Materials For Energy

EQ Energy Sector Analysis: Variable States

Corinna Wu
Feature Editor: Paulina Jaramillo

(Article in Energy Quarterly (EQ) in the March 2011 issue of MRS Bulletin)

On August 14, 2003, a downed high-voltage power line in Ohio triggered a massive blackout across eight states in the Northeast and throughout Southeastern Canada. A total of 50 million people lost power for up to two days. The episode cost an estimated $6 billion and is considered to be the worst electrical system failure in the history of the United States.

The cascade of failures—due to both human error and equipment malfunction—made clear the problems of the United States’ aging and balkanized electrical transmission grid. The blackout spurred the U.S. Congress to pass the Energy Policy Act of 2005, which enforces mandatory reliability standards. Investment in the transmission grid had fallen during the 1980s and 1990s, but after the blackout, funding picked up again.

Against this backdrop, power companies and regulating authorities now have another challenge to face: how to integrate variable and intermittent renewable resources such as solar and wind into the mix. Currently, electricity from non-hydro renewable resources accounts for 3.8% of the total electricity produced in the United States, according to the U.S. Energy Information Administration. In 2009, half of non-hydro renewable electricity came from wind and less than one percent from solar.

Although wind and solar are attractive because they do not produce greenhouse gases, they also pose difficulties because of their inherent variability. If wind and solar must supply a third of the energy generated, the job of meeting changing demand for electricity throughout the day becomes much more difficult. Power plant operators must meet the net load—the difference between user demand and this highly variable renewable output—by scheduling power generation from conventional sources.

An Energy Sector Analysis article published in the Energy Quarterly section in the March 2011 issue of  MRS Bulletin discusses various options to manage net load variability in the electric grid, with a focus on energy storage technologies. For materials scientists, a lot of potential research for grid-level energy storage lies in developing advanced battery technologies. Superconducting magnetic energy storage (SMES) systems are another option and have been used since the 1970s, mostly to release short bursts of energy to smooth out fluctuations in the power supply.

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Gopal R. Rao
Editor, MRS Bulletin
Materials Research Society (MRS)

 

Whispering Gallery Modes in Nanospheres Enhance Light Absorption in Solar Cells

(geentechsolar)

In an effort to improve the efficiency of solar cells, researchers have shifted their focus from the active material of the cell to its coating. Using the phenomenon of Whispering Gallery Modes, which describe the way whispers under cathedral-like domes can be clearly heard far across the room, they designed a commonplace, inexpensive coating that theoretically increases the light delivered to a typical thin-film amorphous-silicon (a-Si) solar cell’s photovoltaic (PV) material by 12-15%.

The researchers attempted to demonstrate that by starting with any thin-film solar cell with smooth surfaces and fabricated on a flat substrate, they could enhance the absorption by applying a coating to the thin film cell, without roughening the flat, smooth surfaces. Their concept involves a layer of nanospheres arrayed above the PV material.

The most exciting aspects of the research are that the nanosphere array layer is calculated to produce a twelve percent to fifteen percent increase in sunlight absorption of typical anti-reflection coated a-Si thin film solar cells, the array can be made from common and cheap silicon dioxide or polystyrene, and known and existing manufacturing processes can be used to add it to typical thin-film solar cells.

The researchers expect further experimental work to clarify ways that spheres of different sizes can be used to tune both size and spacing for even more optimum efficiencies.

(A New Way to a Better Solar Cell)

Reference:
Light Absorption Enhancement in Thin-Film Solar Cells Using Whispering Gallery Modes in Dielectric Nanospheres
To be published in Advanced Materials in the October 2011 issue.

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Gopal R. Rao, Ph.D.
Web Science Editor
Materials Research Society (MRS)

Learning from Energy Initiatives Conducted in Different Regions of the World

The second issue of Energy Quarterly has been published in the December 2010 MRS Bulletin. This month the editorial by Steve M. Yalisove emphasizes the importance of Regional Initiatives, those “far-reaching experiments in sustainable energy” performed in some region of the world, with lessons to be learned by other regions of the world as they set forth to find their own solutions. Energy Quarterly now has presented two such experiments:

• September 2010: How Sunlight Became a Commodity in Germany and
• December 2010: Maintaining Brazil’s ethanol fuel momentum.

Sometimes, such as in the case of Germany scaling up solar energy, it is a question of political will. Germany might not be thought of as the sun center of the world, yet they are producing more than a third of the world’s photovoltaic power. Incentives for individuals to install solar cells on their homes and sell energy back to the utilities moved this program forward. Scaling up solar in Germany also opened a market for thin-film solar cells produced in the United States.

In other cases, local resources play a significant role, such as Brazil’s use of ethanol from their plentiful sugarcane crops. Now Brazil not only produces a large fraction of their automobile fuel domestically, they export ethanol to other countries. With an established ethanol industry, will catalysts and other materials developments make possible further experiments with cellulosic ethanol or other second-generation fuels?

These and other regional initiatives, such as nuclear power in France, wind in Denmark, and Desertec to transport renewable energy from deserts to population hubs, make up a useful set of experiments to examine economic, public policy, and engineering challenges in the energy arena. Energy Quarterly’s approach is to present the underlying science behind the engineering challenges and identify the materials issues that may offer useful solutions. What other lessons can be learned?

 

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Elizabeth L. Fleischer
Editor, MRS Bulletin
Materials Research Society (MRS)

Transparent Conductive Material Could Lead to Power-Generating Windows

(Brookhaven National Laboratory)

Scientists have fabricated transparent thin films capable of absorbing light and generating electric charge over a relatively large area. The material consists of a semiconducting polymer doped with carbon-rich fullerenes. Under carefully controlled conditions, the material self-assembles to form a reproducible pattern of micron-size hexagon-shaped cells over a relatively large area (up to several millimeters). This is the first such material blending semiconductors and fullerenes to be formed to absorb light and efficiently generate charge and charge separation. The material remains largely transparent because the polymer chains pack densely only at the edges of the hexagons, while remaining loosely packed and spread very thin across the centers.

The scientists fabricated the honeycomb thin films by creating a flow of micrometer-size water droplets across a thin layer of the polymer/fullerene blend solution. These water droplets self-assembled into large arrays within the polymer solution. As the solvent completely evaporated, the polymer formed a hexagonal honeycomb pattern over a large area

Credit: BNL and Chemistry of Materials

The scientists verified the uniformity of the honeycomb structure with various scanning probe and electron microscopy techniques, and tested the optical properties and charge generation at various parts of the honeycomb structure (edges, centers, and nodes where individual cells connect) using time-resolved confocal fluorescence microscopy. The scientists also found that the degree of polymer packing was determined by the rate of solvent evaporation, which in turn determines the rate of charge transport through the material.

In terms of practical applications, the material could be used to develop transparent solar panels or even windows that absorb solar energy to generate electricity.

Structural dynamics and charge transfer via complexation with fullerene in large area conjugated polymer honeycomb thin films
Chemistry of Materials, Article ASAP DOI: 10.1021/cm102160m
Publication Date (Web): November 1, 2010

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Gopal R. Rao, Ph.D.
Web Science Editor
Materials Research Society (MRS)

 

Molecular Solar–Thermal Energy Storage

(Massachusetts Institute of Technology)

For capturing the sun’s energy, a thermo-chemical approach, in which solar energy is captured in the configuration of certain molecules which can then release the energy on demand to produce usable heat has been explored only to a limited extent. Unlike conventional solar-thermal systems, which require very effective insulation and even then gradually let the heat leak away, the heat-storing chemicals can remain stable for years. Researchers explored this type of solar thermal fuel in the 1970s, but there were big challenges: Nobody could find a chemical that could reliably and reversibly switch between two states. Such a compound was discovered in 1996, but it included ruthenium, a rare and expensive element, so it was impractical for widespread energy storage. Moreover, no one understood how the compound worked, which hindered efforts to find a cheaper variant.

Credit: Jeffrey Grossman, MIT

Researchers at MIT have discovered a molecule, fulvalene dirutheniumovercome, that is able to store thermal energy and release it. A combination of theoretical and experimental work has also revealed exactly how the molecule accomplishes this. Essentially, the molecule undergoes a structural transformation when it absorbs sunlight, putting the molecule into a higher-energy state where it can remain stable indefinitely. Then, triggered by a small addition of heat or a catalyst, it snaps back to its original shape, releasing heat in the process. The process is a somewhat more complicated than that. The researchers discovered an intermediate step that plays a major role. In this intermediate step, the molecule forms a semistable configuration partway between the two previously known states. The two-step process helps explain why the molecule is so stable, why the process is easily reversible and also why substituting other elements for ruthenium has not worked so far.

The problem of ruthenium’s rarity and cost still remains an issue, but since the fundamental mechanism of how the molecule works is understood, it should be easier to find other materials that exhibit the same behavior. The next step, according to the authors, is to use a combination of simulation, chemical intuition, and databases of tens of millions of known molecules to look for other candidates that have structural similarities and might exhibit the same behavior.

Mechanism of Thermal Reversal of the (Fulvalene)tetracarbonyldiruthenium Photoisomerization: Toward Molecular Solar–Thermal Energy Storage
Angewandte Chemie, Article first published online: 14 OCT 2010, DOI: 10.1002/anie.201002994

 

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Gopal R. Rao, Ph.D.
Web Science Editor
Materials Research Society (MRS)

How Sunlight Became a Commodity in Germany

Between one-third and one-half of the PV power in the world flows in Germany.

If you had to guess which country produces the most electrical power from photovoltaics (PV), you would probably draw candidates from sunny places such as the Middle East, the Mediterranean, or the United States. Germany, with its gray northern European skies, seems an unlikely contender. But there it is: between one-third and one-half of the PV power in the world flows in Germany, amounting to a little more than six gigawatts. According to Philip Ball in his Regional Initiative article in the Energy Quarterly in the September 2010 issue of the MRS Bulletin, this is the result of deliberate policies to encourage the uptake of solar energy, ranging from support for fundamental research to schemes that guarantee competitive pricing for electricity from renewable sources.

While the proportion of Germany’s energy generated by PV might sound small—about 1–2%—it represents a significant fraction of the total contribution (14%) from renewables, and the market is growing exponentially. This, in turn, drives costs down, and the solar-power industry also has created around  50,000 jobs in Germany and brought revenues of €5.6 billion ($6.9 bn) in 2009. Perhaps the biggest stimulus for PV was the German government’s Renewable Energy Sources Act, framed in 2000 and significantly amended in 2004 and 2008. Anyone in Germany now has the right to produce electricity through PV and feed it into the grid, forcing an open market. But the most significant aspect of the Act was the provision of a so-called feed-in tariff for renewable energy. This allows producers to sell their electricity to utilities companies at a guaranteed price over a 20-year period, which is considerably greater than the normal “grid” rate.

Ball discusses various research and development aspects that have been pivotal to this growth of PV in Germany, as well as various materials technologies being currently used. What can other countries learn from the German example? According to the article, it is not just about research; rather, the PV market has to be actively encouraged. Here, what one might call the positive discrimination, the feed-in tariff, of the German government has been central.

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Gopal R. Rao, Ph.D.
Web Science Editor
Materials Research Society (MRS)

Introducing Energy Quarterly

By V.S. Arunachalam and Elizabeth L. Fleischer

When MRS Bulletin published its expanded special issue in April 2008, “Harnessing Materials for Energy,” it was not a project done lightly. The impetus for this effort was the desire to describe the veritable options that materials provide in energy technologies.   These options can then be evaluated in the context of other imperatives such as economic viability and environmental concerns, which all interact to determine societal choices for energy. We were surprised and, of course, pleased by the timeliness, impact, and reception this volume received not only within the materials community but also in the larger world of energy professionals.

But these issues are not posed in a stagnant era. Even the framework for addressing energy challenges is evolving as countries set or collaborate on policies to address resource, security, and environmental needs. Since the publication of the special issue on energy, there have been a few reports of increased photovoltaic solar cell efficiency. The National Ignition Facility in the United States—one of the paths for realizing nuclear fusion—is becoming operational. Off-shore wind power is becoming a reality across Europe. And the government of Germany, despite its recent removal of subsidies, is still pursuing a bold initiative for large-scale grid connections of solar photovoltaics.

MRS Bulletin wants to capture stories of all such innovations as they occur, without a long wait for the detailed reports to appear. This is our driver for starting Energy Quarterly (EQ) . Four times a year, bound along with MRS Bulletin, EQ will host articles that are short, current, and eminently readable. Materials for energy will be the focus, but news from other nearby fields that are relevant will be included. The pages of EQ will include analysis across key energy sectors, lessons from major regional initiatives, interviews with energy leaders who are seen as architects of change, and transformational technology and research news.

This first volume provides a sampling of what we are pursuing. However, the space here is limited, and developments are many and varied. We need your input to help us follow the avenues with the greatest promise and to ensure this “journal within a journal” meets its objectives.  In subsequent days, the items in Energy Quarterly will be posted in the blog, and we encourage the community to comment on these articles and other blog items, expand on key points, and direct readers to additional resources.

V.S. Arunachalam
Chair, Energy Quarterly Organizing Committee

Elizabeth L Fleischer
Editor, MRS Bulletin

Portugal Gives Itself a Clean-Energy Makeover

By Gopal R. Rao

(From the New York Times)

The August 9, 2010, issue of the New York Times has an interesting analysis of Portugal's attempt to harness their renewable energy resources to reduce dependence on foreign oil imports. The report articulates how while these efforts by Portugal have been very successful, with 45% of its electricity currently generated by renewable sources, at the same time, it has paid a price for this rapid transition within a period of five years in terms of higher electricity prices as well as significant changes to their power grid.

Excerpt: LISBON — Five years ago, the leaders of this sun-scorched, wind-swept nation made a bet: To reduce Portugal’s dependence on imported fossil fuels, they embarked on an array of ambitious renewable energy projects — primarily harnessing the country’s wind and hydropower, but also its sunlight and ocean waves.

Today, Lisbon’s trendy bars, Porto’s factories and the Algarve’s glamorous resorts are powered substantially by clean energy. Nearly 45 percent of the electricity in Portugal’s grid will come from renewable sources this year, up from 17 percent just five years ago.

Land-based wind power — this year deemed “potentially competitive” with fossil fuels by the International Energy Agency in Paris — has expanded sevenfold in that time. And Portugal expects in 2011 to become the first country to inaugurate a national network of charging stations for electric cars.

.....

While Portugal’s experience shows that rapid progress is achievable, it also highlights the price of such a transition. Portuguese households have long paid about twice what Americans pay for electricity, and prices have risen 15 percent in the last five years, probably partly because of the renewable energy program, the International Energy Agency says.

Although a 2009 report by the agency called Portugal’s renewable energy transition a “remarkable success,” it added, “It is not fully clear that their costs, both financial and economic, as well as their impact on final consumer energy prices, are well understood and appreciated.”

......

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Gopal R. Rao, Ph.D.
Web Science Editor
Materials Research Society (MRS)

Scaling Up Alternative Energy

By Gopal R. Rao

(From Science)

The August 13, 2010, Issue of Science (Vol 329, Issue 5993, Pages 713-876) is a special issue on energy with the title "Scaling Up Alternative Energy".

As stated in the introductory article "Getting Better To Get Bigger" by David Malakoff, Jake Yeston, and Jesse Smith:

"The end of the age of fossil fuels may be in sight, but what comes after is still a bit of a blur. There are numerous alternatives to coal, oil, and natural gas from electricity generated by solar farms to biofuels brewed from plants. Scaling up these alternative sources of energy, however, has proved a challenge. This special issue explores the progress that researchers are making in developing better alternatives, and the technical, political, and economic pitfalls associated with scaling them up."

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Gopal R. Rao, Ph.D.
Web Science Editor
Materials Research Society (MRS)

Harnessing Solar Energy

By Dr. Vipin Gupta

Sandia National Laboratories

"I'd put my money on the sun and solar energy. What a source of power! I hope we don't have to wait until oil and coal run out before we tackle that."

Thomas Edison said these words to Henry Ford almost 80 years ago. And today, solar energy generation produces 0.1% of the energy used in the United States for electricity, heating, and transportation. Solar technology has come a long way, and yet we are quite far from what Edison envisioned becoming as widespread as his most famous inventions.

If the harnessing of sunlight is to become the cheapest form of energy,the easiest and quickest to install, and the safest, most dependable, and durable power source, we will need to achieve significant technological breakthroughs in solar energy collection, conversion, manufacturing, installation, operation, and upgrading.

An article in the May 2010 issue of Future Photovoltaics (www.futurepv.com) lays out one path to make solar a mainstream power source within one human generation. Capitalizing on the revolutionary achievements attained by the semiconductor, LCD, and microsystems industry, this article presents a way to put solar collection devices on almost anything and everything: open landscape, large built structures, vehicles, consumer gadgetry, and even the human body.

V. Gupta, J. Cruz-Campa, M. Okandan, G. Neilson, Microsystems-Enabled Photovoltaics: A Path to the Widespread Harnessing of Solar Energy. Future Photovoltaics (2010).

Download MEPV article in Future PV May 2010