As Europeans awaited Friday's first major eclipse of the emerging solar age, utilities were bracing for the unprecedented strain on electricity grids as panels switch off and then on again.

The moon will block about 80 percent of the sun's light across Europe from 8 to 11 a.m. London time. In Germany, the eclipse will briefly turn off thousands of panels, which provide about 40 percent of the nation's power on the sunniest days.

A fall of that magnitude will test utilities' ability to keep the lights on as grid operators switch to usually idle natural gas and coal plants.

"When you have plants ramping up and down, there is the potential for outages," Danish power broker Bo Palmgren said. "The hours before and after the eclipse will be interesting." - Bloomberg