For Solar Energy, Magenta Is the New Black

Pink solar panels convert certain types of light into energy for powering greenhouses while allowing other types of light to pass through and feed plants.

Magenta-tinted roof panes on greenhouses can capture enough solar energy to power the structure’s equipment while allowing enough sunlight to pass to grow the plants inside, California researchers reported.

The pinkish tint on the panels catches light from wavelengths that plants don’t use for photosynthesis, which uses chlorophyll to absorb sunshine and turn carbon dioxide into energy.

“Plants are green because they reflect green light. It’s the wavelengths that chlorophyll doesn’t absorb,” Michael Loik, an environmental studies professor at the University of California, Santa Cruz, told Seeker. “That means that if we’re looking for some kind of dye to take out a certain amount of light, we aim for the green that plants don’t use anyway.”

The light captured by these wavelength-selective plastic panels gets converted into electricity by strips of photovoltaic cells. At this point, they turn less of that energy into power than conventional solar cells, and the amount of power generated is small. But they yield enough juice to drive devices like lights or ventilation fans inside the greenhouse, Loik said.

“What we’re talking about is distributed generation for the greenhouse’s own power uses,” he said. “Our prototype generated more than it needed, but that’s a fairly low-demand facility … It’s not really designed to feed back into the grid.”

The findings were published in October in the American Geophysical Union research journal Earth’s Future.

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University of California, Santa Cruz

Greenhouse agriculture has been growing rapidly worldwide. The controlled environment and high CO2 concentrations inside them can boost a farmer’s yield even in harsh conditions. More than 1.2 million acres (489,000 hectares) of crops were grown inside them in 2016, according to industry estimates.

Peeling off a portion of the sunlight that falls on them to produce energy can also reduce the carbon emissions used in agriculture, helping to head off the bigger greenhouse effect that’s warming the planet.

Scientists have been looking at other methods to harvest solar energy through windows as well. But unlike other technologies, these panels can already be purchased: One of Loik’s co-authors started a company to market them. Your pink, power-producing panels will set you back about $15 a square foot for a new installation, or about $22 a square foot to refit an existing structure, Loik said.

But how’s the food?

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Loik and his colleagues tested the panels by growing a variety of fruits and vegetables — including tomatoes, tangerines, cucumbers, lemons, and peppers. The panels also capture some blue light that plants would use otherwise, but it doesn’t appear to have any effect on their growth, they found.

Not only do the roof panels allow enough light for photosynthesis, but plants grown under them appeared to use less water. It’s not clear why yet, but follow-up studies are focusing on the tiny pores in a plant’s leaves that release water vapor.

“Particularly out here in California and in much of the West, water use efficiency is critical,” Loik said.

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