Transparent Solar Windows: You Ain’t Seen Nothing Yet


The idea of transparent solar windows almost sounds too good to be true, and it is, but not entirely. Researchers have been hammering away at the challenge of harnessing sunlight to generate electricity from see-through windows for years. The prize is acres upon acres of new sites for solar panels on buildings, without losing the energy-saving advantages of daylighting. Just look at any glass building and you can practically feel the blooming of the possibilities. The obstacles are many but it looks like a real breakthrough is finally at hand, so to speak.

Transparent Solar Windows, For Real

See-through solar cells have been bouncing around the CleanTechnica radar since at least 2010, when the possibility of creating a transparent solar window was beginning to emerge alongside thin film solar technology.

Thin film solar technology is just what it sounds like. Instead of a stiff, bulky solar panel that nobody can see through, the thin film platform involves fabricating flexible solar cells in the form of a solution that can be literally painted onto various surfaces, allowing sunlight to trickle through.

One early obstacle between fully transparent solar cells and the commercial market is scaling up from laboratory specimens to a marketable size.

That problem has begun to fade out of the picture, but researchers are still fiddling around with graphene and other high-tech tweaks to tackle the real meat of the matter, which is how to formulate a truly transparent solar window that works effectively enough to justify the cost.

MSU Plunges Into Transparent Solar Cell Territory

The latest buzz over transparent solar cells was sparked last August, when Michigan State University announced a makeover of its Biomedical and Physical Sciences Building with fully transparent solar windows.

To be clear, the MSU project is more of a toe-dipping than a plunge. Still, it appears more ambitious than other transparency projects to surface this year. The new MSU solar array consists of a 100-square-foot installation of transparent panels above the main entrance to the building. If all goes according to plan, which presumably it has, the idea is to harvest enough sunlight to light up the atrium.

See-Through Windows That Generate Electricity

The company behind the project is Ubiquitous Energy, which was co-founded by MSU Professor Richard Lunt, who holds the Johansen Crosby Endowed Professor of Chemical Engineering and Materials Science at the school’s College of Engineering.

Got all that? Good! Lunt’s contribution to the field of transparent solar cells is a window that looks exactly like conventional glass, but it sorts out visible light from the invisible light at both ends of the spectrum, meaning ultraviolet and infrared light. The visible light passes through and the rest is put to work generating electricity.

That’s an interesting twist, because normally one would think that visible sunlight does all the heavy lifting in a solar cell. Maybe it does, but researchers like Lunt have also discovered that invisible light can generate a significant share of electricity, too.

Back in 2017 MSU profiled Lunt’s work and explained that he and his team “pioneered the development of a transparent luminescent solar concentrator that when placed on a window creates solar energy without disrupting the view. The thin, plastic-like material can be used on buildings, car windows, cell phones or other devices with a clear surface.”

“The solar-harvesting system uses organic molecules developed by Lunt and his team to absorb invisible wavelengths of sunlight. The researchers can ‘tune’ these materials to pick up just the ultraviolet and the near-infrared wavelengths that then convert this energy into electricity,” MSU adds.

Of course, transparent solar cells do not rank as high on the solar conversion efficiency chart as their conventional counterparts, since they don’t take full advantage of all the sunlight that hits them. Still, Ubiquitous Energy’s technology offers a respectable 10% conversion efficiency at a relatively low cost, due to the use of abundant, inexpensive materials.

The location of the MSU installation also suggests that solar installers can help trim costs by placing arrays of transparent solar cells at or near their end use, which would help reduce expenses related to wiring and other electrical systems.

Onward & Upward For Windows That Work

As for next steps, that’s an interesting question. Our friends over at EnergySage recently took a look at the market, and so far it looks like Ubiquitous Energy is the first to come up with a truly transparent form of photovoltaic technology that looks like a regular window.

EnergySage does take note of another approach, which is to treat only the edges of a window pane as solar cells, leaving most of the surface as standard glass. That approach has been adopted by the solar cell company Physee, marketed under the name POWER+.

“POWER+ is our power generating glass coating. It directs sunlight onto integrated solar cells in PowerWindows. Without impacting the transparency of its glass, windows will produce the same energy as 1/5 of a solar panel placed on a building’s roof,” Physee explains.

The High Tech Window Of The Future

Physee is also applying it solar know-how to greenhouses, though not to generate electricity. The company’s PAR+ coating is designed to boost greenhouse yields by transforming ultraviolet light, which plants can’t use, into visible light, which they can.

Meanwhile, researchers continue to attack the challenge of transparent solar cells.

Some interesting developments this year include a new silicon nanowire design aimed at improving solar conversion efficiency, and applying fullerenes (think carbon and Buckminster Fuller) to improve transparency.

Transparent Solar Windows & The Built Environment

Ubiquitous Energy certainly has put MSU on the solar cell map. Another emerging area of interest in the solar field is floating solar panels, and MSU is all over that, too.

Last year a team of MSU researchers came up with a study indicating that the push for constructing new hydropower dams could be alleviated by using the surface of existing dams to install floating arrays of solar panels.

The common denominator with Lunt’s research is the use of the built environment to generate clean power, rather than destroying natural habitats for new construction.

The emphasis on using pre-developed sites for solar power also extends to farmland. Experts at MSU see a lot of potential in the newly emerged area of agrivoltaics, in which ground-mounted solar panels on farmland are raised several feet higher than the usual practice.

The raised solar panels allow room for grazing livestock or maintaining pollinator habitats. Raised solar panels can also yield regenerative agriculture benefits, by reducing evaporation and conserving water.

Evidence is mounting that yields for certain food crops can also improve due to the partial shade and regenerative benefits of solar panels.

If all goes according to plan, the sparkling green farmhouse of the future will sport rooftop solar panels and transparent solar windows that gaze out upon acres of lush fields and solar panels, too.

By the way, if you’ve been hearing a lot about agrivoltaics recently, remember you heard it here first. CleanTechnica began covering the solar-plus-farming trend back in 2019, including an interesting twist in which solar panels could help rescue, not destroy, an entire industry.

Follow me on Twitter @TinaMCasey.

Photo (screenshot): Transparent solar windows developed by a team of solar researchers at Michigan State University (video credit: MSU).

 

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