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A home pictured with Tesla's solar roof, a car, and new Powerwall battery as the sun falls

The Challenges for Tesla's Solar Roofs

Last week, Tesla—best known for its electric vehicles—announced its latest product: roof tiles with built-in solar cells. To succeed where other companies have failed, engineers say they must strike a delicate balance among cost, aesthetics, safety, and performance.

Widespread adoption would yield clear environmental benefits, of course. Solar power could be a way to lower carbon dioxide emissions and combat global warming, Tesla CEO Elon Musk said in a presentation. Musk sees solar roofs as part of his plan for running the world on clean, sustainable energy.

Yet Ronnen Levinson, a mechanical engineer at Lawrence Berkeley National Lab who studies ways to keep roofs cool, points out that “Tesla isn’t offering a new idea.”

In the past, solar power has had mixed results in the United States. Years ago, the Obama Administration supported the solar power company Solyndra, which went bankrupt in August 2011. Dow Chemical recently tried a solar shingles project that it shut down in July.

Tesla declined to comment for this story. Former Solyndra CEO Brain Harrison and Greg Bergtold, a business advocacy director at Dow Chemical, also declined to comment.

The discernible difference with Tesla’s photovoltaic roofing material, Levinson says, is that the company will offer integrated tiles. Instead of buying a roof, paying for workers to install it, then buying new solar panels and paying for extra labor, you can consolidate the cost--which could be cheaper. Musk said there are about 4 to 5 million new roofs in the United States every year, with more worldwide, so there is a market.

“Over time, every house would become a solar house,” Musk said.

During the presentation, Musk unveiled solar-cell glass tiles that could integrate with Tesla’s new Powerwall 2 battery as well as electric cars. TechCrunch reported that Musk claims the new roofs would last two to three times as long as typical 20-year-cycle roofs and be more impact resistant.

The marketplace challenges this product faces, Levinson says, are a mix of different factors: where you are, how much local electricity costs, whether you are buying a new home and new roof or need to replace a worn-down roof, and what the solar availability is. If you’re away from home during the week and only use electricity on the weekends, then storing electricity might not be practical. Also, not all states and utility companies have measures in place that allow homeowners and businesses to sell their excess solar energy, negating what would otherwise be an additional financial benefit.  

Angèle Reinders, an industrial design engineer at the University of Twente in Enschede, Netherlands, works on integrating photovoltaics into infrastructure. She says consumer acceptance might also be difficult to get.

“If it’s affecting their building or their daily behavior, people are usually quite reluctant to adapt to that new technology,” she says.

In terms of performance, she wondered why Tesla doesn’t specify what technology the solar cells use or their tested efficiency—Musk has claimed that they achieve 98 percent of the efficiency of traditional solar panels. “I would like to talk with Elon Musk and ask him personally,” says Reinders. “You can’t put something on the market and not say what sort of technology’s in it,” she says.

Rodrigo Ferrão de Paiva Martins, a materials scientist at the Instituto de Desenvolvimento de Novas Tecnologias in Caparica, Portugal, is working on thin-film solar cells. He says it’s possible to get a high enough energy efficiency for market practicality.

He begs to differ with Musk, saying that solar shingles are inherently less efficient than traditional solar panels. He notes that they can deliver about 3 to 4 percent conversion efficiency. They become cost effective at about the 10-percent-efficiency mark, and there’s a way to get there by tweaking the manufacturing process.

When solar cells are made, they are typically put in a mold and heated, leaving tiny holes in the material. By heating the materials at higher temperatures than normal, these holes could be smoothed out, improving efficiency.

Levinson, however, pointed out that efficiency can be a misleading way to think of the cost effectiveness problem—because it is a product of several variables such as location and the local price of electricity.

There could also be various technical and safety challenges.

Reinders says that glass would not be the most insulating material for cold climates and stressed that there would be a tradeoff between performance and the need to adhere to building code requirements. In the Netherlands, for example, there are rules that spell out what roofing material must be in terms of fire resistance as well as being non-toxic, durable, and resistant to erosion.

Bjørn Petter Jelle of the Norwegian University of Science and Technology and SINTEF Building and Infrastructure in Trondheim--who is investigating resilient solar cells--says it’s important that the new roofs are resistant to harsh weather conditions such as snow, ice, wind, rain, and ultraviolet radiation.

Also, there is a tradeoff between aesthetics and performance. Jelle knows of a man in a city outside of Trondheim who bought curved Chinese solar panels to match the homes of his neighbors, even though they were less efficient than flat panels.

Levinson says it remains to be seen whether the Tesla product will succeed, but Reinders says “the timing is really well done” with respect to market readiness.

There’s at least one buyer. Don Weidner, a Tesla Model S owner and founder of Formidable Ventures, says “I’m blown away by how good they look.”

He says he just moved into a new house in 2015, but assuming Tesla lives up to Musk’s promise regarding the cost for new roofs, “the very next time I move or build or need a roof, I would absolutely” buy one.

A train on tracks is part of the Advanced Rail Energy Storage project, which stores energy for the electricity grid as the potential energy of a train on a hill.

Arpa-E's $85 Million Plan to Build a Battery the Size of the Grid

As the electric grid is increasingly powered by renewables, it will need energy storage for when the wind isn’t blowing and the sun isn’t shining. But the three top grid-scale energy storage technologies today—pumped hydropower, lithium-ion batteries and “flow” batteries—arguably, aren’t up to the challenge.

The U.S. Department of Energy’s technology incubator ARPA-E (Advanced Research Projects Agency-Energy) wants to change that. It’s going long on a number of high-risk, high-reward R&D projects that might change the entire grid storage equation. U.S. Energy Secretary Ernest Moniz has said he thinks grid-scale battery storage will be the key innovation that enables the grid to completely decarbonize by midcentury. 

“There’s a lot of discussion about what the grid of the future will look like,” says Eric Rohlfing, ARPA-E Deputy Director for Technology. “Of course what we want to do is enable much higher penetration of renewables. So storage is an obvious way to do that… The two key points of grid storage are: it has to be cheap, and it has to be durable—to go through a lot of cycles.”

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Exhaust comes out of the tailpipe of a vehicle

If Germany Bans Internal Combustion Engines, It'll Change the Game

A recently proposed ban on internal combustion engines could improve air quality and lower noise pollution and CO2 emissions in Germany.

“We do not expect it will become a law within the next 12 months,” writes Volker Quaschning, an energy researcher at the Hochschule für Technik und Wirtschaft (HTW) Berlin, in Germany, in an email. “However, the discussion is interesting…because it increases the pressure on the car industry.”

Echoing similar proposals in Norway and other countries, the heads of 13 out of 16 of Germany’s states voted two weeks ago to allow sales of only zero-emission cars starting in 2030. That would be no small matter, considering that Germany—home of BMW, Mercedes-Benz, and Volkswagen—had 44 million registered cars in 2013

The states alone are not able to put the ban into effect; only the German federal government can. But they have started a conversation, and researchers say there would be clear benefits.

First, Quaschning calculated that switching to zero-emission vehicles powered by today’s energy mix—about 30 percent generated from renewable sources and 70 percent from nonrenewable sources such as coal and natural gas—would cause a noticeable decrease in CO2 emissions.

In the June 2013 issue of IEEE Spectrum, Ozzie Zehner argued that this sort of emission analysis of electric vehicles often leaves out an important factor: The emissions released during the manufacturing process can overshadow the benefits. However, 2015 research by the science advocacy group Union of Concerned Scientists found that over its life cycle, an electric car still creates about half of the CO2 emissions of a traditional gasoline-fueled car. And once the car has been driven enough, the emission savings add up.

Without taking into account the emissions released during the manufacturing process, Quaschning’s estimates suggest a 30 percent decrease in transportation emissions. The emissions from the transportation sector account for about 20 percent of Germany’s total emissions.

There’s another advantage of the proposed ban. “Reduction in CO2 is only secondary to the air pollution health benefit,” Mark Jacobson, a civil and environmental engineer at Stanford University in California, writes in an email.

Diesel engines are still widely used in Europe—and the black carbon particles they produce can lead to even greater global warming and health effects than does carbon dioxide, Jacobson writes. Early California Environmental Protection Agency research yielded some of the many bits of empirical evidence showing that diesel fumes directly affect health and can increase the risk of cancer. But as of 2013, about 1.4 out of 2.9 million new German passenger cars were diesels.

An additional rationale for the proposed ban: A switch to electric cars could reduce noise pollution. “Today, there is little knowledge about how a whole city or region feels and sounds, in which only electric and nonmotorized vehicles drive,” Christian Scherf, a spokesman for the Innovation Centre for Mobility and Societal Change in Berlin, writes in an email. “However, we assume that the quality of life is noticeably increased.”

Werner Zittel, a physicist and energy consultant at Ludwig-Bölkow-Systemtechnik, in Munich, says a ban “is feasible.” He believes politicians should set rules and let the car industry react by creating engines that meet the new requirements.

Not all agree. Last week, Forbes reported that Germany’s minister of transportation dismissed the idea out of hand. He told the German wire service DPA that an internal combustion engine ban by 2030 would be “utter nonsense.”

A spokesman for Oliver Krischer, the vice chairman of Germany’s Green Party, says the Green Party supports the ban, but notes that the federal government would not likely pass a law without the transport ministry’s support. To his knowledge, the German parliament hasn’t passed legislation without a ministry’s support in at least the past 10 years.

“It’s kind of a big discussion right now going on in Germany,” he says. But the states made a “clear statement.” 

The Green Party is calling for an all-renewable energy grid by 2030—an idea that Zittel calls “impossible.”

Don Anair, an electrical engineer with the Union of Concerned Scientists in the United States who studies transportation, says, “I think the important thing for Germany is where the electricity grid is heading.”

“You can’t just look at today’s grid mix and say, here’s what the benefits of electric vehicles are years from now,” he says.

Neither the German Ministry of Economics and Energy nor the Ministry of Transportation were available for further comment.

Germany’s next election is in September 2017, which both Quaschning and Krischer say could change the game—both for the extent of Germany’s use of renewables and whether consideration of an internal combustion engine ban will remain in gear.

Thirteen years from now, Anair says, “obviously that would be a dramatic shift in the auto industry.” He does, however, point out that in the United States there are over 25 models of plug-in or fuel cell vehicles—up from “essentially zero” before 2010.

Sales of these vehicles with much less reliance on the combustion of fossil fuel are increasing, but the question remains: How fast can the industry ramp up, and where is the tipping point at which electric vehicles become a normal purchase, he asks.

“This is a technology that’s here to stay,” he says.

A Samsung Galaxy Note 7 phone caught fire on 9 Oct., two days before Samsung Electronics announced that it is permanently discontinuing production of that model.

What's Behind Samsung's Phone Fires?

There’s never a good time for a corporation to get a black eye, but now is a particularly bad time for Korea’s Samsung. The company’s recall of 2.5 million Galaxy Note 7 smartphones, and its shutdown of sales and production also call attention to its recent recalls of other, unrelated products.

“What was remarkable here was that this was the world’s leading company for batteries and for consumer electronics,” says Cosmin Laslau, an electrochemistry expert and technology analyst for Lux Research. “It doesn’t get much more high profile than this.”

Though only 35 fires have been reported so far, one’s enough to ruin your whole day. A single blazing battery grounded a fleet of Boeing 787 Dreamliners some years back—one reason why in September, air safety regulators told people to shut off their Galaxy phones before packing them for a flight.

Right now, nobody in or out of Samsung really knows what’s going on. Investigations of the fires are still unpublished, but today Bloomberg News reports that Samsung has told Korea’s technology standards agency that the problem may involve a manufacturing error. According to that confidential note, the error brought negative and positive poles into contact, causing a short circuit. Samsung SDI Co. was the main battery supplier for the Galaxy Note 7, Bloomberg adds. 

Amperix Technology Limited has also provided some batteries for Samsung’s phone. If all the bad batteries had been in one batch, switching from one supplier to the other should have solved the problem—but it didn’t. “The chances that two suppliers are having similar issues are very low, so there must be more to the story,” Laslau says.

Why didn’t more of the phones burst into flames? And why didn’t the problem emerge right away? Does fire result only when you get a perfect storm of mishaps in several elements of the phone?

The random and rare nature of the fires doesn’t look like what you’d get from a straightforward manufacturing problem, says Bor Yann Liaw, a materials scientist who specializes in batteries at the Idaho National Laboratory, in Idaho Falls. “It is unlikely a [battery] design flaw either, since the products have been tested and have passed all safety requirements. This is probably a system design flaw that causes battery charging to derail from the normal process.”

“It could be a lot of things,” Laslau says. “A production process with impurities, or something to do with the separator [a membrane that prevents the electrodes from coming into contact, causing a short circuit]. Or the batteries could be fine but the energy management system could be charging them too aggressively.”

You can tweak any or all of these elements, but if you do, you’ll sacrifice performance and cost. Any supplier that did that would risk losing the contract to the next guy. 

“A lot of suppliers of batteries are under pressure to charge faster and pack in a lot more specific energy than ever before,” Laslau says. “Where is the tipping point where a major developer will say it will increase its price by 10 to 20 percent in order to make the batteries safer? This may force that type of introspection in the industry.”

This post was corrected on 17 October to clarify a statement about design flaws.

Photograph of solar-cell coated window

Quantum-Dot Coating Could Pull Solar Energy From Your Windows

In big cities, sometimes buildings that don’t have a lot of roof space for solar cells still have large windows that could harness light for electricity. Researchers at the Los Alamos National Laboratory, in New Mexico, reported yesterday in Nature Energy that a thin film of quantum dots on everyday glass could be the key to achieving acceptable efficiency in window photovoltaic systems at low cost.

Mostly, engineers have tried using modules of connected solar cells to capture sunlight falling on windows. Some wondered if it would be possible to do it with less cells. Taking advantage of a mechanism for capturing the light falling on a window and then directing it to a single solar cell “simplifies the device; it makes it less expensive,” says Victor Klimov, a nanotechnology engineer at Los Alamos.

At first, engineers tried using organic dyes as a way to concentrate the light. The problem with that, Klimov says, is that the dyes absorb the light they produce because it appears very similar to the incoming rays from the sun. In 2013, engineers instead started investigating nanometer-scale semiconductors called quantum dots because they allow customizing properties such as what kinds of light they absorb and which ones they don’t.

In the new research, Klimov and his team found that a thin layer of quantum dots on normal glass could have a lifetime of up to 14 years and about 1.9 percent overall energy conversion efficiency. To make these devices practical they’ll have to reach 6 percent, he says, so they’re getting close.

What’s more, adding quantum dots to window glass is surprisingly easy: A machine pours a slurry of quantum dots and PVP polymer onto the glass and a blade spreads it out to form a thin sheet.

The quantum dots consist of a CdSe inner core, a Cd1−xZnxS outer shell, and are coated in silica for protection from oxidation—with the outer shell acting like an absorber. When a photon hits a dot, an electron in the shell is kicked out of its valence band into the conduction band, leaving a hole. The rogue electron and hole jump to the core, where they recombine to produce a new photon with lower energy.

By design, the shell only absorbs high energy photons, and the new photon from the core is free to propagate throughout the glass and quantum dot layers via internal reflections. Eventually, the propagating photons would arrive at the glass edges—where one or more solar cells could pick them up.

In 2015 research, members of the team had tried dispersing quantum dots directly inside a polymer. However, in polymer materials such as this, many of these photons would scatter and escape the material. The optical properties of the new thin quantum-dot layer on glass are such that there’s minimal scattering and the light tends to propagate much longer, Klimov says.

“This is important for showing that these nanocrystals may be used to make large-area and cost-effective diffuse light concentrators,” Vivian Ferry, an energy and electronics researcher at the University of Minnesota who was not involved in the study, but has worked with solar cells and quantum dots, writes in an email. 

When the researchers tested absorption and stability properties, they also found the manufactured device held its own.

“If you’re serious about applications,” Klimov says, “Stability must be comparable to the stability of the solar cell.”

He believes the application technique is inexpensive and accessible enough for the glass industry to use. A coating could even be scraped off and re-used.

Still, there’s plenty of work to do before reaching the break-even point on energy conversion, he says. To meet the efficiency goal, he’s now tinkering with the concentrations of quantum dots used and their absorption properties.

For comparable light concentrators of a similar size, color, and transparency, the Los Alamos system is “pretty good,” writes David Patrick, an energy researcher at Western Washington University who was not involved in the study but has worked on solar light conversion. 

A correction to this article was made on 11 October 2016. The inner core and outer shell materials were inadvertently reversed.

perovskite solar cell

Perovskites Become More Stable

Solar cells based on perovskite crystals have made unparalleled advances in performance in the past decade, but most research on these devices has neglected the question of how stable they might be outdoors for long periods of time. Now two research groups have come up with different ways to improve perovskite solar cell stability, findings detailed in two papers in the journal Science.

One approach added rubidium cations to perovskite. "We believe this may help to relax lattice strain, resulting in a more defect-free overall crystal," says Michael Saliba, lead author of that study and a solar cell researcher at the Swiss Federal Institute of Technology in Lausanne.

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a perovskite solar cell made of many layers

Perovskite Solar Cells Grow Better With a Dash of Acrylic Glass

The conversion efficiency of solar cells based on perovskite crystals has shot up from 3.8 to 22.1 percent in less than a decade, an unprecedented rise in the field of photovoltaics. "Perovskites have rocked the whole photovoltaic community," says Michael Grätzel, director of the École Polytechnique Fédérale de Lausanne’s Laboratory of Photonics and Interfaces. Trying to keep the progress going, he and his colleagues have found a way to grow bigger, better performing perovskite cells—by growing with ordinary acrylic glass.

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Map of Asia Super Grid

Trio of Nations Aims to Hook Asia Super Grid to Grids of the World

Northeast Asia, the region encompassing China, South Korea, and Japan, has not yet gotten around to connecting its electricity grids together. But that’s not stopping these countries from promoting the Asia Super Grid, calculated to become the center of a global energy grid providing abundant, cheap electricity based on renewable energy. 

In Japan, the idea emerged following the 2011 Tohoku earthquake and subsequent Fukushima Daiichi nuclear plant disaster. The possibility of a nuclear disaster so shocked Masayoshi Son, founder and head of the telecom and Internet giant SoftBank Group, that he established the Renewable Energy Institute soon after to help develop and promote renewable energy.

“I was a total layman (in renewable energy) at the time of the earthquake,” Son told a packed audience attending a symposium celebrating the fifth anniversary of the institute in Tokyo last Friday.

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A patch of energy harvesting fabric combines solar-cell threads and triboelectric energy generator fibers

Walk Around in the Sun to Power Wearables With This Cloth

A new wearable fabric that generates electricity from both sunlight and motion could let you power your cell phone or smart watch by walking around outside. Researchers made the textile by weaving together plastic fiber solar cells and fiber-based generators that produce electricity when rubbed against each other.

The 0.32-millimeter-thick fabric is lightweight, flexible, breathable, and uses low-cost materials, its creators say. It could be integrated into clothes, tents, and curtains, turning them into power sources when they flap or are exposed to the sun. By harvesting solar and mechanical energy, the power-generating cloth could work day and night, its inventors say.

“The hybrid power textile could be extensively applied not only to self-powered electronics but also possibly to power generation on a larger scale,” Zhong Lin Wang at Georgia Tech, Xing Fan at Chongqing University in Chongqing, China, and their colleagues write in a research published today in the journal Nature Energy.

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Tapiwa M. Chiwewe is a research scientist at IBM Research in Johannesburg, South Africa, where he and colleagues are expanding the company's machine learning technology to predicting air quality.

Tackling Air Quality Prediction in South Africa With Machine Learning

Machine learning is nipping at the heels of conventional physical modeling of air quality predictions in more and more places. The latest is Johannesburg, South Africa, where computer engineer Tapiwa M. Chiwewe at the newly opened IBM Research lab is adapting IBM’s air quality prediction software to local needs and adding new capabilities. The work is an expansion of the so-called Green Horizons initiative, in which IBM researchers partnered with Chinese government researchers and officials, starting two years ago.

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