy is the principal driver for selecting a technology, then a lower LCOE is the preferred choice.
It came to my mind to do some calculations of how many wind turbines we need to power the whole world with renewable energy. Of course, in the future when we run out of fossil fuels, or we are forced not to use fossil fuels any more to survive on Planet Earth, wind will not be the only alternative source of energy. Considering that hydro, wind, solar, wave, geothermal and other renewables may provide say 70–80% of the world’s energy needs in the future, it is reasonable to predict that wind energy will account for over 20%.