Solar Power Breakthrough
July 26, 2007 ”“
Online encyclopedia Wikipedia describes a nanometer as the length a man’s beard grows in the time it takes for him to raise a shaver to his face. A nanometer is rather short.
Nanotech materials - made from bits of materials in the dimensional realm of 1 -100 nanometers (nm)(nm= one billionth of a meter) - are in the early stages of offering breakthrough opportunities in energy storage and conversion of one form of energy to another - sunlight to electric power for instance.
Nanotech materials are available in products you can buy in the marketplace. State-of-the-art lithium-ion batteries incorporate nanotech in some fashion to make powerful, long-lasting and quick-to-recharge energy storage devices for small electronics and soon, possibly, hybrid and electric cars.
Slowly nanotech is finding its way into solar energy as well.
Thin-film solar cell developer Innovalight and the US National Renewable Energy Laboratory (NREL) have reported that silicon nanocrystals (also known as quantum dots) made by Innovalight tested in wavelengths of light less than 420 nm (the band of light known as indigo) released two electrons for each photon of light striking the crystal. Typically, and at best, ordinary crystals release only one electron per photon.
The release of more than one electron is known as the Multiple Exciton Generation (MEG) effect.
Calculations at NREL show that, theoretically, solar cells exhibiting Multiple Exciton Generation could lead to solar cells with a maximum sunlight-to-electricity conversion efficiency of 44 percent. If sunlight was concentrated on those cells by a factor of 500 (500 times the brightness of normal sunlight) using lenses or mirrors, conversion efficiency would be about 68 percent.
(The theoretical maximum efficiency of today’s conventional cells is about 33 percent under normal light conditions, 40 percent under concentrated light. However, typical off- the-shelf solar cells have a conversion efficiency of 10-20 percent or so depending on the product.)
There’s work to be done, of course. Innovalight’s nano solar crystals have to be developed into working and inexpensive-to-manufacture solar cells. And just as importantly the nanocrystals should be tuned to convert to electricity a greater bandwidth of light than just indigo (blue-purple) light.
Learn more: Innovalight http://www.innovalight.com
National Renewable Energy Laboratory (NREL) http://www.nrel.gov
Subscribers to American Chemical Society's Nano Letters can receive the full research paper “Multiple Exciton Generation in Colloidal Silicon Nanocrystals”