The case for vertical BIPV

A new international study looked at solar panels built into building surfaces, not just roof-mounted systems, and found that vertical or steeply angled panels on walls and façades can perform much better than assumed. Researchers tested 357 designs across 44 cities in 12 countries, comparing rooftop solar arrays to panels built into walls, skylights, shading devices, and other building parts (a setup called building-integrated photovoltaics, or BIPV). Panels facing east and west on walls, combined with a roof array, produced a steadier flow of power through the day rather than one sharp midday peak. This took somewhat more surface area than an ideally tilted roof, but the study describes that extra area as reasonable for most buildings.

The study also challenges the old rule that solar panels should tilt to match a location's latitude. Shallower angles often performed better, especially in cloudier regions or at higher latitudes. For wall-mounted panels, a steep angle around 75 degrees generally outperformed a straight vertical 90-degree mount, though vertical panels still did well, particularly in far-north or far-south locations.

On cost, the researchers argue that standard financial comparisons undervalue this kind of solar because they ignore that a solar skylight or wall panel also replaces a building material the owner would have bought anyway. Once that's factored in, features like skylights and layered façade walls looked most cost-effective, while shading devices lagged, since the material they replace is cheap. The strongest driver of long-term value, more than panel price or output, was how much electricity prices rise over time.