Fingrid will require new wind and solar plants in Finland’s weakest grid areas to provide grid-forming capability, which developers can meet with co-located batteries sized at up to 30% of plant output.
Finnish transmission system operator Fingrid has published technical requirements obliging new large wind and solar plants in converter-dominated parts of its network to provide grid-forming control, either through their own inverters or through separate equipment built at or near the site.
Fingrid announced the measure in late Setpember and published the detailed requirements earlier this month, under its VJV2024 grid code for power plants. They apply to type D plants connecting where the equivalent short-circuit ratio (ESCR) at the connection point is below 1.0. Existing plants and projects that already hold a connection agreement are exempt.
Wind generation in Finland is concentrated in such areas, notably along the west coast, and grid security can be disrupted where there is too little synchronous generation, Fingrid said. Its requirements document says grid-following converters in these areas can cause poorly damped voltage oscillations, weak fault ride-through and overvoltages during three-phase faults, risking the disconnection of plants at scale, and that tuning control parameters alone can’t solve the problem.
Developers can choose between batteries, energy-storage-equipped static synchronous compensators (ES-STATCOMs) and synchronous machines such as synchronous condensers. Minimum sizing rises as the grid weakens. A battery must be rated at ±10% of the plant’s capacity where the ESCR is between 0.9 and 1.0, ±20% between 0.7 and 0.9, and ±30% below 0.7. The equivalent thresholds are 7%, 13% and 20% for an ES-STATCOM, and short-circuit power of 33%, 66% and 100% of plant capacity for a synchronous machine.
The equipment must be online whenever the plant runs at 50% of its rated output or more, and in service before the plant first exports power. It must sit within 60 km of electrical distance from the plant, either inside the plant, at the same substation or on the same 110 kV line, so that a single fault on Fingrid’s meshed network cannot separate the two.
Batteries installed to meet the requirement may trade in electricity and reserve markets, provided that market activity never cuts into their minimum stabilizing capability. A battery providing system services must also comply with Fingrid’s storage grid code. One that does not participate in markets can instead be treated as an ES-STATCOM and sized at the lower thresholds.
Fingrid will present the requirements in a webinar on Oct. 16.
Fingrid already requires grid-forming capability from large batteries under its storage grid code, and Merus Power’s 30 MW/80 MWh project in Rovaniemi is among the systems being built to that standard. The four Nordic transmission system operators said in a joint position paper in November 2025 that grid-forming requirements for wind and solar would follow the evolution of European network codes. India’s Central Electricity Authority has separately proposed mandatory grid-forming inverters and co-located storage for new solar and wind projects.
Pairing batteries with wind is not new in Finland. Ilmatar’s 30 MW/41 MWh Ainola battery, co-located with the Piiparinmäki wind farm in North Ostrobothnia, went online in June 2025, when the country had about 250 MW of battery capacity in operation.
This content is protected by copyright and may not be reused. If you want to cooperate with us and would like to reuse some of our content, please contact: [email protected].