Photovoltaic windows, when they save 40% of consumption?

Photovoltaic windows for buildings, yes or no?

( sustainabilityenvironment.com) – Photovoltaic windows represent a technology still in its infancy, with a very niche market, yet they could already play an essential role in the energy management of modern buildings. This is demonstrated by a new study by the National Renewable Energy Laboratory (NREL) that, for the first time, wanted to assess the impact of integrated photovoltaic technology in different architectures and climate zones.

Windows with high energy efficiency

To date, one third of the world’s energy is consumed by buildings, which account for a similar share of global CO2 emissions. A part of the responsibility for the high energy demand is also the recent architectural trends that have seen a multiplication in the years of glazed facades. “Window-to-wall relationships have steadily increased since the end of World War II,” Lance Wheeler and colleagues at NREL explain in their publication in Cell. “And the demand for glazed facades remains high despite the wide recognition of their poor energy performance and growing concerns about the effects of climate change”.

There are of course also solutions: triple glazing, low-emissivity coatings, thermochromic and photovoltaic glasses can contribute to energy efficiency, reducing building consumption. But when and how is it possible to achieve the greatest results? The question is answered now by the research of the National Renewable Energy Laboratory. The team took into consideration the “highly glazed” buildings, literally “highly glazed”, that is, with a mainly transparent envelope due to a window-to-wall ratio of 95%. This is one of the dominant building trends in skyscrapers and modern metropolis offices.

“I don’t want to sit here and say that we should build buildings with large glass surfaces,” said Lance Wheeler. “We should build highly efficient buildings. But if we choose to continue making them, we must somehow reconcile their lower performance and photovoltaic windows are a way to do it”.

Three technologies of photovoltaic windows

Scientists simulated the impact of three different photovoltaic glass technologies in eight different climates: the technology based on thin amorphous silicon films, CIGS or perovskite, also called semitransparent photovoltaic; that also integrates thin films of absorbed organic solar dyes or sensitized, also called transparent photovoltaic; that “switchable” or “chromic” that combines the technology of dynamic glasses with solar conversion. The result? All three types of fv glass can lead to reductions in consumption.
According to the study, savings in primary energy use and carbon emissions with photovoltaic windows can reach up to 40% compared to a traditional window. Equivalent to a reduction of 37,000 GJ per year for a typical office building with a predominantly transparent building envelope. “Although quantitative results vary by climate zone, the energy performance of buildings in all locations will benefit from next-generation window technologies. Photovoltaic windows, perhaps not intuitively, offer temperate locations like New York City more energy/CO2 savings than sunnier cities like San Diego”.