Tuesday, February 21, 2012

Engineers Create Tandem Polymer Solar Cells That Set Record for Energy-Conversion

In the effort to convert sunlight into electricity, photovoltaic solar cells that use conductive organic polymers for light absorption and conversion have shown great potential. Organic polymers can be produced in high volumes at low cost, resulting in photovoltaic devices that are cheap, lightweight and flexible.

In the last few years, much work has been done to improve the efficiency with which these devices convert sunlight into power, including the development of new materials, device structures and processing techniques.

In a new study, available online this week in the journal Nature Photonics, researchers at the UCLA Henry Samueli School of Engineering and Applied Science and UCLA's California Nanosystems Institute (CNSI) report that they have significantly enhanced polymer solar cells' performance by building a device with a new "tandem" structure that combines multiple cells with different absorption bands. The device had a certified power-conversion efficiency of 8.62 percent and set a world record in July 2011.

Further, after the researchers incorporated a new infrared-absorbing polymer material provided by Sumitomo Chemical of Japan into the device, the device's architecture proved to be widely applicable and the power-conversion efficiency jumped to 10.6 percent -- a new record -- as certified by the U.S. Department of Energy's National Renewable Energy Laboratory.

By using cells with different absorption bands, tandem solar cells provide an effective way to harvest a broader spectrum of solar radiation. However, the efficiency doesn't automatically increase by simply combining two cells. The materials for the tandem cells have to be compatible with each other for efficient light harvesting, the researchers said.

Until now, the performance of tandem devices lagged behind single-layer solar cells, mainly due to this lack of suitable polymer materials. UCLA Engineering researchers have demonstrated highly efficient single-layer and tandem polymer solar cells featuring a low-band-gap-conjugated polymer specially designed for the tandem structure. The band gap determines the portion of the solar spectrum a polymer absorbs.

"Envision a double-decker bus," said Yang Yang, a professor of materials science and engineering at UCLA Engineering and principal investigator on the research. "The bus can carry a certain number of passengers on one deck, but if you were to add a second deck, you could hold many more people for the same amount of space. That's what we've done here with the tandem polymer solar cell."

To use solar radiation more effectively, Yang's team stacked, in series, multiple photoactive layers with complementary absorption spectra to construct a tandem polymer solar cell. Their tandem structure consists of a front cell with a larger (or high) band gap material and a rear cell with a smaller (or low) band gap polymer, connected by a designed interlayer.

When compared to a single-layer device, the tandem device is more efficient in utilizing solar energy, particularly by minimizing other energy losses. By using more than one absorption material, each capturing a different part of the solar spectrum, the tandem cell is able to maintain the current and increase the output voltage. These factors enable the increase in efficiency, the researchers said.

"The solar spectra is very broad and covers the visible as well as the invisible, the infrared and the UV," said Shuji Doi, research group manager for Sumitomo Chemical. "We are very excited that Sumitomo's low-band gap polymer has contributed to the new record efficiency."

"We have been doing research in tandem solar cells for a much shorter length of time than in the single-junction devices," said Gang Li, a member of the research faculty at UCLA Engineering and a co-author of the Nature Photonics paper. "For us to achieve such success in improving the efficiency in this short time period truly demonstrates the great potential of tandem solar cell technology."

"Everything is done by a very low-cost wet-coating process," Yang said. "As this process is compatible with current manufacturing, I anticipate this technology will become commercially viable in the near future."

This study opens up a new direction for polymer chemists to pursue designs of new materials for tandem polymer solar cells. Furthermore, it indicates an important step towards the commercialization of polymer solar cells. Yang said his team hopes to reach 15 percent efficiency in the next few years.

Yang, who holds UCLA's Carol and Lawrence E. Tannas Jr. Endowed Chair in Engineering, is also faculty director of the Nano Renewable Energy Center at the California NanoSystems Institute at UCLA.

The study was supported by the National Science Foundation, the U.S Air Force Office of Scientific Research, the U.S. Office of Naval Research and the U.S. Department of Energy, together with the National Renewable Energy Laboratory.


Thursday, February 16, 2012

Environmental Impacts Cost 41 Cents for Every $1 of Revenue

If companies had to pay for the full environmental costs of their activities, they would have lost 41 cents out of every dollar earned in 2010 – and these costs are doubling every 14 years, according to a Trucost analysis for a KPMG report.

The environmental profit and loss-style analysis for 11 key sectors found the cost to global society of environmentally-sensitive corporate activities for food producers actually outweigh the sectors’ entire earnings, at a whopping $200 billion, and in five other sectors – electricity, industrial metals, mining, marine transport, and airlines – environmental costs could account for more than half their earnings.

In reality, these costs are not borne solely by companies but are passed on at least partially to end-users, KPMG said in the report, Expect the Unexpected: Building Business Value in a Changing World.

But it said the data gives an indicator not only of industries’ impact, but of the potential value at stake. And companies should expect to pay a rising proportion of these costs, posing a near-future financial risk, KPMG said.

Trucost says that environmental costs across the 11 sectors – which also include automobiles, beverages, chemicals, oil and gas, and telecommunications and internet – rose by 50 percent between 2002 and 2010, from US$566 billion to US$854 billion. It says the projected doubling of costs every 14 years is unlikely to be sustainable, even in the medium term.

For the report, Trucost provided a data set based on the operations of over?800 companies between 2002 and 2010 (2010 being the most recent available data), converting 22 key environmental impacts into financial value. These impacts cover water abstraction, wate generation and greenhouse gas emissions, including carbon dioxide, HFCs, nitrous oxide, methane, perfluorocarbons and sulphur hexafluoride. These indicators represent the bulk of the environmental footprint for most companies, KPMG said.

The research also included a meta-review of more than 60 sector reports, from investments banks, business associations, insurers, consultancies, rating agencies and NGOs, addressing the risks and opportunities of the ten global sustainability “megaforces” that will affect every business over the next two decades. According to KPMG, these megaforces are climate change, energy and fuel, material resource scarcity, water scarcity, population growth, urbanization, wealth, food security, ecosystem decline and deforestation.

Trucost said the data is not exact and its estimates should not be taken as absolute. But it said the data does indicate growth in environmental footprints relative to earnings; potential vulnerability to environmental cost; and progress in reducing environmental intensity.


Tuesday, February 14, 2012

New Battery Could Lead to Cheaper, More Efficient Solar Energy

A joint research project between the University of Southampton and lithium battery technology company REAPsystems has found that a new type of battery has the potential to improve the efficiency and reduce the cost of solar power.
The research project, sponsored by REAPsystems, was led by MSc Sustainable Energy Technologies student, Yue Wu and his supervisors Dr Carlos Ponce de Leon, Professor Tom Markvart and Dr John Low (currently working at the University's Research Institute for Industry, RIfI). The study looked specifically into the use of lithium batteries as an energy storage device in photovoltaic systems.

Student Yue Wu says, "Lead acid batteries are traditionally the energy storage device used for most photovoltaic systems. However, as an energy storage device, lithium batteries, especially the LiFePO4 batteries we used, have more favourable characteristics."

Data was collected by connecting a lithium iron phosphate battery to a photovoltaic system attached to one of the University's buildings, using a specifically designed battery management system supplied by REAPsystems.

Yue adds, "the research showed that the lithium battery has an energy efficiency of 95 per cent whereas the lead-acid batteries commonly used today only have around 80 per cent. The weight of the lithium batteries is lower and they have a longer life span than the lead-acid batteries reaching up to 1,600 charge/discharge cycles, meaning they would need to be replaced less frequently."

Although the battery will require further testing before being put into commercial photovoltaic systems the research has shown that the LiFePO4 battery has the potential to improve the efficiency of solar power systems and help to reduce the costs of both their installation and upkeep. Dr Carlos Ponce de Leon and Dr. John Low now plan to take this project further with a new cohort of Masters students.

Dr Dennis Doerffel, founder of REAPsystems and former researcher at the University of Southampton, says: "For all kinds of energy source (renewable or non-renewable), the energy storage device -- such as a battery -- plays an important role in determining the energy utilisation. Compared with traditional lead acid batteries, LiFePO4 batteries are more efficient, have a longer lifetime, are lighter and cost less per unit. We can see the potential of this battery being used widely in photovoltaic application, and other renewable energy systems."


Sunday, February 12, 2012

Consumers want better language, design, & layout for energy info

Energy usage and tariff information generally isn’t easy to understand. To get input on how to solve this problem, U.K. energy regulator Ofgem has been conducting workshops with consumers across Great Britain. The new Consumer First Panel Report lists suggestions from consumers to help them better understand and engage with the electricity and gas market.

The workshops had 110 total participants in six locations across Great Britain last fall, with the goals of:

Identify energy information needed to equip customers to make an informed decision.
Establish the communication channels through which consumers want to receive this information.
Provide insight into how energy information should be presented to encourage engagement.

Here are some suggestions that consumers offered in these workshops:

Simpler language
.Standardized and more easily understood language could better communicate key tariff and consumption information.
Fewer tariffs.Consumers proposed limiting the number of tariffs — but this could be a bad thing if time-varying options are not permitted.
Easier price comparisons.Consumers wanted to make it easier to decide which rate options are right for them.
Guidance. Electricity retailers could work to build better relationships with their customers by helping consumers find the best tariff for them, and by rewarding loyalty.

Smart meters are essential to implement three of these four recommendations in the UK. Without smart meters, actual consumption data is rarely available, since traditional meters are read only quarterly or annually.

Smart meters also provide key tariff and consumption data, because they provide data more often (at least monthly). Also, tariff (cost) data is based on actual consumption, not the estimated consumption most commonly used today.

Smart meter data also makes it easier to compare prices, thus helping consumers find the best tariff option. Actual consumption data can be plugged into smartphone, tablet, or laptop apps which makes these comparisons. Or, retailers can do this on the web. America’s Green Button initiative is one example of how this is becoming a reality in 22 states by April 2012.

It’s worth repeating: Ofgem said that clear information — in simple language — is crucial to making communication materials from energy retailers more effective. This involves improvements to the language, design and layout.

Ironically, Ofgem made this key point in slightly convoluted wording: “How saving messages are communicated and signposted is crucial.”


Wednesday, February 8, 2012

Biosolar Breakthrough Promises Cheap, Easy Green Electricity

Barry D. Bruce, professor of biochemistry, cellular and molecular biology, at the University of Tennessee, Knoxville, is turning the term "power plant" on its head. The biochemist and a team of researchers has developed a system that taps into photosynthetic processes to produce efficient and inexpensive.

Bruce collaborated with researchers from the Massachusetts Institute of Technology and Ecole Polytechnique Federale in Switzerland to develop a process that improves the efficiency of generating electric power using molecular structures extracted from plants. The biosolar breakthrough has the potential to make "green" electricity dramatically cheaper and easier.

"This system is a preferred method of sustainable energy because it is clean and it is potentially very efficient," said Bruce, who was named one of "Ten Revolutionaries that May Change the World" by Forbes magazine in 2007 for his early work, which first demonstrated biosolar electricity generation. "As opposed to conventional photovoltaic solar power systems, we are using renewable biological materials rather than toxic chemicals to generate energy. Likewise, our system will require less time, land, water and input of fossil fuels to produce energy than most biofuels."

Their findings are in the current issue of Nature: Scientific Reports.

To produce the energy, the scientists harnessed the power of a key component of photosynthesis known as photosystem-I (PSI) from blue-green algae. This complex was then bioengineered to specifically interact with a semi-conductor so that, when illuminated, the process of photosynthesis produced electricity. Because of the engineered properties, the system self-assembles and is much easier to re-create than his earlier work. In fact, the approach is simple enough that it can be replicated in most labs -- allowing others around the world to work toward further optimization.

"Because the system is so cheap and simple, my hope is that this system will develop with additional improvements to lead to a green, sustainable energy source," said Bruce, noting that today's fossil fuels were once, millions of years ago, energy-rich plant matter whose growth also was supported by the sun via the process of photosynthesis.

This green solar cell is a marriage of non-biological and biological materials. It consists of small tubes made of zinc oxide -- this is the non-biological material. These tiny tubes are bioengineered to attract PSI particles and quickly become coated with them -- that's the biological part. Done correctly, the two materials intimately intermingle on the metal oxide interface, which when illuminated by sunlight, excites PSI to produce an electron which "jumps" into the zinc oxide semiconductor, producing an electric current.

The mechanism is orders of magnitude more efficient than Bruce's earlier work for producing bio-electricity thanks to the interfacing of PS-I with the large surface provided by the nanostructured conductive zinc oxide; however it still needs to improve manifold to become useful. Still, the researchers are optimistic and expect rapid progress.

Bruce's ability to extract the photosynthetic complexes from algae was key to the new biosolar process. His lab at UT isolated and bioengineered usable quantities of the PSI for the research.

Andreas Mershin, the lead author of the paper and a research scientist at MIT, conceptualized and created the nanoscale wires and platform. He credits his design to observing the way needles on pine trees are placed to maximize exposure to sunlight.

Mohammad Khaja Nazeeruddin in the lab of Michael Graetzel, a professor at the Ecole Polytechnique Federale in Lausanne, Switzerland, did the complex testing needed to determine that the new mechanism actually performed as expected. Graetzel is a pioneer in energy and electron transfer reactions and their application in solar energy conversion.

Michael Vaughn, once an undergraduate in Bruce's lab and now a National Science Foundation (NSF) predoctoral fellow at Arizona State University, also collaborated on the paper.

"This is a real scientific breakthrough that could become a significant part of our renewable energy strategy in the future," said Lee Riedinger, interim vice chancellor for research. "This success shows that the major energy challenges facing us require clever interdisciplinary solutions, which is what we are trying to achieve in our energy science and engineering PhD program at the Bredesen Center for Interdisciplinary Research and Graduate Education of which Dr. Bruce is one of the leading faculty."

Bruce's work is funded by the Emerging Frontiers Program at the National Science Foundation.