From an article in the Financial Times today, about a solar eclipse on March 20th, 2015:

An eclipse of the sun next month could disrupt Europe’s power supplies because so many countries now use solar energy, electricity system operators have warned.

“The risk of incident cannot be completely ruled out,” the European Network Transmission System Operators for Electricity said on Monday, adding the eclipse on March 20 would be “an unprecedented test for Europe’s electricity system”.

[...]

ENTSO-E said the eclipse could play a bigger role in places such as Germany, Europe’s largest economy, which now gets more than a quarter of its electricity from renewable generators and like other EU nations is connected with neighbouring countries’ grid systems.

The organisation also said it had been planning co-ordinated “countermeasures” for several months to help protect the continent’s power system from the eclipse [...]

Patrick Graichen, executive director of Agora Energiewende, a Berlin renewable energy think-tank, said the March 20 eclipse was unlikely to cause any problems because there are several well-known ways of balancing power supplies and there has been plenty of time to plan.

But the eclipse will still be a “stress test” of the flexibility of the European power system, he added, because it will have to adapt to a more abrupt shift in solar power generation than would normally occur, especially if it is a sunny day and all solar power stations were producing at full load.

“Within 30 minutes the solar power production would decrease from 17.5 gigawatts to 6.2GW and then increase again up to 24.6GW. This means that within 30 minutes the system will have to adapt to a load change of -10GW to +15GW,” he said.

The eclipse is supposed to last about 3 hours, but I am skeptical as to how this can be so much more impactful than normal sunlight reduction on a daily basis because of clouds, etc.

Should the eclipse be expected to be much more impactful than a normal cloudy day?