Fingrid requires grid-forming capability from new wind and solar where the ESCR is below 1.0
Serguey Asael Shinder2 min readFinland's transmission system operator Fingrid will require new large wind and solar plants in the weakest parts of its network to provide grid-forming control, pv magazine reported on 15 October. Fingrid announced the measure in late September and published the detailed technical requirements in October under VJV2024, its grid code for power plants.
Who is covered. The rules apply to type D plants connecting at points where the equivalent short-circuit ratio (ESCR) is below 1.0. Plants already in operation and projects that already hold a connection agreement are exempt. According to the report, Fingrid says wind generation in Finland is concentrated in such converter-dominated areas, notably along the west coast, and that grid security can suffer where synchronous generation is scarce. Its requirements document says grid-following converters there can cause poorly damped voltage oscillations, weak fault ride-through and overvoltages during three-phase faults, with a risk of plants disconnecting at scale, and that tuning control parameters alone cannot fix this.
Three ways to comply, sized by grid strength. Developers can use batteries, static synchronous compensators with energy storage (ES-STATCOMs) or synchronous machines such as synchronous condensers. The required size grows as the grid weakens:
- battery: ±10% of plant capacity for an ESCR between 0.9 and 1.0, ±20% between 0.7 and 0.9, ±30% below 0.7;
- ES-STATCOM: 7%, 13% and 20% for the same bands;
- synchronous machine: short-circuit power of 33%, 66% and 100% of plant capacity.
Operating conditions. The equipment must be running whenever the plant produces at 50% of rated output or more, and must be in service before the plant first exports power. It has to sit within 60 km of electrical distance — 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 may earn money, within limits. A battery installed for compliance can trade in electricity and reserve markets as long as that never reduces its minimum stabilising capability; if it provides system services it must also meet Fingrid's storage grid code. A battery that stays out of the markets can be treated as an ES-STATCOM and sized at the lower thresholds.
Context. Fingrid already requires grid-forming capability from large batteries under its storage code, the report notes. The four Nordic TSOs said in a joint paper in November 2025 that grid-forming requirements for wind and solar would follow the development of European network codes.
Source: pv magazine — https://www.pv-magazine.com/2026/10/15/finland-demands-grid-forming-support-for-new-wind-solar-in-weak-grids/