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Saturday, August 16, 2014

2028: The End of the World As We Know It?

“There is nothing radical in what we’re discussing,” journalist and climate change activist Bill McKibben said before a crowd of nearly 1,000 at the University of California Los Angeles last night. “The radicals work for the oil companies.”

Bill McKibben

Taken on its own, a statement like that would likely sound hyperbolic to most Americans—fodder for a sound bite on Fox News. Anyone who saw McKibben’s lecture in full, however, would know he was not exaggerating.

McKibben was in Los Angeles as part of his nationwide “Do the Math” tour. Based on a recent article of his in Rolling Stone, (“The one with Justin Bieber on the cover,” McKibben joked) the event is essentially a lecture circuit based on a single premise: climate change is simple math—and the numbers do not look good. If immediate action isn’t taken by global leaders: “It’s game-over for the planet.”

The math, McKibben explained, works like this. Global leaders recently came to an international agreement based on the scientific understanding that a global temperature raise of 2°C would have “catastrophic” consequences for the future of humanity. In order to raise global temperatures to this catastrophic threshold, the world would have to release 565 gigatons of carbon dioxide into the atmosphere. Here’s the problem: Fossil fuel companies currently have 2,795 gigatons of carbon dioxide in their fuel reserves—and their business model depends on that fuel being sold and burned. At current rates of consumption, the world will have blown through its 565-gigaton threshold in 16 years.

To prevent the end of the world as we know it, it will require no less than the death of the most profitable industry in the history of humankind.

“As of tonight,” McKibben said, “we’re going after the fossil fuel industry.”

Obviously no easy task. The oil industry commands annual profits of $137 billion and the political power to match. As McKibben noted, “Oil companies follow the laws because they get to write them.”

However, there are some numbers on McKibben’s side. Recent polling data shows 74 percent of Americans now believe in climate change, and 68 percent view it as dangerous. The problem environmental activists are facing is in converting those favorable polling numbers into grassroots action.

Enter “Do the Math.”

Using McKibben’s popularity as an author, organizers are turning what would otherwise be a lecture circuit into a political machine. Before rolling into town, Do the Math smartly organizes with local environmental groups. Prior to McKibben’s lecture, these groups are allowed to take the stage and talk about local initiatives that need fighting. Contact information is gathered to keep the audience updated on those efforts. Instead of simply listening to McKibben, as they perhaps intended, the audience has suddenly become part of their local environmental movement.

It’s a smart strategy, and an essential one—because the problem of climate change is almost exclusively a political in nature. Between renewable energy and more efficient engineering, the technology already exists to stave off catastrophic global warming. Though its application is lagging in the United States, it is being employed on a mass scale in other countries. In socially-stratified China, with its billion-plus population and tremendous wealth inequalities, 25 percent of the country still manages to use solar arrays to heat its water. Germany—Europe’s economic powerhouse—in less than a decade, has managed to get upwards of half of its energy from sustainable sources.

The same can happen here in America—provided we have the will to make it happen. McKibben says the key to realizing that goal is to battle the lifeblood of the fossil fuel industry—its bottom line.

To start, he’s calling for an immediate global divestment from fossil fuel companies. “We’re asking that people who believe in the problem of climate change to stop profiting from it. Just like with divestment movement in South Africa over apartheid, we need to eliminate the oil companies veneer of respectability.”

In conjunction with the divestment regimen, continued protests against unsustainable energy projects will also be crucial. McKibben will be in Washington, D.C. on November 18 to lead a mass rally against climate change and the Keystone Pipeline. “We can no longer just assume that President Obama is going to do everything he promised during his campaign. We need to push him.”

“I don’t know if we’re going to win. But I do know we’re going to fight.” More

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Scientists develop pioneering new spray-on solar cells

A team of scientists at the University of Sheffield are the first to fabricate perovskite solar cells using a spray-painting process – a discovery that could help cut the cost of solar electricity.

Experts from the University’s Department of Physics and Astronomy and Department of Chemical and Biological Engineering have previously used the spray-painting method to produce solar cells using organic semiconductors – but using perovskite is a major step forward.

Efficient organometal halide perovskite based photovoltaics were first demonstrated in 2012. They are now a very promising new material for solar cells as they combine high efficiency with low materials costs.

The spray-painting process wastes very little of the perovskite material and can be scaled to high volume manufacturing – similar to applying paint to cars and graphic printing.

Lead researcher Professor David Lidzey said: “There is a lot of excitement around perovskite based photovoltaics.

“Remarkably, this class of material offers the potential to combine the high performance of mature solar cell technologies with the low embedded energy costs of production of organic photovoltaics.”

While most solar cells are manufactured using energy intensive materials like silicon, perovskites, by comparison, requires much less energy to make. By spray-painting the perovskite layer in air the team hope the overall energy used to make a solar cell can be reduced further.

Professor Lidzey said: “The best certified efficiencies from organic solar cells are around 10 per cent.

“Perovskite cells now have efficiencies of up to 19 per cent. This is not so far behind that of silicon at 25 per cent – the material that dominates the world-wide solar market.”

He added: “The perovskite devices we have created still use similar structures to organic cells. What we have done is replace the key light absorbing layer – the organic layer – with a spray-painted perovskite.

“Using a perovskite absorber instead of an organic absorber gives a significant boost in terms of efficiency.”

The Sheffield team found that by spray-painting the perovskite they could make prototype solar cells with efficiency of up to 11 per cent.

Professor Lidzey said: “This study advances existing work where the perovskite layer has been deposited from solution using laboratory scale techniques. It’s a significant step towards efficient, low-cost solar cell devices made using high volume roll-to-roll processing methods.”

Solar power is becoming an increasingly important component of the world-wide renewables energy market and continues to grow at a remarkable rate despite the difficult economic environment.

Professor Lidzey said: “I believe that new thin-film photovoltaic technologies are going to have an important role to play in driving the uptake of solar-energy, and that perovskite based cells are emerging as likely thin-film candidates.”

Self-Cooling Solar Cells For Better Performance & Longevity

August 12th, 2014 by Guest Contributor

The Optical Society

This drawing demonstrates how solar cells cool themselves by shepherding away unwanted thermal radiation. The pyramid structures made of silica glass provide maximal radiative cooling capability. Credit: L. Zhu, Stanford University.

Scientists may have overcome one of the major hurdles in developing high-efficiency, long-lasting solar cells—keeping them cool, even in the blistering heat of the noonday Sun.

By adding a specially patterned layer of silica glass to the surface of ordinary solar cells, a team of researchers led by Shanhui Fan, an electrical engineering professor at Stanford University in California has found a way to let solar cells cool themselves by shepherding away unwanted thermal radiation. The researchers describe their innovative design in the premiere issue of The Optical Society’s (OSA) new open-access journal Optica.

Solar cells are among the most promising and widely used renewable energy technologies on the market today. Though readily available and easily manufactured, even the best designs convert only a fraction of the energy they receive from the Sun into usable electricity.

Part of this loss is the unavoidable consequence of converting sunlight into electricity. A surprisingly vexing amount, however, is due to solar cells overheating.

Under normal operating conditions, solar cells can easily reach temperatures of 130 degrees Fahrenheit (55 degrees Celsius) or more. These harsh conditions quickly sap efficiency and can markedly shorten the lifespan of a solar cell. Actively cooling solar cells, however—either by ventilation or coolants—would be prohibitively expensive and at odds with the need to optimize exposure to the Sun.

The newly proposed design avoids these problems by taking a more elegant, passive approach to cooling. By embedding tiny pyramid- and cone-shaped structures on an incredibly thin layer of silica glass, the researchers found a way of redirecting unwanted heat—in the form of infrared radiation—from the surface of solar cells, through the atmosphere, and back into space.

“Our new approach can lower the operating temperature of solar cells passively, improving energy conversion efficiency significantly and increasing the life expectancy of solar cells,” said Linxiao Zhu, a physicist at Stanford and lead author on the Optica paper. “These two benefits should enable the continued success and adoption of solar cell technology.”

Solar cells work by directly converting the Sun’s rays into electrical energy. As photons of light pass into the semiconductor regions of the solar cells, they knock off electrons from the atoms, allowing electricity to flow freely, creating a current. The most successful and widely used designs, silicon semiconductors, however, convert less than 30 percent of the energy they receive from the Sun into electricity – even at peak efficiency.

The solar energy that is not converted generates waste heat, which inexorably lessens a solar cell’s performance. For every one-degree Celsius (1.8 degree F) increase in temperature, the efficiency of a solar cell declines by about half a percent.

“That decline is very significant,” said Aaswath Raman, a postdoctoral scholar at Stanford and co-author on the paper. “The solar cell industry invests significant amounts of capital to generate improvements in efficiency. Our method of carefully altering the layers that cover and enclose the solar cell can improve the efficiency of any underlying solar cell. This makes the design particularly relevant and important.”

In addition, solar cells “age” more rapidly when their temperatures increase, with the rate of aging doubling for every increase of 18 degrees Fahrenheit.

To passively cool the solar cells, allowing them to give off excess heat without spending energy doing so, requires exploiting the basic properties of light as well as a special infrared “window” through Earth’s atmosphere.

Different wavelengths of light interact with solar cells in very different ways—with visible light being the most efficient at generating electricity while infrared is more efficient at carrying heat. Different wavelengths also bend and refract differently, depending on the type and shape of the material they pass through.

The researchers harnessed these basic principles to allow visible light to pass through the added silica layer unimpeded while enhancing the amount of energy that is able to be carried away from the solar cells at thermal wavelengths.

“Silica is transparent to visible light, but it is also possible to fine-tune how it bends and refracts light of very specific wavelengths,” said Fan, who is the corresponding author on the Optica paper. “A carefully designed layer of silica would not degrade the performance of the solar cell but it would enhance radiation at the predetermined thermal wavelengths to send the solar cell’s heat away more effectively.”

To test their idea, the researchers compared two different silica covering designs: one a flat surface approximately 5 millimeters thick and the other a thinner layer covered with pyramids and micro-cones just a few microns (one-thousandth of a millimeter) thick in any dimension. The size of these features was essential.  By precisely controlling the width and height of the pyramids and micro-cones, they could be tuned to refract and redirect only the unwanted infrared wavelengths away from the solar cell and back out into space.

“The goal was to lower the operating temperature of the solar cell while maintaining its solar absorption,” said Fan. “We were quite pleased to see that while the flat layer of silica provided some passive cooling, the patterned layer of silica considerably outperforms the 5 mm-thick uniform silica design, and has nearly identical performance as the ideal scheme.”

Zhu and his colleagues are currently fabricating these devices and performing experimental tests on their design. Their next step is to demonstrate radiative cooling of solar cells in an outdoor environment. “We think that this work addresses an important technological problem in the operation and optimization of solar cells,” he concluded, “and thus has substantial commercialization potential.”

Paper:  L. Zhu, A. Raman., K. Wang, M. Anoma, S. Fan, “Radiative Cooling of Solar Cells,” Optica 1, 32-38 (2014).

Originaly published on The Optical Society website.

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