All posts by Charles Q. Choi

Best Algorithms to Make Solar Power Storage Profitable

Post Syndicated from Charles Q. Choi original https://spectrum.ieee.org/energywise/energy/the-smarter-grid/best-algorithms-to-make-solar-power-profitable

Which algorithms are best at integrating solar arrays with electrical grid storage?

By analyzing the kinds of algorithms that control the flow of electricity between solar cells and lithium-ion batteries, scientists have identified the best types of algorithms to govern electrical grid storage of solar power.

A dizzying number of algorithms exist to help manage the flow of electricity between photovoltaic cells and lithium-ion batteries in the most profitable manner. These come in a variety of complexities and have diverse computational power requirements.

“Lithium-ion batteries are expensive components, and photovoltaic plant owners have to pay large amounts of money in order to install lithium-ion batteries on plant,” says study lead author Alberto Berrueta, an engineering researcher at the Public University of Navarre’s Institute of Smart Cities in Pamplona, Spain. “Management algorithms are of capital importance in order to preserve a long lifetime for the batteries to make the most out of the batteries.”

To see which types of these algorithms work best at getting the most out of lithium-ion batteries, researchers developed models based off the amount of power generated over the course of a year from a medium-sized roughly 100-kilowatt solar cell array located in Navarre. They focused on concerns such as the computational requirements needed, the price of electricity, battery life, battery costs, and battery charging and discharging rates.

The researchers looked at three families of algorithms currently used in managing electricity from commercial solar cell arrays: dynamic, quadratic and linear. Dynamic algorithms tackle complex, sequential optimization problems by breaking them down into several simpler sub-problems. Quadratic algorithms each involve at least one squared variable and often find use in calculating areas, computing the profit of a product, and pinpointing the speed and position of an object. Linear algorithms each involve variables that are not squared and have the simplest computational requirements.

The scientists found the dynamic algorithms required far more computational power than the other two families of algorithms; as the number of variables grew, they experienced an exponential increase in problem complexity. A commercial PC that would take about 10 seconds to compute the energy flow between the solar cells and lithium-ion batteries using the linear and quadratic algorithms would take 42 minutes with the dynamic algorithms.

Linear algorithms had the lowest computational requirements but suffered in terms of accuracy. For instance, their simplified models did not account for how electrical current can reduce battery lifetime. All in all, the linear algorithms provided an average of 20 percent lower profits than the maximum achievable.

The researchers concluded that quadratic algorithms provided the best trade-off between accuracy and computational simplicity for solar power applications. Quadratic algorithms had about the same low computational requirements as linear algorithms while achieving revenues similar to dynamic algorithms for all battery sizes.

In the future, scientists can investigate which management algorithms might work best with hybrid energy storage systems, Berrueta says. Future research can also investigate which computer models work best at calculating all the factors affecting the lifetime of lithium-ion batteries, including batteries discarded from electric vehicles that might find a second life working in renewable energy plants, he adds.

The researchers detailed their findings at the IEEE International Conference on Environmental and Electrical Engineering in Genoa, Italy, on June 11.

From Brrrr to Vroom: New Additives Promise Better Performance for Electric Cars in Cold Weather

Post Syndicated from Charles Q. Choi original https://spectrum.ieee.org/energywise/green-tech/fuel-cells/lithium-additives

Electrolyte additives can boost lithium-ion battery temperature range

New additives can help lithium-ion batteries perform over a wider range of temperatures, a potential boon for electric cars, a new study finds.

Electric cars struggle with extreme temperatures, which can degrade the electrolyte solutions that conduct ions between the negative electrodes, or anodes, and positive electrodes, or cathodes, within lithium-ion batteries.

A key additive to most of these electrolyte solutions is ethylene carbonate, which helps produce a protective layer that prevents further decomposition of electrolyte components when they interact with the anode. However, ethylene carbonate has a high melting point, which limits its performance at low temperatures.

Materials scientist Wu Xu at Pacific Northwest National Laboratory in Richland, Washington, and his colleagues previously showed they could extend the temperature range of lithium-ion batteries by partially replacing ethylene carbonate with propylene carbonate and adding cesium hexafluorophosphate. However, they wanted to improve the temperature range of lithium-ion batteries even further, so they could perform well from -40 to 60 degrees C.

In the new study, Xu and his colleagues tested the effects of five electrolyte additives on the performance of lithium-ion batteries within this temperature range. Through a combination of computational modeling, decades of experience with the chemical and electrochemical properties of liquid electrolytes and additives, and trial and error, they identified an optimized combination of three compounds that they added to their previous electrolyte solution.

This new mixture caused the formation of highly conductive, uniform and robust protective layers on both the anode and the cathode. At -40 degrees C, batteries containing this blend achieved 67 percent of the discharging performance they saw at room temperature. In comparison, regular lithium-ion batteries only experience about 20 percent discharge capacity, Xu says.

Normally, including a variety of additives within electrolytes results in thick layers on both positive and negative electrodes at low temperatures that are fairly resistant to ion transport, “leading to very poor low-temperature discharge performance,” Xu says. “Our additive mixture still results in very thin surface layers on both electrodes, and their resistance is low, and does not change much with cycling. This is achieved by the synergistic effects of these additives.”

The new batteries also displayed long-term cycling stability at 25 degrees C, retaining more than 85 percent of their original capacity after 1,000 cycles. In addition, at 60 degrees C, the new batteries maintained more than 60 percent of their original capacity after 300 cycles, whereas conventional lithium-ion batteries only kept about 10 percent of their original capacity, Xu says.

The scientists aim to validate these results in “commercial lithium ion batteries under practical testing conditions, and then hope that battery companies will use the electrolytes in their battery systems for electric vehicles,” Xu says. They also hope to experiment with electrolyte additives to improve other aspects of battery performance, such as boosting their charging speed and reducing their flammability, Xu adds.

The scientists detailed their findings June 19 in the journal ACS Applied Materials & Interfaces.

World’s First “Quantum Drone” for Impenetrable Air-to-Ground Data Links Takes Off

Post Syndicated from Charles Q. Choi original https://spectrum.ieee.org/tech-talk/computing/networks/quantum-drone

Chinese researchers are developing an airborne quantum communications network with drones as nodes

Quantum drones under development in China could lead to nigh unhackable airborne quantum communication networks, a new study finds.

Quantum mechanics makes possible a strange phenomenon known as entanglement. Essentially, two or more particles such as photons that get linked or “entangled” can, in theory, influence each other no matter the distance between them. Entanglement is essential to the workings of quantum computers, the networks that would connect them, and the most sophisticated kinds of quantum cryptography—a  means of information exchange that is impervious to hacking.