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Ahmad HemamiAhmad Hemami received his BS degree in Mechanical Engineering from the University of Tehran and his PhD in System Dynamics and Control from the Department of Aeronautical and Mechanical Engineering at the University of Salford, UK. Dr Hemami has several years of industrial, academic and research experience. Among his areas of expertise are robotics, control and automation, and wind energy. He has supervised several MS and PhD students, and has served as a consultant for industry. He has over 100 journal and conference publications. He is an adjunct professor at McGill University (Montreal, Canada).

Time to Start Manufacturing Commercial Vertical Axis Wind Turbines

VAWT art 1A 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.
 
By Ahmad Hemami, McGill University, Montreal, Canada

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How Many Wind Turbines Do We Need?

Table 1. Selected data for diverse regionsIt 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%.
 
By Ahmad Hemami, McGill University, Montreal, Canada

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The Good, the Bad and the Ugly About Wind Turbines

Figure 1 Windtech Future Jan Feb 22It is likely that many of the people who in one way or another work with wind turbines, the environment and energy know about the good, the bad and the ugly of wind turbines. The good news is that the ugly is expected to become less so.
 
By Ahmad Hemami, McGill University, Montreal, Canada

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Two Modes of Operation in Back-to-Back Converters for DFIGs, Is It Worthwhile?

Windtech Future Fig 1 Oct 21Advancing from type 1 turbines with a squirrel-cage generator to a doubly fed induction generator (DFIG) was a great step, as it allowed much better wind power grasp. The ability to take part of the generated power from the rotor through power converters made it possible for a wind turbine to benefit from a large proportion of the available, otherwise lost, energy in winds with higher speed. Also, in order to lower the cut-in speed from about 5 to 3–3.5m/s, it was decided to run a turbine at sub-synchronous speed. This called for switching of the roles in the back-to-back converters. This arrangement has been traditionally continued to all the later and larger turbines.
 
By Ahmad Hemami, McGill University, Montreal, Canada

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How Far Will Horizontal Axis Wind Turbines Grow?

Sway Turbine 10MWAfter continuous growth to 12MW (Haliade 12), now the wind turbine manufacturers are targeting 14 to 15MW, and 20MW turbines are expected to be available within a few years. But how far can this continue, thinking about the large mass of the nacelle, the yaw system and all the other components? Will there be any new design entering the race or will the three-bladed horizontal axis wind turbine (HAWT) in its almost standard form continue to be the norm for wind turbines? It can be envisaged that for some time this will remain the norm until a breakthrough happens.
 
By Ahmad Hemami, McGill University, Montreal, Canada

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Are We Going in the Right Direction?

Windtech Future Failure percentageThinking about the time when a major portion of electricity will be provided by wind, solar and other renewable sources, in which power converters play a significant role, the question of power quality pops up. Presently, in many places the amount of generated energy that passes through these converters is very small but now that there is a shift from type 3 turbines (with doubly-fed induction generator, DFIG) to type 4 (direct drive) for the growing offshore turbines, the presence of harmonics lowers the quality of the generated power. In turbines equipped with a DFIG at least 2/3 of the power travels through the stator winding, i.e. there is a clean sinusoidal waveform with no harmonics, but with direct-drive turbines, inevitably all the generated electricity must pass through converters.
 
By Ahmad Hemami, McGill University, Montreal, Canada

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