An icy matter. In 2008, wind turbines (WTs) with a total power of

Transcription

1 Wind Energy cold climate zones An icy matter The German manufacturer Nordex is developing new blade coatings and has erected several wind turbines in cold climate zones like this N 60 in Bulgaria. Photo: Nordex Until now wind turbines in cold climate zones have been somewhat exotic. But step by step the turbines are conquering icy heights and defying the biting cold in extreme climate zones such as the Antarctic. In 2008, wind turbines (WTs) with a total power of approx. 1,560 MW were up and running in cold climate zones across all 25 EU member states. This is not a terribly impressive figure. Among the reasons why the large wind power potential in the mountains and in the far North has hardly been utilised so far are a lack of technology, uncertain yield forecasts, a lack of experience and high additional costs incurred through the necessary modification of turbines. International certification organisations such as Germanischer Lloyd answer the question of what counts as cold by means of technical guidelines. If the temperature sinks to below 20 C on nine days a year, then this is a cold climate site. Manufacturers who then want to have standard turbines certified as a cold climate version (CCV) must fulfil various requirements. Main components such as transmissions and their lubricants must be designed for temperatures as low as 40 C, and components in the nacelle protected from the extreme cold through heating and ventilation concepts. Special attention is paid towards the choice of materials for moulded parts, concrete and steel elements. They must have certain characteristics and must not become brittle. The certification organisations also make requirements for the automatic recognition of icing. For sensors the requirement is that they must be able to detect icing or the weather conditions for such at least at hub height. In this the manufacturers must prove that their measurement results are plausible. Generally an ice warning leads to a WT being shut down, firstly because the loads on the blades then increase, and secondly because flying chunks of ice would endanger people and the surroundings (S&WE 6/2009, Page 116). Site choice is crucial Over and above the technical requirements is the question of whether or not such a cold adventure is worthwhile at all. Apart from the sometimes difficult grid connection requirements or problems with ac- 130

2 cess to the wind farm in winter, there is no rule of thumb for calculating the lower level of yields which investors must assume. Moreover, the existing standards and recommendations for cold climates apply to extreme temperatures and not to the operation of WTs under icing conditions. In fact the meteorological conditions are very complex and depend on the location. Icing on rotor blades, for example, may be triggered by low-lying clouds in the mountains, snowfall or fog, but may also occur in regions where the temperatures are frequently around freezing. For this reason precise meteorological information is an important element for project developers. With the help of international research projects the industry wants to develop instruments and suitable methods to measure the thickness of ice on blades or to more accurately determine the meteorological conditions at a site. Concepts are also under development using new coating technologies (nano technology), in order to prevent icing in general. Zurich University is working on an anti-freeze coating, for example. In Kotzebue, Alaska, they are experimenting with dark paints to minimise icing. At the Canadian TechnoCentre éolien in Quebec several research projects are under way in cooperation with manufacturers, to develop systems suitable for Nordic conditions. Artificial icing is being created, for example, and its lifetime measured. After the design phase, field tests on WTs at the wind farm in Murdoch ville are planned. A project on the surface treatment of blades is being prepared together with the rotor blade manufacturer LM Glasfiber. Based on ion implantation and UV irradiation, tests are to be made on whether icing can be prevented. Also in the starting phase are tests on multimegawatt turbines to be able to identify the effects of cold temperatures on large turbines. Test series have already begun on 20 different measuring instruments: We test wind measurement instruments and precipitation sensors for NRG Systems, Vaisala and HydroTech, explains Daniel Boulay, a scientist at TechnoCentre éolien. No tools for heavy icing An icing map of Europe has been created in the project Wind Turbines in Icing Environments: Improvement of Tools for Siting, Certification and Operation (New Icetools) at the German Fraunhofer Instiute for Wind Energy and Energy System Technology (IWES). From eight WT sites the regional number of icing days and the degree of icing could be determined for the whole of Europe and a map created. With this tool, which is currently being revised, project developers should receive more concrete details on the climatic conditions. An important result was the finding that even minimal icing on the rotor blades leads to considerable losses of power and to a significant increase in material fatigue, plus that no manufacturers have so far found any technical solutions for heavy icing. The members of the international research group Task 19 (Wind Energy in Cold Climates), which is supported by the International Energy Agency, have come to a similar conclusion. Task 19 is not solely concerned with the effects of low temperatures. More in focus are the consequences of temperatures near freezing and the question of how operations as a whole should run when under extreme conditions. Although the final report has not yet been published, some of the results are already known, for example that the economic risks for operators are hard to estimate. Although there are already commercially available ice detectors, not much experience has been gained and there are no certified calibrations available. On the wishlist are, for example, first class and completely heatable anemometers and sensors, which can continuously show the air humidity, the ice type, the extent of icing and the associated time period. This problem is being looked at by the project Coast 727, with participants including the Swiss company Meteo Test. Anyone going for wind power in the Alpine republic is pretty much forced to look at the subject of cold climates. The question of how icing can be automatically measured has not yet been satisfactorily answered, explains Rene Cattlin, head of the meteorology department at Meteo Test. First it needs to be determined what meteorological measuring instruments and sensors can measure in the first place and whether they can work reliably in extreme conditions too. There is also a big difference between making measurements from the nacelle or on a blade turning in the cold wind. Initial ice-detection prototypes are indeed running fairly reliably, but there are no guarantees he adds. In order to find out more, comprehensive tests will run until the end of the year. Test series with meteorological measuring instruments are being carried out in Germany and Finland. In the Czech Republic and England the research is concentrating on the effects of icing on power lines, while in Sweden and Switzerland methods of detecting icing are being tested on WTs. The results are to be presented in So far there have been few technical means of combating icing. Photo: Kent Larsson 131

3 Wind Energy cold climate zones One of the test turbines in the Coast 727 project is an Enercon E-40 up at 2,332 metres in the Swiss Alps. Photos (3): Markus Russi Switzerland in September at the icing conference IWAIS ( Heating to de-ice blades The test object for blade heating is an E-40 (600 kw) manufactured by the German Enercon, which has been in place up at a height of 2,332 m since 2004 and is operated by Elektrizitätswerk Ursern. Temperatures get down to as low as 30 C on Gütsch Mountain in Switzerland and a maximum gust wind speed of 191 km/h has been measured. We are very happy despite the extreme conditions. The WT has an availability of 99.6 %, says Operations Manager Markus Russi. The question of whether the blades are iced is answered by looking at the power curve. The current power is compared with the value which the WT should be generating under the conditions at the time. If this value is not being reached, then we shut down the turbine and switch the blade heating on, Russi explains. It takes about one and a half hours to de-ice the blades. If the values are still not right after the start-up then the process is repeated. The blade heating is a technically isolated system. Hot air at up to 60 C is circulated within the blades to free them from icing. This is done around 50 to 70 times a year. The main occurrences of icing are in the spring and autumn. In the winter it is not a problem because of the low air humidity, says Russi. Despite losses of approx. 5 % compared to reference sites, wind power in the mountains is worthwhile. In the summer the yields are as thin as the air itself, but in winter the conditions are very good. We get 70 % of our electricity yield then and can thus compensate for the power losses with hydropower. Wind power is an ideal supplement for us, says the Operations Manager. As a result of the positive experiences, Ursern has ordered three more E-48 turbines with blade heating. Two systems in the Czech Republic The decision on turbines was of somewhat larger dimensions for the Erz Mountains in the Czech Republic. For almost two years, 21 Enercon E-82s have been in operation at the Krystofovy Hamry wind farm at a height of 850 metres. The operator is the company ecoenerg Windkraft. The availability has so far been at 97 %, with yield losses of 4 to 6 %. Apart from strong gusts it is mainly fog which often causes icing. Once again the power curve of the turbines is used to identify icing. There are two different systems being used for de-icing. In the one system there is a heating element in each blade, which get their power from their own generator via the slip ring. The closed system runs along the leading edges and one after another heats chambers separated by dividers within the blades at temperatures of up to 50 C. Because of the blade lengths of 53 metres the process takes about four hours. In the other system, heating mats developed by Enercon are undergoing testing. These are laminated onto the inner surface of the blades along the leading edges. This option is more prone to break-downs and larger repairs have been difficult to carry out. For the planned expansion of the wind farm the decision will thus fall in favour of heating elements in the blades, concludes Albrecht Förster from Heliotec. The company is responsible for the technical operation of the wind farm. The operators of the Tauern wind farm in Austria have come to a positive conclusion without blade heating and with different turbines. A turbine caretaker was taken on especially for the wind farm, and travels around in winter using a snowbob. For 5 years now, 13 V 66 Vestas turbines have been in operation at the largest wind farm to be built so far up in the mountains. In 2008 most of the turbines had an availability of close to 99 %, although the monthly statistics of individual turbines showed strong fluctuations. Compared directly, the availability of the WTs as a whole was higher in previous years. Problems with components are not due to the location, though. All in all, the Austrian pilot project is running very well. Due to the climatic conditions the WTs stand still for an average of a week a year, as the height means that icing is not a problem. We get two-thirds of our yield in the winter, reports Richard Distl from the Austrian company Imwind, which is responsible for the operation management. The cold climate features include nacelle heating, special transmission oil and a sensor which detects icing on the rotor blades by measuring their resonant frequency. As the wind farm is next to a skiing area, a warning sounds in the case of icing and the ski-slopes are then closed for safety reasons. Long winter in Sweden Various project developers are preparing to conquer the cold climate zones of Sweden. Until now, hydropower has dominated in this Scandinavian country. The amount of installed wind power capacity was 1,021 MW in As a result of the EU climate targets, a significant expansion is expected. The Swedish Government is financing several pilot projects in the north of the country to the tune of 132

4 international informative independent THE MAGAZINE for Renewable Energies 12 ISSUES IN 2009 ISSN ,50 International issue nternational issue SUN & WIND ENERGY 9/2009 will be published in September 2009 and informs about 25,000 professionals worldwide on the top themes in the sector. THE MAGAZINE for Renewable Energies ISSN SOLAR THERMAL Trends in thermosiphonic systems 9,50 International iss PHOTOVOLTAICS PREVIEW ISH 2009: marketplace for climate protection Highlights of S&WE 9/2009 Technical transfer in mechanical engineering WIND ENERGY Preview: EWEC 2009 in Marseille Photovoltaics Preview of EU PVSEC World map: silicon and wafer Solar thermal Pre-insulated pipe systems The coatings market Wind energy AUSTRIA Strong in solar thermal and bioenergy? US RENEWABLES Roadmap for change? WIND ENERGY Weather forecasts Overview of European offshore wind farms Design and manufacture of rotor blades Biomass Fair preview Interpellets Country specials South Africa: a medal for renewables? Sustainable Scandinavia Light for Ethiopia SOLAR ENERGY FOUNDATION SOLAR THERMAL Market overview of solar control units Renewable energy degrees in the US Solar Thermal Dream team: heat pumps and solar photovoltaics The MagazIne for Renewable energies Module certification: barrier and benefit BIomaSS Pellets markets: worldwide growth FOCUS ON THE JOB ISSN Harvesting the wind US wind power market 9,50 International issue Don t miss your opportunity to reach the fast-growing renewable energy market. SUN & WIND ENERGY truly is The guidepost of the renewable energy community. Point out the way to your company! Call today to secure your successful advert in the next issue of SUN & WIND ENERGY. Let us talk about your individual advertising campaign. Your contact persons: Christian Krosse Yvonne Müller Tobias Fedeler Phone: Phone: Phone: ck@sunwindenergy.com ym@sunwindenergy.com tf@sunwindenergy.com Advertising deadline : 14 th August 2009

5 Wind Energy cold climate zones One of the problems in the Alps is transporting the turbines along the narrow roads. 234 million Swedish Krona ( 21.5 million). The conditions are challenging: Down-times for WTs in winter can be up to two months. Yield losses are calculated in as being 6 to 7 % in the summer and 25 to 30 % in the winter, says Göran Ronsten. He is Project Manager at o2 Vindkompaniet AB and is in charge of the project Cost Effective Large Scale Deployment of Wind Energy in Icing Climates. The Swedish Government is supporting one of the company s projects. 30 WTs totalling 90 MW are to be installed in the northern Swedish municipality of Härjedalens or Sjisjika. So far the decision on turbines has tended towards Vestas. There are good wind conditions at the sites, but icing is a challenge. We want to gain more experience through pilot projects, says Ronsten on their motivation. And the Swedes are in a hurry. The two offshore projects being planning at Utgrunden and Bockstigen are currently too expensive. Consequently, o2 Vindkompaniet has decided to develop wind power projects in the cold climate zones, explains Ronsten. Problems have cropped up here, however. Because of the economic crisis, no manufacturer has so far shown any interest in developing anti-icing solutions with us, he says regretfully. So far o2 has worked together with Vestas. Within the framework of Coast 727, a V 90 with 2 MW without blade heating is being operated in Sveg. Between December 2007 and April 2008 yield losses lay at 5 %. So far there are only hot-air-based solutions from Enercon. Our partnership with Vestas is not etched into stone. We want to purchase turbines with anti-icing systems as soon as possible, and to help develop new systems, says Ronsten clearly. At the moment Enercon, with its patented heating systems, is looking good on the cold side of the business. The Swedish planning competitor Svewind AB has already decided on type E-82 turbines. 40 turbines are to be installed on Mount Gabriel (Gabrieles Berget), 900 kilometres north of Stockholm at a height of 120 metres. A further 12 are planned for installation at Dragliden, 600 kilometres north of the capital. Here, the turbines are to stand at a height of approx. 350 metres. Both locations are classical cold climate sites. Svewind put the first two E-82s into operation at the end of The turbines with blade heating work well. We also reckon that turbines without a transmission are better for these sites, concludes Wolfgang Kroop, CEO of Svewind AB. The Dragliden site lies in the Swedish municipality of Pitea. Together with partners, Svewind wants to push ahead the installation of 1,101 WTs over an area of 450 km², and they have put in the relevant applications to the Swedish authorities for checking and approval. Enercon has a 25 % stake in the implementation company. Svewind has high hopes for the Dragliden site: We want to technically reduce the icing times as much as possible and optimise the icing detection. There is a lot of snowfall in the region and it can get pretty cold, with temperatures down to 30 C. This is why it is very important to gain initial operating experience and to look at the question of access in winter. One special point to make is that we have installed two E-82s, with tower heights of 108 and 138 metres. This makes direct comparisons possible, says Kropp, describing the project. Among the environmental protection issues will be whether and how wind power will affect the large reindeer herds. When asked why the Swedish project developers were being drawn towards the unpopulated and cold north instead of the highly populated south, Kropp has a simple answer: The south of Sweden is too highly populated. This makes it difficult to put up wind farms because opposition forms everywhere. Torsten Thomas 134

6 Wind turbines for cold climate zones The market for wind power in cold climate zones is rising slowly but steadily. This is true not just for the USA and Canada. Enercon is building the first wind farm in the Antarctic and many manufacturers are working on modified turbines. pre-heated so that the oil can reach operating temperatures. In order to guarantee the functioning of the components and electronics, the components are equipped with heating systems. REpower leaves open the question of how the system works. In Canada, icing plays a role because of the damper climate and strong snow falls. We have built up our own know-how for this, explains Rainer Rieckenberg, head of turbine development. By 2020 the market share for cold climate versions of wind turbines in Europe could make up at least 10 %. In numerical terms, Georg Kury from the New Icetools Project at Fraunhofer IWES estimates the amount of installed power to be approx. 9,000 MW by then. Main markets are Switzerland, Austria, Eastern Europe and the Scandinavian countries. Additionally, there is the enormous potential in Canada and North America. So far German Enercon is in the lead technologically. Their products are in demand, with a well-performing icing detection system and two different systems for blade heating. Cold climate fittings are currently available for the types E-48, E-70 and E-82. South Pole Enercon has managed to score a particular coup in the Antarctic. A wind farm with 15 E-10s is to be erected for the German Alfred Wegner Institute s Neumayer III research station for polar and marine research (AWI). The first WT is already supplying electricity. This small wind turbine type has been modified for polar conditions. The station experiences temperatures of down to 50 C and wind speeds get up to a peak of 40 m/s. The blades of the gearless and separately excited threeblade turbine are made of aluminium. The turbine starts operation at 2 m/s, reaches its rated power at 12 m/s and shuts down at 35 m/s. The turbine is permanently heated so that the components don t freeze up when they are stationary. The research station is to have a fully self-sufficient power supply thanks to the wind farm, in combination with hydrogen and fuel cells, explains project leader Saad El Naggar. One turbine weighs just three tonnes and stands on a star-shaped foundation. It can be assembled on the ground and then easily raised past its tipping axis using a pulley, he says. Inner Mongolia The German manufacturer REpower wants to put up MM 82 and MM 92 turbines (both 2 MW) at the total of five wind farms. For this purpose an MM 82 test turbine has been running in Inner Mongolia (China) for almost two years and has already survived icy temperatures. It is designed for operation at down to 30 C and to survive temperatures of down to 40 C. The steel, bearings, oil and grease have accordingly been selected for low temperatures. After any periods of immobility the transmission is Canada Wind power in Canada so far only covers 1 % of electricity demand. The province of Ontario lay ahead in 2008 with 781 MW of installed power, followed by Québec with 531 MW. The state energy supplier Hydro-Québec wants to increase the installed capacity of wind power in the province to 3,500 MW by The first call for tenders was won by Enercon (1,051 MW) and REpower (954 MW). All the wind farms are at cold climate sites and installation is planned for 2011 onwards. Both manufacturers must produce 30 % of the WTs in Canada itself. Eastern Europe and Russia Vestas Central Europe is more tempted towards the cold regions of Eastern Europe and Russia. They have certified low temperature versions of the V 52, V 80 and V 90. They are designed for temperatures of 30 C. Additional heating units provide air conditioning in the nacelle. Sensors register icing through a change in the natural oscillation frequencies of the rotor blades. They have the sole task of switching off the turbine in order to guarantee people s safety. As the world market leader does not have any blade heating, any iced blades are only freed of their loads by natural thawing processes. Torsten Thomas The first of 15 small wind turbines in the Antarctic is already up. 14 further E-10s with 30 kw each are to follow. The station has the long-term aim of becoming self-sufficient. Photo: Saad El Naggar 135