So you pop your car into "Neutral" and steer off the road as you coast.  It's not convenient, it's not as safe as you'd like, but you are able to control the car and get off the road, in one piece, so you can call someone to bring you a gas can or, if you're not so lucky, to fit a new fuel pump into your budget.  

The physical property that allowed you to coast off the road is called "Inertia".   All of that mass rolling at 70 mph has momentum.   If not - if your car had snapped to a cold stop in the middle of the road when your engine stopped - the semi that was following you down the road might have shown you what Wile E. Coyote felt like after most of those "Roadrunner" cartoons.  

The mass blackout on the Iberean peninsula last month illustrates the importance of inertia in running a first-world power grid. More importantly, it highlights the fact that solar and wind power grids don't have inertia.

Conventional generators produce alternating current, creating a stable output of current and voltage that alternates at a frequency which is directly – synchronously – linked with the rotating turbines which drive the generators in gas, coal, nuclear or hydropower plants. All of these turbines rotate at a speed of 3000 revolutions per minute, so producing electricity with current and voltage that varies in a sine wave shape with a frequency of 50 cycles per second (ie 50 Hz).

Electrical equipment is highly sensitive to this frequency and can break if it deviates too much from 50 Hz. For this reason, power stations, substations, switching equipment and other devices in the grid have fail-safes which will cause them to trip out should frequency fall outside acceptable bounds.

The generator, like your care, has inertia.  So all of that rolling mass in those steam and hydroelectric generators - tons of metal spinning at fifty revolutions per second - takes a while to "spin down", giving power networks a reserve of time to respond to problems in the power grid.  

Solar power has no inertia; it's on, or it's off.   Wind power has mechanical generation, but the frequency is random, and dependent on having, or having enougn, wind.  So if a power grid doesn't have that inertia - those few minutes while the generators are still cranking away out of pure momentum - there'll be nothing to prevent those fail-safes from kicking in and shutting down the grid before backup power can be brought online.

 That's precisely what happened in Spain and Portugal - and what is likely to happen in other countries with newly-"green" power grids.  

That's a lot of background for what is turning into a fairly fast legislative push to reverse 45 years of hysteria about nuclear power in Europe.  Example:  the Danish Folketing, or Parliament, reversed a 40 year ban on nuclear power, in a vote whose debate likely took less time than writing this article has, so far:

The totemic change – rammed through in a parliamentary vote – passed with only a few murmurs from the country’s MPs, two thirds of whom supported it.

“It was so fast I thought I’d missed it,” says Mark Nelson, an energy consultant who was invited to watch the vote on Thursday.

“I was texting a parliamentarian, and I’m like, ‘Was that it? Did it pass?’”

The historic nature of the vote should be in no doubt. Denmark’s ban has been in place since 1985 and was so draconian that it forbade the government from even considering atomic energy as an option.

Denmark has led Europe in adopting and mandating "green" energy, getting about 3/5 of its energy from renewables today.  But it hasn't been cheap; a kilowatt hour in Denmark costs over triple the average cost in the US.  

But the instability of the supply of Russian oil and natural gas since the start of the Ukraine War, the explosion in demand for electreicity with the growth of AI data centers, and the sight of the Iberian peninsula going and staying dark, may be starting to convince Europe that it's time to look into a slightly darker shade of green.