Cool New Solar Stuff

I always love reading about cool new breakthroughs allowing renewable energy to be produced in ways that are more flexible and less costly. The fact that there are so many such advancements on a fairly regular basis these days speaks to the strong market signals that are being sent.

As we have talked about here before, getting energy is becoming increasingly expensive and difficult. The upside of that unfortunate fact, is that the market signals are finally being sent and the market is responding.

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August 12, 2008

Flexible Nanoantenna Arrays Capture Solar Energy

by Roberta Kwok, Idaho National Laboratory

Florida, United States [RenewableEnergyWorld.com]

Researchers have devised an inexpensive way to produce plastic sheets containing billions of nanoantennas that collect heat energy generated by the sun and other sources. The researchers say that the technology, developed at the U.S. Department of Energy's Idaho National Laboratory (INL), is the first step toward a solar energy collector that could be mass-produced on flexible materials.

While methods to convert the energy into usable electricity still need to be developed, it is envisioned that the sheets could one day be manufactured as lightweight "skins" that power products such as hybrid cars or iPods with potentially higher efficiency than traditional solar cells. The nanoantennas also have the potential to act as cooling devices that draw waste heat from buildings or electronics without using electricity.

The nanoantennas target mid-infrared rays, which the Earth continuously radiates as heat after absorbing energy from the sun during the day. In contrast, traditional solar cells can only use visible light, rendering them idle after dark. Infrared radiation is an especially rich energy source because it also is generated by industrial processes such as coal-fired plants.

"Every process in our industrial world creates waste heat," says INL physicist Steven Novack. "It's energy that we just throw away." Novack led the research team, which included INL engineer Dale Kotter, W. Dennis Slafer of MicroContinuum Inc. and Patrick Pinhero, now at the University of Missouri.

The nanoantennas are tiny gold squares or spirals set in a specially treated form of polyethylene, a material used in plastic bags. While others have successfully invented antennas that collect energy from lower-frequency regions of the electromagnetic spectrum, such as microwaves, infrared rays have proven more elusive. Part of the reason is that materials' properties change drastically at high-frequency wavelengths, Kotter says.

The researchers studied the behavior of various materials — including gold, manganese and copper — under infrared rays and used the resulting data to build computer models of nanoantennas. They found that with the right materials, shape and size, the simulated nanoantennas could harvest up to 92 percent of the energy at infrared wavelengths.

The team then created real-life prototypes to test their computer models. First, they used conventional production methods to etch a silicon wafer with the nanoantenna pattern. The silicon-based nanoantennas matched the computer simulations, absorbing more than 80 percent of the energy over the intended wavelength range. Next, they used a stamp-and-repeat process to emboss the nanoantennas on thin sheets of plastic. While the plastic prototype is still being tested, initial experiments suggest that it also captures energy at the expected infrared wavelengths.

The nanoantennas' ability to absorb infrared radiation makes them promising cooling devices. Since objects give off heat as infrared rays, the nanoantennas could collect those rays and re-emit the energy at harmless wavelengths. Such a system could cool down buildings and computers without the external power source required by air-conditioners and fans.

More technological advances are needed before the nanoantennas can funnel their energy into usable electricity. The infrared rays create alternating currents in the nanoantennas that oscillate trillions of times per second, requiring a component called a rectifier to convert the alternating current to direct current. Today's rectifiers can't handle such high frequencies.

"We need to design nanorectifiers that go with our nanoantennas," says Kotter, noting that a nanoscale rectifier would need to be about 1,000 times smaller than current commercial devices and will require new manufacturing methods. Another possibility is to develop electrical circuitry that might slow down the current to usable frequencies.

If these technical hurdles can be overcome, nanoantennas have the potential to be efficient harvesters of solar energy. Because they can be tweaked to pick up specific wavelengths depending on their shape and size, it may be possible to create double-sided nanoantenna sheets that harvest energy from different parts of the sun's spectrum, Novack says.

The team's stamp-and-repeat process could also be extended to large-scale roll-to-roll manufacturing techniques that could print the arrays at a rate of several yards per minute.

The researchers will be reporting their findings on August 13 at the American Society of Mechanical Engineers 2008 2nd International Conference on Energy Sustainability in Jacksonville, Florida.

Roberta Kwok is a Research Communications Fellow at Idaho National Laboratory.

Storing the Sun

Three cheers for MIT!! They have made a major breakthrough in the ability to store solar power -- which is a key need if it is going to emerge as a mainstream form of power. This is a very exciting development -- and shows what can happen when America's ingenuity is applied to problem-solving rather than blame spreading.
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ClimateWire

ENERGY: MIT scientists announce breakthrough

Christa Marshall, ClimateWire reporter - Aug. 1, 2008

Harvesting the sun's energy at night may no longer be an impossible dream.

In new research that some experts said could have sweeping implications for a major source of carbon-free electricity, two Massachusetts Institute of Technology scientists have found a cheap way to potentially store solar power.

By a process mirroring photosynthesis, they have discovered how to split oxygen and hydrogen from water at low cost and using little electricity. The mechanism creates the possibility that the gases could hold power generated by the sun -- and possibly wind -- in fuel cells for later use in homes and businesses.

"What this allows is for the large-scale deployment of a technology that has yet to take off," said Daniel Nocera, an MIT professor of energy who performed the research, featured today in the journal Science.

"Until now we hadn't really been able to find a practical way to duplicate what a leaf does," he said.

Nocera and postdoctoral fellow Matthew Kanan recreated photosynthesis in the lab by putting an electrode in water filled with phosphate and cobalt metal. When a small amount of electricity was applied to the electrode, the chemical mix formed a thin film and produced oxygen bubbles.

Using existing technology, the team then used a nearby platinum electrode to produce hydrogen from a leftover oxygen proton.

Technology currently exists to split water in a similar fashion, but it relies on large equipment requiring massive amounts of electrical juice and an alkaline environment. In addition to being abundant and cheap, the cobalt-phosphate duo has the advantage of working in a small amount of water at room temperature.

'Major discovery' but not a 'silver bullet'

Nocera predicted that within 10 years, his technology could allow homeowners to live almost free of the electrical grid -- with photovoltaic cells powering most daytime needs and solar-powered storage operating at night.

Indeed, Nocera said he already was using the "photosynthesis" technique with a solar power panel in an MIT lab, although he acknowledged it was a bit "flimsy." The technology also could potentially be used to power cars if plug-in models became available, he said.

"This is a major discovery with enormous implications for the future prosperity of humankind," said James Barber, a professor of biochemistry at Imperial College London who was an early researcher of photosynthesis. He was not involved with Nocera's research.

A spokeswoman for the Solar Energy Industries Association, Monique Hanis, said the group typically doesn't comment on peer-reviewed studies, but that the industry as a whole is searching for ways to improve efficiency.

Still, others cautioned that the study provides a potential solution for only one aspect of using solar power to produce hydrogen and oxygen.

"This is not a silver bullet," said John Turner, a research fellow at the National Renewable Energy Laboratory (NREL). "This is just one part of a three-legged stool."

According to Turner, one of the biggest challenges for storage involves figuring out how to mass produce a new type of photovoltaic panel specifically designed for working with a fuel cell. Science hasn't figured out how to design such a tool, much less mass-produce it in a commercial infrastructure that doesn't currently exist, he said.

Nocera agreed that engineering work needed to be done to integrate his research with technology that captures sunlight. He said scientists at MIT and elsewhere were tackling the problem. Companies including Polaris Venture Partners have already contacted the MIT office expressing interest in the research, he said.

Harnessing the fickle sun

"Photovoltaics are expensive because they're not making enough of them at scale," Nocera said. "And manufacturers are only going to start making a lot of them with a storage mechanism."

The fickle nature of sunlight is one of the biggest challenges for the industry, along with uncertainty about federal tax credits and a need for transmission lines ferrying solar electrons to population centers.

Another challenge is that the element typically used to derive hydrogen from oxygen on electrodes, platinum, is expensive and scarce, but Nocera said ongoing investigation is making progress on that front.

And every small advance is important, according to many solar industry watchers. Solar power has doubled in installed capacity since 2005, with an 83 percent jump last year outside California, but still constitutes a small percentage of U.S. electricity, according to figures from the Solar Energy Industries Association.

"If we could just have three hours a day of solar storage, the price of photovoltaic technology would not really have to come down much at all to be competitive," said Larry Kazmerski, director of the National Center for Photovoltaics at NREL.

That potential has prompted Nocera to stare at plants for years and ponder how to use their natural chemical processes to revolutionize power generation. Work on the study officially began in December, but the thought process had a much longer history.

"This research has been 25 years in the making," he said.