According to a PV Windows study conducted by experts at the National Renewable Energy Laboratory (NREL), skyscrapers dominate metropolitan skylines, yet even enormous glass-walled structures can be made more energy-efficient by the inclusion of thermally efficient photovoltaic (PV) windows.
Their research, which was published in the journal One Earth, presents guidelines for building design that can result in a building with net-zero or even net-positive energy usage.
“There are preconceived notions of what an energy-efficient building looks like, and it usually is not highly glazed, and it probably isn’t very tall,” said Lance Wheeler, a scientist at NREL who specializes in integrating PV technology into windows. “We found that there are other ways to build high-efficiency buildings.”
In an article called “Photovoltaic windows reduce energy use and CO2 emissions by 40% in highly glazed buildings,” co-authored by Wheeler and his twin brother Vincent, an assistant professor at the University of Wisconsin-Stout. The brothers created a program called PVwindow that enables users to simulate building designs using PV window models in order to conduct the analysis.
The other co-authors, all from NREL, are Janghyun Kim, Tom Daligault, Bryan Rosales, Chaiwat Engtrakul, and Robert Tenent.
More than a third of the world’s energy and nearly as much of its carbon dioxide emissions come from buildings. However, according to the experts, new buildings can become a vital tool in the fight against climate change by combining PV with high thermal efficiency window technology. For instance, The Equitable Building in New York has a 25% window-to-wall ratio. The city’s Bank of America Tower, which was built 101 years later and opened in 2016, has a ratio of 71%.
To clearly demonstrate the influence glazing has on building energy performance, the researchers focused much of their analysis on buildings with a window-to-wall ratio of 95%, referred to as “highly glazed.” Although not yet widely used, advancements in glazing technologies like triple-pane windows helped enhance the energy efficiency of buildings.
“I don’t want to sit here and say we should be building highly glazed buildings,” Lance Wheeler said. “We should be building highly efficient buildings. But if we choose to keep making these buildings, we’ve got to reconcile their lower performance somehow, and PV windows are one way to do that.”
The effects of three various PV glazing technologies, including switchable PV technology developed by NREL, were simulated by the researchers. In eight cities with various climates, several glazing technologies were used in a structure. The researchers used EnergyPlus and OpenStudio software packages in addition to PVwindow.
Highly glazed structures require the use of a significant amount of energy to cool the occupants due to a large number of windows and sunlight entering the structure. PV windows insulate a building thermally while also generating power from the absorbed energy. In climates with weather that changes significantly with the seasons over the course of a year, researchers discovered a distinct trend in PV generation. The models showed that in Denver, for instance, on-site PV generation can reduce half the day-average building electricity load for a 12-story structure with extensive glazing. Additionally, they found that Denver’s PV windows might cut 2 million pounds of carbon dioxide emissions each year.
The simulations exhibited decreased energy use and carbon dioxide emissions in the eight climate zones and showed a step-like improvement in performance for each of the three variants of PV glazing that were studied.
The researchers discovered that when a structure has more windows than wall space, energy use increases. However, when the ratio is raised and PV glazing is added, energy consumption decreases. Larger floor-to-floor heights along with PV glazing do indeed cut down on building energy demand. This skyscraper can achieve net zero if the PV glazing is combined with photovoltaic panels on the exterior of the structure, especially those facing east and west to capture early morning and late afternoon solar.
“Picture a skyline in, like, New York City where there are these high-rise buildings that are entirely glass,” Wheeler said. “They’re fully glazed. The Freedom Tower has millions of square feet of glass. It could be a power plant in itself.”
The researchers stated that PV glass might be used in conjunction with rooftop solar to boost the amount of electricity produced, with the potential to generate more power than a building requires by utilizing high-efficiency PV windows and distinctive building geometry. Without compromising the architectural freedom of the heavily glazed front of buildings, the move could address climate change goals.
Source: NREL
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