For decades researchers have investigated a theoretical means to double the power output of solar cells–by making use of so-called “hot electrons.” Now researchers at Boston College have provided new experimental evidence that the theory will work. They built solar cells that get a power boost from high-energy photons. This boost, the researchers say, is the result of extracting hot electrons.
The results are a step toward solar cells that break conventional efficiency limits. Because of the way ordinary solar cells work, they can, in theory, convert at most about 35 percent of the energy in sunlight into electricity, wasting the rest as heat. Making use of hot electrons could result in efficiencies as high as 67 percent, says Matthew Beard, a senior scientist at the National Renewable Energy Laboratory in Golden, CO, who was not involved in the current work. Doubling the efficiency of solar cells could cut the cost of solar power in half.
Conventional solar cells can only efficiently convert the energy of certain wavelengths of light into electricity. For example, when a solar cell optimized for red wavelengths of light absorbs photons of red light, it produces electrons with energy levels similar to those of the incoming photons. When the cell absorbs a higher-energy blue photon, it first produces a similarly high-energy electron–a hot electron. But this loses much of its energy very quickly as heat before it can escape the cell to produce electricity. (Conversely, cells optimized for blue light don’t convert red light into electricity, so they sacrifice the energy in this part of the spectrum.)
The Boston College researchers made ultra-thin solar cells just 15 nanometers thick. Because the cells were so thin, the hot electrons could be pulled out of the cell quickly, before they cooled. The researchers found that the voltage output of the cells increased when they illuminated them with blue light rather than red. “Now we’re getting the electrons from the blue light out before they lose all of their excess energy,” says Michael Naughton, a professor of physics at Boston College….
The researchers also hope to increase the number of hot electrons they collect from the absorbed light. To do this, they are turning to an approach taken by Martin Green, a professor at the University of New South Wales in Australia and a leader in using hot electrons in solar cells. This method involves incorporating a layer of quantum dots, which act as a sort-of filter, selectively extracting higher-than-normal-voltage electrons, Beard says. Naughton says that Solasta has already demonstrated that it’s possible to incorporate such quantum dots into the company’s nanowires.
A “digital quantum battery” concept proposed by a physicist at the University of Illinois at Urbana-Champaign could provide a dramatic boost in energy storage capacity–if it meets its theoretical potential once built.
The concept calls for billions of nanoscale capacitors and would rely on quantum effects–the weird phenomena that occur at atomic size scales–to boost energy storage. Conventional capacitors consist of one pair of macroscale conducting plates, or electrodes, separated by an insulating material. Applying a voltage creates an electric field in the insulating material, storing energy. But all such devices can only hold so much charge, beyond which arcing occurs between the electrodes, wasting the stored power.
If capacitors were instead built as nanoscale arrays–crucially, with electrodes spaced at about 10 nanometers (or 100 atoms) apart–quantum effects ought to suppress such arcing. For years researchers have recognized that nanoscale capacitors exhibit unusually large electric fields, suggesting that the tiny scale of the devices was responsible for preventing energy loss. But “people didn’t realize that a large electric field means a large energy density, and could be used for energy storage that would far surpass anything we have today,” says Alfred Hubler, the Illinois physicist and lead author of a paper outlining the concept, to be published in the journal Complexity.
Hubler claims the resulting power density (the speed at which energy can be stored or released) could be orders of magnitude greater, and the energy density (the amount of energy that can be stored) two to 10 times greater than possible with today’s best lithium-ion and other battery technologies.
What’s more, digital quantum batteries could be fabricated using existing lithographic chip-manufacturing technologies using cheap, nontoxic materials, such as iron and tungsten, atop a silicon substrate, he says. The resulting devices would, in principal, waste little or no energy as they absorbed and released electrons. Hubler says it may be possible to build a benchtop prototype in one year.
Today, however, digital quantum batteries are merely a patent-pending research concept. Hubler has applied for Defense Advanced Research Projects Agency funding to develop such a prototype, but the concept presents significant challenges. It’s not clear that the nanofabricated materials wouldn’t break down once loaded with energy, says Joel Schindall, a professor of electrical engineering at MIT.
California Gov. Arnold Schwarzenegger (R) said on Sunday that he “fundamentally disagrees” with former Gov. Sarah Palin on global warming, the latest in a weeklong back-and-forth between the two.
“We fundamentally disagree on this issue and that’s okay,” he said of criticism from the former Alaska governor and 2008 GOP candidate for vice president.
Schwarzenegger, appearing Sunday on CNN’s “State of the Union,” then defended his state’s policies to impose mandatory reductions in greenhouse gases and deploy more renewable energy.
Schwarzenegger had criticized Palin’s Dec. 9 Washington Post op-ed in which she called on President Obama to boycott the now-completed Copenhagen climate talks and attacked Democratic climate legislation.
Palin opposes requiring greenhouse gas emissions curbs and has said evidence showing human activities are warming the planet is “junk science.”
Schwarzenegger criticized her, wondering aloud in the Financial Times whether she cares about the topic or instead wrote the column to further her political ambitions. He also said her call for Obama to boycott the climate summit was “nonsense talk” on ABC’s “Good Morning America” Dec. 15, according to several news accounts.
Pleasure yachts and tall ships line the wharves and quays of Nyhavn here in the Danish capital. Shipping in Denmark goes back to the Vikings and their long ships that made perilous sea crossings even beyond Greenland. Now what may be the future of shipping is docked around the corner from Nyhavn at Kvaesthusmolen pier, a bright orange and yellow North Sea supply ship from Norway dubbed “Viking Lady”"”the first ship to employ a fuel cell in history.
As a result of flourishing world trade, shipping is now responsible for roughly three percent of global emissions of greenhouse gases, or more than one billion metric tons of carbon dioxide every year, along with smog-forming nitrogen oxides, acid-rain causing sulfur dioxides and soot. In fact, emissions of nitrogen oxides from one ship burning diesel in a year are greater than those from 22,000 cars. That’s because ships burn bunker fuel or diesel to cleave through the waves but, according to Tor Svensen, CEO of Det Norske Veritas (DNV) Maritime, “it is possible for shipping to reduce emissions, even taking into account growth in world trade.”
In fact, ships could reduce CO2 emissions by 500 million metric tons by 2030 while increasing profits, according to an analysis done by DNV. After all, fuel costs for a tanker ship are fully 41 percent of its total operating costs. A tax on CO2 emissions of just $15 would drive cuts of 700 million metric tons, according to Svensen. Energy savings of as much as 40 percent can be achieved through better hull design, more efficient engines and even the type of paint used on the ship. “Just by polishing the propeller occasionally, one can do a lot,” says Alte Palomaki, a spokesman for ship and turbine-maker Wartsila Corporation.
But in the case of the 5,900 metric ton Viking Lady, Norwegian shipping company Eidesvik and its partners have gone further, installing a 320-kilowatt molten carbonate fuel cell that operates on liquefied natural gas (and can be reconfigured, if necessary, to run on methanol). Storage tanks for the hydrogen and carbon dioxide that gets the fuel cell started press up against the stern of the 92.2 meter-long ship (in case of explosion) as do the machines to regasify the fuel. The fuel cell operates at 650 degrees Celsius and is warm to the touch, even on a blustery, frigid day in Copenhagen’s harbor.
Already, liquefied natural gas is cheaper than diesel””if you can find it. Engineer and project developer Kjell Sandaker of Eidesvik notes there are as many as 15 such fueling stations along the Norwegian coast and the bright orange Viking Lady gases up once a week as its onboard turbines also directly burn the gas to supply electricity to the engines, though they can also burn diesel if necessary. The ship’s 220 cubic meter tank can hold roughly 90 metric tons of liquefied natural gas at a time.
“If the ships are ordered, we believe filling stations will also come,” DNV’s Svensen says. Already, at least one cruise ship that might employ the technology is under construction. “In the North Sea, when drilling for oil they find gas,” Eidesvik’s Sandaker says. “By going on gas, we increase fuel efficiency” and decrease emissions.
But the $EU 12 million fuel cell from MTU On Site Energy is just in the testing phase, which will continue until mid-2010, and is not responsible for driving any of the four electric engines or propellers””after nearly a decade of development work. “It’s been two weeks working,” Sandaker says. “It’s been through its first storm in the North Sea.”
The investment was made, in part, to get an understanding of fuel cell technology and how it might be applied to shipping, according to DNV’s Viking Lady project head Tomas Heber Tronstad. Initial estimates are that such fuel cells would cut CO2 emissions from an individual ship by 50 percent. But the investment was also made because Norway has a tax on nitrogen oxide emissions that paid an immediate return for installing gas rather than diesel engines, says Eidesvik CEO Jan Fredrik Meling. Compared to a traditional ship, even without using the fuel cell, the Viking Lady reduces nitrogen oxide emissions by 90 percent, CO2 emissions by 20 percent and eliminates sulfur dioxide and soot emissions.
“The technology has existed for years,” Meling adds. “Demand must be created.” And old ships can be retrofitted with catalytic converters, like those in cars, to bring down emissions, according to Wartsila’s Palomaki.
Ultimately, whether the Viking Lady remains unique in the annals of shipping will depend on the political decisions that come out of the Copenhagen climate conference and in national capitals. “It will take 20 to 30 years for this technology without government support,” says DNV’s Tronstad. “If they want to act on climate soon, this is a technology that is available today.”
“Vertical farming” is a term coined by Columbia University professor of environmental health and microbiology Dickson Despommier to describe the concept of growing large amounts of food in urban high-rise buildings””or so-called “farmscrapers.”
According to the vision first developed in 1999 by Despommier and his students, a 30-story building built on one city block and engineered to maximize year-round agricultural yield””thanks largely to artificial lighting and advanced hydroponic and aeroponic growing techniques””could feed tens of thousands of people. Ideally the recipients of the bounty would live in the surrounding area, so as to avoid the transport costs and carbon emissions associated with moving food hundreds if not thousands of miles to consumers.
“Each floor will have its own watering and nutrient monitoring systems,” Despommier elaborated to online magazine Miller-McCune.com, adding that every single plant’s health status and nutrient consumption would be tracked by sensors that would help managers ward off diseases and increase yield without the need for the chemical fertilizers and pesticides so common in traditional outdoor agriculture.
“Moreover, a gas chromatograph will tell us when to pick the plant by analyzing which flavenoids the produce contains,” Despommier said. “It’s very easy to do”¦These are all right-off-the-shelf technologies. The ability to construct a vertical farm exists now. We don’t have to make anything new.”
With world population set to top nine billion by 2050 when 80 percent of us will live in cities, Despommier says vertical farming will be key to feeding an increasingly urbanized human race. His Vertical Farm Project claims that a vertical farm on one acre of land can grow as much food as an outdoor farm on four to six acres. Also, vertical farms, being indoors, wouldn’t be subject to the vagaries of weather and pests.
“The reason we need vertical farming is that horizontal farming is failing,” Despommier told MSNBC, adding that if current practices don’t change soon, humanity will have to devote to agriculture an area bigger than Brazil to keep pace with global food demand. Another benefit of vertical farming is that former farmland could be returned to a natural state and even help fight global warming. As agricultural land becomes forest and other green space, plants and trees there can store carbon dioxide while also serving as habitat for wildlife otherwise displaced by development.
Vertical farming is not without critics, who argue that the practice would use huge amounts of electricity for the artificial lights and machinery that would facilitate year-round harvests. Bruce Bugbee, a Utah State University crop physiologist, believes that the power demands of vertical farming””growing crops requires about 100 times the amount of light as people working in office buildings””would make the practice too expensive compared to traditional farming where the primary input, sunlight, is free and abundant. Proponents argue that vertical farms could produce their own power by tapping into local renewable sources (solar, wind, tidal or geothermal) as well as by burning biomass from crop waste.
The CIGS thin-film developer aims to raise up to $300 million and use proceeds to finance the final build-out of its second factory complex.
Solyndra plans to go public and raise up to $300 million, the company said Friday.
The high-profile solar company didn’t specify how many shares or at what price for its stock offering, according to its filing with the U.S. Securities and Exchange Commission.
Fremont, Calif.-based Solyndra has garnered lots of spotlight for its technology and for winning a $535 million federal loan to build its second factory complex near its headquarters.
The groundbreaking ceremony for the factory project in September this year was a big publicity event that drew Energy Secretary Steve Chu and California Gov. Arnold Schwarzenegger (and a speech by Joe Biden that was broadcast via satellite).
Few thin-film companies worldwide are public companies. But Solyndra wouldn’t be the first CIGS developer to go public. Ascent Solar Technologies (NSDAQ: ASTI) in Thornton, Colo., went public in 2006 and is putting CIGS thin films on plastic.
The IPO will be closely watched, and the degree of its success would pave the way for other thin-film companies that want to go public in the next year. Thin-film solar developers use little or no silicon in their cells, an approach to reduce manufacturing costs.
Solyndra uses copper, indium, gallium and selenium as key ingredients in the solar cells, and getting them to work well is a big challenge. But CIGS cells could do a better job of converting sunlight into electricity than other materials being used, such as cadmium-telluride and amorphous-silicon.
Most of the silicon cells in the panels today use crystalline silicon, which has historically been much more expensive.
Solyndra has announced more than $2 billion in sales deals in the United States and Europe. The announcements have painted an impressive picture of the company, which began commercial shipment in July 2008.
Solyndra sold 17.2 megawatts of panels from Jan. 1 to Oct. 3 of this year, the company said in the SEC filing. It sold 1.6 megawatts last year.
Solyndra posted $58.8 million in revenue and posted $119.8 million in net loss for the first nine months of this fiscal year (ending Oct. 3 2009), the company said in the SEC filing.
It generated $6 million in revenue and posted $232.1 million in net loss in the previous fiscal year that ended on Jan. 3, 2009.
Its customers include Alwitra, Carlisle Syntec Phoenix Solar, Geckologic, Solar Power Inc. and Sun Systems.
Solyndra said it has agreements in place for delivering up to 865 megawatts of solar energy systems (panels and racks) by the end of 2013.
The company’s existing factory is running at an annual production rate of 45 megawatts, and it plans to expand that to 110 megawatts by the end of the next fiscal year, according to its SEC filing.
The second factory complex, which is under construction, would first have the annual production rate of 250 megawatts by the first half of 2012. The $535 million federal loan would pay for this, first phase of the factory project.