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Matthew O'Connor/MEDILL

Traditional solar cells made from silicon only respond to a small portion of the electromagnetic spectrum, around 1.1 electron volts (eV). A new photovoltaic solar cell material developed at the Lawrence Berkeley National Laboratory reacts with nearly the entire spectrum to potentially double power output.


New photovoltaic material could deliver twice the solar power

by Matthew O'Connor and Justin Eure
Feb 03, 2011


Sunshine

Courtesy NASA's Solar Dynamics Observatory

A multiwavelength extreme ultraviolet image of the sun.

From sun surface to solar panel

The sun is a massive fusion engine, one of the most dramatic manifestations of Einstein’s famous equation E=mc2.

Essentially, the formula shows that a portion of any atom’s mass comes from the energy binding it together.

The force that holds subatomic particles together is, strangely enough, much more powerful than gravity. It allows for the formation of all matter. Unleashing that nuclear force generates massive amounts of energy.

This is the principle that inspired the atomic bomb, an awesome and terrible eruption of that binding energy. But the explosions that ended World War II were the product of nuclear fission, or the splitting of an atom.

The fission process, as engineered by humans, is powerful but very inefficient. Significant energy releases as unusable and dangerous radiation. The reaction is more efficient than the burning of fossil fuels, certainly, but far from ideal.

In the dense heart of the sun, however, two smaller atoms are actually fused into one. The abundant hydrogen atoms are most commonly converted into helium, releasing binding energy as light-bearing photons.

Nuclear fusion occurs in the sun's core under extreme pressure from gravity and at temperatures of nearly 27 million degrees Fahrenheit. Scientists are still struggling to replicate the process. The photons fire outward through the solar system, traveling about 93 million miles to bombard the earth with energy.

“[Photons] interact with matter and make things move faster, which generates heat,” said astrophysicist Ronald Taam of Northwestern University.

The energy generated by the impact of these photons can be harnessed by solar cells and transformed into electricity.
A new solar cell material could double the energy output of traditional solar photovoltaics, by reacting to nearly the entire light spectrum.

Developers at the Lawrence Berkeley National Laboratory in Berkeley, Calif., announced the research on the new material last week.

“It’s a completely new technology,” said physicist Wladek Walukiewicz, who headed the cell's development. “It’s game changing.”

Traditional solar photovoltaic panels are made from silicon, and respond to only a small portion of the light spectrum. Panels have been developed that react with a wider range of light – multi-junction cells – but they are very complicated to make and too expensive for consumers.

“They’re useful in satellites for example, where you need as much bang as you can get and you don’t care so much about the buck,” said Seth Darling, research scientist in the Center for Nanoscale Materials at Argonne National Laboratory, outside Chicago. “But for large-scale Earth-based solar power, that sort of technology is a very, very long way off from being cost competitive.”

That’s where Walukiewicz and his colleagues’ research comes into play. Rather than bonding multiple materials together to create a cell that can react to different light wavelengths, such as multi-junction technology, Walukiewicz cell is made from a single semiconductor compound. It allows for the capture of more light photons from nearly all wavelengths.

And that compound they developed, gallium arsenide nitride, is fabricated from relatively commonplace components. In fact, the gallium arsenide base is one of the most frequently used semiconductors and is fabricated in a familiar industrial method, Walukiewicz said.

“If people hear about gallium arsenide, they like it because they know what it is,” he said. “It’s not some exotic material.” That translates to lower prices for consumers.

When evaluating solar technology, it all comes down to cost – measured over the lifetime of the installation. One approach is lowering the cost of panels, which can be done by producing them on a larger scale. Another option is developing a way to get more energy out. People want a return on their investment.

Fortunately, sunlight is free, abundant and not likely to run out for another 5 billion years.

The global demand for oil, however, will increase far beyond potential supply by 2094, according to a 1999 study by the American Petroleum Institute. At that point, it becomes economically unsustainable, not to mention environmentally hazardous, to extract oil and sell it to consumers. And that prediction sits at the optimistic end of the spectrum.

If mankind could replicate solar fusion and harness its power directly, the energy produced would likely exceed any projected needs. The energy unlocked by the sun in one pound of hydrogen gas could provide power to the entire United States for one week, said Ronald Taam, astrophysicist at Northwestern University. A pound of gas, a week of power.

“In maybe 50 years they might have controlled fusion,” Taam said of current experimentalists. Until then, we will have to settle for whatever energy-charged bounty the sun throws our way.

The goal, then, is to catch more sunlight, and to do so cheaply and efficiently.

“That’s sort of the tact that is being taken here,” Darling said. “[It could be] a way to improve efficiencies on what you could possibly do with something like plain silicon. “

The new material is still in development stages but could be available for practical applications in as few as three years, Walukiewicz said.

Currently, we use about 17 terawatts of electricity worldwide, and that is projected to nearly double by 2050, Darling said. And most of that power will likely still come from fossil fuels.

“It is a frightening energy mix in that timeframe due to climate change and other issues,” he said. “This is why we need these breakthrough technologies in solar to really change that picture.”

While he recommends a combination of energy sources that include nuclear, wind and fossil fuel, Darling said that solar is the only source that could provide all the energy we need.

“The potential is as close to limitless as just about any energy source can be,” he said. “There’s enough energy coming from the sun, and that we could capture feasibly, to actually power the planet.”