How Do Solar Windows Work?

Sun beaming off of building with many windows; windows reflecting sunny sky with some clouds.

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Solar windows are sheets of glass with photovoltaic properties. This allows solar windows to not only let light into buildings but to absorb the sun's energy and convert it into electricity.

While still in development, solar windows are a promising technology in the transition to cleaner energy. Along with other types of building-integrated photovoltaics (BIPV) such as solar roofs and solar paint, solar windows are integrated into the structure of a building rather than adding on to it.

How Solar Windows Work

While traditional solar panels are conventionally dark-colored in order to absorb as much sunlight as possible, traditional windows need to be transparent. Therefore, developers of solar windows need to both let light in and generate enough electricity to make their manufacture and installation cost-effective.

A number of potential solutions for solar windows are still in the research-and-development stage, while a few have recently reached the marketplace.

Ink and Film

A photovoltaic ink or thin photovoltaic film is applied on top of the glass, either during the manufacturing process or retrofitted onto existing windows. NEXT Energy Technologies produces a transparent photovoltaic ink made from organic semiconducting materials that can be printed directly onto windows.

By contrast, Solar Window Technologies produces thin sheets of flexible glass coated with a photovoltaic liquid, designed to be installed on existing skyscraper windows.

Micro-Panels and Shades

Small traditional PV "micro-panels" are placed in the four sides or corners of windows so as not to obstruct a significant amount of light. Fully opaque or semi-transparent “solar blinds,” such as those marketed by SolarGaps, take the micro-panel idea a step further, with miniature solar panels able to rotate to follow the path of the sun while they also act as window shades.

Interlayers Between Panes

Double-pane windows are manufactured with solar cells between the two panes. EnergyGlass produces transparent interlayers of inorganic nanoparticles that are laminated between two layers of glass. The extra layer also provides more insulation than single- or double-pane windows, so solar windows can reduce heating and cooling costs at the same time that they produce electricity.

Quantum Dots

Quantum dots are nano-sized PV cells that are implanted within the glass itself. Quantum dot technology uses transparent nanocrystals (essentially, tiny glass beads) and quantum mechanics to convert solar energy into electricity.

Rather than absorbing visible light (and thus reducing the amount of light that passes through windows), quantum dots convert invisible ultraviolet light, which contains more energy than visible light. Absorbing UV light also reduces its harmful effects on humans and furniture.

Quantum dots implanted in windows can also redirect infrared light toward photovoltaic cells, though infrared light contains less energy than visible light, making it a less efficient converter of electricity.

The Market for Solar Windows

Solar glass technology is still evolving. Currently, developers are still trying to make solar windows economical—both for the manufacturer and for the consumer.

Startups, including NEXT Energy Technologies and SolarGaps, have often relied on government R&D support to bring their products to market. NEXT Energy Technologies first demonstration project in Fremont, California, announced in April 2022, was supported by a $3 million grant from the California Energy Commission, while SolarGaps received funding from the European Union.

As in every new technology, not every product succeeds. Physee, a Dutch developer of sustainable building technology, installed its PowerWindows as a pilot project in a Dutch bank in 2017. Yet each window only generated enough electricity to charge multiple smartphones at the same time. While developing and marketing other innovative technologies, Physee has yet to bring PowerWindows to the market.

The Future of Solar Windows

The manufacturing of window glass is a multi-billion dollar industry, and new building construction presents an enticing opportunity for solar glass developers. In the United States alone, construction begins on some 1.8 million new homes each year, according to the U.S. Census. Since January 2020, all newly constructed homes in California have been required to have solar PV as an electricity source—an addressable market of over 100,000 new homes a year.

Making retrofits efficient and economical is perhaps even more important. Buildings account for some 16% of greenhouse gas emissions, mostly from heating and cooling, according to the IPCC. A study by Architecture 2030 predicts that two-thirds of all buildings in 2040 will be buildings that exist today—meaning retrofitting existing buildings will be vital in the struggle to mitigate climate change. Whether in new construction or in retrofits, solar windows will need to play a vital role in the quest to electrify everything.

Frequently Asked Questions
  • Are solar windows eligible for government incentives?

    While it is wise to consult a tax professional, it is likely that your solar windows can receive tax credits or other incentives from your state or federal government, including in Canada.

  • Do solar windows use toxic materials?

    Most companies, such as Ubiquitous Energy, use only natural, non-toxic materials in their solar windows.

  • Are solar windows as efficient as solar panels?

    Currently, solar windows are less efficient and less cost-effective than rooftop solar panels, but things change fast in the solar industry, with frequent improvements in technology, increasing economies of scale, and significant price drops. Stay tuned.