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September 16, 2014updated 29 Jul 2021 11:49am

New transparent solar panels could fit invisibly over windows and phone screens

By Barbara Speed

Much as they’d hate to admit it, most people are far more likely to make eco-friendly life changes if they require the absolute minimum in effort and inconvenience. Yes, we all want a low-carbon future; no, we don’t want a wind farm next door.

Lucky, then, that a new type of solar panel has arrived. It isn’t ugly, inconvenient or loud; in fact, it’s practically invisible. The panel, developed by a team at Michigan University, is transparent, and could be used to fit over windows – or tablets, electronic signs or mobile phones.

This technology is a step forward from similar panels, which are see-through but tinted, and therefore less useful. As Richard R. Lunt, one of the new panel’s creators, puts it: “No one wants to sit behind coloured glass.”

There’s a reason it’s been so difficult to develop transparent solar panels. Completely transparent materials let nearly 100 per cent of light through (that’s how you can see what’s on the other side). But solar panels function by siphoning off some of the light as energy: if they let all the light through, how can they collect any energy?

The breakthrough made by the Michigan State researchers was to find a way of collecting invisible wavelengths. Their panels are embedded with salts that absorb infrared and UV wavelengths; something called a “transparent luminescent solar concentrator” then converts these into wavelengths that traditional solar panels can absorb. These are then channelled to the edges of the panel, where thin black strips of the cells used by traditional solar panels convert them into electricity. The result? A panel that lets all visible light through, but still collects solar energy.  

This faintly confusing diagram from the panel’s creators shows the process. The squiggly purple line represents non-visible waves, obviously:

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The technology is still in its early stages: the prototype is only 1 per cent efficient, which means that the panels can only turn 1 per cent of the sunlight that hits them into usable energy. The scientists hope to increase this to 5 per cent, but even this is far lower than most commercial panels: the most efficient panel created so far had an efficiency of 47 per cent; even other semi-transparent solar panels manage 7 per cent.

The unobtrusiveness of the transparent panel might outweigh these drawbacks. It’s unclear how expensive they would be, but if they use less energy to produce than traditional panels, the low efficiency might not matter that much.

There’s another advantage. Solar panel maintenance – which means clearing dust and dirt from the surface so light can reach it – is something users would do automatically, to enable their existing routines. Like, say, texting. Or spying on their neighbours.

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