Plastic Solar Cell Efficiency Hits 6% in U.S. Lab
 Winston-Salem, North Carolina [RenewableEnergyAccess.com]
Cheap plastic solar cells are now closer to becoming a reality thanks to a team of U.S. scientists at the Wake Forest University Center for Nanotechnology and Molecular Materials. The researchers announced last month they had pushed the efficiency of plastic solar cells to more than 6 percent.
That percentage may not seem like a huge landmark compared to a photovoltaic (PV) cell achieving an efficiency rating of say 40.7 percent, which was the milestone attained by Spectrolab, Inc. in December 2006. But until two years ago, the highest efficiency ever achieved for plastic solar cells was just three percent.
In 2005, David Carroll, director of the Wake Forest nanotechnology center, and his research group announced they had come close to reaching 5 percent efficiency. Now, a little more than a year later, Carroll said his group has surpassed the 6 percent mark.
"Within only two years we have more than doubled the 3 percent mark," Carroll said. "I fully expect to see higher numbers within the next two years, which may make plastic devices the photovoltaic of choice."
Because they are inexpensive and light weight, especially in comparison to traditional silicon solar panels, researchers have worked for years to create flexible, or "conformal," organic solar cells that can be wrapped around surfaces, rolled up or even painted onto structures.
In theory, plastic solar cells could be used as a replacement for roof tiling or home siding products or incorporated into traditional building facades. These energy harvesting devices could also be placed on automobiles since plastic solar cells are much lighter than the silicon solar panels structures do not have to be reinforced to support additional weight.
In a paper published in the journal Applied Physics Letters, the Wake Forest researchers describe how they have achieved record efficiency for organic or flexible, plastic solar cells by creating "nano-filaments" within light absorbing plastic, similar to the veins in tree leaves. This allows for the use of thicker absorbing layers in the devices, which capture more of the sun's light.
In order to be considered a viable technology for commercial use however, solar cells must be able to convert about 8 percent of the energy in sunlight to electricity. Wake Forest researchers hope to reach 10 percent in the next year, said Carroll, who is also associate professor of physics at Wake Forest.
A large part of Carroll's research is funded by the United States Air Force, which is interested in the potential uses of more efficient, light-weight solar cells for satellites and spacecraft.
Other members of Carroll's research team include Jiwen Liu and Manoj Namboothiry, postdoctoral associates at Wake Forest's nanotechnology center, and Kyungkon Kim, a postdoctoral researcher at the center, who has moved to the Materials Science & Technology Division at the Korea Institute of Science and Technology in Seoul.
Copyright 1998-2004 RenewableEnergyAccess.com. All rights reserved.
 Solar PV Takes Off at U.S. Air Force Base
Las Vegas, Nevada [RenewableEnergyAccess.com]
MMA Renewable Ventures will fund, own and operate Nellis Air Force Base photovoltaic system through third-party financing.
Much like the powerful message photovoltaic (PV) installations planned for commercial stores such as Target and Wal-Mart send to the public about the practical benefits of solar power, large-scale projects that involve the U.S. military also have the potential to lead to the widespread use of renewable energy at the "civilian" level.
The Nellis Air Force Base in Nevada, which, along with being the "Home of the Fighter Pilot," will soon house a 15-megawatt (MW) PV system, is one such project. Slated to be the largest solar PV system in North America once completed later this year, construction on the system is now under way after an official groundbreaking ceremony took place in the Mojave Desert yesterday.
"The Department of Defense has a long history of developing and commercializing technology that later gains widespread application use. The potential to harness the federal government's purchasing power to rapidly deploy solar and bring down the costs is being realized with this project, and we anticipate increased use by federal agencies mindful of the need for energy security and price stability," said Noah Kaye, director of public affairs for the Solar Energy Industries Association (SEIA).
MMA Renewable Ventures will finance, own and operate the system that will occupy 140 acres of land leased from the Air Force at the western edge of the base - and sell the power to Nellis under the terms of a Power Purchase Agreement.
The ground-mounted solar system will feature approximately 70,000 panels and employ an advanced tracking system, designed and deployed by PowerLight, a subsidiary of SunPower Corp., to follow the sun.
"In addition to its sheer size and the Air Force's impressive dedication to furthering renewable energy deployment, the Nellis project demonstrates how a carefully crafted third-party finance solution can effectively meet the needs of even the largest federal and municipal energy consumers," said Matt Cheney, CEO of MMA Renewable Ventures.
Even though the system is rated at approximately 15 MW, the patented PowerLight PowerTracker system will capture up to 30 percent more energy than an equivalent ground-mounted fixed-tilt system -- and produce the same amount of power generated as a fixed-mounted rooftop solar system with a rating of 18 MW.
With the ability to supply more than 25 percent of the power used at the base, the Nellis solar energy system is expected to generate over 25 million kilowatt-hours of clean electricity annually and support the more than 12,000 military and civilians responsible for Air Force advanced combat training, tactics development and operational testing.
"The Nellis solar power plant is the start of the way ahead for future [Department of Defense] and community partnerships," said Col. Michael Bartley, commander of the 99th Air Base Wing at Nellis. "The base will benefit from the energy produced, the environment benefits from using clean solar energy, and we may even test state-of-the-art security measures at the site. This is a good thing for everyone."
Copyright 1998-2004 RenewableEnergyAccess.com. All rights reserved.
3D Solar Cells Boost Efficiency, Reduce Size
by John Toon
Atlanta, Georgia [RenewableEnergyAccess.com]
Unique three-dimensional (3D) solar cells that capture nearly all of the light that strikes them could boost the efficiency of photovoltaic (PV) systems while reducing their size, weight and mechanical complexity.
The new 3D solar cells capture photons from sunlight using an array of miniature "tower" structures that resemble high-rise buildings in a city street grid. The cells could find near-term applications for powering spacecraft, and by enabling efficiency improvements in PV coating materials, could also change the way solar cells are designed for a broad range of applications.
 "Our goal is to harvest every last photon that is available to our cells," said Jud Ready, a senior research engineer in the Electro-Optical Systems Laboratory at the Georgia Tech Research Institute (GTRI). "By capturing more of the light in our 3D structures, we can use much smaller photovoltaic arrays. On a satellite or other spacecraft, that would mean less weight and less space taken up with the PV system."
The 3D design was described in the March 2007 issue of the journal JOM, published by The Minerals, Metals and Materials Society. The research has been sponsored by the Air Force Office of Scientific Research, the Air Force Research Laboratory, NewCyte Inc., and Intellectual Property Partners, LLC. A global patent application has been filed for the technology.
The GTRI photovoltaic cells trap light between their tower structures, which are about 100 microns tall, 40 microns by 40 microns square, 10 microns apart -- and built from arrays containing millions of vertically aligned carbon nanotubes. Conventional flat solar cells reflect a significant portion of the light that strikes them, reducing the amount of energy they absorb.
Because the tower structures can trap and absorb light received from many different angles, the new cells remain efficient even when the sun is not directly overhead. That could allow them to be used on spacecraft without the mechanical aiming systems that maintain a constant orientation to the sun, reducing weight and complexity -- and improving reliability.
"The efficiency of our cells increases as the sunlight goes away from perpendicular, so we may not need mechanical arrays to rotate our cells," Ready noted.
The ability of the 3D cells to absorb virtually all of the light that strikes them could also enable improvements in the efficiency with which the cells convert the photons they absorb into electrical current.
In conventional flat solar cells, the photovoltaic coatings must be thick enough to capture the photons, whose energy then liberates electrons from the photovoltaic materials to create electrical current. However, each mobile electron leaves behind a "hole" in the atomic matrix of the coating. The longer it takes electrons to exit the photovoltaic material, the more likely it is that they will recombine with a hole -- reducing the electrical current.
Because the 3D cells absorb more of the photons than conventional cells, their coatings can be made thinner, allowing the electrons to exit more quickly, reducing the likelihood that recombination will take place. That boosts the "quantum efficiency" -- the rate at which absorbed photons are converted to electrons -- of the 3D cells.
Fabrication of the cells begins with a silicon wafer, which can also serve as the solar cell's bottom junction. The researchers first coat the wafer with a thin layer of iron using a photolithography process that can create a wide variety of patterns. The patterned wafer is then placed into a furnace heated to 780 degrees Celsius.
Hydrocarbon gases are then flowed into furnace, where the carbon and hydrogen separate. In a process known as chemical vapor deposition, the carbon grows arrays of multi-walled carbon nanotubes atop the iron patterns.
Once the carbon nanotube towers have been grown, the researchers use a process known as molecular beam epitaxy to coat them with cadmium telluride (CdTe) and cadmium sulfide (CdS), which serve as the p-type and n-type photovoltaic layers. Atop that, a thin coating of indium tin oxide, a clear conducting material, is added to serve as the cell's top electrode.
In the finished cells, the carbon nanotube arrays serve both as support for the 3D arrays and as a conductor connecting the photovoltaic materials to the silicon wafer.
The researchers chose to make their prototypes cells from the cadmium materials because they were familiar with them from other research. However, a broad range of other photovoltaic materials could also be used, and selecting the best material for specific applications will be a goal of future research.
Ready also wants to study the optimal heights and spacing for the towers, and to determine the trade-offs between spacing and the angle at which the light hits the structures.
The new cells face several hurdles before they can be commercially produced. Testing must verify their ability to survive launch and operation in space, for instance. And production techniques will have to be scaled up from the current two-inch laboratory prototypes.
"We have demonstrated that we can extract electrons using this approach," Ready said. "Now we need to get a good baseline to see where we compare to existing materials, how to optimize this and what's needed to advance this technology."
Intellectual Property Partners of Atlanta holds the rights to the 3D solar cell design and is seeking partners to commercialize the technology.
Another commercialization path is being followed by an Ohio company, NewCyte, which is partnering with GTRI to use the 3D approach for terrestrial solar cells. The Air Force Office of Scientific Research has awarded the company a Small Business Technology Transfer (STTR) grant to develop the technology.
In addition to Ready, others Georgia Tech researchers contributing to the work include R.E. Camacho, A.R. Morgan, M.C. Flores, T.A. McLeod, V.S. Kumsomboone, B.J. Mordecai, R. Bhattacharagjea, W. Tong, B.K. Wagner, J.D. Flicker and S.P. Turano.
John Toon is a writer with the Research News & Publications Office at the Georgia Institute of Technology. This article is republished with permission from the Georgia Institute of Technology Research News.
Copyright 1998-2004 RenewableEnergyAccess.com. All rights reserved.
Tracking the Sun: Concentrating Solar Power Faces Bright Future
Nevada Solar One is the largest concentrating solar power plant to be built in 15 years.
by Stephen Lacey, Podcast Editor
Las Vegas, Nevada [RenewableEnergyAccess.com]
 The sun sits high over the Nevada desert in the Eldorado Valley, gleaming off the upside down rows of mirrored parabolic trough collectors at the Nevada Solar One power plant. Gilbert Cohen, senior vice president of Acciona Solar, stands beneath one of the collectors and points to the mountains in the horizon.
"When the sun rises and gets above 10 degrees, the system will start tracking and we stay with it all day," he says.
That means 180,000 parabolic trough collectors controlled by 760 trackers moving flawlessly in concert, following the sun's path and collecting the heat to make clean electricity. That's the beauty of concentrating solar power (CSP), also known as solar thermal.
At 64 megawatts (MW) of generation capacity, Nevada Solar One is the largest CSP plant to be built in 15 years. While the plant won't come online until April, its construction marks the revival of an industry that has seen almost no market growth in over a decade.
The plant was developed by Acciona Energy and Solargenix Energy -- two companies that have worked hard behind the scenes to get the CSP industry up and running again.
The plant uses parabolic trough collectors to generate electricity. The mirrored troughs face the sky and direct sunlight to a large metal and glass receiver in the middle of the trough that holds circulating oil. The oil travels to heat exchangers, which heat water and create steam to run a turbine. Parabolic troughs are one of three commercialized CSP technologies.
Further down the row of parabolic troughs, Plant Manager Bob Cable admires the impressive devices before him.
"I've been working with this technology for the last decade," Cable says. "I've seen some impressive gains in technological advancement, and now we're seeing more broad acceptance of the technology as the market becomes more attractive."
Indeed, after roughly a decade of little growth for the industry, CSP is coming back strong. And it's not just parabolic trough collectors that are experiencing a boom. Power towers, which use heliostats to focus solar energy on a central receiver to produce steam, and dish systems, which use reflectors to power a generator at the dish's focus point, are making great strides in technological capabilities, lower costs and market acceptance.
But according to Thomas Rueckert, Program Manager for CSP Management at the U.S. Department of Energy, parabolic troughs are the most advanced.
"Because of the track record [the parabolic trough industry] had in southern California with the 354 megawatts (MW) operating -- and actually improving in performance -- I think you're seeing the financial institutions more willing to embrace trough technology because it's proven and the risks are less," said Rueckert.
 Rueckert was referring to the 354 MW of parabolic trough collectors installed in California's Mojave Desert between 1984 and 1990. Those plants are still operating today, currently producing energy at around $0.12-$0.14/ per kilowatt-hour (kWh) and proving the technology can provide clean, reliable energy to the grid.
The Nevada Solar One plant will produce electricity at around $0.15-$0.17/kWh. While those costs are double what area residents pay for electricity, Nevada Solar One will sell energy to two utilities through a power purchase agreement (PPA). The PPA will ensure a fixed cost for the electricity over a long period, making the solar power economical down the line.
Now that global investment in CSP is increasing, technology costs are decreasing and renewable portfolio standards (RPS) in the U.S. are requiring more solar generation, project costs for all CSP technologies should come down significantly in the coming years, said DOE's Rueckert.
"All of those things have really opened the door," he said. "And it's interesting that all three technologies are pushing forward, which was kind of unexpected."
Back at Nevada Solar One, Acciona Solar's Cohen stands before the group of reporters and members of the solar industry who have come to witness the rebirth of CSP.
"The potential is huge. It was difficult to get the attention of the financial institutions in the U.S., but right now we have their attention. We get a lot of people asking us, 'how can we develop this technology?'"
Dr. Alex Marker, Research Fellow for Schott North America, Inc., stands to the side of Cohen, nodding his head. Schott is certainly feeling the positive impact of increased CSP development. To meet the demand for its glass receivers, the company brought a new receiver manufacturing facility online in Germany last summer and is developing another facility in Spain that will come online in early 2008.
"I think [the market] is going to grow drastically," says Marker, looking over at the receivers in the troughs. "We're happy to be a part of this new development."
Now that financial institutions are noticing CSP, companies like Acciona and Solargenix will be able to tap into the vast resource potential in the Southwestern U.S.
According to figures from DOE's Solar Lab, 20,000 MW of CSP capacity could come online in the U.S. by 2020 with the proper investment and technological capabilities. Rueckert seemed optimistic that a large amount of those resources will be tapped.
"When this plant comes online next month, it's going to be a great success," he said. "The market is exploding and things are really taking off."
Copyright 1998-2004 RenewableEnergyAccess.com. All rights reserved.
IPCC: Lawmakers Must Act Now
by Stephen Lacey, Staff Writer
Washington, DC [RenewableEnergyAccess.com]
 Now that the Intergovernmental Panel on Climate Change (IPCC) has made it clear that the solutions to climate change are available without hindering economic progress, U.S. lawmakers must act immediately to ensure a prosperous future based on sustainable development, say clean energy experts.
The latest IPCC report released last Friday titled "Mitigation of Climate Change," concludes that aggressive development of existing renewable energy technologies, increased energy efficiency requirements, and a global greenhouse gas emissions trading scheme are needed to combat global climate change. All of these solutions, stated the IPCC, are deployable in an economically feasible way with firm political support.
During a press conference in Bangkok last week, IPCC Chairman Dr. Rajendra Pachuari said the report is "stunning in its brilliance and razor sharp in its relevance. It's really a remarkable step forward."
But it will be up to the policymakers to help turn these hypothetical solutions into real action, says Marchant Wentworth, legislative representative for the Clean Energy Program at the Union of Concerned Scientists.
"It's important to understand that facts are one thing but political power is another," says Wentworth. "What it's going to take is raw political power to get...legislation through the Congress."
Some politicians have dismissed taking action in the past, saying that efforts outlined by the IPCC would hurt the U.S. economy and the "American Way of Life." But the new report concludes that inaction will be far more detrimental to the global economy than action. The IPCC estimates that stabilizing greenhouse gases will cost less than 3 percent of global GDP over the next 25 years. Some economists estimate that inaction will jeopardize roughly 30 percent of global GDP by 2100.
In fact, say many analysts, sustainable development and renewable energy will be a boon to the global economy. The U.S. will benefit from lower energy prices and increased jobs as the renewable energy industries grow.
"I think policymakers are now beginning to see not only the importance of responding to global warming by promoting alternative energy, but policy makers are now recognizing the value for their home states and for their districts," says Jerome Ringo, president of the Apollo Alliance, a national organization that promotes clean energy as an economic driver.
"Of course, by promoting these new alternative energies, it's going to create new jobs and new opportunities for their constituencies of which they represent," says Ringo.
According to the IPCC, if immediate action is not taken, greenhouse gas emissions will increase between 25-90 percent in the next 25 years, causing global temperatures to rise and creating a host of environmental problems. In order to slow such a catastrophe, global emissions need to be reduced 50 percent by 2050.
The U.S., which is the world's leading polluter, must reduce greenhouse gas emissions 80 percent by mid-century in order to help the global community reach that number. However, it won't be easy for the U.S. to achieve these emissions reduction goals. While most politicians support renewable energy and energy efficiency requirements, many are hesitant to support carbon taxes or an emissions trading scheme, which are vital to combating climate change.
But attitudes in Washington are changing as the economic implications for inaction become clearer. Over the last year, the door has opened for renewable energy to play a larger role in our energy mix says UCS' Wentworth.
"What I think we've managed to do with the IPCC reports and all the rest of the climate change impacts work...is to point out the consequences for inaction," he says. "Now we have to make clear to policy makers that the solutions are at hand and they're not going to bankrupt the country."
Copyright 1998-2004 RenewableEnergyAccess.com. All rights reserved. |
