Great things from small things

 By Robin Wylie

At the nano-scale, things behave differently. And today the unique properties of various nanomaterials are being used to increase the efficiency of tomorrow’s renewable energy technology. Robin Wylie explores the many ways in which cutting-edge nanotechnology is already being used to improve energy sector…

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Nanotechnology is more than just a buzzword — it’s the future.

In recent years scientists have begun to discover that manipulating matter on the scale of nanometers (billionths of a meter) can endow everyday materials with extraordinary new properties.

Nanotechnology is a young field, but it is already showing huge promise in countless fields of science and technology. Medicine, engineering and even the clothing industry, are already all benefiting from nanotechnological applications (water-repellent t-shirt anyone?).

So it should come as no surprise that nanotechnology could also help with one of humanity’s most pressing challenges — the quest for clean energy.

Making carbon nanotuber safer for the environment

Catching Rays

So far, most nanotechnological research in the renewables sector has centered around solar power. In the past decade over 30 major studies have been published investigating the application of nanotechnology to solar power generation — exceeding the research output of wind, hydro, hydrogen, bioenergy and geothermal combined.

One of the biggest drawbacks with modern solar power devices is their efficiency: even the most advanced devices only absorb a fraction of the incoming solar radiation, and can only a fraction of that radiation is converted into electricity (the rest is mostly lost as heat and reflected light).

Most solar power generators in use today are solar cells, which use long, thin crystals of silicon to convert sunlight into an electric potential. These can absorb a maximum of about 48 percent of incoming solar radiation, about half of which can be converted into electricity.

However, recent studies have shown that nanotechnology could be able to dramatically increase the absorptivity of solar cells, by replacing the crystalline silicon in solar cells with nanostructured silicon.

For example, a 2008 study from Stanford University showed that solar cells composed of silicon “nanowires” and “nanocones” can absorb approximately 90 percent of incoming solar radiation (at certain angles of incidence) — almost twice the amount that can be absorbed by traditional thin-film solar cells. (What’s more, the nanomaterials only used around one percent the amount of silicon needed to build a conventional solar cell, suggesting that nano-engineered solar cells could be significantly cheaper to produce, as well as being more efficient.)

And a later study found that nano-engineered solar cells could be even more efficient. The researchers constructed a prototype solar cell using nanowires, which they found was able to absorb up to 96 percent of incoming solar radiation. And subsequent research from NASA showed that carbon nanotubes, when used as a coating on silicon, can absorb an astonishing 99 percent of the ultraviolet, visible, infrared and far-infrared light that strikes it.

Devices which use liquid to absorb solar energy could benefit from a dose of nanotechnology too. Doping a liquid with nanoparticles has been found to significantly boost its solar absorptivity, and consequently these “nanofluids” have attracted intense interest from solar power researchers in recent years.

Encouragingly, their findings have been overwhelmingly positive. Since the start of the 2010s, numerous research teams have shown that by replacing the fluid used in solar collectors (typically water) with a nanofluid, the thermal efficiency of these devices can be increased by up to 88 percent (or by over 200 percent at higher temperatures).

Electron microscope image of carbon nanotubes grown on smooth silicon. Credit: NASA Blueshift

Beyond Solar

But other kinds of renewable energy stand to benefit from nanofluids too.

Take geothermal power for instance. One way of extracting geothermal heat is by injecting cold fluid into naturally heated rocks in the subsurface (usually in volcanically active areas), before extracting the (now heated) fluid and using it to generate electricity.

Nanofluids could potentially boost the heat-retaining properties of the fluids used in geothermal extraction, in much the same way as they (demonstrably) can in solar power generation. Consequently, geothermal plants might eventually be able to extract more heat energy from the subsurface, thus increasing their efficiency and profitability.

Despite this promise, researchers have yet to study the potential of nanofluids in the geothermal industry experimentally.

But while nanotechnology might be a futuristic concept in the geothermal industry, another renewable energy source is already reaping its benefits.

Hydrogen is one of the most abundant elements on Earth, and can be used to generate electricity in a fuel cell, from which the only byproduct is water. As well as being clean burning, hydrogen is also 2-3 times more efficient a fuel source than conventional gasoline, making it one of this century’s most exciting new energy technologies.


SEE MORE: Solar’s window of opportunity by RP Siegel



However, hydrogen fuel cells suffer from some fundamental drawbacks, which are currently preventing the technology being rolled out on a wide scale.

One of the most serious of these drawbacks is storage. In order to generate power from hydrogen in an economically fashion, molecular hydrogen needs to be stored in such a way that it can be quickly released during energy production.

Enter nanotechnology. Recent research has shown that spherical “core-shell” nanoparticles could make an excellent storage medium for hydrogen. Hydrogen atoms diffuse into the center of these nanospheres; however, due to the extremely small size of the spheres and their large surface-area-to-volume ratio, the stored atoms always remain relatively close to their surface, allowing the hydrogen to be quickly released as needed for electricity generation.

Different kinds of nanomaterial might also fit the bill for storing hydrogen. Several studies have found that nanostructures such as “nanoblades,” carbon nanotubes and carbon nanofibers could all be effective media for hydrogen storage too.

Scientists have only just begun to tinker at the nanoscale, and already the results are astonishing, in renewable energy and in many other fields of study. The best is surely yet to come.

about the author
Robin Wylie
Freelance earth/space science journalist. Currently finishing off a PhD in volcanology at University College London.