He didn’t pull his punches. As far as renewable energy is concerned, there is only wind and solar, he said. The others don’t matter, and they never will. So much for wave and tidal power.
He celebrated the rapid fall in wind-power costs over recent years, but pointed out that the industry remains unable to always deliver electricity when it is needed.
There was one area he declined to commit on, though. Is there an upper limit for the size and power of wind turbines? "I remember the first time I was asked that question," he said.
"I said that 250kW was as far as we could go. Well, I learned from that mistake. The next time I was asked, I said 500kW. I have never answered that question since."
Smart thinking rather than obsessing over size was Stiesdal’s core message for the industry’s future. The offshore sector has shifted to 6-8MW machinery, but there is still plenty of scope for smaller turbines, he argued.
What is missing is industrialisation of foundation designs with quicker and cheaper installation techniques. If these were readily available, the economic case for sticking with 3-4MW models would be overwhelming.
The benefits of step-by-step improvement far outweighs breakthrough technology, he said. Taller towers and longer blades, for example, have allowed essentially unchanged machinery to make huge improvements in production output.
While admitting that the global driver for renewable energy is mitigation of climate change, Stiesdal hammered home the financial case. "The only way we can win is on a purely economic basis," he said. "We have to make wind power so cheap that nobody can afford not to use it."
Step-by-step upscaling is one of the main themes emerging from our fifth annual Turbine of the Year awards. Rated capacities across all categories continue to grow, with blades and drivetrains following suit.
Siemens’ offshore model provides a good example. The first prototype, installed in 2011, was 6MW with a rotor diameter of 120 metres. Now in full-scale production, it has grown to 7MW with a rotor diameter of 154 metres, and work is well under way on boosting capacity to exceed 8MW.