Fly eyes

Fly eyes: insects may not take over the world but may help save it with clean energy (Getty Images: mikroman6)

The eye of a 45-million-year-old fly can increase the power output of a solar panel by 10 per cent. Dr Karl is inspired by how an ancient insect helped solve a modern problem.

One of the first things that I learnt as an engineer was the old saying, “Never reinvent the wheel”. Welcome to the rapidly growing field called ‘biomimetics’ where we go out of our way to mimic biology, and copy what nature has already invented, to solve problems in our modern world.

Take the example of how the eye of a 45-million-year-old fly can increase the power output of a solar panel by 10 per cent.

Some 45 million years ago, on our planet there was a fly that (we think) was active in the dim light around dawn and dusk. One particular fly got caught in the slowly flowing sap of a tree, and ended up both dying and being almost perfectly preserved in what became a block of solid amber.

Some 45 million years after it died, modern scientists looked at it with a high-powered electron microscope. They noticed some very fine regular corrugations on the front of the fly’s eyes. These corrugations were a regular 250 nanometres apart — less than half the wavelength of blue light.

It turns out that often, very fine corrugations or lines can, via the physics phenomena of diffraction or interference, produce beautiful colours. For example, there are similar very fine structures on the wing of the morpho butterfly, which lives in Central and South America. These structures create blue light that can sometimes been seen from an aeroplane flying overhead.

But the exact opposite was happening in the case of the fly. No colours were being emitted — in fact, no light at all was being reflected. All the light landing on the front surface of the fly’s eye was entering the eye.

Now think of the last solar panel you looked at. Did you catch a shiny reflection off the glass at the front, as you looked at it from different angles? Probably yes.

Now here’s where we can learn from nature.

The light from the solar panel that landed inside your eyeball was being wasted. It should not have reflected off the front of the solar panel. No, it should have gone into the solar panel and got turned into electrical power.

And that’s exactly what our biomimetics engineers have done. It was tricky.

First they had to work out the refractive index of the glass on the front of the solar panel.

Then they had to find a glue that was both totally transparent and had the same refractive index as the glass — and that would survive for decades under direct sunlight.

And then they had to find a plastic with the same properties (totally transparent, same refractive index as the glass) and that would also survive for decades — and furthermore would be relatively easy to machine with the very fine regular corrugations.

They did all this, and then glued the plastic with fine corrugations onto the front of the glass of the solar panel.

So now, thanks to copying nature, we have solar panels that absorb all the light that lands on them, and they reflect none — and produce 10 per cent more power.

But we want to do more than just ape what nature makes — we want to copy her manufacturing methods.

Think about the plastic glued onto the front of the solar cell panel. It took a lot of temperature and pressure and fancy manufacturing processes to end with this finely corrugated plastic — but nature did it with organic chemicals at room temperature and pressure.

We know that catalysts and some kind of fancy self-assembly were involved — but we don’t know the fine details, yet.

The goal is to get cells to grow these structures for us.

But what structures? There are so many.

Well, think about water. Ten per cent of humans don’t get clean drinking water. But in the Namib Desert in Africa, one of the hottest and driest environments in the whole world, there lives a desert beetle. It has beautifully evolved microstructures that harvest its drinking water — from the air around it.

The beetle faces into the morning fog coming off the ocean, and lifts up its back end, to an angle of about 45 degrees. There are little bumps on the back end that are hydrophilic (that is, water loving). They capture tiny droplets of water, which coalesce into bigger drops. Once the drops get big enough, they roll downhill into special channels that are hydrophobic (that is, water hating). They don’t allow the water to stick. And then, gravity takes over, and the drops roll downhill all the way to the beetle’s mouth.

Dr Andrew Parker from the Natural History Museum in South Kensington in London reckons he can build structures that can collect one litre of water per square metre per hour — by copying these structures from nature.

With fly’s eyes and beetles’ backs, insects might not take over the world, but instead help save it with clean power and clean water.