An astronomical delight this summer is going to pose a terrestrial problem.

Operators of Ontario’s power grid are bracing for a sharp drop in electricity generated by solar panels during a summer solar eclipse coming Aug. 21, CTV News has learned.

Those with commercial or residential solar panels will see a drop-off in generation when the moon passes between Earth and the sun, turning day into night. That will have those users – tens of thousands of them – switching over to the conventional grid, raising worries about overburdening a system that will already be running at a summer peak.

“We have significant quantities of solar in Ontario,” said Leonard Kula, CEO of the Independent Electricity System Operator, which operates the electricity grid in the province. It’s been preparing for the eclipse for more than a year.

“We will see a reduction of about 70 per cent of the solar generators in Ontario that on the day will be about 10 per cent of our supply.”

The IESO is preparing to have gas plants and the turbines at Niagara Falls make up the difference on eclipse day.

“From around about 1:30 to 3:30, give or take a bit, there will be an increasing drop in the activity from the sun, that is the solar energy they are collecting,” said Paul Delaney, a York University astronomy professor.

“If you’re an organization that relies very heavily on solar power, at 2:32 (pm) on Monday, Aug. 21, you’re going to be way down.”

The province has enough solar power generation capacity to power a city of 2 million people when maximized.

The shadow of the moon will race across Ontario at about 3,700 kilometres an hour and the entire event will last about three hours. At its maximum, 75 per cent of the sun will be obscured in Ontario.

This solar eclipse is just a dress rehearsal for a full solar eclipse coming in 2024 when Ontario is expected to rely even more heavily on solar power.

With a report from CTV Toronto’s Paul Bliss