Interview: Stiesdal on new records, old turbines, and growth

DENMARK: In late-2002 Bonus Energy installed four of its new 2.3MW turbines at the Rønland near-shore project in Denmark. Earlier this month, Siemens said the turbines had each become the first to reach the 100GWh mark.

As part of this, Windpower Monthly used the occasion to speak to Siemens Wind Power and Renewables Division CTO Henrik Stiesdal about the turbines, the past growth and future of wind, and his own plans post-retirement.

Firstly, we're talking about 2.3MW turbines hitting this target. What's your take on this?

I'm a sucker for anniversaries. For the first time ever you now need a nine-digit metre on a turbine. Until now all turbines have been able to be measured in millions or tens of millions. For the first time you need the metre to register in the hundreds of millions.

It's also an indication that turbine development reached a certain stage about ten years ago where what we now consider mainstream was established. You could ask, why did these turbines hit the nine-digit record, and why was it not the 3.6MWs that were installed for the first time only a few years later? The main answer is that the Rønland turbines were on the "corner" of the growth curve. Before 2003, turbine sizes grew exponentially. From 1980 our best-selling turbines doubled in rating every four years. That went on for more than 20 years, until the 2.3MW rating became the best seller – and then it changed to a more or less flat curve. It is only now that the 3MW is gradually taking over as the best seller.

Until 2003 the turbines grew so quickly that no earlier turbine had the opportunity to catch up with the later version. From 2003, the growth rate became much slower. We're still making bigger turbines but at a slower rate.

Why did that growth stop? Is it no longer there and will it ever come back?

We're not the only ones that have had first a period of exponential growth, and then reached a corner and see growth become more or less flat. Two examples of the same thing are commercial aircraft and crude-oil tankers. I did a calculation for commercial aircraft, their yardstick is not horse power or anything like that, it's the maximum take-off weight. I did not calculate right from the beginning of flying but took 1935 as the starting point in order to consider only relevant technologies. It was in the mid-30s that the aircraft mainstream went from larger or smaller parts in wood and fabric to all-aluminium structures. From that time on, the commercial aircraft industry saw exponential growth until 1970 when the Boeing 747 came in. Then the growth more or less stopped. From then on there were slightly bigger aircraft, like new versions of the 747 and the Airbus A380 — these aircraft are bigger than the original Jumbo Jet from 1970 — but not by much. The other example of an initial phase of exponential growth, followed by a plateau is commercial oil tankers. In both cases the factor causing the exponential growth to stop was logistics. With aircraft the challenges became getting people out of the aircraft and having runways that were long enough. And for the tankers, if you are moving a half-million tonne ship at full speed and need to stop, even at full throttle in reverse it will take you half an hour.

How will the flat growth curve affect the wind industry?

The growth curve is one of the places where I believe we will see a distinct difference between onshore and offshore wind power. Until now the market has been dominated by onshore. Onshore logistics are a big issue, moving anything beyond 60 metres in length is beginning to become a big issue and the towers are getting very tall. This is why the growth curve could not continue at the initial pace. So, as was the case for aircraft and tankers, the reduced growth is not driven by technological limitations but by logistics. The 3MW class is gradually replacing the 2.3MW as the best seller, but the slope of the curve is now maybe 10% of what it was in the 1990s. Offshore the curve will continue at higher pace, but not nearly at the same speed as it did from 1980 to 2003.

So how different is today's 2.3MW to the machine you installed at Rønland?

The 2003 version of the 2.3MW at Rønland has fixed-speed, active stall regulation and a generator that is directly coupled to the grid. Nowadays turbines have variable speed and pitch regulation. But the older technology still performs well. The Rønland project also has four Vestas turbines.

Where they installed at the same time?

Yes, around New Year 2003. They are almost the same diameter, but the rating is 2MW not 2.3MW. So they have a slight disadvantage. In the mid-range they perform the same but in the high-range we have an edge. But the Vestas turbines will also hit the 100 million kWh mark within the next year or so.

You were talking about the pre-2003 growth curve, I guess it was a good period for you to be involved in wind. Now a lot of development seems to be more incremental. Is there still room for some sort of disruptive technology in wind?

No, I must say I doubt it. But we need to be careful about how we define disruptive. I often get asked things like will it all be downwind, vertical axis, two bladed or whatever… Will that change things? No, that won't change things. Of course there will be people who pursue these alternative technologies but in the big picture it will be what is now mainstream. I am 100% convinced about that.

I guess it's about how you define disruptive.

In 1998 I bought a VW Passat and ran it for 14 years. It had a fuel consumption corresponding to 12km per litre. In 2012 I bought a new Passat. It does about 24km per litre, at the same driving pattern. A part of the explanation is that the new car is a diesel, but it is nowhere the full explanation. Fourteen years of innovation on fuel systems, combustion, and the car does maybe 60% more per litre of fuel. That could look like the result of a disruptive innovation, but it's the result of incremental innovation. You could be excused for assuming that in 1998, with a car industry that was at the time maybe 80 years old, and considered to be completely mature, it had reached the end of improvement. And yet, now I'm driving a car that covers 60% more distance per volume of fuel than it did 14 years before. This shows the power of innovation.

You're set to retire this year. Matthias Schubert left Repower/ Senvion a couple of years ago. There seem to be few people left from that pre-2003 growth period?

The reason I'm leaving is not that the work is not as entertaining as it was during the growth period. It is as interesting today as it was ten or 20 years ago. It is 35 years since I sold my first turbine design to Vestas; it's 10 years since the Siemens acquisition. There are very few left in the industry who have been there through the whole history of the modern wind industry – we actually have a few in Siemens. But I doubt that there are others left from the pioneering days in management. I guess that I'm the last. To some extent this may be a loss to a company, but on the other hand, when you have a senior person who always "knows better" because he has seen it all, this may make it more difficult for the next generation to come up. The company loss will be offset by the gain that new people will be allowed to come in and fill the gaps. Yes they will lose access to some of the old knowledge, and they may make mistakes, but experience comes from making mistakes – and for my part I have a lot of experience because I made many mistakes over the years! All in all, I think this is a good opportunity for company to rethink how they do innovation.

I find it hard to believe you will be leaving wind completely.

The main purpose is to be able to take it easier. I did a calculation on how much time I'd spent at work and if you compare that with the workload of a normal engineer in Denmark, my "working age" is 75. So I need to be able to take more time off. But old habits die hard and my love for wind is the same so I hope to be able to do support work for Siemens and I hope we reach an agreement. The idea of having "the old man" like me hanging around could cause problems but I hope something can be worked out. There are many other offers, from academia and so on, but when retiring one needs to be careful not to land in the same workload again.

You've spoken about the need for storage before. Do you think the area is ready for some "exponential development"?

Among the things I have worked on in the later years is a new thermal energy storage concept. Being able to store wind electricity could be the missing link, and I'd like to follow up on that. I've followed the debate on wind for decades, and here in Denmark, we had in the 1970s and 1980s a very polarised debate on whether we should have nuclear. The voices against renewables from the nuclear lobby were very strong. In the end Denmark chose renewables, but there are still strong voices for nuclear. The headline against wind 25 years ago was that the electricity produced by all the turbines in the country was sufficient for no more than supplying the power for the country's water bed heaters. This sort of "it doesn't matter" remark disappeared a long time ago. Later the opposition stated that wind was too expensive. We know wind is now quite a lot cheaper than nuclear, so that has stopped also. Then the argument against was the impact on the landscape. But we have solved that with a combination of fewer, larger turbines, and offshore, of course. So now the final argument is that wind is not reliable, there's no certainty of power when you need it. That argument we need to counter. I have high hopes that we will demonstrate a viable storage solution within a limited number of years.

Now you're coming to the end of your time at Bonus/ Siemens. What is your proudest achievement during that time?

I am sometimes asked what I am most proud of, and frequently the blade technology or the direct-drive turbines are mentioned. I am of course happy to have been part of the teams that created these very nice solutions, but to be quite honest, I am probably most proud of something different. In the 80s, the Californian market collapsed and a lot of manufacturers went bankrupt. One of the only survivors was Bonus. In 1988 we were approached by a big Danish investment company that owned a lot of turbines in California manufactured by other Danish companies, which they could not keep running because the original manufacturer was bankrupt. They also had two wind farms with Bonus turbines, which operated very well, and given our good track record on quality and performance, they asked if we could take over on their other projects. We said no because the other turbines were not of a technical quality that we could stand behind, but we could take over if we were allowed to upgrade them to a decent standard. And this was then agreed.

I ran that project, measured the loads based on where the turbines were located, figured out the design upgrades, and we got a system going where we manufactured the upgrade kits in Denmark and built a factory in the US to install them. It was a great success. We concluded the project in 1992 and the owner took over the service. I did not visit the sites for almost 20 years but went over a couple of years ago and the turbines were all still running whereas similar turbines that were owned by others and weren't upgraded were no longer there. This project kept our company running during the lean years in the late 1980s, and it kept alive the Danish adventure in wind. I always felt that it was a decent way of doing a good job, and that I'm very happy about. On a side note, when I visited the location of our factory after 20 years, it struck me that we must have worked with dwarfs at the time. It was so small! But this is more about how we are all adopting to the large factories of today, when the wind industry is at a level we could only dream about 20 years ago.