green solar

Green solar panels that blend in with nature; red solar panels on a terracotta roof; white solar hidden on a wall. Researchers have discovered a way to turn typically black and blue solar panels a shade of green, and potentially any colour imaginable.

The researchers speculate this could lead to a greater uptake of solar, with architects, homeowners and city planners potentially more open to the technology if it is more aesthetically pleasing and congruous with the surrounds.

The study, published in Applied Physics Letters, imprinted existing solar panels with silicon nano-patterns to scatter green light, giving the panels a green hue, though also decreasing power production by about 10 per cent.

“Some people say, ‘Why would you make solar cells less efficient?’ But we can make solar cells beautiful without losing too much efficiency,” lead author Verena Neder said.

Neder, a researcher at Netherlands research body AMOLF, said the new method of design was easy to apply, and an attractive architectural design element that could widen the use of solar.

Left: The nanopatterned module appears green, independent of the angle. Right: Schematic of silicon nanoscatterer arrays on top of a sapphire cover slide, integrated into a commonly used solar panel design. Image: Neder et al.

She also noted that the efficiency loss was much less that coloured solar technology on the market currently, such as dyes and reflective coatings. And unlike existing technologies, the hue remains the same from most angles.

The technology used for the coloured solar panels is called soft-imprint lithography, which works like an “optical stamp” to imprint a dense array of silicon nanocylinders onto the solar cell surface.

The nanocylinders are about 100 nanometres wide and exhibit electromagnetic resonance that scatters a particular wavelength of light. This reduces the solar cell’s efficiency by about two per cent. Current solar panels sold to consumers have an efficiency of about 22 per cent, the researchers said.

“In principle, this technique is easily scalable for fabrication technology,” AMOLF scientific group leader and senior author Albert Polman said.

“You can use a rubber stamp the size of a solar panel that in one step, can print the whole panel full of these little, exactly defined nanoparticles.”

While there is a slight efficiency cost, the researchers said the technology could also be used in creating tandem solar cells, which stack several layers of cells that each absorb a particular part of the light spectrum. This could lead to efficiencies of more than 30 per cent.

Now they’ve mastered green, the next step is to create red and blue solar cells, which when combined open to door to any colour imaginable – even white.

“You have to combine different nanoparticles, and if they get very close to each other they can interact and that will affect the colour,” Polman said.

“Going to white is a really big step.”

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