River Water and Salty Ocean Water Used to Generate Electricity

Anywhere freshwater enters the sea, such as river mouths or estuaries, could be potential sites for a power plant using such a battery, said Yi Cui, associate professor of materials science and engineering, who led the research team.

The theoretical limiting factor, he said, is the amount of freshwater available."We actually have an infinite amount of ocean water; unfortunately we don't have an infinite amount of freshwater," he said.

As an indicator of the battery's potential for producing power, Cui's team calculated that if all the world's rivers were put to use, their batteries could supply about 2 terawatts of electricity annually -- that's roughly 13 percent of the world's current energy consumption.

The battery itself is simple, consisting of two electrodes -- one positive, one negative -- immersed in a liquid containing electrically charged particles, or ions. In water, the ions are sodium and chlorine, the components of ordinary table salt.

Initially, the battery is filled with freshwater and a small electric current is applied to charge it up. The freshwater is then drained and replaced with seawater. Because seawater is salty, containing 60 to 100 times more ions than freshwater, it increases the electrical potential, or voltage, between the two electrodes. That makes it possible to reap far more electricity than the amount used to charge the battery.

"The voltage really depends on the concentration of the sodium and chlorine ions you have," Cui said."If you charge at low voltage in freshwater, then discharge at high voltage in sea water, that means you gain energy. You get more energy than you put in."

Once the discharge is complete, the seawater is drained and replaced with freshwater and the cycle can begin again."The key thing here is that you need to exchange the electrolyte, the liquid in the battery," Cui said. He is lead author of a study published in the journal Nano Letters earlier this month.

In their lab experiments, Cui's team used seawater they collected from the Pacific Ocean off the California coast and freshwater from Donner Lake, high in the Sierra Nevada. They achieved 74 percent efficiency in converting the potential energy in the battery to electrical current, but Cui thinks with simple modifications, the battery could be 85 percent efficient.

To enhance efficiency, the positive electrode of the battery is made from nanorods of manganese dioxide. That increases the surface area available for interaction with the sodium ions by roughly 100 times compared with other materials. The nanorods make it possible for the sodium ions to move in and out of the electrode with ease, speeding up the process.

Other researchers have used the salinity contrast between freshwater and seawater to produce electricity, but those processes typically require ions to move through a membrane to generate current. Cui said those membranes tend to be fragile, which is a drawback. Those methods also typically make use of only one type of ion, while his battery uses both the sodium and chlorine ions to generate power.

Cui's team had the potential environmental impact of their battery in mind when they designed it. They chose manganese dioxide for the positive electrode in part because it is environmentally benign.

The group knows that river mouths and estuaries, while logical sites for their power plants, are environmentally sensitive areas.

"You would want to pick a site some distance away, miles away, from any critical habitat," Cui said."We don't need to disturb the whole system, we just need to route some of the river water through our system before it reaches the ocean. We are just borrowing and returning it," he said.

The process itself should have little environmental impact. The discharge water would be a mixture of fresh and seawater, released into an area where the two waters are already mixing, at the natural temperature.

One of Cui's concerns is finding a good material for the negative electrode. He used silver for the experiments, but silver is too expensive to be practical.

His group did an estimate for various regions and countries and determined that South America, with the Amazon River draining a large part of the continent, has the most potential. Africa also has an abundance of rivers, as do Canada, the United States and India.

But river water doesn't necessarily have to be the source of the freshwater, Cui said.

"The water for this method does not have to be extremely clean," he said. Storm runoff and gray water could potentially be useable.

A power plant operating with 50 cubic meters of freshwater per second could produce up to 100 megawatts of power, according to the team's calculations. That would be enough to provide electricity for about 100,000 households.

Cui said it is possible that even treated sewage water might work.

"I think we need to study using sewage water," he said."If we can use sewage water, this will sell really well."

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Batteries Charge Quickly and Retain Capacity, Thanks to New Structure

Braun's group developed a three-dimensional nanostructure for battery cathodes that allows for dramatically faster charging and discharging without sacrificing energy storage capacity. The researchers' findings will be published in the March 20 advance online edition of the journalNature Nanotechnology.

Aside from quick-charge consumer electronics, batteries that can store a lot of energy, release it fast and recharge quickly are desirable for electric vehicles, medical devices, lasers and military applications.

"This system that we have gives you capacitor-like power with battery-like energy," said Braun, a professor of materials science and engineering."Most capacitors store very little energy. They can release it very fast, but they can't hold much. Most batteries store a reasonably large amount of energy, but they can't provide or receive energy rapidly. This does both."

The performance of typical lithium-ion (Li-ion) or nickel metal hydride (NiMH) rechargeable batteries degrades significantly when they are rapidly charged or discharged. Making the active material in the battery a thin film allows for very fast charging and discharging, but reduces the capacity to nearly zero because the active material lacks volume to store energy.

Braun's group wraps a thin film into three-dimensional structure, achieving both high active volume (high capacity) and large current. They have demonstrated battery electrodes that can charge or discharge in a few seconds, 10 to 100 times faster than equivalent bulk electrodes, yet can perform normally in existing devices.

This kind of performance could lead to phones that charge in seconds or laptops that charge in minutes, as well as high-power lasers and defibrillators that don't need time to power up before or between pulses.

Braun is particularly optimistic for the batteries' potential in electric vehicles. Battery life and recharging time are major limitations of electric vehicles. Long-distance road trips can be their own form of start-and-stop driving if the battery only lasts for 100 miles and then requires an hour to recharge.

"If you had the ability to charge rapidly, instead of taking hours to charge the vehicle you could potentially have vehicles that would charge in similar times as needed to refuel a car with gasoline," Braun said."If you had five-minute charge capability, you would think of this the same way you do an internal combustion engine. You would just pull up to a charging station and fill up."

All of the processes the group used are also used at large scales in industry so the technique could be scaled up for manufacturing.

They key to the group's novel 3-D structure is self-assembly. They begin by coating a surface with tiny spheres, packing them tightly together to form a lattice. Trying to create such a uniform lattice by other means is time-consuming and impractical, but the inexpensive spheres settle into place automatically.

Then the researchers fill the space between and around the spheres with metal. The spheres are melted or dissolved, leaving a porous 3-D metal scaffolding, like a sponge. Next, a process called electropolishing uniformly etches away the surface of the scaffold to enlarge the pores and make an open framework. Finally, the researchers coat the frame with a thin film of the active material.

The result is a bicontinuous electrode structure with small interconnects, so the lithium ions can move rapidly; a thin-film active material, so the diffusion kinetics are rapid; and a metal framework with good electrical conductivity.

The group demonstrated both NiMH and Li-ion batteries, but the structure is general, so any battery material that can be deposited on the metal frame could be used.

"We like that it's very universal, so if someone comes up with a better battery chemistry, this concept applies," said Braun, who is also affiliated with the Materials Research Laboratory and the Beckman Institute for Advanced Science and Technology at Illinois."This is not linked to one very specific kind of battery, but rather it's a new paradigm in thinking about a battery in three dimensions for enhancing properties."

The U.S. Army Research Laboratory and the Department of Energy supported this work. Visiting scholar Huigang Zhang and former graduate student Xindi Yu were co-authors of the paper.

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Electric Grid Reliability: Increasing Energy Storage in Vanadium Redox Batteries by 70 Percent

In a paper published by the journalAdvanced Energy Materials,researchers at the Department of Energy's Pacific Northwest National Laboratory found that adding hydrochloric acid to the sulfuric acid typically used in vanadium batteries increased the batteries' energy storage capacity by 70 percent and expanded the temperature range in which they operate.

"Our small adjustments greatly improve the vanadium redox battery," said lead author and PNNL chemist Liyu Li."And with just a little more work, the battery could potentially increase the use of wind, solar and other renewable power sources across the electric grid."

Unlike traditional power, which is generated in a reliable, consistent stream of electricity by controlling how much coal is burned or water is sent through dam turbines, renewable power production depends on uncontrollable natural phenomena such as sunshine and wind. Storing electricity can help smooth out the intermittency of renewable power while also improving the reliability of the electric grid that transmits it. Vanadium batteries can hold on to renewable power until people turn on their lights and run their dishwashers. Other benefits of vanadium batteries include high efficiency and the ability to quickly generate power when it's needed as well as sit idle for long periods of time without losing storage capacity.

A vanadium battery is a type of flow battery, meaning it generates power by pumping liquid from external tanks to the battery's central stack, or a chamber where the liquids are mixed. The tanks contain electrolytes, which are liquids that conduct electricity. One tank has the positively-charged vanadium ion V5+ floating in its electrolyte. And the other tank holds an electrolyte full of a different vanadium ion, V2+. When energy is needed, pumps move the ion-saturated electrolyte from both tanks into the stack, where a chemical reaction causes the ions to change their charge, creating electricity.

To charge the battery, electricity is sent to the vanadium battery's stack. This causes another reaction that restores the original charge of vanadium ions. The electrical energy is converted into chemical energy stored in the vanadium ions. The electrolytes with their respective ions are pumped back into to their tanks, where they wait until electricity is needed and the cycle is started again.

A battery's capacity to generate electricity is limited by how many ions it can pack into the electrolyte. Vanadium batteries traditionally use pure sulfuric acid for their electrolyte. But sulfuric acid can only absorb so many vanadium ions.

Another drawback is that sulfuric acid-based vanadium batteries only work between about 50 and 104 degrees Fahrenheit (10 to 40 Celsius). Below that temperature range, the ion-infused sulfuric acid crystallizes. The larger concern, however, is the battery overheating, which causes an unwanted solid to form and renders the battery useless. To regulate the temperature, air conditioners or circulating cooling water are used, which causes up to 20 percent energy loss and significantly increasing the battery's operating cost, the researchers noted.

Wanting to improve the battery's performance, Li and his colleagues began searching for a new electrolyte. They tried a pure hydrochloric acid electrolyte, but found it caused one of the vanadium ions to form an unwanted solid. Next, they experimented with various mixtures of both hydrochloric and sulfuric acids. PNNL scientists found the ideal balance when they mixed 6 parts hydrochloric acid with 2.5 parts sulfuric acid. They verified the electrolyte and ion molecules present in the solution with a nuclear magnetic resonance instrument and the Chinook supercomputer at EMSL, DOE's Environmental Molecular Sciences Laboratory at PNNL.

Tests showed that the new electrolyte mixture could hold 70 percent more vanadium ions, making the battery's electricity capacity 70 percent higher. The discovery means that smaller tanks can be used to generate the same amount of power as larger tanks filled with the old electrolyte.

And the new mixture allowed the battery to work in both warmer and colder temperatures, between 23 and 122 degrees Fahrenheit (-5 to 50 Celsius), greatly reducing the need for costly cooling systems. At room temperature, a battery with the new electrolyte mixture maintained an 87 percent energy efficiency rate for 20 days, which is about the same efficiency of the old solution.

The results are promising, but more research is needed, the authors noted. The battery's stack and overall physical structure could be improved to increase power generation and decrease cost.

"Vanadium redox batteries have been around for more than 20 years, but their use has been limited by a relatively narrow temperature range," Li said."Something as simple as adjusting the batteries' electrolyte means they can be used in more places without having to divert power output to regulate heat."

This research was supported by DOE's Office of Electricity Delivery and Energy Reliability and internal PNNL funding.

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Testing Smart Energy Systems

In an innovative test laboratory, the SmartEnergyLab, they are investigating how to network various electrical household appliances and operate them remotely. In the residential housing sector in particular there is still a great deal of potential for smart energy-management systems that are capable of tailoring local power generation and consumption optimally to the power grid: What is the best time of day for utilizing solar power? How can we store the energy produced and possibly feed it back into the power grid at a lucrative price?

"Smart energy-systems technology for the consumer end of the distribution grid is the key to sustainable, secure energy supply," explains Christof Wittwer, group manager at Fraunhofer ISE. By mapping all the thermal and electrical energy flows, the lab constitutes a unique platform for analyzing, assessing and developing smart homes and smart grid solutions for the distribution grid."Basically, our lab is a simulator for potential energy systems for houses," says Wittwer.

The lab is equipped with renewable as well as electric and thermal producers and storage devices for tomorrow's single-family dwellings and apartment buildings. It boasts a stand-alone 5kW cogeneration plant, a two-cubic-meter buffer storage tank, a photovoltaic simulator, several PV inverters and various stand-alone inverters, a lithium-ion battery pack, a lead battery bank, a charging infrastructure for electric vehicles as well as other equipment. The combination of virtual and real components means researchers can simulate almost any energy system. For any given system they then assess and evaluate the potential energy savings for the customer associated with managing that system.

The service portfolio includes everything from"Integration assessment of thermal and electrical equipment in the system,""Function and communications testing for energy management systems" to the"Efficiency assessment of energy management and generation equipment." Energy suppliers and grid operators from across Germany are already leveraging the know-how of the Freiburg-based experts to determine the potential inherent in the decentralized management of this kind of equipment. Tariff models need to be assessed and their impact on the power grids investigated.

At the Hannover Messe from April 4 to 8, researchers on the joint Fraunhofer Energy Alliance will be showcasing a small yet very sophisticated device: The Smart Energy Gateway -- a component from the test lab -- organizes the way in which data is shared between energy supplier and consumer. The smart box networks the power meters for heat, water and electricity and ensures that the right control function is used to increase efficiency based on current consumption figures and tariff information. But the Gateway is not just a networked meter and energy management optimization device: It can also be used to control household appliances or heaters and to program on/off times. When should the heat pump, the washing machine or the dishwasher come on? In future, one worry you won't have when you're on vacation is whether you forgot to switch the stove off.

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Better Batteries for Electric Cars

Electric cars are the future -- a view shared by government and the automotive industry alike.  By 2020, a million passenger cars with an electric drive should be on the roads in Germany. The ADAC, the German motoring organization, found out in a survey, 74 percent of those surveyed would buy an electric car if they did not have to compromise in terms of cost, comfort and safety.

Consumers are not willing to compromise one iota when it comes to range. Around one third of drivers are looking for a range of at least 500 kilometers. And here is the crux: A lack of charging stations and limited battery life have so far prevented compact electric vehicles from going mainstream. The lithium-ion batteries used by most automakers are simply too heavy, too expensive and go flat too quickly. New materials should improve the performance, service life and safety of the energy storage device, yet the development of these kinds of materials is time-consuming and costly. In the Fraunhofer System Research for Electromobility (FSEM) project, researchers from the Fraunhofer Institute for Industrial Mathematics ITWM in Kaiserslautern are developing software to simulate lithium-ion batteries, which should in turn speed up this process and make it more efficient. The new software is dubbed BEST, short for Battery and Electrochemistry Simulation Tool.

A lithium-ion battery consists of two porous electrodes kept apart by a separator filled with electrolyte. Lithium ions flow between the electrodes when the battery is charged and discharged."Battery performance depends on the materials used in the components. These materials need to work in harmony with each other," explains Jochen Zausch, a scientist in the Complex Fluids group at Fraunhofer ITWM."Various material combinations can be simulated using our software, enabling us to come up with the ideal mix. The kind of trial-and-error testing done in the past is no longer necessary."

The Fraunhofer ITWM researchers have managed to simulate on macroscopic and microscopic level the entire battery cell as well as the transport and reaction processes of the lithium ions themselves."We can show the microscopic structure of the electrodes. Every individual pore measuring 10 micrometers can be seen -- something none of today's off-the-shelf programs can do. The position and shape of the electrodes can also be varied," says Zausch. By resolving the structure of the electrodes in three dimensions, parameters such as lithium ion concentrations and current density can be calculated. For these computations a specializes"Finite Volume" code is used that was developed and implemented at the ITWM. The distribution of the current flow provides an indication of heat production in the battery. Therefore, the software can pinpoint possible hotspots that may overheat and can lead to ignition of the battery. Aging effects can also be assessed using BEST. After all, temperature development within the battery affects its service life. The scientists intend to upgrade the program to include aging models which would make these kinds of studies even easier to conduct.

"Ultimately, BEST should help both automakers and manufacturers of electric storage devices to build robust, safe batteries with greater range and, at the same time, improved acceleration," says Zausch in conclusion. The software can be seen at the Hannover Messe from April 4 to 8.

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Solar Power Systems Could Lighten the Load for British Soldiers

With the aim of being up to fifty per cent lighter than conventional chemical battery packs used by British infantry, the solar and thermoelectric-powered system could make an important contribution to future military operations.

The project is being developed by the University of Glasgow with Loughborough, Strathclyde, Leeds, Reading and Brunel Universities, with funding from the Engineering and Physical Sciences Research Council (EPSRC). It is also supported by the Defence Science and Technology Laboratory (Dstl).

The system's innovative combination of solar photovoltaic (PV) cells, thermoelectric devices and leading-edge energy storage technology will provide a reliable power supply round-the-clock, just like a normal battery pack. The team is also investigating ways of managing, storing and utilising heat produced by the system.

Because it is much lighter, the system will improve soldiers' mobility. Moreover, by eliminating the need to return to base regularly to recharge batteries, it will increase the potential range and duration of infantry operations. It will also absorb energy across the electromagnetic spectrum, making infantry less liable to detection by night vision equipment that uses infra-red technology, for instance.

Minister for Universities and Science David Willetts said:"The armed forces often need to carry around a huge amount of kit and the means to power it. It's great that specialists from a range of science disciplines are coming together to develop lighter, more reliable technology that will help to make life easier for them in the field."

Although substantial research into solar power for soldiers has already been conducted worldwide, this new UK project differs in its use of thermoelectric devices to complement solar cells, delivering genuine 24/7 power generation capability. The project team is also investigating how both types of device could actually be woven into soldiers' battle dress, which has never been done before.

During the day, the solar cells will produce electricity to power equipment. During the night, the thermoelectric devices will take over and perform the same function. The system will also incorporate advanced energy storage devices to ensure electricity is always available on a continuous basis.

"Infantry need electricity for weapons, radios, global positioning systems and many other vital pieces of equipment," says Professor Duncan Gregory of the University of Glasgow."Batteries can account for over ten per cent of the 45-70kg of equipment that infantry currently carry. By aiding efficiency and comfort, the new system could play a valuable role in ensuring the effectiveness of army operations."

PV cells, thermoelectric devices and advanced energy storage devices are already widely used in a range of applications. A key aim of the project team, however, is to produce robust, hard-wearing designs specifically for military use in tough, hostile conditions.

Because it will harness clean, free energy sources, the new power system will also offer significant environmental advantages compared with the conventional battery packs currently used by the British army.

To tackle the many challenges that the project presents, the team includes specialists from a wide range of disciplines including chemistry, materials science, process engineering, electrical engineering and design. Feedback from serving soldiers will also play a crucial role in optimising the power system for front-line use.

"We aim to produce a prototype system within two years," says Professor Gregory."We also anticipate that the technology that we develop could be adapted for other and very varied uses. One possibility is in niche space applications for powering satellites, another could be to provide means to transport medicines or supplies at cool temperatures in disaster areas or to supply fresh food in difficult economic or climatic conditions."

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