February 2014

A team of Harvard scientists and engineers has demonstrated a new type of battery that could fundamentally transform the way electricity is stored on the grid, making power from renewable energy sources such as wind and solar far more economical and reliable.

The novel battery technology was reported in a paper published in Nature on January 9. Under the OPEN 2012 program, the Harvard team received funding from the U.S. Department of Energy’s Advanced Research Projects Agency–Energy (ARPA-E) to develop the innovative grid-scale battery, and plans to work with ARPA-E to catalyze further technological and market breakthroughs over the next several years. 

The paper reports a metal-free flow battery that relies on the electrochemistry of naturally abundant, inexpensive, small organic (carbon-based) molecules called quinones, which are similar to molecules that store energy in plants and animals.

The mismatch between the availability of intermittent wind or sunshine and the variability of demand is the biggest obstacle to getting a large fraction of our electricity from renewable sources. A cost-effective means of storing large amounts of electrical energy could solve this problem.

The battery was designed, built, and tested in the laboratory of Michael J. Aziz, Gene and Tracy Sykes Professor of Materials and Energy Technologies at the Harvard School of Engineering and Applied Sciences (SEAS). Roy G. Gordon, Thomas Dudley Cabot Professor of Chemistry and Professor of Materials Science, led the work on the synthesis and chemical screening of molecules. Alán Aspuru-Guzik, Professor of Chemistry and Chemical Biology, used his pioneering high-throughput molecular screening methods to calculate the properties of more than 10,000 quinone molecules in search of the best candidates for the battery.

Flow batteries store energy in chemical fluids contained in external tanks—as with fuel cells—instead of within the battery container itself. The two main components—the electrochemical conversion hardware through which the fluids are flowed (which sets the peak power capacity), and the chemical storage tanks (which set the energy capacity)—may be independently sized. Thus the amount of energy that can be stored is limited only by the size of the tanks. The design permits larger amounts of energy to be stored at lower cost than with traditional batteries.

By contrast, in solid-electrode batteries, such as those commonly found in cars and mobile devices, the power conversion hardware and energy capacity are packaged together in one unit and cannot be decoupled. Consequently they can maintain peak discharge power for less than an hour before being drained, and are therefore ill-suited to store intermittent renewables.

“Our studies indicate that one to two days’ worth of storage is required for making solar and wind dispatchable through the electrical grid,” said Aziz.

To store 50 hours of energy from a 1 MW wind turbine (50 MWh), for example, a possible solution would be to buy traditional batteries with 50 MWh of energy storage, but they’d come with 50 MW of power capacity. Paying for 50 MW of power capacity when only 1 MW is necessary makes little economic sense.

For this reason, a growing number of engineers have focused their attention on flow battery technology. But until now, flow batteries have relied on chemicals that are expensive or difficult to maintain, driving up the energy storage costs.

The active components of electrolytes in most flow batteries have been metals. Vanadium is used in the most commercially advanced flow battery technology now in development, but its cost sets a rather high floor on the cost per kWh at any scale. Other flow batteries contain precious metal electrocatalysts such as the platinum used in fuel cells.

The new flow battery developed by the Harvard team already performs as well as vanadium flow batteries, with chemicals that are significantly less expensive, and with no precious metal electrocatalyst.

“The whole world of electricity storage has been using metal ions in various charge states but there is a limited number that you can put into solution and use to store energy, and none of them can economically store massive amounts of renewable energy,” Gordon said. “With organic molecules, we introduce a vast new set of possibilities. Some of them will be terrible and some will be really good. With these quinones we have the first ones that look really good.”

Aspuru-Guzik noted that the project is very well aligned with the White House Materials Genome Initiative. “This project illustrates what the synergy of high-throughput quantum chemistry and experimental insight can do,” he said. “In a very quick time period, our team honed in to the right molecule. Computational screening, together with experimentation, can lead to discovery of new materials in many application domains.”

Quinones are abundant in crude oil as well as in green plants. The molecule that the Harvard team used in its first quinone-based flow battery is almost identical to one found in rhubarb. The quinones are dissolved in water, which prevents them from catching fire.

To back up a commercial wind turbine, a large storage tank would be needed, possibly located in a below-grade basement, said co-lead author Michael Marshak, a postdoctoral fellow at SEAS and in the Department of Chemistry and Chemical Biology. Or if you had a whole field of turbines or large solar farm, you could imagine a few very large storage tanks.

The same technology could also have applications at the consumer level, Marshak said. “Imagine a device the size of a home heating oil tank sitting in your basement. It would store a day’s worth of sunshine from the solar panels on the roof of your house, potentially providing enough to power your household from late afternoon, through the night, into the next morning, without burning any fossil fuels.”

“The Harvard team’s results published in Nature demonstrate an early, yet important technical achievement that could be critical in furthering the development of grid-scale batteries,” said ARPA-E program director John Lemmon. “The project team’s result is an excellent example of how a small amount of catalytic funding from ARPA-E can help build the foundation to hopefully turn scientific discoveries into low-cost, early-stage energy technologies.”

Team leader Aziz said the next steps in the project will be to further test and optimize the system that has been demonstrated on the bench top and bring it toward a commercial scale. “So far, we’ve seen no sign of degradation after more than 100 cycles, but commercial applications require thousands of cycles,” he said. He also expects to achieve significant improvements in the underlying chemistry of the battery system. “I think the chemistry we have right now might be the best that’s out there for stationary storage and quite possibly cheap enough to make it in the marketplace,” he said. “But we have ideas that could lead to huge improvements.”

By the end of the three-year development period, Connecticut-based Sustainable Innovations, LLC, a collaborator on the project, expects to deploy demonstration versions of the organic flow battery contained in a unit the size of a horse trailer. The portable, scaled-up storage system could be hooked up to solar panels on the roof of a commercial building, and electricity from the solar panels could either directly supply the needs of the building or go into storage and come out of storage when there’s a need. Sustainable Innovations anticipates playing a key role in the product’s commercialization by leveraging its ultra-low cost electrochemical cell design and system architecture already under development for energy storage applications.

“You could theoretically put this on any node on the grid,” Aziz said. “If the market price fluctuates enough, you could put a storage device there and buy electricity to store it when the price is low and then sell it back when the price is high. In addition, you might be able to avoid the permitting and gas supply problems of having to build a gas-fired power plant just to meet the occasional needs of a growing peak demand.”

This technology could also provide very useful backup for off-grid rooftop solar panels—an important advantage considering some 20 percent of the world’s population does not have access to a power distribution network.

William Hogan, Raymond Plank Professor of Global Energy Policy at Harvard Kennedy School, and one of the world’s foremost experts on electricity markets, is helping the team explore the economic drivers for the technology.

Trent M. Molter, President and CEO of Sustainable Innovations, LLC, provides expertise on implementing the Harvard team’s technology into commercial electrochemical systems.
“The intermittent renewables storage problem is the biggest barrier to getting most of our power from the sun and the wind,” Aziz said. “A safe and economical flow battery could play a huge role in our transition off fossil fuels to renewable electricity. I’m excited that we have a good shot at it.”

In addition to Aziz, Marshak, Aspuru-Guzik, and Gordon, the co-lead author of the Nature paper was Brian Huskinson, a graduate student with Aziz; coauthors included research associate Changwon Suh and postdoctoral researcher Süleyman Er in Aspuru-Guzik’s group; Michael Gerhardt, a graduate student with Aziz; Cooper Galvin, a Pomona College undergraduate; and Xudong Chen, a postdoctoral fellow in Gordon’s group.

This work was supported in part by the U.S. Department of Energy’s Advanced Research Project Agency–Energy (ARPA-E), the Harvard School of Engineering and Applied Sciences, the National Science Foundation (NSF) Extreme Science and Engineering Discovery Environment (OCI-1053575), an NSF Graduate Research Fellowship, and the Fellowships for Young Energy Scientists program of the Foundation for Fundamental Research on Matter, which is part of the Netherlands Organization for Scientific Research (NWO).  

—Source: Harvard School of
 Engineering and Applied Sciences

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Premature failures of mechanical systems have a significant impact on the cost of wind turbine operations and thus the total cost of wind energy. Recently, the Energy Department’s National Renewable Energy Laboratory (NREL) took a giant step forward in the quest for more reliable, lower-cost wind power with the addition of the new 5 MW Dynamometer Test Facility at its National Wind Technology Center (NWTC). The new facility dramatically expands the capability of NWTC engineers and their industry partners to verify the performance and reliability of wind turbine drivetrain prototypes and commercial machines.

The facility is capable of testing drivetrains up to 5 MW— large enough to test virtually any land-based turbine — and employs dynamically variable loading capabilities that will allow researchers to better simulate conditions a turbine might experience in the field.

“These new capabilities make this a very special facility, one of the largest and finest of its kind in the world,” NWTC director Fort Felker said. “It gives NREL an enhanced ability to do comprehensive testing of modern multi-megawatt wind turbine systems in a laboratory environment to verify their performance and reliability before they are widely deployed.”

A Cutting-Edge Test Facility for the Future of Wind Energy
A dynamometer system replaces the rotor and blades of a wind turbine and allows researchers to control the turbine drivetrain’s mechanical and electrical systems while simulating normal and extreme operating conditions. Historically, this testing has been done under torque (rotating) loads only. The new state-of-the-art facility at the NWTC, funded with the support of the Energy Department and the American Recovery and Reinvestment Act (ARRA), incorporates a non-torque loading system into the testing regimen, a hydraulic device that allows for simulation of both the rotational and bending loads that a wind turbine rotor places on a drivetrain.

“The non-torque loading system is what really sets this facility apart from other comparable test sites,” NWTC Dynamometer project manager Mark McDade said. “This allows us to test the drivetrain system with the types of loads that it will see in a real-world application. It’s a very important feature for a test apparatus because the adverse impacts these types of loads can have on a system are significant.”

The system features a 6-MW motor, which provides the power to a turbine during testing. The motor turns at very high speed and low torque. The motor drives a gearbox, which transforms the output to the high torque and low speed that is appropriate for a wind turbine drivetrain. This provides the rotating loads on the test article.

Add to this motorized torque testing the non-torque loading capability unique to the NWTC, and NREL is able to put a wind turbine drivetrain through the most realistic loading tests possible in a laboratory.

Reliable Wind Turbines for Industry Mean Lower Costs for Consumers
Dynamometer testing is used by the  industry to confirm proper operation and reduce the risk of deploying wind turbine prototypes before they are put into service. By reproducing operating conditions in a laboratory environment, engineers can verify the performance of a turbine’s systems, including generators, gearboxes, power converters, bearings, brakes, and control systems. Conducting these tests before  deployment is important because unanticipated failures can be detected and corrected early in the development process, leading to a lower cost of ownership for wind farm operators—and ultimately lower-cost wind energy for the consumer.

“These machines are expected to operate reliably in the field, often in harsh conditions, for 20 years or more,” Felker said. “The ability to comprehensively test these systems in the lab, to verify their reliability and performance before they go into service, is a critically important capability for the wind industry.”

The first tests being done at NREL’s new dynamometer facility are on a 2.75 MW wind turbine the DOE acquired in partnership with General Electric. The GE system is being used for the calibration and commissioning of the testing equipment in the facility, which will also provide the industry partner with useful data on this particular turbine model.

“The only way to deliver advanced technology at a lower cost of energy with high reliability is to be able to test and learn,” GE senior manager for wind technologies Tom Fischetti said at the dedication event for the facility. “Being able to do that here at ground level instead of in the field, 300 feet in the air, is very important to GE and the rest of the wind industry. This is state-of-the-art technology, and we are excited to be able to partner with NREL and the Energy Department by being the first user of the facility.”

Helping the Power Grid and Wind Turbines Work Better Together
Another important new capability that enhances the value of the work being done at NREL’s 5 MW Dynamometer Test Facility is the Controllable Grid Interface (CGI), a powerful energy systems integration tool that allows engineers to precisely control the electrical grid conditions that a test article will see.

The CGI simulates various grid disturbances, such as over-voltage or under-voltage events, allowing engineers and industry partners to determine how grid-connected systems will react to these events in a controlled environment. This type of testing—performed offline from the grid, but simulating a real-world grid environment—enables users to verify performance, assure compliance with standards, and understand failures in a fraction of the time and cost that it takes to perform similar tests in the field. Figure 1

The CGI can also help engineers determine how these systems will be able to provide ancillary services to the grid, as well as test and optimize the grid-integration-related performance of a unit before it is deployed.

“This is a significant capability for NREL, and one that is very complementary to the work that will be done in the dynamometer,” McDade said. “As more and more renewable energy generation and storage technologies are added to our electricity mix, it is critically important that we understand how these systems will perform on the larger electric grid, how they will react to disturbances, and how they will be able to provide benefit to the grid from a systems integration standpoint.”

The CGI can test not only the integration performance of wind turbines, but also that of a wide variety of grid-integrated energy systems, such as utility-scale solar photovoltaic (PV) generation, PV inverters, and energy storage systems.

Working Today Toward the Technologies of Tomorrow
In addition to enabling deployment-readiness testing, the new NREL test facility will be able to examine future technology innovations, such as advanced drivetrain systems, that promise to usher in the next generation of higher-performance, lower-cost wind turbines.

Research at the facility will accelerate the development of new wind energy technologies, providing an opportunity to verify the concept and performance of prototype technology improvements at the pilot level before moving them into the marketplace.

This capability will allow research engineers to test a specific component, such as a generator or a gearbox, within the scope of a full system, to confirm that it meets its performance, efficiency, and reliability goals before introducing it into the operating fleet of wind turbines.

The NWTC has continued to grow its testing capabilities over time to meet the ever-expanding needs of the wind industry. This is the third dynamometer test facility at the laboratory, adding to the existing capabilities of previously installed 225-kilowatt and 2.5-MW test systems. The two smaller systems have directly contributed to the growth of the higher-performance, lower-cost, and more reliable wind turbines seen in use today. The new 5-MW facility is the next step forward toward even larger wind systems with increased performance expectations.

“Important basic R&D will be done in this facility to answer the key engineering questions that will allow us to develop the next generation of wind turbine technology,” Felker said. “We need to continue to push the cost of energy down while at the same time improving the performance and reliability of these systems. A laboratory environment such as this, where we can seek the answers to these questions is an important step toward meeting those goals.” 

Source: National Renewable Energy Laboratory.
NREL is a national laboratory of the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, operated by the Alliance for Sustainable Energy, LLC.

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