How butterfly wings could revolutionise solar panels

In the hunt for sustainable energy, solar power has emerged as a front runner for supplying part of the world’s energy needs. And Will Tingle has been finding out how three species of butterfly have the potential to make them an even more attractive source of power, in every sense of the word…

Will - There can be no doubt that solar panels offer a cheap and decentralised way of generating energy, but there are always improvements to be made when it comes to getting the most power out of each panel. That's where our first two butterflies come into play. The more light you can get to hit a panel, the more energy you can produce. Thanks to work supported by UK Research and Innovation, we can take inspiration from nature to channel more light towards these solar modules. To find out more, I've been speaking with the University of Exeter's Katie Shanks.

Katie - When we think about nature, it's probably the ultimate trial and error. We wanted to make very lightweight optics, and butterfly wings do that perfectly.

Will - And was there a particular species that you focused on?

Katie - So I started looking at the cabbage white butterfly, which has very lightweight reflective wings. And then I also started looking at the glasswing butterfly, which has opposite properties. So it's very transparent, very anti-reflective. And so in that way, I had two blueprints to help understand and develop our own optics for solar panels.

Will - So I think I see what you're getting at with the glasswing butterflies. Obviously, as the name suggests, they have these translucent wings. And if you're saying that they can absorb light very well, that sounds pretty useful if you're a solar panel. But why did you go for cabbage white?

Katie - The cabbage white actually does this very interesting behavior in the morning, where it sunbathes with its wings in a V-shape. And the V-shape of the cabbage white's wings helps focus light onto its body, onto its flight muscles, so it can fly quicker than other butterflies would. And so if you're increasing the amount of energy, the amount of sunlight into your solar panel, you're increasing the amount of energy out without actually having to increase the solar panel material you're using.

Will - So it's the idea then that you can have kind of the best of both worlds there. If you have an outer sort of shape of this cabbage white reflecting the light in, and then this glasswing butterfly structure on the solar panel itself, you've got this almost hyper concentration of light hitting the solar panel.

Katie - Exactly.

Will - Obviously, the butterflies themselves produce these structures with very specialised proteins in their wings that create certain shapes that can refract or reflect the light as they desire. That's probably not an option to use. So what materials are you using to try and replicate these effects?

Katie - We're looking at, for example, for the cabbage white butterfly, titanium dioxide material. For the glasswing butterfly, we're actually, I'm working with the collaborators at Pittsburgh University who can actually etch these structures into glass.

Will - Is this something you could apply to already created solar panels, or does this have to be a fresh new solar panel that needs producing?

Katie - So that's a good question. So applying it to current solar panels is feasible. I guess the question would be, would you be uninstalling and installing a solar panel? And it would come down to how old that solar panel was and if it was worthwhile also upgrading the solar cell technology as well.

Will - Do you foresee this being something that could be rolled out worldwide? Is it versatile? Is it durable enough, do you think?

Katie - So one of the interesting properties of these nanostructures, the glasswing nanostructures, is that they also have properties such as hydrophobic. So whenever water hits them, whenever rain hits them, it rolls off easily. In terms of durability, they shouldn't be any less durable than current solar panels.
And in terms of rollout and scalability, we've already analysed how this technology will perform in different areas of the world. So solar panels on a wall or installed vertically near the equator, where the sun is very high in the sky, we see about a 15% increase in energy output throughout the year. And in the same extreme condition of, say, a horizontal panel, but closer to the north or the south poles, again, we have close to the 15% increase. So it's kind of those non-ideal installations, which we'll be seeing more of as we install more solar panels. And for vehicles as well, that's where there's the biggest impact and where we think there's going to be a lot of demand.

Will - Katie Shanks. So that's how butterflies are giving solar input a boost. But there is another facet of solar cells that is also worth considering. If they are to become an increasing presence in our lives, do they have to look like a big black square? Well, perhaps not. You may be familiar with the blue morpho butterfly. If not in name, then by the fact that it's the giant blue butterfly that signifies you're in the tropics in most forms of media. But did you know that that blue isn't a pigment? Instead, it's the result of light hitting scales on the butterfly's wings. These scales interfere with the light and only reflect the blue wavelengths of light. Well, if you could harness that structure on the wings as a kind of a window pane and slide it on top of a solar cell, well, you could turn them blue, or it turns out pretty much any other colour you want, as I've been hearing from Fraunhofer Institute for Solar Energy Systems, Sophie Gledhill.

Sophie - What we've done in the Fraunhofer Institute for Solar Energy Systems is develop a technology which we call the morpho colour. And this technology allows the solar modules to have a designed colour, working on the similar principles as the morpho butterflies. So we deposit these thin multi-layer films of alternating high and low refractive indexes on either microstructured glass or a microstructured polyester based film. You either laminate your microstructured glass with your multi-layered films into your module, or alternatively, if it's on a flexible film, you can also laminate that in between the glass and the module. And so it's very compatible with any standard solar technology and any module manufacturers can produce this technology in a range of colours and forms as they so desire.

Will - I'm imagining the skyscrapers of the future coming with these solar panels on them.

Sophie - Yes, so skyscrapers or heritage buildings, where you have to blend your material, your solar panels into the original building materials, say making terracotta solar modules. The morpho colour technology, which is what we produce at the Fraunhofer Institute for Solar Energy, has been licensed to a Swiss module construction company, Megasol. And they've announced a really cool new project to construct a massive rainbow solar module display in the pride flag colours so that you have a strip of red, a strip of orange modules, yellow, green, blue and violet on one side of the roof in the St. Pauli football stadium in Hamburg.

Will - Crucially, I guess, the bog standard solar panel, as I understand it, is made black by default because that absorbs the most light. Is this going to decrease the amount of light that can go into that solar panel?

Sophie - So of course, for the colour to be perceived by the eye, there is also some reflection in the specific wavelengths. For example, the green solar cell, you need to reflect in the green wavelengths, but you would reflect back with a very low amplitude and a very narrow bandwidth. And this corresponds to a marginal loss in the light energy in these wavelengths. However, for a green solar module with the morpho colour coating, that yields about 95% of the efficiency of compared to a standard black module. And we have this marginal loss in reflectance with the specified colour.

Will - Sophie Gledhill. So with the power of three butterflies combined, more efficient and more vibrant solar panels could be coming soon to a town near you.

Katie's work was carried out with the support of UK Research and Innovation.