After years of discussion, the wind energy industry will soon have its first major updates to international design standards for cold climates. The first committee draft is being compiled now.
– We hope to have a first committee draft ready for national voting by the end of 2014 and be able to release a new edition of the standard in 2016, says Ville Lehtomäki, research scientist at VTT, Finland and Coordinator of the Cold Climate sub-committee that is part of an international task group responsible for reviewing the current turbine design standard.
Today the minimum design requirements for wind turbines are determined in the International Electrotechnical Commission’s document IEC 61400-1.
Ville Lehtomäki, VTT
The standard addresses the structural safety of all subsystems of the wind turbine such as control and protection mechanisms, internal electrical systems, mechanical systems and support structures.
The first version of the IEC-standard was put together in the 1990’s. The current version is from 2005, with some minor updates from 2010.
– So far the design standard hasn’t recognized cold climate requirements in turbine design, says Lehtomäki.
– Our proposed cold climate updates will be a huge step forward when it comes to turbine design and structural safety in cold climates.
The previous work of international expert group Task 19 focusing on cold climate wind energy issues was extremely useful in many parts of the new proposed standard.
In the new edition of IEC 61400-1 there is proposed about ten pages dedicated to cold climate issues from basic low temperature and icing definitions to specific structural design considerations, new iced turbine design load cases, sub-component system design and ice assessment recommendations. Based on the extensive updates, a cold climate class turbine is proposed to boost transparency and clarity between turbine manufacturers and other stakeholders.
One of the main concerns when operating a turbine in cold climate is ice.
While developing the new edition of the standard, the Cold Climate sub-committee reviewed findings from two test cases regarding iced turbine vibrations, one in Sweden and one in Canada.
Even though the climates at the two testing sites differ, the general finding was that the ice mass build-up on the blades was not as large as expected. It was also found that the aerodynamic penalty effects of icing are very important to take into account in turbine design.
So far the findings have also shown that the vibrations are creating more vibrations on the towers than on individual blades.
– But even small amounts of ice will make the blades less efficient and decrease the output power of the turbine, says Lehtomäki.
Once the build-up of ice for a modern, over 70 meter rotor diameter turbine reaches several hundred kilos per blade, the turbine will stop.
One of the largest challenges for the industry is that icing severity varies significantly from one year to another. While average wind conditions can vary as much as plus/minus 15 percent from one year to the next, icing can have a 200 percent yearly variation.
– A proper site ice assessment includes dedicated icing measurements at minimum of hub height for one to two years and making the very important long-term correlation analysis similarly as for wind speed assessments, says, Lehtomäki.
Insufficient ice assessment (wrong or no ice instruments, too optimistic estimates etc.) and incorrect technology solutions can cost a developer huge sums of money.
– To get the minimum requirements for a turbine in cold climate doesn’t just increase turbine structural safety, it also significantly lowers the business uncertainty, says Lehtomäki.
Plenty of people at Winterwind 2014, a lot of good discussions and sessions, some hard core mingling in the corridors. We had photographer Niclas Thunborg hanging out with crowd shooting pictures of the speakers, participants and general happenings. If you were there you can remember the good times, if you weren’t – this is what you can expect next year.
If you want to see more pictures, please go to our Facebook-page. Feel free to tag yourself in the pictures.
A huge thanks to all of you who contributed to make Winterwind 2014 a great success; presenters, session chairs, delegates, sponsors, exhibitors, PCO and the conference centre Södra Berget.
Hope to see you next year!
Ulla Hedman Andrén
Project manager Winterwind
What’s the most important you have learned at Winterwind 2014?
Antti Leskinen, CEO of APL Systems Inc.
Actually, last night we made up the guidelines for a new R&D-project, based on what we learned here. The atmospehere is very relaxed, and people are taking very openly about their work and problems. That has really surprised me. We’re actually practicing Open Innovation at this conference.
Gert-Olof Holst, CEO Eno Energy Sweden AB:
For us as suppliers it’s important to meet the larger companies and see how they think and plan. Also, I try to catch up on the current R&D. But of course, the networking is one of the most important things here.
Teresa Arlaban, Research and patent manager within the R&D department, Acciona Windpower:
There are still a lot of questions to answered, by all the players involved. It’s not just manufacturers of wind turbines that have to provide well functioning de-icing systems with warranties, but also wind farm developers and operators having to learn how to properly asess the losses they can prevent with de-icing systens. There’s a lot of work to be done together.
Stefan Olofsson, studying in Strömsund to become wind energy technician:
It’s been a very interesting conference. I never thought that ice was such a big problem in the business. That’s something I’m going to remember during the rest of my education. Also there’s been a really positive experience to meet so many and friendly people that you have been able to ask almost anything
Gail Hutton, senior statiscian, RES Group:
The seminar by VTT about the ability to map ice was very interesting. It’s not enough to now how much ice you have, you also have to know HOW ice develops and the financial implications of that. I also very much enjoyed meeting other researchers doing similar work as me and chatting with academics.
Greger Nilsson left the research institute and took the power ascender to a new business. Now the former researcher is repairing blades far above the ground.
With his new company Blade Solutions Greger Nilsson is getting into the booming market of repairing blades. He knew a lot about composites from his work as a material expert at Swerea Sicomp before he started his company in October last year, but not much about wind energy, and even less about rope access.
”I had to take a crash course in up-tower repairing before I started my business,” he says.
Greger Nilsson at work.
Now he’s offering inspections and subsequent blade repairing with UV-curable resins, which cure within minutes and whose cure mechanism is not heat dependent.
For small repairs that require no fiber reinforcement, he uses RENUVO MPS (multipurpose system) resin, which is applied directly to the damaged area via a standard cartridge gun. The MPS resin, which is suitable for use on polyester or epoxy substrates, is a monocomponent system that requires no separate hardener.
For structural damages he uses UV-curing prepregs, (pre-impregnated glass fibres). To get top quality laminates, he also use vacuum assisted curing.
”When you develop a repair scheme, it’s critical that you understand the nature of composites, resins, fibers and orientation,” Greger Nilsson says.
For up-tower repair, there are several means of access: including crane-hoisted baskets, sky platforms anchored to the turbine, rope access during which repair technicians (generally in teams of two) lower themselves from the turbine via ropes to allow 360° access to the tower, nacelle and blades.
If possible, Greger Nilsson uses power ascenders. ”It’s cheaper for the customers and offers a great deal of flexibility for me.”
See the dot far above. Not your average day at work…
After half a year in the business he concludes there’s a lot of work to be done:
”I find wrinkles from faults made in the manufacturing process, puncture holes and cracks in the blade shells, which leaves the core exposed to water penetration, damages from lightning and leading-edge erosion.”
So far Greger Nilsson has done work for utility Skellefteå kraft, manufacturer Nordex, operator Kalix Vind. Competitors include Finnish company Bladefence, Danish Rytter Telecom and the turbine manufacturers themselves.
During operation, as blades rotate, the blade tips can reach speeds of 180 mph/290 kmh. At that speed, rain- and wind-borne contaminants and sand can heavily erode leading and trailing edges
Composite wind turbine blades are designed to last for 20 years in the field. But those who service them say that without proper maintenance and repair, their actual service life will fall short, and during that shorter life, overall turbine efficiency will diminish. In fact, every defect on the surface of a wind blade disrupts its aerodynamic efficiency and, as a result, reduces the turbine’s power production.
In the harshest environments, leading-edge erosion is evident as soon as two years after installation
Not even the technical equipment, made to measure the icing, could withstand the harsh conditions in Åsele in northern Sweden. Severe icing stopped the ice detectors from working properly or broke them completely.
The conclusion from the field tests of five detectors at the site Stor-Rotliden in Åsele is that none of the detectors are reliable enough to mesure icing on the turbines during production.
”Sometimes they mesured no ice when they were covered with ice, other times different detectors showed different levels of icing. Quite often they broke down,” says Helena Wickman, who did the analyzing for Vattenfall as a part of her thesis in engineering physics at Uppsala University.
”The climate was simply to extreme for the detectors. During less extreme icing they showed okey results.”
”If the reliability of the detectors during the more severe icing events could be increase they could be used for site assessment to give a rough idea of the icing climate.”
Wind power in cold climate requires ice detectors both during the prospecting phase, in the site assessment, and during production for controlling of the turbines to help mitigate problems due to ice, like production losses, fatigue loadings, ice throws and increased noise.
Owners of wind turbines want high productivity in order to obtain the required return on investment, but icing can easily lead to a 10 percent loss of production, which can dramatically affect profits.
Stor-Rotliden is utility Vattenfall’s largest on-shore wind farm in Sweden. The site was operational in August 2011.
With multi-megawatt turbines, downtime costs can easily run into hundreds of Euros per hour.
Vattenfall’s field test shows a bleak picture of what the market can offer today.
”But we really put hem through harsh conditions,” says Helena Wickman, who today works as a wind and site consultant at Meventus.
”They might perform better in less cold climate or if you placed them on a heated boom and kept the boom free from other equipment.”
The tested detectors were:
- the T 40 series from HoloOptics (HoloOptics),
- 0872F1 Ice Detector from Goodrich (Goodrich),
- LID-3300IP from Labkotec (LID),
- IceMonitor from SAAB Combitech (IceMonitor)
- IGUS BLADcontrol from Rexroth Bosch Group (IGUS).
- Two different combinations of anemometers, used for wind measurements, were analyzed for ice detection purposes. The first combination consisted of the three anemometers Thies 4.3350.00.0000 from Adolf Thies GmbH & Co.KG (Thies), Vaisala WAA252 from Vaisala Oyj (Vaisala) and NRG Icefree3 from NRG Systems (NRG). The second combination uses three differently heated NRG anemometers.
Predictability was the name of the game during the opening session of Winterwind 2014. Being able to predict icing, weather and wind can make or break a business case.
”We have seen up to 20 percent in lost annual production due to icing. That’s a catastrophy!” said Alberto Mendez, vice President Wind Power at Vattenfall, one of Sweden’s largest wind energy operators.
He went on to conclude that a 20 percent loss annually implies 40 percent loss of production during winter.
”And a fraction of a 20 percent loss is the difference between being in good shape or being bankrupt as a wind operator,” Mendez continued.
He gave the manufacturers an acknowledgement that things have improved during the last five years, with more and better de-icing systems on the market.
”But manufacturers are still not meeting our full expectations, the technology is not there. We spend seven months a year in Sweden with uncertainty, with icing issues. We get a lot of surprises. That’s a bit scary.”
”The very low power prices in Scandinavia makes it a very tough market. The margin for error and ability to absorb uncertainty is limited among developers and operators.”
The demand from operators like Vattenfall is not just better de-icing systems, but also performance warranties. How this kind of guarantees would look like is a matter of debate.
Among the manufacturers of turbins with de-icing systems there are a reluctance to make promises, due to the lack of ability to predict the weather and the performance of their systems.
Sue Ellen Haupt
So both operators and manufacturers have a lot to gain from better forecasting. That’s also why the delegates listened carefully when Sue Ellen Haupt, director of the Weather Systems and Assessment Program of the National Center for Atmospheric Research (NCAR) in USA, spoke about NCARS Weather Research and Forecasting model (WRF).
The American research and development center is federally funded and the WRF modeling system is possible to download free of charge. It has become an important tool of the trade and has grown to have a large worldwide community of users (over 20,000 in over 130 countries), and workshops and tutorials are held each year at NCAR.
Basically you put your local data into the computer model and then use numerical weather prediction, statistical learning (blending all knowledge into one seamless model) and Nowcasting technology* to get a picture of how the weather is going to be the next hour, or the next 24 hours or the next week.
”It’s important to be able to forecast when the wind is going to be available, it really helps the utilities and and balancing authorities, both on a day-ahead-basis, with for example energy trading, and in real time, for grid stabilization.”
Andrew Garrad, President of the European Wind Energy Association (EWEA) and member of the supervisory board of newly formed DNV GL, concluded that it doesn’t matter if you have the best available turbines if you don’t have the right predictions.
”If you get the wind speeds wrong, you’ve had it. Money can fix a lot, but not the wind. It’s a thing money can’t buy,” he said.
He also stressed that wind energy now is being a major player in the energy market
”The more reliable we can make the production, the more valuable it will become. The aim must be to make wind energy look like a conventional power station.”
Alberto Mendez – from his perspective as an owner and operator of wind farms – agreed: ”It’s extremely important for us to get better weather prediction models.”
* Nowcasting combines a description of the current state of the atmosphere and a short-term forecast of how the atmosphere will evolve during the next several hours. A convergence of technical developments has set the stage for a major jump in nowcasting capabilities. New communications technologies, including broadband Internet, wireless communication, social media, and smartphones, has made the distribution and application of real-time weather information possible nearly anywhere.
In the beginning there were high hopes and a great sense of adventure. Customers lined up to buy wind turbines without really knowing what it was like to operate and maintain them in cold climates.
Manufacturers weren’t that much wiser; in some cases they had to send people up the turbines to hack ice off the blades.
Pretty soon reality hit the pioneers: ice, and plenty of it, accumulated rapidly on the blades and, as wind turbines grew larger, it proved difficult to remove.
In the 90’s,VTT worked with Bonus to design blade surface heating foils. Some 20 wind turbines, ranging in size from 150 kW to 1 MW, were equipped with these systems. One of the two systems installed in Sweden is still in operation more than 15 years later.
Enercon introduced its ice detection and hot air based de-icing system in 2004. At Winterwind 2012, Enercon presented potential net energy production gains of up to 25% with their latest de-icing system.
These systems, and others that have followed, have had a significant impact on production in cold climates, but there’s still no quick fix for ice. Investors are now requesting performance guarantees with respect to icing, which no WT manufacturer currently offers.
De-icing systems can keep ice away, but their performance varies greatly depending on the technology used and the location of the wind turbine.
The lack of performance guarantees for operation in icing conditions means investment risk, and no investor likes unquantifiable risk.
Owners are now demanding warranties from the manufacturers. It is, of course, hard for Enercon, Vestas, Siemens, Nordex, Gamesa and the other companies to guarantee a specific performance in such very diverse – and unpredictable – conditions. Icing can be a persistent and yet rapidly fluctuating problem.
But what we are talking about here is risk sharing for a significant part of the market in a fast growing industry.
Owners already absorb a lot of risk related to permits, public opinion, noise reduction and environmental issues. Performance warranties must be a joint project, shared across the whole industry.
Apart from warranties we also need independent validation of de-icing and anti-icing systems within research projects and the development of intelligent turbine control systems for de-icing systems.
From being a small niche market, cold-climate projects today make up 25% of the world wind market, according to consultants BTM.
The heyday of “let’s try that!” is over. We’re world leaders now. So let’s show the world what we can do together!
Chairman Swedish Wind Power Association
Just a few days left to Winterwind 2014. We’re a group of people working day and night right now to make this a great experience for you.
This year Winterwind will be held in a municipality where there are large investments into wind energy. In June, Mörtjärnsberget will open it’s first stage of development with a total of 37 turbines. The project is a joint venture between SCA, a Swedish hygiene and forest products company and Norwegian power company Statkraft.
We will meet at the top of the South Mountain in Sundsvall, in Hotel Södra Berget, currently one of the largest convention and conference hotels in the northern part of Sweden. From the hotel and convention hall we will have a striking view over Sundsvall and the surrounding area.
From being a small niche market, cold-climate projects today comprise 25 procent of the world wind market, according to consultancy BTM. It’s a development we have noticed in the growing number of participants at Winterwind and a escalating interest for wind energy in cold climate.
This year Recharge, one of the leading publications in the renewable energy sector, will cover Winterwind. Sweden’s largest tech magazine, Ny Teknik (New Technology), is also represented at the conference.
Andrew Garrad, President of the European Wind Energy Association (EWEA) and one of the wind industry’s most experienced and knowledgeable profiles will hold one of the keynotes.
Other keynotes will be held by Sue Haupt, Director of the Weather Systems and Assessment Program of the Research Applications Laboratory of NCAR, Alberto Mendez, Vice President Wind Power at Vattenfall and Joe Beurskens, chair of The European Technology Platform for Wind Energy (TPWind)
Then, of course, it’s YOU!
Early on we decided to make Winterwind a special topic conference for professionals and researchers. Delegates keep coming back year after year, forming a community and sharing valuable knowledge with each other.
You are the driving force behind Winterwind. And we are very much looking forward to meet you over a fika (coffee and a little something) in the corridors, in between seminars, exhibitions and posters.
See you in Sundsvall!
Ulla Hedman Andrén
Sand and ice erodes the rotor blades. Repairs usually take considerable time. But Bladefence has introduced a new, quick method of repairing cracks.
Bladefence uses a resin system that reacts when exposed to UV-light. The process from viscous glue to hardened material can take less than five minutes.
Conventional methods may require up to 24 hours for the epoxy resin to fuse the carbon fiber or fiberglass in the blades.
Normal methods also require an ambient temperature of at least +15 °C and a relative humidity of < 60 % for the initiation of the chemical process in the resin.
”With our method we can operate down to + 5 °C and tolerate 90 % relative humidity, ” says Ville Karkkolainen, managing director of the Finnish company Bladefence.
What does this mean for turbine owners?
”One of the key benefits of rapid repair is reduced turbine downtime. With multi-megawatt turbines, downtime costs can easily run into hundreds of Euros per hour.”
”It also extends the time during which repairs can be carried out from three to six months a year.”
More repairs can be done, in other words…?
”Yes. With a small time window, turbine owners only carry out vital repairs. Less important issues are not addressed. Now they have the time – and the financial resources – to fix even the small cracks.”
But do you really have to fix every minor flaw?
”Even a small crack allows water to penetrate fiberglass and make it wet. In the winter this water freezes and expands inside the blade, widening the crack.”
What causes cracks?
”Some blades cope better than others. But the most important factors are location and local conditions.”
”A steel mill or coal power plant nearby has a huge effect on the blades. Ice is another problem. I’ve seen the top coat of a blade worn down in a year from small airborne particles hitting the blade surface.”
”We also have problems with chunks of ice coming off the nacelle or one rotor blade and hitting other blades.”
Blade problems haven’t been discussed as much as faulty gear boxes – is this changing?
”In recent years it has become clear that not only gearboxes but also wind turbine blades require regular, high quality maintenance. I think we are moving towards a common best practice in the market where blades are maintained annually and not just when it’s absolutely necessary.”
Ville Karkkolainen is the managing director of Bladefence, an independent Finnish service provider specializing in wind turbine blade inspection, maintenance and repair. The company was established in 2010, has twelve employees and is looking to hire another ten.