Science & Technology - Posted by Deborah Williams-Hedges-Caltech on Tuesday, February 28, 2012 11:13 - 5 Comments 
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(1 votes, average: 5.00 out of 5) Loading ...Full spectrum boosts solar cell power
"With a slightly more complex solar cell it becomes possible to convert all colors of the light from the sun to electricity, and an efficiency of up to 70 percent is achievable," says nanophotonics expert Albert Polman. (Credit: iStockphoto)
CALTECH (US) — Printing specially engineered nanostructures on solar cells allows them to reach as high as 70 percent efficiency.
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The text of this article by Futurity is licensed under a Creative Commons Attribution-No Derivatives License.
It has long been thought that conversion efficiency of solar cells cannot exceed 34 percent for a single material or less than about 45 percent for the most efficient cells. A thermodynamic limit is responsible for this practical limitation.
By clever light management, however, efficiency as high as 70 percent is achievable. Harry Atwater, applied physicist at California Institute of Technology (Caltech) and his Dutch colleague Albert Polman describe how this can be done in the journal Nature Materials.
A solar cell is a device that converts sunlight into electrical power. This conversion process, however, is typically not very efficient: a conventional silicon solar cell commercially available today converts only 15-20 percent of the energy of the sunlight to electricity and a large fraction (80-85 percent) is lost as heat.
Blue and green light are converted to electricity with an efficiency less than 50 percent, while infrared light is not absorbed by a silicon solar cell at all. The highest record efficiency ever realized by a silicon solar cell is only 27 percent.
Light that is not converted in the solar cell leads to thermodynamic disorder known as entropy and therefore a reduced cell voltage. As a result, the maximum achievable efficiency is limited to 34 percent, the so-called Shockley-Queisser limit.
Also, the incomplete trapping of light inside the solar cell and defects in the solar cell material’s crystal structure cause a loss in efficiency.
By managing the light in a clever way, a large portion of these problems can be solved. By using specially engineered nanostructures, printed on the solar cells’ surface, the light can be better trapped.
In their article, Atwater and Polman describe several recipes with which these improvements can be realized. They are based on the integration of photonic nanostructures and circuits on the solar cell. The inspiration for some of these ideas comes from the optical integrated circuit technology, where structures to guide and control light are routinely made.
Atwater, who directs the DOE Light-Material Interactions Energy Frontier Research Center at Caltech, notes, “Before 2000 scientists and technologists had developed materials and devices with high electronic quality, but little attention was paid to optical design.
“But in the last decade, revolutions in photonic material design and large-area nanostructure fabrication have given researchers and technologists tools to enable a new era of ultrahigh efficiency photovoltaics.”
Also, adds Atwater, “historically, the solar cell community has assumed that cells could either be made with low efficiency and low cost, or high efficiency and high cost. It’s now apparent that this is a false dichotomy, and that high efficiency and low cost are both achievable.”
Polman, who is lab director of the FOM Institute for Atomic and Molecular Physics in Amsterdam, notes, “The solar cell community has driven down solar panel cost, yet is very conservative and has not boosted efficiency significantly.
“But solar panels with a high efficiency take up much less space, because you need fewer panels to generate the same amount of power. That saves costs of land, installation, and infrastructure. With a slightly more complex solar cell it becomes possible to convert all colors of the light from the sun to electricity, and an efficiency of up to 70 percent is achievable.”
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5 Comments
antoniocristovao
The problem of solar panel is their price. If can lower, more people will use solar panels
Imagine every available sun-facing roof across the country covered in solar cells feeding into the grid. What worry then about base load power supply? Indoor plumbing, electrical wiring, telephone plugs and Internet cabling all evolved only in the second half of the 20th century from luxury options to mandatory essentials in new buildings. High cost, low demand, untested technology, a lack of trained fitters, plus scare stories about fires and explosions were always the objection from builders, yet who can imagine moving into a new house without water pipes, gas fittings, electrical and telephone plugs as standard? Why is solar not the new essential in all new constructions? Vested interests are rapidly overshadowed by increasing efficiencies. The more that are built, the better and cheaper they get.
Christopher M. Vanderwall-Brown
I did a little math on my own. If the value of 989-971 W per m^2 of sunlight is correct for the energy contained therein, and this article’s listed 70% holds true, if 180 million US homes (using a 40×60 square foot roof size as our standard for calculation) replace their roofs, or cover their roofs with these new solar cells, the total output on any given clear day could be as much as 110 terawatts. The US grid produces about 1.09 terawatts of electricity.
The excess could be used to convert water (of some kind) into hydrogen and oxygen for use in steam cooled combine hydrogen power plants. We could also have home hydrogen storage tanks, or if not feasible, local hydrogen conversion stations. The US could completely depart from using fossil fuels.
At first I thought the idea was nutty, but after reading this I’m really wondering if it could work, provided the supporters don’t get assassinated for proposing a plan that in not so many years would result in the complete obliteration of the oil industry. Most if not all nations who are claimed to produce terrorists or support their activities would no longer have means of funding, as unless they were producing hydrogen, people would no longer have need of their services i.e. we wouldn’t have to buy oil from the Middle East, Venezuela, etc. The US Oil Industry would go broke, unless they could find a way to use oil constructively–such as for chemistry.
People who run their homes on natural gas, could switch to hydrogen. You’d be able to tell there was a leak, by either an additive in the gas, or because your voice would become higher than with helium.
If this works, and goes into production, I hope these scientists win the Nobel. :)
Christopher M. Vanderwall-Brown
Edit: 70% efficiency for energy conversion.
And the listed values are for the quantity of energy contained in a square meter of sunlight.
I am praying for that all days.