Europe's ageing power grid and lack of energy storage capacity will require trillions of dollars in investments to cope with rising green energy output, increasing electricity demand and to avoid blackouts.

Electricity is pulsing through Spain and Portugal again after a massive outage knocked out power in both countries on Monday. So too are questions.

The sweeping power outage that hit Spain and Portugal this week has raised questions about the electricity grid in a region not normally known for blackouts.