Europe’s grid-connection requirements are increasingly treating power-system stability as a development and financing issue for renewable projects. The shift is particularly relevant in Southeast Europe, where wind, solar and battery additions are being made to transmission networks with ageing assets, long cross-border routes, concentrated conventional generation and limited local voltage support.
ENTSO-E published new technical guidance on forced oscillations in July 2026 after two years of work with WindEurope. The guidance supports two new provisions proposed for the revised Network Code on Requirements for Grid Connection of Generators, known as RfG 2.0, covering permissible amplitude and duration of oscillations produced by power park modules.
Forced oscillations and their relevance to grid-connection requirements
The guidance addresses periodic fluctuations injected into the network by generating equipment. ENTSO-E says the requirements will apply not only to wind farms but also to solar photovoltaic plants and electricity-storage modules.
The scope covers utility-scale renewable projects under development in Serbia, Montenegro, Bosnia and Herzegovina, North Macedonia, Albania, Bulgaria, Romania, Croatia and Greece. Forced oscillations are distinct from grid-code topics such as fault ride-through, reactive-power control, active-power control and frequency response.
Forced oscillations occur when generating equipment repeatedly injects power variations at a particular frequency. In wind turbines, those variations can be linked to tower movement, blade-passing effects, wind shear, turbulence, waves or active tower-damping systems.
For solar and battery installations, oscillatory behaviour can arise through converter controls, plant controllers, filters and interactions between multiple power-electronic devices. The risk increases when the injected frequency is close to a natural mode of the transmission system.
In that case, resonance can amplify the disturbance and produce fluctuations larger than those at the source. A local control issue can then propagate across a synchronous area, stress equipment, trigger protection systems or contribute to cascading disconnections.
RfG 2.0 frequency range and measurement approach
The draft RfG 2.0 provisions cover forced oscillations in the range of 0.1–20 Hz for larger Type C and Type D power park modules. The lower part overlaps with inter-area and local electromechanical modes associated with synchronous power systems.
Frequencies between approximately 2 Hz and 20 Hz increasingly reflect interactions among converters, control systems and network equipment. The upper boundary is partly practical because measurements above 20 Hz would generally require point-on-wave equipment not yet standard across European transmission systems.
The framework therefore allows compliance assessment to rely on high-resolution phasor measurements, specialised power-quality recorders and advanced data-processing tools. ENTSO-E’s approach is aimed at ensuring that oscillation behaviour remains within permissible limits for the relevant module types.
Compliance evidence beyond OEM certificates
Grid compliance cannot be demonstrated solely using generic OEM certificates and conventional RMS dynamic models. Developers may need site-specific measurements, validated frequency-domain behaviour, higher-resolution simulation models and evidence that turbine-inverter-plant-controller interactions remain stable under credible operating conditions.
This requirement is described as particularly relevant for projects using equipment from Chinese or Turkish manufacturers. The concern is not technology origin but whether control models, source-code protections, validation procedures and technical support align with European and Serbian grid-compliance processes.
An OEM may provide a black-box RMS model suitable for load-flow, short-circuit and conventional dynamic studies while declining to release electromagnetic-transient representations needed to investigate converter interactions . A model can also produce different results after translation into software used by EMS operators including CGES, HOPS, ESO, Transelectrica or IPTO .
Version control is another exposure point because firmware updates during construction can invalidate studies completed during development. For a 150 MW wind farm, the compliance package can include turbine-level and plant-level RMS models as well as EMT models.
Wind versus solar versus storage verification scope
The wind compliance set can also include harmonic impedance data, plant-controller logic, reactive-power-control validation, fault ride-through simulations and frequency-response tests . Oscillation studies and field measurements during staged energisation are also part of the described work scope.
The studies must cover the main transformer and collection system plus shunt reactors where applicable. They also need to address STATCOM or synchronous condenser where applicable and include characteristics of the grid at the connection point .
Wind turbines are treated separately from solar because they combine converter controls with rotating mechanical structures and aerodynamic excitation. Larger turbine rotors and taller towers introduce different natural frequencies and damping requirements compared with other technologies.
Wind projects typically have higher capacity factors and often connect through long 110 kV, 220 kV or 400 kV lines in remote areas. That changes system value and stability behaviour relative to a solar plant with the same nominal capacity.
Solar introduces scale combined with limited visibility because distribution networks increasingly contain hundreds of smaller inverter-based installations. ENTSO-E plans a separate expert process during the fourth quarter of 2026 to examine non-observable embedded generation, particularly solar PV .
Batteries add bidirectional operation and rapidly changing control modes through charging, discharging, frequency response, reactive support and standby within short intervals. Control transitions can create interactions not captured by simple steady-state modelling.
The guidance notes that grid-forming batteries may improve system strength but require more demanding verification than conventional grid-following systems. This affects how developers prepare evidence for grid-connection approval processes across different module types.
Cost impacts from studies timing to contract obligations
The financial exposure begins before commissioning through additional engineering workstreams. A medium-sized Southeast European wind project is cited as having total investment costs of approximately €1.2 million–€1.6 million per MW, depending on terrain, turbine supply, balance-of-plant costs and grid infrastructure.
For a 150 MW project this implies an indicative investment envelope of €180 million–€240 million. A comprehensive grid-compliance workstream involving specialised studies, instrumentation, OEM model development and independent verification may absorb 0.5–1.5% of CAPEX—roughly €0.9 million–€3.6 million.
The described cost impact is manageable when incorporated during FEED and procurement but becomes more expensive after equipment selection. Late discovery that selected turbines or inverters require a STATCOM or additional harmonic filtering can add several million euros and delay energisation by six to 18 months.
A 12-month grid-connection delay can reduce project equity returns by approximately 1.5–3 percentage points, depending on leverage, interest during construction, power-price conditions and whether an EPC contractor or OEM accepts liability . Delays can also affect debt availability periods, PPA long-stop dates, equipment warranties and eligibility deadlines under support schemes.
EPC scope, owner’s engineer oversight and staged commissioning tests
The contract structure is described as important alongside engineering because turbine and inverter supply agreements should include binding obligations on model usability and validation for TSO studies. Those agreements should also cover participation in factory and site testing plus correction of non-compliance while maintaining model consistency following firmware changes .
EPC contracts should allocate responsibility for complete plant response at the point of connection since EPC performance guarantees depend on access to underlying converter logic models held by OEMs . A bankable arrangement requires aligned obligations across EPC contractors, OEMs, plant-controller suppliers, transformer vendors and compensation-system providers.
An Owner’s Engineer oversight role is described as central through a live grid-compliance matrix linking each requirement to design evidence, simulation models, responsible parties, test protocols, acceptance criteria and final certificates . Model submissions should be version-controlled alongside actual equipment settings.
The described approach includes factory acceptance testing verifying that delivered controllers match models used for approved studies . Commissioning then proceeds through staged energisation starting with transformer and collection-system behaviour before introducing individual generating units.
Turbines or inverter blocks are added progressively while recording voltage, frequency as well as active power, reactive power harmonics and oscillatory behaviour . Final plant-controller tests are expected to cover normal dispatch ramping curtailment voltage control frequency response plus credible disturbances .
RfG 2.0 timetable for European Commission approval into national implementation
The regulatory timetable described provides room but limited certainty for developers entering procurement or construction during the transition period. ENTSO-E expects the European Commission to complete the amended RfG during 2026, followed by national implementation taking up to three years.
Projects entering procurement or construction during that period face a moving compliance baseline because plants designed around today’s minimum national requirements could become technically outdated before receiving final operational notification . Serbia’s market integration is tied to regulatory alignment since its transmission system is synchronously connected to Continental Europe.
Lenders financing projects with operating lives of 25–30 years are described as unlikely to accept equipment meeting only narrow local interpretations without demonstrating compatibility with emerging European standards . The rules are framed around treating grid compliance as an ongoing design discipline supported by transparent models testing support and enforceable performance guarantees .
