Solar power heads in a new direction: thinner

The MIT team found that an effective solar cell could be made from a stack of two one-molecule-thick materials: Graphene (a one-atom-thick sheet of carbon atoms, shown at bottom in blue) and molybdenum disulfide (above, with molybdenum atoms shown in red and sulfur in yellow). The two sheets together are thousands of times thinner than conventional silicon solar cells. Credit: JEFFREY GROSSMAN AND MARCO BERNARDI

Atom-thick photovoltaic sheets could pack hundreds of times more power per weight than conventional solar cells.
CAMBRIDGE, Mass. — Most efforts at improving solar cells have focused on increasing the efficiency of their energy conversion, or on lowering the cost of manufacturing. But now MIT researchers are opening another avenue for improvement, aiming to produce the thinnest and most lightweight solar panels possible.

Such panels, which have the potential to surpass any substance other than reactor-grade uranium in terms of energy produced per pound of material, could be made from stacked sheets of one-molecule-thick materials such as graphene or molybdenum disulfide.

Jeffrey Grossman, the Carl Richard Soderberg Associate Professor of Power Engineering at MIT, says the new approach “pushes towards the ultimate power conversion possible from a material” for solar power. Grossman is the senior author of a new paper describing this approach, published in the journal Nano Letters.

Although scientists have devoted considerable attention in recent years to the potential of two-dimensional materials such as graphene, Grossman says, there has been little study of their potential for solar applications. It turns out, he says, “they’re not only OK, but it’s amazing how well they do.”

Using two layers of such atom-thick materials, Grossman says, his team has predicted solar cells with 1 to 2 percent efficiency in converting sunlight to electricity, That’s low compared to the 15 to 20 percent efficiency of standard silicon solar cells, he says, but it’s achieved using material that is thousands of times thinner and lighter than tissue paper. The two-layer solar cell is only 1 nanometer thick, while typical silicon solar cells can be hundreds of thousands of times that. The stacking of several of these two-dimensional layers could boost the efficiency significantly.

“Stacking a few layers could allow for higher efficiency, one that competes with other well-established solar cell technologies,” says Marco Bernardi, a postdoc in MIT’s Department of Materials Science who was the lead author of the paper. Maurizia Palummo, a senior researcher at the University of Rome visiting MIT through the MISTI Italy program, was also a co-author.

For applications where weight is a crucial factor — such as in spacecraft, aviation or for use in remote areas of the developing world where transportation costs are significant — such lightweight cells could already have great potential, Bernardi says.

Pound for pound, he says, the new solar cells produce up to 1,000 times more power than conventional photovoltaics. At about one nanometer (billionth of a meter) in thickness, “It’s 20 to 50 times thinner than the thinnest solar cell that can be made today,” Grossman adds. “You couldn’t make a solar cell any thinner.”

This slenderness is not only advantageous in shipping, but also in ease of mounting solar panels. About half the cost of today’s panels is in support structures, installation, wiring and control systems, expenses that could be reduced through the use of lighter structures.

In addition, the material itself is much less expensive than the highly purified silicon used for standard solar cells — and because the sheets are so thin, they require only minuscule amounts of the raw materials.

The MIT team’s work so far to demonstrate the potential of atom-thick materials for solar generation is “just the start,” Grossman says. For one thing, molybdenum disulfide and molybdenum diselenide, the materials used in this work, are just two of many 2-D materials whose potential could be studied, to say nothing of different combinations of materials sandwiched together. “There’s a whole zoo of these materials that can be explored,” Grossman says. “My hope is that this work sets the stage for people to think about these materials in a new way.”

While no large-scale methods of producing molybdenum disulfide and molybdenum diselenide exist at this point, this is an active area of research. Manufacturability is “an essential question,” Grossman says, “but I think it’s a solvable problem.”

An additional advantage of such materials is their long-term stability, even in open air; other solar-cell materials must be protected under heavy and expensive layers of glass. “It’s essentially stable in air, under ultraviolet light, and in moisture,” Grossman says. “It’s very robust.”

The work so far has been based on computer modeling of the materials, Grossman says, adding that his group is now trying to produce such devices. “I think this is the tip of the iceberg in terms of utilizing 2-D materials for clean energy” he says.

This work was supported by the MIT Energy Initiative.


Carbon Offsets: Bringing the World Back to Zero

Energy Innovation: From the Crowd

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It’s A Twister!

Nobody’s figured out how to harness the awesome power of a tornado, but a Canadian engineer has come close: he’s working on creating a tornado that will generate electric power in what he calls an “Atmospheric Vortex Engine.” (Isn’t that what powered Star Trek‘s Enterprise?)


Japanese Breakthrough will make Wind Power Cheaper than Nuclear

A surprising aerodynamic innovation in wind turbine design called the ‘wind lens‘ could triple the output of a typical wind turbine, making it less costly than nuclear power.

NOTE: Some major wind projects like the proposed TWE Carbon Valley project in Wyoming are already pricing in significantly lower than coal power — $80 per MWh for wind versus $90 per MWh for coal — and that is without government subsidies using today’s wind turbine technology.

The International Clean Energy Analysis (ICEA) gateway estimates that the U.S. possesses 2.2 million km2 of high wind potential (Class 3-7 winds) — about 850,000 square miles of land that could yield high levels of wind energy. This makes the U.S. something of a Saudi Arabia for wind energy, ranked third in the world for total wind energy potential.

Let’s say we developed just 20 percent of those wind resources — 170,000 square miles (440,000 km2) or an area roughly 1/4 the size of Alaska — we could produce a whopping 8.7 billion megawatt hours of electricity each year (based on a theoretical conversion of six 1.5 MW turbines per km2 and an average output of 25 percent. (1.5 MW x 365 days x 24 hrs x 25% = 3,285 MWh’s).

The United States uses about 26.6 billion MWh’s, so at the above rate we could satisfy a full one-third of our total annual energy needs. (Of course, this assumes the concurrent deployment of a nationwide Smart Grid that could store and disburse the variable sources of wind power as needed using a variety of technologies — gas or coal peaking, utility scale storage via batteries or fly-wheels, etc).

Now what if a breakthrough came along that potentially tripled the energy output of those turbines? You see where I’m going. We could in theory supply the TOTAL annual energy needs of the U.S. simply by exploiting 20 percent of our available wind resources.

Well, such a breakthrough has been made, and it’s called the “wind lens.”

Imagine: no more dirty coal power, no more mining deaths, no more nuclear disasters, no more polluted aquifers as a result of fracking. Our entire society powered by the quiet “woosh” of a wind turbine. Kyushu University’s wind lens turbine is one example of the many innovations happening right now that could in the near future make this utopian vision a reality.

Yes, it’s a heck of a lot of wind turbines (about 2,640,000) but the U.S. with its endless miles of prairie and agricultural land is one of the few nations that could actually deploy such a network of wind turbines without disrupting the current productivity of the land (Russia and China also come to mind). It would also be a win-win for states in the highest wind area — the Midwest — which has been hard hit by the recession. And think of the millions upon millions of jobs that would be created building a 21st century energy distribution system free of the shackles of ever-diminishing fossil fuel supplies.

It’s also important to point out that growth in wind power capacity is perfectly symbiotic with projected growth in electric vehicles. EV battery packs can soak up wind power produced during the night, helping to equalize the curve of daytime energy demand. So the controversial investment currently being entertained by President Obama to pipe oil down from the Canadian Tar Sands would — in my utopian vision — be a moot point.

It is indeed a lofty vision, but the technology we need is now in our reach. And think of the benefits of having our power production fed by a resource that is both free and unlimited. One downside often cited by advocates of coal and gas power is that wind turbines require a lot more maintenence than a typical coal or gas power plant. But in a lagging economy this might just be wind power’s biggest upside — it will create lots and lots of permanent jobs, sparking a new cycle of economic growth in America.


Mongolia Confronts Smog with Launch of First Wind Farm

Newly installed turbines at the Salkhit Mountain wind farm, 70 kilometres from Ulan Bator

Mongolia on Thursday opened its first wind farm, a landmark $122 million project that aims to shift the country’s reliance on coal and tackle the pollution choking its capital Ulan Bator.

A total of 31 turbines have been erected at the facility, which are expected to power five percent of electricity needs in a country undergoing rapid transformation on the back of a spectacular boom in mining—particularly coal.

Backers hope the 50-megawatt facility erected 70 kilometres (43 miles) south-east of Ulan Bator at a windy ridge called Salkhit will be the first step in a national drive to harness cleaner energy in the mineral-rich country.

“Salkhit represents the first private sector-initiated project in what is still a highly-regulated, inexperienced-in-private-investments market,” said Boldbaatar Tserenpuntsag, from Mongolian investment firm Newcom, which is backing the wind farm.

“This positive experience will pave the way for future investments in the energy and other vital infrastructure sectors and acts as a concrete demonstration of the government’s green development agenda.”

Fifteen of the wind turbines were switched on at Thursday’s opening ceremony, with the remainder to become operational next month.

The Mongolian capital was ranked the planet’s second-most polluted city by the World Health Organization in a 2011 report, largely due to its coal-fired power stations and residents burning coal to keep warm in winter, when temperatures can plummet to a punishing minus 30 degrees Celsius (minus 22 Fahrenheit).

The new wind farm—which will supply 140-170 million kilowatt/hours of power each year to the national grid—will reduce demand for coal by 122,000 tonnes a year, helping the government meet a target for renewable resources to make up 20 percent of the country’s energy needs.

Eighty percent of energy requirements currently come from coal in Mongolia, where more than $1 trillion worth of untapped resources are underground.

Backers of the plan hope to extend Mongolia’s wind capacity by 20 times, transforming the country of three million people into one of Asia’s renewable energy centres.

Ulan Bator’s one million residents will be among the first to benefit from the new energy source, backers claim.

During the winter, dense, grey clouds of smog often linger for days in the city, which lies in a narrow valley, and pollution is six to seven times higher than even the most lenient WHO standards.

The city’s three coal-fired power plants are one of the main causes. Also, residents of the poor outlying “ger” districts—named for the nomads’ tents used for housing—burn coal, tyres and rubbish as a heat source in the harsh winter.

The area’s population has ballooned in recent years, as more nomads arrive in Ulan Bator to seek a share of Mongolia’s new-found wealth based on natural resources.

The organisation ranks the Iranian city of Ahvaz as the world’s most polluted city in terms of airborne particles.