Another Day, Another Win For Solar Power


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Now that the US solar industry has introduced rooftop solar panels to the mass market, see-through solar power windows are the next hill to climb. If a thin film of see-through solar cells can be applied to window glass, millions of buildings can perform as solar power generating stations without sacrificing natural daylight indoors.

Yes, Mere Windows Can Be Solar Power Generating Stations

Transparent solar cells fit into the category of building-integrated solar power. One key benefit of building-integrated solar is the ability to squeeze more renewable energy from structures, rather than disturbing land for new solar arrays. Building-integrated systems can also reduce the cost of solar power, by leveraging exterior walls, roofing materials, and other elements of a structure.

For example, rooftop solar panels require the installation of racking systems to hold them in place, which adds labor and material costs. In contrast, a window with built-in solar cells can be ordered up from the factory, just like any other building element.

Additionally, thin film can be applied to a wide range of surfaces that are unavailable to silicon-based solar panels. It can be painted, sprayed, or applied by well known printing processes.

Solar Power Windows & The Thin Film Connection

If you’re wondering why fully transparent, see-through solar power windows are not available commercially at scale, that’s a good question. One challenge for thin film innovators is to catch the invisible ends of the light spectrum for energy-harvesting, while enabling visible light to pass through.

For innovators eyeing the commercial market, another challenge relates to the nature of architectural glass.

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,” I reported for CleanTechnica last year.

One US firm with a solution for both problems is the startup NEXT Energy Technologies, a spinoff from the University of California – Santa Barbara that emerged as a winner of the school’s New Venture Competition back in 2010. In 2017, the company won a $2.5 million matching grant from the US Department of Energy, enabling it to adapt a commonly used slot-die process to its thin film window coating. In addition to shaving down manufacturing costs, the slot-die method enables NEXT to deploy its thin film on architectural glass.

In 2021, NEXT also received a California Energy Commission grant of $3 million, which the company applied to confirm its solar window production process at the pilot-level scale. The process involves integrating thin film within the window glass manufacturing steps, resulting in a ready-made product at the end of the line.

CleanTechnica spotted NEXT in 2022, when the company supplied a sample of its see-through solar power windows to the California headquarters of the popular outdoor gear firm Patagonia.

Last year NEXT surfaced again, when the company received a $3 million grant from the California Energy Commission, aimed at scaling up the production process.

The Commercial Market For Solar Power Windows

The commercial market is significant because it offers the opportunity to harvest solar energy from a much wider field, compared to the relatively small area of typical household windows. Thin film solar technology is generally less efficient at converting solar energy to electricity than the familiar silicon solar cells, but broad swaths of solarized glass could generate enough solar power to make the investment worthwhile.

The challenge is to get building industry stakeholders to pay attention. NEXT accomplished that in a big way last month, when word dropped that the company supplied a sample of its solar power window glass to the Los Angeles offices of the high-powered global architectural firm Gensler.

“The NEXT viewing wall, hosted at the Gensler office in LA, demonstrates the progress we’ve made in developing an Organic Photovoltaic (OPV) that can be applied to various surfaces, including vision glass and spandrel, turning a facade into a renewable source of clean energy,” NEXT explained, referring to a carbon-based class of thin film solar cells (spandrel is an opaque glass generally used to hide wiring and other unsightly building elements).

“NEXT Energy Technologies’ transparent OPV is an innovation breakthrough for architects that will really change the game plan for sustainable buildings in the near future and for net zero construction for decades to come by turning a building’s glass facade into a source of clean, renewable energy,” adds NEXT board member Andy Cohen, who is also a Co-Chairman at Gensler.

Solar Power Windows & The Green Buildings Of The Future

It remains to be seen if NEXT’s solar power windows can get a foothold in the market, but the longstanding green building trend has been gathering momentum, and new technologies can enable green building advocates to take it to the next level. The green building industry began as an energy efficiency movement. New products like solarized windows can transform buildings into renewable energy generators, too.

Gensler has already been priming itself to advocate for next-level sustainability in the building industry. In an article posted on the Gensler website last year, Cohen also summarized the case for accelerating the green building trend.

“By leveraging renewable energy sources and efficient design choices, the next generation of buildings can achieve net zero energy status, producing enough clean energy — free of fossil fuels — to compensate for the structures’ annual energy consumption,” Cohen explained.

More See-Through Solar For Green Buildings

If and when the solar power window industry breaks into the marketplace, that sound you hear will be researchers at the US Department of Energy celebrating. The Energy Department has been advocating for OPV thin film technology since the early 2000s.

“Despite a conversion efficiency of only five percent at the time, a 2007 Department of Energy draft report identified some key benefits of developing OPV technology, including ‘the inherent low materials cost and low-energy, high-throughput processing technologies, and because of the huge variety of possible organic systems,” I reported for CleanTechnica in 2012.

CleanTechnica also took note of some early-stage developments in thin film solar technology back in 2010, when researchers at Energy Department’s Los Alamos and Brookhaven laboratories deployed carbon molecules called fullerenes.

The initial attempts at fabricating transparent solar glass were small in scale, but by 2012 other research teams demonstrated the potential for coating small, 26-inch square panes of glass with thin film solar cells.

Keep an eye out for more activity stirring in the solar power window field. The US firm SolarWindow (formerly New Energy Technologies), for example, has been working on a roll-to-roll thin film manufacturing process, and researchers at the University of Michigan have come up with a new fullerene formula aimed at extending the lifespan of solarized windows.

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Image: New solar power window technology is finally edging into the commercial market, to transform buildings from energy-sucking structures into renewable energy generating stations (courtesy of Gensler).

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