Thursday, November 10, 2011

A Gallery of Solar Capture Technologies

The Earth is deluged with vast amounts of energy from the sun on a constant basis. Humans have utilised solar energy from their earliest days, living on the proceeds of photosynthesis either directly or indirectly. As humans discovered fire, they cleverly enlarged their utilisation of solar energy to keeping warm on cold winter nights.

Modern humans have set their sites on powering a large part of their commercial and industrial infrastructure with solar energy, and have become extremely ingenious toward that end. Pictured below are several unconventional approaches to solar energy, which go beyond the simple silicon photovoltaic approach:
Plasmonic Photovoltaics

“The greatest significance thus far is to show an alternative method to rectennas and PV devices for IR and visible light conversion,” Melosh [Stanford U.] told “The conversion efficiencies aren't amazingly high compared to a PV in visible, so it’s not going to replace PVs, but it could be used for energy scavenging later on.”

The new device’s MIM architecture is similar to that of a rectenna. However, whereas rectennas operate with long-wavelength light such as microwaves and radio waves, the new device operates with a broad spectrum of infrared to visible wavelengths. _Physorg

Northwestern U. Plasmonic via Brian Westenhaus

Another type of plasmonic super-absorption device comes from Northwestern U. Brian Westenhaus has more.
Nanowire Photovoltaics

The [U. Illinois] researchers found conditions for growing nanowires of various compositions of the III-V semiconductor indium gallium arsenide. Their methodology has the advantages of using a common growth technique without the need for any special treatments or patterning on the silicon wafer or the metal catalysts that are often needed for such reactions.

The nanowire geometry provides the additional benefit of enhancing solar cell performance through greater light absorption and carrier collection efficiency. The nanowire approach also uses less material than thin films, reducing the cost. _Physorg

Solar Antennas

A promising approach to solar antennas from Caltech
Another approach to solar antennas from Stanford
Super Light Absorber Nanotube Coating

The team of engineers at NASA's Goddard Space Flight Center in Greenbelt, Md., reported their findings recently at the SPIE Optics and Photonics conference, the largest interdisciplinary technical meeting in this discipline. The team has since reconfirmed the material's absorption capabilities in additional testing, said John Hagopian, who is leading the effort involving 10 Goddard technologists.

"The reflectance tests showed that our team had extended by 50 times the range of the material’s absorption capabilities. Though other researchers are reporting near-perfect absorption levels mainly in the ultraviolet and visible, our material is darn near perfect across multiple wavelength bands, from the ultraviolet to the far infrared," Hagopian said. "No one else has achieved this milestone yet."

The nanotech-based coating is a thin layer of multi-walled carbon nanotubes, tiny hollow tubes made of pure carbon about 10,000 times thinner than a strand of human hair. They are positioned vertically on various substrate materials much like a shag rug. The team has grown the nanotubes on silicon, silicon nitride, titanium, and stainless steel, materials commonly used in space-based scientific instruments. _Physorg

Thin Film Nanopillar
The cells designed by Solasta are built on a substrate forested with long, thin, vertically arrayed nanopillars. The pillars are coated first with metal, then with a thin layer of semiconducting material such as amorphous silicon, and then with a layer of transparent conductive oxide. Though the silicon layer is thin, a photon still has a relatively long path to travel down the length of the nanopillars, and a good chance of transferring its energy to an electron. Freed electrons then travel perpendicularly over a very short path to the metal at the core of each pillar, and shimmy down this electrical pole off the cell. "Electrons never have to travel through the photovoltaic material," says Zhifeng Ren, professor of physics at Boston College. "As soon as they're generated, they go into the metal." _TechnologyReview
This is only the beginning of the ingenious designs which are intended to shift Earthlings into a grand new solar age.

The problem, of course, is the diffuse and intermittent nature of sunlight. The invention of cheap and efficient electrical storage would partially solve that problem -- especially for desert areas near the equator, which receive plentiful sunlight on a regular schedule.

But even with cheap, efficient storage, the diffuse nature of sunlight requires large areas of land to be covered by solar collectors. At this time, even at 100% conversion efficiency, and at a cost of $0.00 per panel, large scale solar energy would not be practical or affordable for most parts of the globe.

Solar photovoltaic energy is instead a niche field, more suitable for small scale applications. Solar thermal is another matter. Solar thermal principles should be incorporated into the construction of every home and building which is built in the developed world from now on.

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