Repowering potential of German onshore wind energy

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Challenges

There are many reasons for the current backlog. The available grid connection capacities are not always used efficiently, and the existing grids are reaching the structural limits of their capacity⁶. Despite the simplifications introduced by the legislature in the meantime, planning and approval procedures continue to pose a challenge for project developers. It often takes several years between the submission of an application for the construction of a plant and its commissioning. In addition, wind turbine operators often face considerable resistance from the public or environmental groups. Criticism ranges from disruption of the landscape to harm to protected species.

The solution: repowering?

Repowering is one possible solution to many of the existing challenges: old wind turbines are replaced with more modern and powerful models. Thanks to larger rotor diameters, higher hub heights, and more efficient generators, the rated output of newly constructed turbines has increased significantly over the past 20 years—from an average of around 1 megawatt (MW) in 2000 to around 5 MW today. In addition, electricity yield can be increased thanks to more stable wind speeds in higher wind layers and higher capacity factors, i.e., the utilization of rated power over the course of the year. Figure 2 shows a common rule of thumb: repowering can triple or even quadruple electricity yield while maintaining the same area and reducing the number of turbines by about half.⁷

 

 

Furthermore, repowering reduces bureaucratic hurdles: there is no need for time-consuming land acquisition, as proven sites with existing grid infrastructure, which may need to be reinforced, are used. Less resistance from the population is also to be expected, as the turbines are erected at familiar locations and no additional encroachment on untouched natural areas is necessary. In addition, potential hazards to animal species are reduced, as the smaller number and more modern design of the turbines means that disruptive influences can be minimized.⁸
 

Repowering potential in Germany

The impressive potential of repowering in Germany is shown in the model developed in Figure 3. It assumes that all wind turbines will be replaced after 20 years of operation, that all turbines erected before 2005 will be repowered evenly by 2030, and that repowering will triple today's capacity. In the diagram, the light green line represents the cumulative installed capacity of onshore wind energy until 2024 and then the development required to achieve the German government's targets for 2030. The gray bars show the annual increase in recent years. The dark green bars illustrate the potential contribution of repowering, and the blue bars show the necessary expansion of wind energy through the development of new sites. The following key findings emerge from the scenario considered:

The scenario assumes a tripling of capacity through repowering. In fact, the targets for onshore wind energy could be achieved with a 3.4-fold increase in yield through repowering alone, with current studies showing that such a factor is not inconceivable.⁹ The repowered turbines would achieve a total capacity of 73.1 GW, and the development of new sites would no longer be necessary.

Continued operation or repowering?

Repowering represents a strategic investment decision for wind farm operators. They must weigh up whether an investment in repowering and the resulting revenues from electricity generation exceed the economic benefits of continuing to operate the existing old turbines. This question is closely linked to the framework conditions set out in the Renewable Energy Sources Act (EEG). As is well known, since 2017, electricity from renewable energies has no longer been subsidized via a fixed feed-in tariff, but via tenders with limited volumes. The winners of the tender receive a value equal to their bid for 20 years. For example, the average value to be applied on the bid date of May 1, 2025, was 6.83 cents per kilowatt hour (kWh).¹¹ In addition, a correction factor was introduced in the EEG in 2021 to continue the promotion of low-wind locations, which increases their value to be applied by up to 4.56 percent (EEG 2021).¹²

After 20 years of operation, there are two options for a wind farm: continued operation with sales at low and volatile electricity exchange prices, or repowering, which (still) allows for a fixed value to be applied within the market premium model for another 20 years. What is important for profitability is that the operator wins the tender with its bid, while at the same time ensuring that this bid enables a positive profit. A study by Fuchs et al. concludes, based on a fictitious example, that continuing to operate the old wind farm only makes sense if approval for the new wind turbines is rejected and positive margins can continue to be achieved from electricity generation. The latter is not a given (even without further depreciation), as low revenues at the exchange electricity price are offset by high maintenance and repair costs.

Due to the significantly higher feed-in from modern wind turbines, existing grid connections usually have to be checked and often adapted, as the requirements for voltage, reactive power, and short-circuit behavior also change. In practice, this usually involves upgrading transformers, cables, and protection technology, as well as implementing current grid connection rules (e.g., VDE-AR-N 4120) to ensure the safe and stable integration of the increased feed-in capacity.^{13 14}

Legislative course setting

The legal framework is a key factor in the feasibility of repowering projects, and this has been significantly simplified in recent months, particularly with regard to the possibilities for repowering. For example, extensive adjustments were made by the Act to Improve Climate Protection in Immission Control, to Accelerate Immission Control Approval Procedures, and to Implement EU Law, which was published in the Federal Law Gazette on July 8, 2024, and came into force one day later. This omnibus bill, described by coalition circles as the most significant amendment to the Federal Immission Control Act (BImschG), accelerated the approval process for immission control legislation in order to contribute to achieving the net greenhouse gas neutrality target set out in the Federal Climate Protection Act for 2045.​
 
In addition to shortened approval periods and greater digitization and streamlining of approval procedures, the legislature has made extensive adjustments to the regulations governing repowering. Section 16a(2) sentence 1 of the Federal Immission Control Act (BImSchG) thus clarifies that a measure must be classified as repowering regardless of the extent of the structural differences in size, the increase in output or the change in the number of installations in relation to the existing installation.​ ​​​In addition, the scope of repowering has been significantly expanded. For example, the period to be observed between the dismantling of the existing plant and the construction of the new plant has been doubled from 24 to 48 months, and the distance to be maintained between the existing plant and the new plant has been increased to five times the total height of the new plant (previously, twice the total height was the required distance). § 16b (2) sentence 2 BImSchG. As a result, project developers have much more flexibility in their planning without having to forego the simplifications for repowering projects.

If the location of a plant is changed by no more than 8 meters, the total height is increased by no more than 20 meters, and the rotor span is reduced by no more than 8 meters, only the stability and the harmful environmental effects caused by noise and adverse effects caused by turbulence need to be examined, Section 16b (7) sentence 3 BImSchG.

​In the case of only minor changes within the meaning of Section 16 (7) sentence 3 BImSchG and in cases where the output or yield of an onshore wind turbine is increased without structural changes or without the replacement of parts and without a change in the approved operating hours, a deemed approval applies after six weeks have elapsed, provided that the authority has not previously decided on the application or a hearing has been requested, Section 16b (9) sentence 1 BImSchG. Finally, repowering does not require the operator of the existing plant and the project developer to be the same entity. The operator of the existing plant must only have approved the project developer's application by the time the authority makes its decision, Section 16b (10) sentence 1 BImSchG.

Furthermore, repowering projects cannot be opposed on the basis of the exclusionary effect of Section 35 (3) sentence 3 BauGB, which results from existing concentration area planning, Section 245e (3) BauGB. Rejection of the project can only be considered if, in exceptional cases, the basic principles of planning are affected. The only exceptions to this are Natura 2000 areas and nature reserves.
 

Success stories in practice

The North Frisian municipality of Galmsbüll shows that repowering is not a new invention – a repowering project was already implemented here between 2005 and 2007 in the form of a community wind farm. In addition to individual operating companies, citizens contributed one-third of the total costs, with demand significantly exceeding supply. The project enabled 38 wind turbines with a total capacity of 12.4 MW to be replaced by 21 turbines with a total capacity of 60 MW.¹⁶

Another successful example is the project completed this year by the VSB Group at the Elster wind farm in Saxony-Anhalt. Thanks to the repowering project, the wind farm now occupies a third less space and can supply around 150,000 people with electricity.¹⁷ With an investment of €200 million, 50 old turbines were replaced by 16 state-of-the-art turbines, enabling a sixfold increase in annual electricity production to 235 GWh in the future.^{18 19}
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Conclusion

For wind farm operators, repowering is a powerful lever for simultaneously increasing yield, planning security, and acceptance. If the wind farm is located in its own grid or distribution area ​​(including energy suppliers), there are further advantageous circumstances that facilitate the project: existing locations with existing grid connections supplemented by direct access to the customer side. Strategically, repowering is clearly preferable to continued operation, at least after the fixed feed-in tariff expires. From around the 15th year of operation, wind farm operators such as municipal utilities should therefore consider the following points:

Careful analysis of these points is essential, especially while the fixed market premium under EGG still exists, as otherwise it is difficult to determine the optimal time window for repowering from an economic perspective. In addition, municipal utilities should also consider the targeted acquisition of old wind farms in their own grid and supply area. Examples such as Statkraft show that the market for such business models has long been established: the group invested around €413 million in the purchase of 35 old wind farms in Germany. This enables municipal utilities to secure locations, leverage repowering potential, and at the same time strengthen regional value creation, competitiveness, and security of supply in the long term.²⁰