See-Through Solar Panels, Coming Soon To A Farm Near You – CleanTechnica

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The emerging science of agrivoltaics has barely gotten off the ground, and researchers are already figuring ways to make it even better. The goal is to amp up the electricity output in concert with optimizing crop growth within a ground-mounted solar array. In the latest development, new research indicates that transparent, see-through solar technology can “share” the same sunlight between power generation and food systems, benefiting the farmer while perhaps mollifying rural solar opponents.

See-Through Solar Windows Really Are A Thing

The images of rows of shiny black solar panels peppering the bucolic farmlands of the US have been handily deployed by solar opponents to portray solar arrays as an aesthetic intrusion and an inappropriate use of farmland.

The inappropriate argument may have held some water in the early years of the US solar industry, when developers preferred to cut costs by minimizing ground cover. However, after agrivoltaic research began to materialize about 10 years ago, the air has gone out of the inappropriate balloon.

Agrivoltaics refers to the practice of continuing to farm the land within a solar array. Initial efforts emerged about 10 years ago with a focus on grazing livestock and establishing pollinator habitats for crop support. Those are still the two main areas of activity. However, the field is also rapidly branching out into human foods, and advocates are steadily building the economic case for agrivoltaic projects as well.

That leaves the aesethetic argument to deal with. Personally, I find solar arrays no more or less unaesthetic in a rural setting than acreage filed with hothouses, plastic hoop tunnels, plastic mulch cover, grain silos, livestock pens, poultry houses, fields of barren stubble, and other elements of a modern commercial agricultural operation, to say nothing of the diesel-powered machinery and the regular doses of herbicides and pesticides needed to keep everything in order, but that’s just me.

Besides, I don’t live in the country, I just visit. So, I’m not passing judgement on the aesthetic argument. To the extent that there is one, though, see-through solar panels could help mollify some objections by providing for a less jarring contrast to the eye.

See-Through Solar Meets Agrivoltaics

Solar innovators have already been pursuing transparent, see-through solar technology as a means of expanding the reach of solar development into the built environment. Specifically, the idea is to enable windows to fulfill their primary function of letting light in and letting people see out, while doing double-duty as clean electricity generators. Doors, roofs, curtain walls, and other building building elements made of glass are also candidates for a clean power makeover.

That sounds simple enough. However, there being no such thing as a free lunch, the devil is in the details. On the plus side, years of R&D are finally beginning to pay off, and the transparent PV field is closing in on commercialization (see more see-through solar background here).

And, that’s where the new agrivoltaic research comes in, provided by a multinational team of scientists based in Sweden. All the details are available online under the title, “Wavelength-selective solar photovoltaic systems to enhance spectral sharing of sunlight in agrivoltaics” in the latest edition of the journal Joule.

For those of you on the go, the researchers make the case for agrivoltaic developers to adopt alternative solar technologies that throw less shade than conventional, opaque silicon solar panels.

By alternative, they mean light-sorting technologies that come under the umbrella of “wavelength-selective solar photovoltaic technologies (WSPV),” including see-through solar technology. The argument in favor is based on studies demonstrating that plants do not need the full spectrum of light in order to optimize growth.

See-Through Solar & Land-Use Efficiency

The researchers indicate that agrivoltaic arrays can be designed (and are being designed) to optimize the beneficial impacts of a semi-shaded environment, including improvements in water resources and soil health, while allowing for healthy crop growth.  Conventional silicon solar panels can get the job done to a respectable extent, especially when combined with bifacial solar systems and other complementary technologies.

Adding wavelength selectivity to the agrivoltaic toolkit is a game-changer that would enable more solar panels to take up space without impinging on crop growth, adding the important element of an uptick in land-use efficiency to the equation.

The research team is particularly excited about the potential for see-through solar windows to fit the bill.

“Worth mentioning is a special category of WSPV system technologies known as transparent photovoltaics (TPV), where absorption for energy conversion occurs mainly in the ultraviolet (UV) and near-infrared (NIR) regions, while the intended transmission wavelengths span the entire visible (VIS) spectrum,” they explain, noting that see-through solar is already associated with buildings as well as other applications.

Based on their state-of-the-science review, the researchers propose that the up-and-coming international agrivoltaic classification system be expanded to include three degrees of transparency. See-through solar would be the most transparent, followed by semi-transparent and opaque technologies. Currently, the proposed classification system includes four agrivoltaic categories that describe the type of photovoltaic system, the type of racking (or mounting) structure, solar tracking, and the agricultural products that will co-exist with the solar panels.

The Solar Revolution Has Just Begun

As for how all this wavelength selectivity is going to happen, the research team lists several options including “tuning photoactive layers, applying colored semi-transparent layers, utilizing mirrors and lenses, or designing spectrally selective luminophores,” with that last item referring to luminescent molecules.

Meanwhile, other agrivoltaic researchers are not waiting around for the see-through solar paint to dry. A research team based at Swansea University, for example, has developed a free tool that enables agrivoltaic stakeholders to assess the impact of different kinds of semi-transparent solar technologies on different crops.

“A key factor for optimising agrivoltaics is selecting the appropriate PV material, which requires an understanding of how the material absorbs different wavelengths (colours) of light, as well as its bandgap,” states Swansea University

“By carefully selecting PV materials with specific bandgaps and absorption properties, researchers can fine-tune the ‘colour’ of light transmitted through semi-transparent PVs to hit the crops, which mainly absorb red and blue light to photosynthesise, reflecting green light,” the school elaborates.

To get some perspective on the potential for high impact, consider that researchers at Michigan State University, who are credited with developing the world’s first truly see-through solar panel, estimate that building-integrated transparent solar technology could supply about as much electricity as conventional rooftop solar panels in the US, if both were fully built out.

That calculation was published back in 2017, before the agrivoltaic industry began to take off. If you have any perspective on how the addition of agrivoltaic arrays will impact the see-through solar industry, drop a note in the comment thread.

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Photo (cropped): The emerging science of agrivoltaics is on track to collide with see-through solar panels, a new photovoltaic technology pioneered by researchers at Michigan State University (courtesy Michigan State University).