Photovoltaic Windows Cut Energy Use in Highly-Glazed Buildings

Researchers at the National Renewable Energy Laboratory (NREL) reported in a November 2022 study that highly-glazed skyscrapers can reduce energy use and emissions by 40% with high-performance glazing.

The report precedes a 2023 analysis by the International Energy Agency that found emissions from the buildings sector rose 26 million tons (Mt) in 2022, far exceeding this past decade’s annual average growth (around 7 Mt yearly). However, “unprecedented” increases in the use of solar photovoltaic (PV) systems, wind and coal-to-gas switching led to a softening in emissions growth in 2022.

NEXT Energy Technologies Inc. officials announced the results of a multi-year photovoltaic (PV) window project in 2022. Researchers found that while energy usage increases when a building has more windows than walls, adding PV glazing decreases energy usage.

The study, Photovoltaic Windows Cut Energy Use and CO2 Emissions by 40% in Highly Glazed Buildings, was conducted using a software called PVwindow. Developed by Lance Wheeler, a scientist at NREL, and his twin brother, Vincent, an assistant professor at the University of Wisconsin–Stout, the software allows users to model the design of PV windows for building simulations.

The researchers considered buildings with a window-to-wall ratio of 95% for most of their analysis to clearly illustrate the impact glazing has on building energy performance. Improvements in glazing technologies, such as triple-pane windows, helped improve the energy efficiency of buildings but are not yet widely used.

“I don’t want to sit here and say we should be building highly glazed buildings,” Lance told NREL. “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.”

As part of the study, the researchers simulated three types of PV technologies: non-wavelength-selective PV technology, wavelength-selective PV technology and dynamic PV technology, also called switchable or chromic PV technology. The study centered on buildings in eight cities throughout the U.S.

One of the buildings was in Denver. The researchers found that on-site PV generation could reduce the day-averaged electricity load of a heavily glazed 12-story building by half and eliminate two million kilograms of carbon dioxide emissions annually.

The analysis concluded that while energy usage increases when a building has more windows than walls, adding PV glazing decreases energy usage. Additionally, the researchers stated that “combining PV glazing with PV panels installed on the building’s exterior, particularly on the east and west facades to capture morning and evening sunlight, can enable a skyscraper to achieve a net-zero energy status.”