See-through solar windows turn ordinary energy-sucking, carbon-spewing buildings into climate action heroes (image courtesy of NEXT Energy Technologies).

Chalk Up Another Win For Invisible Solar Windows

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The dream of a truly see-through, colorless solar window is becoming a reality. That is bad news for fossil energy stakeholders, but great news for the global energy transition. The new technology replaces ordinary window and architectural glass with specially coated look-alikes that generate zero emission electricity, raising the potential for applications in millions of new and existing buildings around the world.

More Good News About Invisible Solar Windows

The latest news on the solar window score comes from the US startup NEXT Energy Technologies. If that name rings a bell, NEXT stirred up the Intertubes last December when the popular outdoor gear company Patagonia announced that it would install NEXT’s see-through photovoltaic technology at its headquarters in California.

Patagonia did not name the solar supplier at that time, so CleanTechnica took a guess at which PV innovator won the assignment. It turned out to be the wrong guess. Still, the point is that more than one company is in contention to bring see-through solar windows to market in short order.

For now, it looks like NEXT has the edge. On April 14, the company announced that it received a $3 million RAMP grant from the California Energy Commission in recognition of its “emerging best-of-class innovative technology.”

The influx of cash will help NEXT scale up an initial production line to produce architectural window glass (RAMP stands for Realizing Accelerated Manufacturing and Production for Clean Energy Technologies).

“The specific purpose of NEXT’s agreement is to fund the scale-up of a Low-Rate Initial Production (LRIP) line for the assembly of solution-processed Organic Photovoltaics (OPV) on architectural window glass into window-PV modules that are ready for integration into commercial Insulated Glass Units (IGUs),” NEXT explains.

Solar Windows Are Ready For Their Closeups

Last week’s grant follows a previous RAMP grant of $3 million to help NEXT get its technology through an earlier phase of development. That grant was issued in 2021, with the aim of confirming a pilot-level application of NEXT’s proprietary thin film solar coating onto sheets of heat-treated glass.

“The method will allow for a more seamless application into the window manufacturing process that leads to much higher margins with low capital cost equipment,” NEXT explained.

That’s a bit more complicated than it sounds. Architectural glass looks smooth to the eye, but the surface is a patchwork of distortions that can interfere with the solar conversion efficiency of thin film coatings. NEXT came up with an approach that integrates the solar coating into the window glass manufacturing process, which also means there is no need for a separate factory to apply the coating. The glass manufacturer can get everything done in-house.

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Buildings Are Ready For Their Clean Power Closeups

Much of the mainstream media activity around clean technology has focused on electric cars, along with large-scale solar arrays and wind farms. Glass and other building materials have been getting short shrift, even though buildings account for a significant amount of energy consumption and greenhouse gas emissions.

Nevertheless, buildings are beginning to scratch their way into the climate media spotlight, thanks partly to the surging popularity of heat pumps.

Replacing ordinary window glass with solar windows can make a significant difference, especially in the commercial market which NEXT is aiming to tap. The US Department of Energy calculates that commercial buildings alone account for about 35% of the nation’s electricity consumption, including buildings in both the public and private sectors. Adding to the hurt, the US Environmental Protection Agency calculates that an average of 30% of the energy used in commercial buildings goes to waste.

The first iteration of NEXT’s commercial-grade solar windows will scale to a maximum of 5 x 10 feet. At that size, NEXT estimates that a typical high-rise office buildings would produce about 20 million kilowatt-hours of electricity annually from its windows, or enough to offset its power needs in the range of 10-20%.

Group Hug For US Taxpayers

In addition to public funding from California’s RAMP program, NEXT has also gotten some love from the US Department of Energy’s T2M3 (Technology to Market 3) early stage energy technology funding program. In 2017 the program awarded a total of $25.7 million to launch 20 different technologies off the drawing board and into commercial development.

NEXT was among the lucky winners. The company nailed a 50-50 matching award of $2.5 million. “This project is researching the integration of organic photovoltaic materials with commercial windows to accelerate transition of a lab-made, commercially relevant prototype to a fully developed prototype that has passed initial reliability and certification testing and is ready to begin pilot manufacturing,” the Energy Department noted. “The prototype will be slot-die coated, large area modules as opposed to previous spin-coated, small area modules.”

That might have sounded like a pipe dream six years ago, but here we are today.

Next Steps for Solar Windows: Rooftop Agrivoltaics?

In terms of solar conversion efficiency, organic thin film solar technology still lags behind the familiar, tried-and-true silicon solar cells that are commonplace today. Still, thin film has other advantages that make up for the difference.

On the plus side, thin film solar cells can be fabricated in a solution, then sprayed, painted, printed, or otherwise deposited onto a surface using well known industrial processes. That opens up a wide range of new applications, including window glass.

Thin film technology also has the advantage of being lightweight and flexible, in contrast to its rigid silicon counterparts.

The technology really shines in the cost department. Silicon is expensive compared to thin film formulas. NEXT is not giving away the proprietary secret behind its formula, but the company does note that it deploys low cost, earth-abundant materials. In addition, NEXT’s solar window solution is applied to glass with a slightly modified slot-die process that is widely used in the electronics and display industries, helping to cut costs.

Integrating the solution with a common building material is another cost saver. Rather than adding the cost of rooftop silicon solar panels to a building, NEXT’s solar windows simply piggyback onto an existing cost. This approach “allows for much lower module and balance of system costs compared to other photovoltaic technologies by utilizing substantial costs that are already being paid for in conventional windows by building owners,” the Energy Department observes.

In addition to cutting costs, building-integrated solar windows free up valuable roof space for other uses.

We’re thinking rooftop greenhouses and rooftop agrivoltaics could come into play, but that’s just one idea. Agrivoltaics refers to farming practices that integrate solar panels, so there could be some applications on land as well.  If you can think of any, drop us a note in the comment thread.

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Image: Transparent solar windows generate zero emission electricity without sacrificing daylight (courtesy of NEXT Energy Technologies).


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Tina Casey

Tina specializes in advanced energy technology, military sustainability, emerging materials, biofuels, ESG and related policy and political matters. Views expressed are her own. Follow her on LinkedIn, Threads, or Bluesky.

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