The race to capture solar energy at U of T

The global race to harvest the sun's energy has researchers all over the world competing to develop the new technologies that they hope will end our reliance on fossil fuels.

One of the latest announcements is from a team at Michigan State University that's developed a clear pane of plastic that could be used on windows to capture sunlight. ScienceDaily, an online publication of research news, reports that the luminescent solar concentrator, as it's called, has the potential to revolutionize commercial or industrial window design by turning windows into large-scale collectors of solar energy.  

But even while science writers enthusiastically describe the promise of this latest solar technology, researchers immersed in the field tend to greet the news more cautiously.

Professor Ted Sargent, a leader internationally in the development of "paintable" solar cells, which has spawned related research around the world, says "what's clearly different and clearly interesting" is that the Michigan team's work allows them to take a significant part of the sun's rainbow spectrum, convert it into a single colour and "put it off to the edges" of the plastic pane.

‘If this development can go all the way," says Sargent, it offers the possibility of yet another venue for deploying solar cells. Instead of just putting solar panels on the roof of a house, says Sargent, these transparent cells could be placed on windows and windshields.

But Sargent says that in the search for the solar technology breakthrough that will transform the world, "this one's not there yet."

"They kind of get the light ready in an appealing way," says Sargent. Problem is, the mostly transparent material is "nice for a window, but solar cells have to absorb light, so it's not good for collecting light."

Many new developments in the solar field are plagued by those kinds of trade-offs — between cost of production and efficiency. In the case of a luminescent solar concentrator for windows, Sargent says if it can be manufactured cheaply enough it has the potential for wide-spread application by turning windows and window walls around the world into solar harvestors, but at the cost of inefficiently capturing the full potential of the sun's energy.

Sargent's own work in nanotechnology led to an ink-based solar cell — essentially suspending the ingredients of solar cells in liquid that could be "painted' onto any surface.

In a Tedx Toronto talk, Sargent describes the incredible potential of solar energy:  "Every hour enough energy reaches the earth from the sun to power the earth for an entire year."

It's all about the technology," says Sargent.  "Cheap and efficient is the holy grail."

Led by Sargent, a researchers at U of T are re-imagining the solar cell. Conventional cells use silicon, "a beautiful semi-conductor material", limited by what Sargent calls "a quality of rigid perfection," accompanied by equally rigid costs associated with the manufacturing process and installation.

Sargent's team has developed a solar cell that he says is more akin to printing a newspaper - a semi-conductor ink printed onto a flexible backing.  Unlike silicon-based cells, in this application solar cells are painted on a light-weight flexible carpet that can be spread out on a roof, a road or any other surface exposed to the sun.

"You can literally paint surfaces with this ink" - a cheap way to make a solar cell, says Sargent. "And it's very black - the perfect absorber of visible light and of infrared light."

That capacity to absorb infrared light is especially powerful because the spectrum includes as much infrared as visible light.  But, says Sargent, the infrared portion of the sun's spectrum is often ignored  And yet, when the sun beats down on our face, much of the heat we feel is infrared light.

Sargent's group led the world in making most efficient solar cells in the world based on ink-based colloidal quantum dots.  A finished solar cell — about the size of a postage stamp - has the ability to both absorb the sun's energy and to extract it as electricity.

In an interview with Metro Morning's Matt Galloway, Sargent said that at this point, the technological breakthrough that will revolutionize the world's energy production is "years, not decades away.

But it will require teams of researchers working in many different disciplines to get there, "from chemistry to physics to material science."

In Sargent's case, It's led to a collaboration with Saudi Arabia's KAUST (King Abdullah University of Science and Technology), a new but well-funded university that has made the development of cheap, efficient solar energy one of its main research goals.

The collaboration carries intriguing strategic possibilities.

Historically, Saudi Arabia's major export is fossil fuels but in the future, says Sargent, Saudi Arabia intends to be a world leader in exporting technology associated with solar energy.

It's supported by that other natural resource that Saudi Arabia has in such abundance — sunshine.

And nature itself is teaching researchers to think differently.  In the international race to develop cheap, efficient solar technology, Sargent is increasingly turning to nature to learn its processes.

"It's remarkable what nature does," says Sargent. "It's the epitome of 'efficient-enough' solar capture. How much does it cost for grass to grow or for a leaf to grow on a tree? Nature has its own systems."

Sargent speaks with the kind of respect that can only come from a lifetime of trying to crack one of the world's most urgent environmental challenges.  Nature, says Sargent, proves that it's possible to cover the earth with solar harvestors.  "It's an inspiration and challenge to researchers to do the same."