Second time around

A new era in windpower in Germany is emerging with the successful launch of several repowering projects and the prospect of many more to follow.

Germany’s coastal landscape is beginning to change. Wind turbines that have been a feature of the shoreline for ten years or more are starting to come down. In their place, just half their number are going up – but these are much bigger turbines and a whole lot more efficient.

Europe leads the world in developing wind power projects. Germany was among the first to enter the field and still generates more power from wind than any other EU country. A number of Germany’s oldest wind projects are now being redeveloped with old technology being replaced by new. But why does it make sense now for these repowering projects to be undertaken and what are the prospects of it becoming an increasing trend?

Figure 1. Siemens’ 2.3 MW MkII turbine features in several repowering projects
Click here to enlarge image

According the Global Wind Energy Council (GWEC), Europe has historically been the strongest market for wind energy development. In 2005, the European Union saw another record year with installations above 6000 MW, thereby reaffirming its undisputed status as the world’s biggest wind market. The figures demonstrate a healthy underlying trend in the European market where the top five contributing countries in 2005 were Germany, Spain, Portugal, Italy and the UK.

At the end of June 2006 Germany had an installed windpower capacity of 19 299 MW, accounting for more than six per cent of the country’s total installed capacity. The target for 2020 in Germany is 20 per cent of electricity generation from wind turbines. Much of this growth will come through the development of offshore wind parks but to reach this target both new offshore wind farms and repowering of existing onshore sites is needed.

Bigger and better

Repowering wind energy projects refers to the replacement of older, smaller and less efficient wind turbines with new state-of-the-art equipment. Repowering of existing wind energy sites offers great potential. By replacing existing small wind turbines with larger machines, more generating capacity can be obtained in the same site area. Repowering projects have become economically viable as technology has advanced but in Germany there is also the impact of a tapering feed-in tariff that is influencing developers. “Money is a driver. German wind power projects started with a €0.09 ($0.11) feed-in tariff but this reduces down to around €0.06 towards the end of the 20-year period,” explains Norbert Giese, managing director of offshore projects for Siemens Windpower in Germany. “It makes sense for those at the lower end to start again through a repowering project and enjoy the higher tariff.”

An existing wind park has the advantage that it already has secured the necessary permits. “You can use your existing power station site for wind turbines far more efficiently” argues Giese. “Put simply; with half the number of turbines you can double the capacity and triple the energy output. This is because you are using much larger turbines with greatly improved efficiency.” The improved efficiency comes not only from the integral effectiveness of the machines but also arises from the increased hub height of modern wind turbines. “At the Braderup wind park in north west Germany for example, 40m high towers have been replaced with towers ranging from 60-80m, depending on the size of the turbine,” says Giese.

Repowering naturally starts at sites that combine the best wind conditions with the oldest wind turbines installed. In Europe the first repowering projects started in Denmark by repowering a large number of old machines from the 1980s. In the USA there have also been a few repowering projects particularly in California where smaller 1980s machines were replaced by significantly larger current generation models.

After the boom for new wind turbines in Germany in the past few years, the repowering of already existing sites is becoming more and more important. Larger units will replace the smaller and older wind turbines, especially at sites with strong wind conditions. It is expected that in the next decade the installed onshore capacity in Germany will almost be doubled while the numbers of actual installed turbines will decrease.

Repowering has the potential to play an even stronger role but numerous Federal States and local regions have issued regulations concerning vicinity and height restrictions. “These regulations could hold back repowering but there are discussions happening to relax the rules – this is a political process but I am optimistic,” says Giese. The movement towards repowering in Germany has only been going around one and a half years and so far has centred on where the German wind industry began, at the coastline in North Friesland.

Latest projects

Siemens Power Generation currently has orders to supply a total of 17 wind energy turbines for three repowering projects in Germany. Of these, seven 3.6 MW wind turbines will be for the Marienkoog project, and will replace 15 aging wind turbines. The operator of these plants is Bàƒ¼rgerwindpark Galmsbàƒ¼ll GmbH. With an installed capacity of over 50 MW, this project will be the largest wind farm in Germany when it begins commercial operation scheduled for mid-2007. The coastal site makes it suitable for the largest machines, which are now on such a scale that transportation to many inland sites is impractical.

Another seven 2.3 MW wind turbines will be for the Norderhof Wind Park in the North Frisian area, in Schleswig-Holstein. Also, in Bremerhaven, aging wind turbines are being replaced by new equipment. At the Weddewarden Wind Park, three 2.3 MW machines, with a rotor diameter of 93 m and a hub height of 103 m, are replacing small units. This will increase the installed capacity from 2 MW to nearly 7 MW. Apart from higher efficiency of the new wind turbines, the increase of the hub heights was a driving force in using the sites.

New heights

Siemens already replaced 15 existing smaller wind turbines for one of the first repowering projects in Germany, the Bàƒ¼rgerwindpark Braderup GmbH & Co. KG, in northern Schleswig-Holstein. Braderup enjoys strong wind conditions but has some of Germany’s oldest wind turbines. It is the first project so far to have gained approval to surpass the 100 m total height limitation imposed in Nordfriesland.

In 1994 a wind farm association was founded with 33 people from Braderup and the surrounding areas. At that time, the association built and operated 15 wind turbines, each with a rated electrical output of 750 kW. In 2004, when the subject of repowering arose in Germany the members of the small association in Braderup not only talked about the new situation, they also took action. They decided to purchase eight modern wind turbines of two different types from Siemens Wind Power: four SWT-2.3-82 VS models, each with a hub height of 58.5 m, a rotor diameter of 82 m and a rated output of 2.3 MW, and four of the Siemens PG flagship, the SWT-3.6-107. These models have a hub height of 80 m, a rotor diameter of 107 m and an installed electrical capacity of 3.6 MW. The 107 m rotor diameter means that the rotor blades sweep an area of 9000 m2.

Figure 2. Forecast for regional wind power growth 2006-2010
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The objective of the repowering was to obtain substantially more electrical power revenue from the same footprint and that was impressively achieved. With only half the number of turbines (there are now eight instead of the former 15 turbines) and twice the installed capacity (now 23.6 MW instead of the former 11.25 MW), it is now possible to produce three times as much power – 57 MWh as compared to 19.3 MWh. The environment is also three times better off with a CO2 savings of 51 300 tonnes compared to the earlier 17 370 tonnes.

State permission

Obtaining permission from the Schleswig state environmental agency to raise the overall height of the turbines to more than 100 m was a significant factor in achieving an increased output. Increased yield at this site is in large measure the result of this height increase. This is due to the fact that wind speed increases dramatically with increasing height above ground level. In order to handle the increase in generated power, a new substation was built jointly with other wind farms in cooperation with the company E.ON Netz in North Friesland. The substation steps down the electrical power to the 110 kV level for distribution.

New opportunities

One consequence of the emergence of a repowering market in the wind sector has been the creation of a market in used equipment that is being brokered to new projects in emerging markets such as Eastern European countries or for spare parts for existing projects. This is enabling these countries to begin developing green energy projects at a fraction of the cost of new equipment. In some cases the second-hand equipment is used in demonstration projects to test wind conditions. Currently, second-hand wind turbines are being demanded in Poland, Russia, Romania, Bulgaria and Turkey, where new renewable energy laws have included legislation allowing for the development of wind farms.

Giese is optimistic about the future for wind repowering in Germany and elsewhere, based on the economics and improved technical efficiency of equipment. “There are still a few more new sites to develop in Germany but after that you are only left with the repowering market or going offshore. We are just starting now, but at the end of the day we will have a 100 per cent repowering market in Germany,” says Giese. Other countries ripe for repowering projects include Denmark, The Netherlands and one region of Spain, since these are the places with the oldest turbines or those from manufacturers no longer in business.

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