For all the enthusiasm around solar panels on city rooftops, there’s one inconvenient truth: buildings cast shadows. In high-latitude places like Canada, Sweden or Finland, this is particularly troublesome. The low-angled winter sun makes solar access a scarce commodity and makes efficient building design a complex challenge.
But researchers in Concordia University, Montréal [45.5°N, 73.6°W] have developed a breakthrough method to address this: a new, highly detailed 3D ray-tracing solar shading model that simulates how the sun interacts with buildings in dense urban environments. The innovation is timely, precise and adaptable and could be the key to smarter solar planning not just in Quebec, but in cities across the northern hemisphere.
What’s New Here: From Approximate to Accurate
Until now, energy simulations for buildings have typically relied on simplified shading models. These tend to assume average sun positions, ignore nearby obstructions or estimate shadows based on basic geometry. It’s a bit like planning your wardrobe for the year based on monthly averages: it doesn’t tell you whether you’ll need a raincoat next Thursday.
This new model brings a quantum leap in precision. Using 3D ray tracing—a method more commonly seen in high-end animation or optical physics—it accurately tracks how direct sunlight strikes every surface of a building, hour by hour, season by season. The method calculates the shadows cast not just by the building itself, but by all its neighbours, trees, topography and urban clutter.
This means energy modellers and architects can finally stop relying on guesswork when estimating solar gains. The model gives them a tool that’s as rigorous as it is local.
Implications: Tailoring Solar Solutions to Cold, Dense Cities
The implications are especially potent for northern cities. In a place like Stockholm or Montreal, solar energy potential is often underestimated due to old models that assume long shadows all year round. This leads to missed opportunities in planning—and often to the claim that solar “doesn’t work here”.
By contrast, the ray-tracing model shows exactly when and where solar energy can be harnessed, even in urban pockets surrounded by tall buildings. That’s essential for designing buildings that make the most of passive solar heating in winter, while avoiding overheating in summer.
And crucially, the model isn’t just about new builds. It could be applied to existing neighbourhoods to retrofit and re-optimise rooftop solar installations, helping cities wring every watt out of their limited sun.
Canada, the Nordics — and You
For readers in countries with similar latitudes and urban densities (Norway, Denmark, Scotland or even northern Japan) this work is directly relevant. The methods can be adapted to any city where the sun shines at a slant and where space is contested.
But even urban dwellers far from these latitudes should take note: what this model demonstrates is the value of hyper-local, precise energy modelling. As we move toward net-zero buildings and districts, every beam of sunlight—and every shadow—counts.
Endnotes
1. ‘Why solar panels don’t work well in Canadian winters’, CBC News, 2019-02-11.
2. ‘How buildings cast long shadows over Canada’s solar ambitions’, The Globe and Mail, 2023-06-28.
Source
Development of a 3D Ray Tracing-Based Direct Solar Shading Model for Urban Building Energy Simulation, Renewable Energy, 2025-06-27
Boˆreal 