As far as I know, the power outage in Portugal and Spain did not start with renewables

Grids are best modelled as a system, jointly operating. Insufficient damping is the cause as per the grid operator (1).

Can be solved in multiple ways such as make it a france problem (stronger interconnects to a system with more turbines), storage, improved DC-AC transformers for small (<1MW) solar plants. (*)

Pumped storage is indeed one of the best known technologies for grid stability, as it provides both storage, and turbines with inertia. Hard to build though, finding funding and appropriate locations. Then solar suddenly isn’t as cheap if one takes into accou t the cost to make it a reliable source of energy.

(*) the report mentions an estimated 700MW of production auto-shutting down as grid frequency dropped. Most likely these are the inverters of small scale solar installations, which are frequency following (measure then adjust) rather than synchronizing, and simply shut off when out of bound. To quote:

The rapid schedule changes in photovoltaic generation driven by price fluctuations in electricity markets. From an electrical standpoint, such abrupt changes in inverter - based generation introduce significant imbalances into the system, because regulation mechanisms haven´t operated yet. These imbalances must be compensated mainly through interconnections, particularly the one with France . Severe imbalances lead to drastic shifts in power flows across the network, which in turn alter the capacitive and inductive behaviour of the grid. Consequently, system voltages can vary rapidly. This effect is further exacerbated when such generation oper ates under power factor control and doesn´t provide dynamic voltage control, as it limits the dynamic reactive power support that could otherwise help stabilise voltage