New approach to solar cells

February 3, 2011
This is a transmission electron microscope image of nanoparticles in an experimental solar cell. Credit: Gergely Zimanyi, UC Davis

An interdisciplinary team of UC Davis and UC Santa Cruz researchers is taking a novel approach to solar power, one that promises to lead to a technological breakthrough. By using nanoparticles of germanium, silicon and other materials, the researchers hope to produce solar cells far more efficient than the current state of the art.

The project was recently awarded $1.5 million over three years from the National Science Foundation.

Conventional solar cells all operate on the same principle of "one photon in, one electron out," said Gergely Zimanyi, professor of physics at UC Davis and principal investigator on the NSF grant. In other words, one particle of light, or photon, hits the solar cell and generates one electron to produce an electrical current.

The efficiency — energy out compared to energy in — of a solar cell operating according to this principle is capped by a theoretical maximum of 31 percent. But by constructing solar cells from extremely small nanoparticles, the UC researchers aim to generate several for each photon, raising the maximum efficiency to between 42 and 65 percent.

The one-photon-in/multiple-electrons-out paradigm has been demonstrated at the Los Alamos National Laboratory, Zimanyi said — but the Los Alamos group did not build a functioning solar cell based on this paradigm. The UC Davis/UC Santa Cruz team includes scientists with experience making from nanoparticles, giving hope that the group will be able to construct a fully functioning and well-optimized solar cell from and nanoparticles, he said.

The team members are: Zimanyi; UC Davis chemistry professors Susan Kauzlarich and Delmar Larsen; Professor Giulia Galli, who holds a joint appointment in physics and chemistry; Professor Zhaojun Bai, Department of Mathematics and Computer Science; Debashis Paul, professor in the Department of Statistics; and Susan Carter, professor of physics at UC Santa Cruz.

The interdisciplinary nature of the team was crucial to getting the proposal funded, Zimanyi said. "NSF asked for a collaborative effort between materials sciences, chemistry and mathematical sciences," he said.

Zimanyi, Galli and Bai will conduct theoretical and computer-modeling studies, with Paul providing statistical expertise; Kauzlarich's lab will synthesize the new , Larsen's group will characterize them and Carter's lab at UCSC will develop a working device. A prototype cell has been already constructed prior to getting the grant and exhibited an efficiency of about 8 percent, which Zimanyi described as a very encouraging result given the limited resources going into its construction.

The team will collaborate with the California Solar Energy Collaborative, which is based at UC Davis and led by Pieter Stroeve, professor of chemical engineering and materials science. The team also plans an outreach effort, primarily via its public webpage:

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5 / 5 (1) Feb 03, 2011
I like the concept, if the efficiency could rise to 50% it will be very good
not rated yet Feb 03, 2011
I just read on an article that came out today that the UK is using 21% efficient solar powered cells (the highest yet), and if we can raise the theoretical maximum to 42-65% then it'll be no time until we're producing inexpensive solar cell technology at 35%, and then it'll raise more reaching the 50%s soon after that.
not rated yet Feb 03, 2011
Correct me if I'm wrong, but if photosynthesis is only 2% efficient at capturing energy - then this solar cell technology pretty much puts the final (and well deserved nail) in the coffin of biofuels that compete with human food for peak petro-chemical fertilizers and peak phosphates - which is all primary biofuel (like algae oil) production systems. No wonder Shell bailed on its algae oil investment.
not rated yet Feb 04, 2011
it's a amtter of scale/economy. It's very easy to have huge tracts of ocean converted into biofuel generators - which could easily make up for the difference in efficiency.

Both approaches have their merits. Shell bailed because they saw (for the foreseeable future) no way that biofuels could be manufactured cheaper than pumping oil out of the ground. They are not in the business of being green (and have pretty much given up of ever having such an image) so there's no point for them to invest in biofuels (the same money can more easily go into bribing governements into subsidies for oil/oil production and the slowing down of any alternative energy legislature).
not rated yet Feb 04, 2011
All biofuels have the same problem - scalability. The improvement in solar cell efficiency is welcome but if the manufacturing process is as costly as for current PV panels, it'll never make much of an inroad in, say, domestic applications, which still require rebates and unrealistic feed-in tariff rates to be attractive.
5 / 5 (1) Feb 04, 2011
If you have 40% efficient panels then you'd need about 1/4 of as many compared to 10 to 11% efficient panels.

So if the 40% efficient panels are less than 4 times as expensive per square meter they are better.

Additionally, using fewer panels means less wires required and less of other components (such as the self-orienting motors used in large farms,) which also lowers the cost of the entire system.

If you need 1/4th as many panels then even if the panels are relatively expensive they may be "better" due to the other costs saving since the entire system is 1/4th the size.

If they actually obtained 65% efficiency in photovoltaics, that would make Solar Towers obsolete, since real turbine based systems cannot exceed about 66% efficiency, at least as far as pure electricity production goes. Which means that a solar tower's maximum theoretical efficiency would be ~66%

This is assuming we are measuring efficiency as "total solar flux per meter^2 in vs electricity out".
not rated yet Feb 04, 2011
So not only do you need 1/4th as many panels, but you need 1/4th as many wires, and the average length of the wires is halved.

So the same megawatts class power plant constructed with 40% efficient panels could be 1/4th the area, and would use 1/8th of the total length for power lines.

X = number lines
y = average length

XY = wire used in 10% photovoltaic power plant.

(0.25X)*(0.5Y) = wire used in 40% power plant.

= 0.125XY

considering the current price of copper and other materials used in electrical cables, this is a temendous savings potential. For every ton of copper used in a 10% efficient plant, you'd use only 0.125 tons in the 40% efficient plant. At current prices for copper near $9900 per metric ton, this would save 7/8, or $8662.5.

The savings in copper starts to be a significant fraction of the total cost of the operation.

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