The share of renewable energy sources (RES) within the power system is increasing rapidly, with wind energy and photovoltaics becoming the most dominant sources. As a result, these fluctuating generators must transition from being pure energy suppliers to active contributors to security of supply and grid stability. Consequently, stable grid operation is becoming increasingly complex. A critical aspect of this transition is the provision of reactive power, a task that has traditionally been the responsibility of large-scale conventional plants at the transmission level but is now shifting towards decentralized units.

Over the past 25 years, the German onshore wind sector has experienced exponential growth, with installed capacity surging from 6 GW to over 68 GW by the end of 2025, supported by nearly 29,000 units currently in operation. Looking ahead, Germany's national targets aim for a further expansion to a total capacity of 115 GW by 2030. This rapid scaling is driven by significant technological advancements; contemporary turbines now feature average capacities of 5.5 MW. Consequently, grid connection patterns are shifting. While historically over 75 % of connections occurred at the MV level, current trends show a rising reliance on HV grid infrastructure, which now accounts for 30 % of new grid integrations.

Integrating distributed renewable energies implies a gradual shift of generation from transmission to distribution levels, bringing about a fundamental change in operational responsibilities. A crucial issue in this context is the provision of reactive power, which is intrinsically linked to voltage stability across all grid layers. To address these evolving needs, technical requirements have been tightened based on the VDE-AR-N 41XX series of standards. In addition to these regulatory mandates, the transition is supported by economic mechanisms, most notably the introduction of a dedicated German market for reactive power in April 2025 to incentivize voltage control services.

The paper analyzes the development of wind-based reactive power provision capabilities across German EHV, HV, and MV grids over the past 25 years, utilizing public data from the German regulatory authorities. It evaluates the corresponding former and future regulatory framework and grid codes for the different grid levels focusing on technical minimum requirements. By combining both analyses, the development of the reactive power potential of the wind sector at the EHV, HV, and MV levels is quantified, evaluated and presented.

Our analyses demonstrate that the largest share has historically been, and still is, at the MV level, while the share at the HV level is increasing. Alongside minimum grid code requirements, this market-based approach is also addressed and evaluated. The findings provide valuable insights, particularly for DSOs and TSOs.