Taking the Heat

Researchers say skylights can help heat homes and reduce use of fossil fuels

BY LAUREL HAMERS

Skylights aren’t just pretty—they’re sustainable, according to a new University of Oregon study. Passive solar heating systems collect natural light via skylights or windows and use it to heat spaces without electricity. In the first detailed survey of direct solar heating resources in the US, building scientist Alexandra Rempel and earth scientist Alan Rempel found such installations could meet a third of residential space heating needs nationwide.

The news is a boon for the increasingly urgent effort to reduce fossil fuel use, say the UO researchers, who conducted the study with engineer Sandipan Mishra of Rensselaer Polytechnic Institute in New York. Heating uses about half of most home energy budgets and is the biggest source of carbon emissions from homes, because most heating systems in the US still rely on oil or natural gas.

“In the course of studying sustainable architecture, it became clear there were lots of resources we weren’t tapping into,” says Alexandra Rempel, of the School of Architecture & Environment.

Passive solar heating is one of them. Although it’s been used for centuries, it hasn’t been put widely into practice as a sustainable design technique. “People were dismissing the possibility that there could be enough solar energy available in cold climates,” she says.

That’s partly because many passive solar heating systems have used vertical glass, like big windows. It’s a good strategy when you have direct sunlight, Rempel says. But in cloudier and cooler climes, scattered solar energy comes from the upper reaches of the atmosphere, regardless of where the sun is in the sky. Tilted glass, like a skylight set into a sloped roof, is perfectly situated to capture this energy.

To find out just how much solar energy was being left unused, the researchers pulled together data on solar radiation levels, outdoor temperatures, and heating energy use across the US, at different times of year. The team, which included former UO students Sierra McComas, BS ’16 (environmental studies), MLA ’19, and Stacie Duffey, MPA ’19, factored in variables like the sun’s position in the sky and the length of daylight hours. Then they mapped out places and times of year when passive solar heat resources exceeded heating needs.

Per their calculations, there’s about 7 megawatt hours of solar energy available per household annually during periods when homes need heating. Current technology could capture about half of that, assuming 10 square meters of glass per roof. That means solar heating could supply about a third of a typical family’s heat.

“The idea isn’t that it would take over traditional heating completely, but it would diminish the amount you need,” Alexandra Rempel says.

The study provides detailed breakdowns for urban areas in different climates—data that could be useful for cities looking to curb emissions. Urban areas with cold winters (like Boston and Chicago) or frequent cloud cover (like Seattle) could particularly benefit, they found.

For the Rempels, who are married, this work is more than just theoretical. During the pandemic, they installed a set of skylights in their home, plus sliding insulation panels to keep heat in at night. They estimate the upgrades will reduce their heating bills by 80 percent.

Alexandra Rempel is also promoting the merits of skylights to architects and building designers. In the future, she suggests, cities could provide rebates or tax breaks for passive solar heating.

“Money is a go-to incentive,” she says. But with skylights, which fill homes with light, she adds, “there’s also the improved experience.”

Laurel Hamers is a staff writer for University Communications.