Solar 101
Do Solar Panels Work Under Cloudy Weather? Debunking the Myths
Yes, solar panels still produce power on cloudy days. See how clouds affect output, why Ontario's climate works for solar, and what it means for your roof.
Yes, solar panels still produce power on cloudy days. See how clouds affect output, why Ontario's climate works for solar, and what it means for your roof.
One of the most common doubts we hear from Ontario homeowners is simple: if the sky is gray half the year, will solar panels really pay off? It is a fair question, and the short answer is yes. Solar panels keep producing electricity when the sun is behind clouds, just at a lower level than on a clear day. This guide explains how that works, how much clouds actually matter, and why a cloudy climate like ours is still a good fit for solar.
Some critics claim panels are dead weight whenever clouds roll in. That is not accurate. Panels respond to light, not to heat or to a bright blue sky, and clouds do not block all of it. On an overcast day a system typically produces a fraction of what it would under full sun. Commonly cited ranges put that fraction somewhere between roughly 10 and 25 percent of normal output, depending on how thick the cloud cover is, the time of year and the angle of the roof. Light or broken cloud costs much less than a heavy gray overcast.
On a clear day, direct sunlight reaches the panels at full intensity. Clouds scatter and absorb part of that light, so less of it arrives in a straight line. Thick cloud can cut the intensity at ground level dramatically, and heavy overcast cuts it further still. But a large share of the light that does get through arrives as diffuse light, bounced in many directions, and panels can still convert it into electricity.
A useful comparison is sunburn. You can get burned on a cloudy afternoon because ultraviolet and visible light pass through clouds. Solar cells work from that same light, which is why a system keeps ticking over, quietly, even when the sun is not visible.
Germany is the example people often point to. It has a climate with less annual sunshine than many parts of Canada, yet it has been one of the world's largest solar markets for years. The reason is not luck. Strong policy support, careful system design and the simple fact that solar works across a wide range of climates all contributed. If solar can make sense in northern Europe, it can make sense in the Greater Toronto Area.
Living somewhere cool and often overcast should not rule out solar. In fact, panels lose a little efficiency when they get very hot, so cooler air can help them perform. Ontario also gets long summer days with strong production, and a system is sized and priced around its whole-year output, not around a single gray week in November. Winter snow is a related question we cover in detail in do solar panels work in the winter.
A solar system is judged by its annual output. Long, bright summer days build up a large surplus, and under Ontario's net metering rules that surplus can be credited against the bills for darker months. To see how those credits work, read our guide to net metering in Ontario. The Ontario Energy Board and the Independent Electricity System Operator publish official background on the grid and metering rules if you want to read more at the Ontario Energy Board and the IESO.
Clouds are only one factor. Roof orientation, tilt, shading from trees or neighbouring buildings, panel quality, inverter design and dust or snow cover all change how much a system makes over a year. Many of these are within a good installer's control. For example, our systems use SolarEdge inverters, which manage output panel by panel so one shaded or dim panel does not drag down the rest. A free site assessment looks at all of these factors for your specific roof before any proposal is written.
Yes. They work at reduced output, and they work all year in Ontario. The idea that solar only suits sun-baked regions is a myth. The right questions are how big the system should be, how your roof is oriented and what your electricity usage looks like. If you want a quick estimate, try our solar calculator or book a free assessment through our contact page.
Terawatt Solar designs every system around actual Ontario conditions, not showroom conditions. Our ESA-licensed crews install in-house, with no subcontractors, and every project starts with a free site assessment at your home. Learn more about our residential solar service or call us at (877) 648-3323.
Yes. Panels still generate electricity from diffuse light on cloudy days, though output is lower than under direct sun. Annual production is what determines your savings.
No. Ontario has long, bright summer days and a net metering system that credits surplus power, so a properly sized system can offset a large part of a household's yearly electricity use.
Panels tend to run a little more efficiently in cool conditions than when very hot, so cold, clear days can be productive. The effect is modest, and sizing and shading matter more.
