System stability for power systems with a high share of inverter-based renewables (IBRs) is a topic of much discussion. Experience of recent blackouts has highlighted two key characteristics, in addition to inertia, which are needed to ensure system stability:

• Ability to regulate voltage automatically,

• Ability to provide and tolerate high short-circuit currents during and after a fault.

Experience from the 2025 Spanish blackout has indicated that wind and solar power should contribute more than they historically have to the first characteristic. Grid-forming IBRs (presently being developed for wind turbines based on solar PV experience) can provide steady-state reactive power for voltage regulation, as can Type 5 wind turbines driving synchronous generators under AVR control. The reactive power capability depends on the active power being generated, which gives rise to a synergy between wind farms and solar PV, whose active power output is often inversely correlated. The second characteristic is more challenging for IBRs. The paper discusses a mechanical difference between wind turbines and solar PV systems which presents a fundamental barrier to cost-effective implementation of grid-forming IBR wind turbines. By contrast, the proven SyncWind Type 5 wind turbine power-train overcomes that barrier, providing a robust pathway to renewable grid stability.