Glass-walled structures in urban landscapes can be made more energy efficient by adding thermally efficient photovoltaic (PV) windows, according to an analysis by researchers at the National Renewable Energy Laboratory (NREL).
Their findings, published in the journal One Earth, outlined building design rules that can yield a structure with net-zero or even net-positive energy consumption.
To conduct the analysis, researchers developed a software called PVwindow that allows users to model the design of PV windows for building simulations.
NREL said that buildings account for more than a third of the world’s energy consumption and almost as much of global carbon dioxide emissions.
By combining PV with high thermal performance window technologies, new buildings can become a tool in combatting climate change, the researchers noted. Modern office buildings stand out for their glass facades. The Equitable Building in New York, for example, has a window-to-wall ratio of 25%. By comparison, the city’s Bank of America Tower opened in 2016, 101 years later, with a ratio of 71%.
The researchers considered buildings with a window-to-wall ratio of 95%—dubbed “highly glazed”—for most of their analysis. Improvements in glazing technologies such as triple-pane windows helped improve the energy efficiency of buildings but so far have not been widely adopted.
The researchers simulated the impact of three different types of PV glazing technologies. Different glazing technologies were implemented in a building in eight cities, each in different climates. In addition to the NREL-developed PVwindow, the researchers relied on EnergyPlus and OpenStudio software platforms.
In practice, PV windows provide thermal insulation for a building and use the absorbed energy to generate electricity. Over the course of a year, the researchers found what they said is a clear trend in PV generations in climates with weather that changes strongly with the season.
The simulations revealed that in Denver, for example, on-site PV generation can cut in half the day-averaged building electricity load for a heavily glazed 12-story structure. They also determined PV windows in Denver could eliminate 2 million kilograms of carbon dioxide emissions annually.
The simulations showed a step-like increase in performance for each of the three different versions of PV glazing studied and demonstrated reduced energy consumption and carbon dioxide emissions in the eight climate zones.
The researchers found that energy use climbs when a building has more windows than wall space. However, the energy use drops when the ratio is increased and includes PV glazing. They found that larger floor-to-floor height coupled with PV glazing reduced building energy use. They said that combining the PV glazing with photovoltaic panels on the outside of the building—particularly facing east and west to capture early morning and late-day sun—could result in a net zero skyscraper.
They said that PV glazing could be paired with rooftop solar to increase the amount of electricity generated, with the potential to create more power than a building needs by using high-efficiency PV windows and unique building geometry.
