About 350,000 plug-in electric vehicles (EVs) have been sold in the US from 2008—when they first entered the market—to mid-2015. Although EVs still represent a small fraction of the country's 250 million total vehicles, the continual increase in sales suggests that EVs will become even more popular over the next few decades. This raises the question of how millions of EVs may be charged at once on a grid that was not originally intended to supply such large amounts of power.
The main problem, as researchers Rui Carvalho and coauthors from the UK and Slovakia explain in a recent paper published in the New Journal of Physics, is congestion—not road traffic congestion, but charging traffic congestion. In their paper, they show that when the number of EVs being plugged into the network reaches a critical point, the system undergoes a phase transition from a "freeflow" state (where all vehicles can be fully charged within the expected time period, say 4 hours) to a congested state. In the congested state, some vehicles have to wait for increasingly long times to fully charge, resulting in queues of vehicles rapidly building up that will then face even longer charging times.
"With high penetration of electric vehicles, charging at home will increase the stress on the 'last mile' of local distribution networks," Carvalho, a researcher at Durham University in the UK, told Phys.org. "The conventional solution would be to lay copper under the road, so as to increase network capacity. The cost of upgrading the last mile of the network, however, would be prohibitive, and we present an alternative, much cheaper approach that could be implemented with minimal hardware requirements: a software layer and controllers at the point of charge."
As the researchers explain, the congestion problem can be avoided, at least to an extent, by managing how the power is allocated throughout the charging network. A good management strategy can increase the critical number of vehicles that pushes the system over the threshold into its congested state, thereby allowing more vehicles to be charged in their normal charge time.
In their paper, the researchers compared two charging strategies ("max-flow" and "proportional fairness") with the aim to guide network designers in deciding which algorithms to implement in the real world. Both algorithms investigated here rely on recent advances that combine tools from optimization and critical phenomena. As vehicles randomly plug in to the network, the network must continually solve the congestion control problem and allocate each vehicle an instantaneous power using the algorithm. The researchers compared the outcomes of both algorithms using simulations that are only possible due to techniques developed since 2012.
Researchers make important step towards a solar cell that generates hydrogen.
Researchers have developed a very promising prototype of a new solar celll. The material gallium phosphide enables their solar cell to produce the clean fuel hydrogen gas from liquid water. Processing the gallium phosphide in the form of very small nanowires is novel and helps to boost the yield by a factor of ten. And does so using ten thousand times less precious material.
According to Bakkers, it's not simply about the yield -- where there is still a lot of scope for improvement he points out: "For the nanowires we needed ten thousand less precious GaP material than in cells with a flat surface. That makes these kinds of cells potentially a great deal cheaper," Bakkers says. "In addition, GaP is also able to extract oxygen from the water -- so you then actually have a fuel cell in which you can temporarily store your solar energy. In short, for a solar fuels future we cannot ignore gallium phosphide any longer."
GaP has good electrical properties but the drawback that it cannot easily absorb light when it is a large flat surface as used in GaP solar cells. The researchers have overcome this problem by making a grid of very small GaP nanowires, measuring five hundred nanometers (a millionth of a millimeter) long and ninety nanometers thick. This immediately boosted the yield of hydrogen by a factor of ten to 2.9 percent. A record for GaP cells, even though this is still some way off the fifteen percent achieved by silicon cells coupled to a battery.
Materials melt faster when the lines of heat spread through the cold material like the branches of a tree—and the melting rate can be steadily increased by allowing the tree architecture to freely evolve over time, researchers have discovered.
Solar photovoltaic (PV) systems generate "free" electricity from sunlight, but manufacturing them is an energy-intensive process. It's generally assumed that it only takes a few years before solar panels have generated as much energy as it took to make them, resulting in very low greenhouse gas emissions compared to conventional grid electricity. However, the studies upon which this assumption is based are written by a handful of researchers who arguably have a positive bias towards solar PV. A more critical analysis shows that the cumulative energy and CO2 balance...
Solar cells today are getting better at converting sunlight to electricity, but commercial panels still harvest only part of the radiation they're exposed to. Scientists are working to change this using various methods. One approach is to hybridize solar cells with different materials to capture more of the sun's energy.
Eunkyoung Kim and colleagues turned to a clear, conductive polymer known as PEDOT to try to accomplish this. The researchers layered a dye-sensitized solar cell on top of a PEDOT film, which heats up in response to light. Below that, they added a pyroelectric thin film and a thermoelectric device, both of which convert heat into electricity. The efficiency of all components working together was more than 20 percent higher than the solar cell alone. With that boost, the system could operate an LED lamp and an electrochromic display.
Saudi Arabia produces much of its electricity by burning oil, a practice that most countries abandoned long ago, reasoning that they could use coal and natural gas instead and save oil for transportation, an application for which there is no mainstream alternative. Most of Saudi Arabia’s power plants are colossally inefficient, as are its air conditioners, which consumed 70 percent of the kingdom’s electricity in 2013. Although the kingdom has just 30 million people, it is the world’s sixth-largest consumer of oil.Now, Saudi rulers say, things must change. Their motivation isn’t concern about global warming; the last thing they want is an end to the fossil-fuel era. Quite the contrary: they see investing in solar energy as a way to remain a global oil power. The Saudis burn about a quarter of the oil they produce—and their domestic consumption has been rising at an alarming 7 percent a year, nearly three times the rate of population growth.
Tags: Saudi Arabia, energy, resources, consumption, Middle East, sustainability.
In an engineering first, Stanford University scientists have invented a low-cost water splitter that uses a single catalyst to produce both hydrogen and oxygen gas 24 hours a day, seven days a week. The researchers believe that the device, described in anopen-access study published today (June 23) in Nature Communications, could provide a renewable source of clean-burning hydrogen fuel for transportation and industry.
“We have developed a low-voltage, single-catalyst water splitter that continuously generates hydrogen and oxygen for more than 200 hours, an exciting world-record performance,” said study co-author Yi Cui, an associate professor of materials science and engineering at Stanford and of photon science at the SLAC National Accelerator Laboratory.
Hydrogen has long been promoted as an emissions-free alternative to gasoline. But most commercial-grade hydrogen is made from natural gas — a fossil fuel that contributes to global warming. So scientists have been trying to develop a cheap and efficient way to extract pure hydrogen from water.
A conventional water-splitting device consists of two electrodes submerged in a water-based electrolyte. A low-voltage current applied to the electrodes drives a catalytic reaction that separates molecules of H2O, releasing bubbles of hydrogen on one electrode and oxygen on the other.
In these devices, each electrode is embedded with a different catalyst, typically platinum and iridium, two rare and costly metals. But in 2014, Stanford chemist Hongjie Dai developed a water splitter made of inexpensive nickel and iron that runs on an ordinary 1.5-volt battery.
In conventional water splitters, the hydrogen and oxygen catalysts often require different electrolytes with different pH — one acidic, one alkaline — to remain stable and active. “For practical water splitting, an expensive barrier is needed to separate the two electrolytes, adding to the cost of the device,” Wang explained.
“Our water splitter is unique because we only use one catalyst, nickel-iron oxide, for both electrodes,” said graduate student Haotian Wang, lead author of the study. “This bi-functional catalyst can split water continuously for more than a week with a steady input of just 1.5 volts of electricity. That’s an unprecedented water-splitting efficiency of 82 percent at room temperature.”
Wang and his colleagues discovered that nickel-iron oxide, which is cheap and easy to produce, is actually more stable than some commercial catalysts made of expensive precious metals. The key to making a single catalyst possible was to use lithium ions to chemically break the metal oxide catalyst into smaller and smaller pieces. That “increases its surface area and exposes lots of ultra-small, interconnected grain boundaries that become active sites for the water-splitting catalytic reaction,” Cui said. “This process creates tiny particles that are strongly connected, so the catalyst has very good electrical conductivity and stability.”
You likely have heard the stories of the bankruptcies of Solyndra, Fisker Automotive and Evergreen Solar, heard about the green tech funds on Sand Hill Road that just didn't deliver and the less than rosy stock prices of clean energy ...
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